Approaches toward enhancing survival probability following deep anterior lamellar keratoplasty

Abstract

The greatest advantage of deep anterior lamellar keratoplasty over full-thickness corneal transplantation is the elimination of graft failure caused by endothelial rejection. Despite this advantage, a deep anterior lamellar keratoplasty graft can fail because of several factors, such as complications related to the donor–recipient interface, graft epithelial abnormalities, graft vascularization, stromal graft rejection, and recurrence of herpetic keratitis. Increased deep anterior lamellar keratoplasty graft survival is mainly built upon optimization of the ocular surface to provide a hospitable environment for the graft. Any predisposing factors for graft epithelial abnormalities, corneal neovascularization, and preexisting vernal keratoconjunctivitis should be identified and treated preoperatively. Prompt recognition and appropriate treatment of interface-related complications and stromal graft rejection usually result in good anatomic outcomes, with no detrimental effects on vision.

Keywords

complications related to the donor–recipient interface deep anterior lamellar keratoplasty epithelial abnormalities graft failure graft rejection graft survival herpetic keratitis vascularization vernal keratoconjunctivitis

Introduction

Until recently, full-thickness penetrating keratoplasty (PK) was the first-line keratoplasty technique for the management of corneal pathologies. There is already a substantial body of literature to suggest good long-term clinical outcomes of PK for various indications that enjoys a very high success rate.¹ Immunologic rejection, mainly in the form of endothelial rejection, is a major risk factor for PK graft failure.¹ Another important risk factor for graft failure includes nonimmunologic conditions including ocular surface disorders, infectious keratitis, trauma, and glaucoma.¹ After the introduction of deep anterior lamellar keratoplasty (DALK), PK is no longer the default technique of keratoplasty in corneal pathologies with normal endothelium. DALK has gained popularity due to the elimination of complications encountered with PK, such as suprachoroidal hemorrhage, and it enjoys a less troublesome postoperative course due to the absence of endothelial rejection.² In addition, the technique requires less stringent criteria for the selection of donor tissue.² These features, along with the lower postoperative endothelial cell loss, are the greatest advantage of DALK over PK, especially in patients who are at high risk of graft rejections. Despite these advantages, a DALK graft can fail because of nonimmunologic factors, such as persistent postoperative double anterior chamber, haziness of surgical interface, graft epithelial abnormalities, infectious keratitis, recurrence of primary pathology in graft including corneal dystrophies, graft vascularization, and scarring. Furthermore, subepithelial and stromal graft rejection may still occur postoperatively and if left untreated, can lead to lamellar graft failure. In contrast to PK in which increased graft survival is generally built upon immunosuppressive therapy to reduce the risk of endothelial graft rejection, the graft survival in DALK mostly depends upon optimization of the ocular surface to provide a hospitable environment for the graft. In addition, appropriate management of interface-related complications and stromal graft rejection is essential for achieving good visual and anatomic outcomes. In this review article, we aim to discuss the treatable etiologies of graft failure after DALK and provide measures that can improve graft longevity in this type of surgery.

Review

This article aims to discuss the treatable etiologies of graft failure after DALK (Table 1) and highlights measures that can improve graft longevity. Other causes of graft failure that cannot be prevented (i.e. recurrence of corneal stromal dystrophy) are not discussed in this review. A review of the literature was performed in PubMed, including all English articles published from January 2004 to October 2019. Search terms were ‘deep anterior lamellar keratoplasty’ with ‘graft failure’, ‘interface-related complications’, ‘epithelial abnormalities’, ‘vernal keratoconjunctivitis’, ‘vascularization’, ‘angiogenesis’, ‘graft rejection’, and ‘herpetic keratitis’. The ethical board approval was not required for this review article.

Table 1.

Treatable Etiologies of Graft Failure After Deep Anterior Lamellar Keratoplasty as Presented in Text.

Complications associated with donor–recipient interface
• Intraoperative Descemet’s membrane perforation
• Postoperative Descemet’s membrane nonattachment
• Interface wrinkling
• Interface haziness

Postoperative graft epithelial abnormalities
• Donor-related factors
• Surgical factors
• Recipient-related factors

Vernal keratoconjunctivitis

Corneal graft neovascularization

Graft rejection

Recurrence of herpes simplex keratitis

Complications associated with donor–recipient interface

Although DALK eliminates many complications that are seen in full-thickness PK, there are a few complications that are due to the presence of surgical interface between the donor graft and recipient bed in this lamellar keratoplasty technique. These complications which can cause graft failure include intraoperative Descemet’s membrane (DM) perforation, postoperative double chamber formation, interface wrinkling, and interface haziness (Figure 1). DM perforation can take place during different steps of surgery, including trephination, needle insertion, bubble puncturing, deep stromal excision, and graft suturing. The rate of intraoperative DM perforation is between 4% and 50%, depending on surgeon experience, indications for corneal transplantation, the presence of corneal scarring near the DM, and surgical techniques.^3–6 This complication is more frequently encountered in eyes with keratoconus as compared with other conditions requiring corneal transplantation.⁷ Advanced ectasia with corneal thickness less than 250 μm increases this risk.⁸ The ratio of scar depth to minimal corneal thickness can predict perforation rates during pneumatic dissection.⁹ The risk of DM perforation is lowest with the big-bubble technique (6%) and highest with manual dissection technique (26%).¹⁰

Figure 1.

Complications related to donor–recipient interface after deep anterior lamellar keratoplasty. (a) The formation of double anterior chamber that is characterized by graft stromal edema and recipient Descemet’s membrane nonattachment and (b) multiple folds are evident in the surgical interface.

Intraoperative DM perforation can result in postoperative DM detachments and graft edema, endothelial cell loss, and interface opacity (Figure 1(a)).^11–13 The size of perforation and the stage at which it happens are crucial for successful completion of DALK. Perforations that occur during the early stage of the surgery lead to slower visual recovery secondary to the retention of posterior corneal stroma. A large DM perforation leads to a flat anterior chamber intraoperatively necessitating several air injections, which is associated with a greater extent of endothelial cell loss.¹⁴

Interface haze may result from incomplete stromal dissection and can cause a reduction in visual acuity.⁵ Factors that are associated with failure to achieve pneumatic dissection in big-bubble DALK include shallow trephination, small trephination size, and presence of corneal scar.^15,16 Strong adhesions between the corneal stroma and DM, which is present in corneal scar, make it difficult to achieve a bare DM during big-bubble DALK.¹⁷ Interface wrinkling is due to a mismatch between the size of recipient bed and donor graft (Figure 1(b)); it is often located peripherally and has no impact on vision. Interface wrinkling is usually transient, and it tends to improve 1 year after surgery. Eyes with advanced keratoconus (mean keratometry >60 D), however, may develop persistent interface wrinkling in the central cornea that may affect vision by inducing higher order aberrations.¹⁸

Management

Big-bubble technique has become the most popular surgical technique for DALK. The main challenge associated with this technique is the placement of the cannula through recipient cornea at an appropriate depth and as close as possible to the DM. This maneuver often requires mastery through a long learning curve, leading to an initial success rate of only 50% for novice cornea-trained surgeons.^3,19 Performing an initial deep trephination maximizes the chances of achieving pneumatic dissection during DALK.¹⁶ Several surgeons have adopted modifications to the original technique to increase the rate of big-bubble formation. Feizi and colleagues²⁰ introduced peripheral air injection in which a 27-G needle is inserted into the corneal stroma from the trephination site toward the limbus. They found that the rate of successful big-bubble formation is 81.3% with this modification.²⁰ Peripheral air injection has a shorter learning curve, and it is more successful in the hands of less-experienced surgeons.²¹ In addition, in case of DM perforation during peripheral air injection, it is possible to change the site of needle insertion to the opposite limbus or even inside the trephination. In this condition, the perforated DM will not interfere with big-bubble formation.^20,21

Accurate evaluation of the needle depth is difficult by conventional en face microscopy. Therefore, different intraoperative instruments, including corneal pachymetry and anterior-segment optical coherence tomography, have been used to insert the needle into deep stroma and increase the likelihood of big-bubble formation.^22–24

Different measures can be used for the management of intraoperative DM perforation depending on the step of surgery at which the perforation takes place as well as the location and size of the defect. These measures include suturing of perforation, intraoperative stromal patching, use of fibrin glue, and conversion to a manual dissection technique.²⁵ Perforations that occur during trephination is closed by tight sutures, followed by manual dissection of the corneal stroma. Afterward, donor graft is fixed to the recipient bed using full-thickness sutures in the site of perforation. If perforation occurs during posterior stromal removal, that area should be excised last, and a thin layer of stroma should be left in place covering it. At the end of surgery, the anterior chamber is partially filled with air or expansile gas. If a perforation occurs during the suturing step, air injection into the anterior chamber at the conclusion of procedure will be sufficient.

Postoperatively, shallow DM detachments are often self-limited and resolve spontaneously. Surgical intervention, however, is required for the management of large pseudoanterior chambers, including fluid drainage and air or expandable gas injection. This procedure can be repeated if a single injection fails to attach DM.

Interface wrinkling, another complication exclusively encountered after DALK, can be prevented by oversizing the donor graft by 0.25 or 0.50 mm because mismatch between the size of donor graft and recipient bed is responsible for the development of this complication.³ Interface-related complications such as failure of DM to attach, haziness, and wrinkling that persist postoperatively and affect the vision may necessitate a full-thickness PK.

Graft epithelial abnormalities

The integrity of the graft epithelium after DALK is an imperative factor in graft clarity. Graft epithelial abnormalities after DALK include punctate epithelial keratopathy, filamentary keratitis, and epithelial defects (Figure 2). Epithelial defects which are present in 93.3% of grafts on postoperative day 1 may persist longer than 14 days in 0.8–6.0% of DALK cases performed to treat keratoconus.^26–29 Graft epithelial defects can lead to subepithelial and stromal opacities, infectious keratitis, corneal melting, and perforation, which may delay visual rehabilitation and result in graft failure in 25% of patients.^30–32 Epithelial instability after DALK is caused by donor-, surgery-, and recipient-related factors. It is crucial to recognize the perioperative ocular surface abnormalities and take the appropriate measures to resolve them to enhance the chances of graft longevity after DALK.

Figure 2.

Epithelial graft abnormalities after deep anterior lamellar keratoplasty. (a) Filamentary keratitis characterized by the presence of multiple filaments in a background of severe dry ocular surface and graft epithelial irregularities and (b) A persistent epithelial defect with characteristic heaped-up edges. The regenerated surface epithelium in other areas appears irregular and hazy. A bandage contact lens is placed on the eye.

Donor-related factors

Donor-related factors that can influence graft epithelium during the early postoperative period after DALK include those related to diabetes in the donor, death-to-preservation time, storage time, the storage media, and donor quality. History of diabetes in the donor is an independent risk factor for presence of graft epithelial defects postoperatively.³⁰ The prevalence of epithelial defects on the first postoperative day varies depending on the type of storage media; it ranges from as high as 80% with organ culture medium to as low as 31% with cold storage medium.^30,33 The impact of death-to-preservation time and storage time on the corneal graft surface early postoperatively is controversial.^30,33 Chou and colleagues³⁰ found that the postmortem time before enucleation is more important than the storage time in the development of graft epithelial abnormalities. Similarly, a DALK study found that the likelihood of graft epithelial defects is significantly increased with increased death-to-preservation time.³⁴ Although some investigators failed to establish an association between storage time and an increased odds of postoperative graft epithelial abnormalities, others reported a positive correlation.^{30,33,35–41} Some damage to the graft epithelium might occur due to antibiotics used in the storage media.

Other donor features such as the assigned ‘graft rating’ can influence the rate of postoperative graft epithelial abnormalities. Naturally, a tissue with higher quality exhibits a lower rate of epithelial defects after DALK.⁴² Feizi and colleagues⁴² revealed that the presence of graft epithelial defects on the first day after DALK has a significant association with graft rating reported by the eye bank and storage time. Since the introduction of DALK, many surgeons have been using less stringent criteria for selecting tissue for DALK surgery as compared with PK, leading to the use of corneal tissues of less-than-ideal quality and with longer preservation times. This explains the higher rates of epithelial defects after DALK than those reported after PK in the immediate postoperative period.^33,35,43,44

Surgical factors

Further damage to the graft epithelium can occur intraoperatively during donor preparation for DALK. Because of the way the donor tissue is oriented while DM is being stripped off; the epithelium may suffer multiple injuries from being against the donor punch block. Other surgical factors that have detrimental effects on graft epithelium postoperatively are longer surgical duration and intraoperative graft desiccation.³⁰ A proper surgical technique with a perfect alignment of the graft and host edges is crucial in ensuring adequate epithelial growth over the donor cornea postoperatively; for example, an overriding margin will impede migration of the epithelial cells to the donor tissue. Sutures that are placed too tight prevent uniform distribution of tear film over the corneal surface, hindering adequate graft epithelialization.^33,36

Recipient-related factors

An intact graft epithelium on the first postoperative day provides a ‘jump start’ for maintaining a healthy graft surface, meanwhile the importance of the status of the recipient’s ocular surface should not be overlooked. Epithelial regeneration in graft depends on the interaction among multiple factors such as the presence of healthy eyelids, tear film, limbal stem cells, and nerve fibers. Several neurotrophic factors, including insulin growth factor, nerve growth factor, substance P, and acetylcholine, are secreted by corneal nerves and direct epithelial cell division and maturation.^45–47 All superficial and deep corneal nerve fibers are cut during trephination. The process of graft re-innervation is slow and incomplete with an abnormal pattern and can further be delayed in vulnerable patients with preexisting conditions, such as fifth nerve palsy and previous episodes of herpes simplex keratitis, leading to severe neurotrophic keratopathy.⁴⁸

Furthermore, graft epithelial abnormalities can be exacerbated by the preexisting dry eye and limbal stem cell deficiency and pathologic process in the eyelids and conjunctiva. Eyelid abnormalities including trichiasis, keratinized lid margins, and cicatricial- or involutional-related eyelid malpositionings can cause microtrauma to the graft.^49,50 Conjunctival fibrosis, symblepharon, and fornix foreshortening can destabilize the tear film and interfere with normal blinking.^51,52 Dry eye syndrome can be caused by aqueous tear deficiency or lipid tear abnormality. In severe cases, dry eye syndrome ultimately leads to corneal pannus, persistent corneal epithelial defects, epithelial keratinization, and damage to the limbal stem cells.^36,53,54 The limbal stem cells can be severely damaged following chemical and thermal injuries. Placing corneal transplants into eyes with limbal stem cell deficiency can result in persistent epithelial defects, vascularization, and scarring of the graft, leading to graft failure.⁵⁵

Management

Preoperative measures

Thorough evaluation of eyelids and ocular surface, including slitlamp examination, conjunctival and corneal staining with Lissamine green and fluorescein, and impression cytology, is critical to improve the graft prognosis in cases with ocular surface disorders.⁵⁶ Coexisting ocular surface diseases, including exposure keratitis, dry eye, meibomian gland dysfunction, and limbal stem cell deficiency, should be preoperatively diagnosed and properly managed. Surgical correction of lid margins as well as diseases of the tarsal plate is among the most vital preoperative measures to enhance graft survival. Treatment plans for dry eye must be tailored to the underlying disease and its severity. Artificial tears and lubricants are commonly used to facilitate corneal epithelialization.⁵⁷ Severe cases require more intense treatment, including topical anti-inflammatory agents or more invasive procedures such as punctual occlusion and tarsorrhaphy.⁵⁷ Meibomian gland dysfunction should be treated with lid hygiene, topical antibiotic, short course of topical corticosteroid, as well as oral doxycycline in selected cases.^58,59 Patients with limbal stem cell deficiency have notoriously poor outcomes if keratoplasty is performed as a solo procedure; in these cases, limbal stem cell transplantation, including keratolimbal allograft, living-related conjunctival limbal allograft, conjunctival limbal autograft, and cultivated limbal stem cell transplants, should be performed simultaneously to restore ocular surface. A great advantage of DALK is that it allows both corneal and stem cell transplantation to be performed at the same time in cases with limbal stem cell deficiency that have a normal endothelium.^60,61

Intraoperative measures

Although the corneal graft is eventually resurfaced by the recipient’s epithelial cells, an intact donor epithelium on day 1 predicts a smoother postoperative course for the corneal graft. This is the rationale for using a graft with intact epithelium in patients with preexisting ocular surface disorders. The donor epithelium should not be removed intraoperatively, and desiccation of the ocular surface should be prevented by frequent irrigation with balanced salt solution.³⁰ In addition, donor DM should be removed very gently to minimize damage to the graft epithelium. Other important issues are perfect apposition of donor and recipient edges and proper suturing technique. These factors are crucial for the smooth migration of recipient epithelial cells to corneal graft and for the maintenance of a normal tear meniscus.^33,36

Postoperative measures

Postoperative care aims to promote healing of the graft epithelial defect and prevent a progression to graft ulcer. In the case of persistent epithelial defects, patients should be monitored frequently and all eye drops associated with graft epithelial toxicity should be discontinued. The prolonged use of preservatives in an already-compromised ocular surface can damage the epithelial surface, resulting in worsening of the ocular surface disorders.⁶² Antibiotic eye drops are recommended in the presence of graft epithelial abnormalities to prevent infections. Topical steroids may inhibit the epithelial healing process and should be used with caution. Removal of tight sutures at the areas with surface irregularities can solve epithelial healing problems. Other therapeutic approaches are frequent nonpreserved artificial tears, lubricants, punctal occlusion, moist inserts, treatment of meibomian glad dysfunction, and topical vitamin A.^63–65 Bandage soft contact lenses have been used for the management of epitheliopathy, as they facilitate reepithelialization by protecting the advancing epithelial cells from being sloughed off by the blinking eyelids, maintaining a tear layer in constant contact with the cornea, as well as providing anesthetic relief.^66,67 Large-diameter scleral contact lenses are recommended for the prevention of microtrauma to the cornea caused by lid margin pathologies.^68,69

Autologous serum drops (20%) have been advocated in patients with persistent epithelial defects. It harbors a wide variety of growth factors which are found in serum, including epidermal growth factor, vitamin A, transforming growth factor-beta, and neurotrophic factors.^49,70,71 These substances are essential in wound healing and promote migration, proliferation, and differentiation of the corneal epithelial cells.⁷⁰ Autologous serum is contraindicated in cases with some concomitant conditions, including blood dyscrasias. Alternatively, allogeneic serum obtained from healthy donors can be used. Umbilical cord blood serum is an allogeneic serum which is rich in epitheliotrophic growth factors, such as insulin-like growth factor, transforming growth factor-beta, epidermal growth factor, and vascular endothelial growth factors (VEGFs).^72,73

Surgical intervention is usually indicated for persistent corneal epithelial defects not responding to medical treatment. Several options are available, such as punctual occlusion, amniotic membrane transplantation (AMT), and tarsorrhaphy. Tarsorrhaphy is most commonly used in the management of persistent corneal epithelial defects; however, the unacceptable cosmetic result is usually a major concern for patients.⁷⁴ AMT, in addition, is a widely used method to promote corneal epithelial healing. AMT, which can be used as a graft or patch, restores an intact basement membrane, suppresses T-cell proliferation and decreases surface inflammation, facilitates surface epithelialization, and prevents corneal neovascularization and scarring.^75,76 All of these features provide a favorable stromal microenvironment for better epithelial cell adhesion and proliferation.

Vernal keratoconjunctivitis

Vernal keratoconjunctivitis (VKC) is a bilateral chronic inflammatory disease of the conjunctiva. This condition frequently affects young male patients, but in tropical regions of the world it may affect both sexes equally.⁷⁷ The pathomechanism of VKC involves both chronic immunoglobulin E (IgE)-mediated mast cell degranulation and immune reactions mediated by T-helper 1- and T-helper 2-lymphocyte derived cytokines, as well as other inflammatory cells.^78,79

Itching is the most characteristic symptom and may be accompanied by watering, mucous discharge, injection, blurred vision, pain, and photophobia. Itching and other symptoms may be continuous or more pronounced in certain seasons. Clinical signs include conjunctival hyperemia, giant papillae on the upper palpebral conjunctiva, Horner-Trantas dots, and limbal gelatinous infiltrates. Significant vision loss in VKC is usually associated with certain corneal findings with punctate epithelial keratopathy being the most common. Keratoconus, which is caused by frequent eye rubbing in some atopic pediatric patients, is also frequently accompanied by VKC leading to reduced visual acuity.⁷⁷

Patients with VKC may require corneal transplantation to treat their keratoconus, corneal scarring, or corneal vascularization. Although no significant differences were reported in visual acuity or graft survival rates after corneal transplantation for keratoconus in eyes with or without VKC, there are concerns that the outcomes might be worse in VKC patients with keratoconus; several factors such as chronic inflammation, ocular surface abnormalities, and peripheral corneal vascularization are the likely culprits (Figure 3).^80–83 Feizi and colleagues⁸³ reported an excellent visual outcome following DALK in keratoconus-affected eyes with VKC, with 88.5% of eyes attained final best-corrected visual acuity (BCVA) ⩾ 20/40 as compared with 91.6% in eyes with only keratoconus. They observed no difference between the study groups in spherical equivalent refractive error and mean keratometric value. However, suture-related complications, including peripheral vascularization and abscess formation, were more frequently encountered in the VKC group, resulting in a significantly larger amount of keratometric astigmatism.⁸³ In addition, the rate of second or more graft rejection episodes was significantly higher in the VKC group.⁸³ A report of reactivation of VKC and shield ulcer after DALK in pediatric patients with keratoconus exists.⁸⁴ Shield ulcers may result in graft failure due to graft opacification, vascularization, and rejection.⁸⁴

Figure 3.

Reactivation of vernal keratoconjunctivitis in a patient with keratoconus who underwent deep anterior lamellar keratoplasty. The photograph shows an injected eye with peripheral corneal vascularization involving both host and donor in addition to the presence of suture abscesses and graft epithelilal haziness.

Management

DALK should be performed only after good medical control of VKC and any exacerbation of ocular inflammation should be aggressively treated after the surgery. In addition, it is advisable to defer surgery to the cooler seasons when the disease becomes more quiescence. Postoperatively, the patient should be observed closely to timely diagnose the reactivation of the disease and to initiate appropriate treatment regimen. This regimen includes topical short-term pulsed steroids, with a topical antihistamine and mast cell stabilizer. After the inflammation is brought under control, topical steroids are discontinued and patients are maintained on topical antihistamines and mast cell stabilizers throughout the warm seasons of the year.

Since topical corticosteroids have extensive side effect profiles, initial treatment should begin with low potent steroids such as fluorometholone or loteprednol. More potent steroids such as prednisolone acetate or dexamethasone should be used in more resistant cases.⁸⁵ Supratarsal injection of triamcinolone acetonide constitutes a safe option for recalcitrant cases and significantly reduces ocular symptoms and signs and the frequency of recurrences.⁸⁶

Mast cell stabilizers, such as cromolyn sodium and lodoxamide, are a mainstay for prophylaxis and frequently used as first-line therapy. These drugs should be applied four to six times per day and it may take up to 2 weeks for them to show a clinical response.⁸⁷ Lodoxamide is superior to cromolyn sodium in reducing symptoms and signs of the disease.⁸⁷ Antihistamines are usually used in mild VKC; but they have limited effects in the more severe form of the disease. Some antihistamines can exacerbate symptoms because they have a drying effect. Ketotifen and olopatadine have both antihistamine and mast cell stabilization properties, and can effectively reduce the symptoms and signs of VKC, with evidence favoring ketotifen as being more effective.⁸⁸

Topical non-steroidal anti-inflammatory drugs (NSAIDs) have been reported to be a useful therapeutic option in VKC.^89,90 Ketorolac or diclofenac can be used in combination with abovementioned antihistamine drugs to provide rapid relief of symptoms.⁹¹ Their use, however, should be limited to short-term treatment because they can cause corneal melting and perforation.⁹²

Drug-resistant VKC can be effectively treated with topical cyclosporine 0.05% in conjunction with topical corticosteroids.^93,94 The immunophilin cyclosporine A is a calcineurin inhibitor that inhibits T-lymphocyte activation by inhibiting the expression of the interleukin (IL)-2 receptor, and the activation of mast cells and eosinophils, thereby decreasing tear cytokine concentration.^95,96 Topical cyclosporine 0.1% has a good efficacy and 30% of patients with VKC are able to discontinue topical steroid use.⁹⁷ This drug has an excellent side-effect profile.⁹⁸ The most common side effect is eye irritation (12%), and >1% of patients may develop infectious complications (e.g. herpetic keratitis or bacterial corneal ulcer).⁹⁷ Higher concentrations of 1–2% have been reported to be effective and safe for severe form of VKC.^99,100

Tacrolimus, another calcineurin inhibitor, inhibits the activation of T lymphocytes and prevents the release of inflammatory mediators.¹⁰¹ Chatterjee and Agrawal¹⁰² evaluated the effect of 0.03% tacrolimus ointment on patients with steroid-refractory VKC. The majority of patients did not require additional steroid therapy after 4 weeks of treatment with tacrolimus.¹⁰² Miyazaki and colleagues¹⁰³ reported that 0.1% topical tacrolimus is effective in VKC patients with corneal complications, including epitheliopathy or shield ulcers.

Patients with refractory VKC may require oral corticosteroids or other immunomodulatory agents such as omalizumab.¹⁰⁴ Allergen-specific immunotherapy may also be effective and can prevent the side effects often encountered with topical therapies.¹⁰⁵ Surgical intervention, ranging from scraping to superficial keratectomy, may be required for the management of complications such as nonhealing corneal plaques or shield ulcers. Early diagnosis of shield ulcer, debridement of the plaque, and initiation of topical medications are essential to maintain the graft clarity in patients with VKC who undergo DALK and develop this complication.⁸⁴

Corneal graft neovascularization

Corneal neovascularization is induced during several conditions, including active blepharitis, limbal stem cell deficiency, persistent epithelial defects, infectious keratitis, allergy, trauma, chemical burns, corneal graft rejection, and autoimmune diseases.^106,107 These pathologies result in disequilibrium between proangiogenic and antiangiogenic factors that can lead to the migration and proliferation of vascular endothelial cells into the corneal stroma.¹⁰⁸ Corneal vascularization is a significant sight-threatening complication because the newly formed vessels lack structural integrity and leak fluid and can lead to persistent inflammation, stromal edema, intrastromal lipid and protein deposition, and opacification.^106,107

Corneal neovascularization predisposes transplanted corneas to rejection by facilitating both the presentation of donor antigens to the recipient immune system and the entrance of recipient activated immune cells to the corneal graft.¹⁰⁹ Therefore, the survival of corneal allografts, including DALK grafts, transplanted in a vascularized recipient bed is low (Figure 4). Treatment of corneal neovascularization either preoperatively or postoperatively is crucial for enhancing corneal graft survival and improving visual outcomes. Intraoperatively, an interrupted suturing technique with the placement of suture knots in the donor is indicated when DALK is performed in a vascularized recipient bed.¹¹⁰ Postoperatively, these patients should be followed up closely to allow for selective suture removal when corneal vessels reach the graft. This approach prevents aggravation of angiogenesis.

Figure 4.

Corneal graft vascularization after deep anterior lamellar keratoplasty. This late complication is characterized by invasion of blood vessels deep in the donor–recipient interface. Leakage of fluid, lipid, and proteinaceous materials from these vessels causes the interface haze as seen here.

Management

Several measures, including corticosteroid medications, laser photocoagulation, photodynamic therapy, and fine needle diathermy (FND), have been used to treat corneal neovascularization. Corneal new vessel formation is usually associated with an inflammatory process. Therefore, topical corticosteroids can effectively diminish inflammation and consequent corneal angiogenesis.¹¹¹ Nevertheless, chronic use of corticosteroids may cause prominent adverse effects, including superinfection, cataract formation, and secondary glaucoma.¹¹¹ Moreover, these medications have limited antiangiogenic properties and cannot effectively decrease preexisting vessels.¹¹²

VEGF plays a key role in pathologic neovascularization and lymphangiogenesis in the eyes.^113–115 Subconjunctival, perilimbal, and intrastromal anti-VEGF monoclonal antibodies such as bevacizumab have been used successfully for the management of corneal vascularization.^113–115 These agents can prolong the survival of corneal allograft transplanted in a vascularized recipient bed. Foroutan and colleagues¹¹⁶ found that perilimbal injection of bevacizumab resulted in partial regression of newly formed vessels at the donor–recipient interface after DALK. All patients had an increase in visual acuity, which was secondary to improved corneal clarity.¹¹⁶ The majority of patients, however, required repeated injection as obvious regression of blood vessels did not take place within a month after the first injection.¹¹⁶ The drawback of this treatment is that mature blood vessels do not respond to anti-VEGFs, necessitating surgical approaches including laser photocoagulation and FND.¹¹⁷

The 577-nm yellow dye laser and argon laser has been used to effectively obliterate corneal vascularization.^118,119 The drawback of this treatment is that laser photocoagulation obliterates corneal efferent vessels and has limited effects on afferent vessels because these deeply located vessels have a fast blood circulation.¹¹⁸ Other complications include damage to the other structures, including corneal endothelium, iris, or crystalline lens.¹²⁰

FND is an inexpensive and useful procedure which can equally obliterate afferent and efferent vessels at different corneal planes. Multiple treatments may be required to achieve the desired result.¹²¹ Corneal perforation is a possible serious complication that usually occurs during passing of the needle in corneas with thin stroma.¹²¹ Other potential complications which are reversible include intrastromal hemorrhages, transient opacification of the cornea, and striae.¹²¹ Intrastromal hemorrhage is the most common complication and may occur intraoperatively or immediately after surgery. This complication resolves over a few weeks but can leave behind crystalline deposits in corneal stroma.¹²¹

Graft rejection

Although DALK eliminates the possibility of endothelial graft rejection, there is still a risk of other types of graft rejection postoperatively.¹²² The rate of graft rejection following DALK varies from 0% to 20%, with an average follow-up period range from 12 to 77 months.^123,124 Overall, the incidence of graft rejection after DALK is 50% less than that observed after PK.¹²⁵ There are three types of graft rejection following DALK, including epithelial, subepithelial, and stromal rejection (Figure 5). The clinical features of these rejection reactions after DALK are similar to those observed in rejection after PK. Stromal rejection is defined as diffuse or sectoral graft stromal infiltrates/edema, vascularization crossing the donor–recipient junction, or both involving the previously clear graft or surgical interface (Figure 5(b)).¹²⁶ Stromal graft rejection should be differentiated from other etiologies of graft stromal inflammation, including herpetic keratitis (see below).¹²⁷

Figure 5.

Graft rejection after deep anterior lamellar keratoplasty. (a) Subepithelial rejection characterized by multiple patches of subepithelial infiltrates throughout the graft resembling those seen in viral epidemic keratoconjunctivitis and (b) stromal rejection characterized by sectoral stromal edema and infiltration in addition to vascular invasion of the peripheral graft.

The majority of episodes of stromal graft rejection occur within the first year after keratoplasty with sutures still in place, although it has been reported as long as 3 years after DALK.^{123,128–130} Risk factors for DALK graft rejection are younger recipient age, African American race, corneal neovascularization, loose sutures, suture infiltrate, and VKC.^3,16,131

Injection, reduced vision, and photophobia are main complaints in symptomatic patients.¹³⁰ Rejection episodes, however, can be identified in the absence of symptoms during a routine follow-up examination.¹³⁰ Therefore, high-risk patients need to be warned of this potential late complication and its symptoms and signs so they can return to clinic promptly. Surgeons also need to be aware that more frequent follow-up examinations are required in high-risk patients to diagnose rejection episodes gone unnoticed. Early diagnosis of stromal rejection after DALK and its prompt treatment is essential to prevent the late sequel of graft rejection including interface vascularization and opacification of the graft, and eventually graft failure.

Management

It has been assumed that one of the advantages of DALK over PK is a relatively short-term corticosteroid regimen. However, subsequent studies have found substantial rates of stromal rejection after DALK, particularly with a relatively short topical corticosteroid dosing regimen.^125,126 Therefore, extending the steroidal treatment for up to 1 year after DALK, similar to those used in PK, can significantly reduce stromal rejection episodes.¹²⁶ The advantages and disadvantages of long-term steroidal treatment, however, should be considered for every single patient. Another measure which can reduce the risk of allograft rejection after DALK is the use of long-term preserved corneal tissues that lack live cells, including keratocytes and antigen-presenting cells.¹³²

Graft rejections after DALK tend to be successfully treated with frequent topical corticosteroids that are tapered off over several weeks as symptoms regress.^126,133 Timely recognition and aggressive treatment usually results in good visual and anatomic outcomes.¹²⁸ Although intravenous pulse steroid in combination with topical steroid therapy was used for the treatment of stromal graft rejection after DALK,¹²³ all patients reported in the literature responded to topical steroids such as betamethasone, dexamethasone, and prednisolone.^5,13,16,134 Steroids with low intraocular penetration, such as loteprednol, rimexolone, or fluorometholone, may be used if steroid-induced glaucoma develops.¹³⁵

Recurrence of herpes simplex keratitis

Herpes simplex keratitis (HSK) is the most common etiology of corneal blindness in industrialized countries.¹³⁶ It is characterized by a high risk of recurrence that increases over time and results in corneal scarring and neovascularization. One sequel of HSK is neurotrophic keratitis, which is caused by damage to the corneal nerves. Neurotrophic keratitis can result in persistent corneal epithelial defects and corneal stromal melts as a consequence of excessive degradation of stromal collagen.¹³⁷ Despite advances in antiviral therapy in the last three decades, corneal transplantation is still required in a large number of cases to restore visual acuity.

PK has traditionally been the technique of choice for HSV-related corneal scarring. Recently, DALK has become an increasingly preferred surgical treatment in such patients which can achieve satisfactory vision, less recurrence of keratitis, less drug-induced complications, less allograft rejections, and a higher long-term graft survival rate.¹³⁸ The graft survival rate has been reported in 72% after DALK for herpetic keratitis.¹³⁹ Despite these advantages, there is a substantial risk of recurrence of HSV keratitis (Figure 6) and graft failure, making the graft prognosis relatively poor compared with other indications for DALK, including keratoconus and corneal stromal dystrophies.^140,141

Figure 6.

Recurrence of herpes simplex keratitis after deep anterior lamellar keratoplasty. (a) A classic epithelial lesion in a corneal graft with a characteristic linear branching corneal ulcer (dendritic ulcer). (b) The epithelial lesion is examined after staining with fluorescein dye.

Management

Performing corneal transplantation during the active stage of the disease leads to higher rates of graft failure.¹⁴² Therefore, DALK should be performed in the inactive stage of the disease after a period of quiescence.¹⁴³ Prophylactic oral acyclovir (400 mg twice a day) is advisable for at least 12 months after DALK to reduce the recurrence of HSK.¹⁴⁴ Despite this prophylactic measure, episodes of recurrence have been reported both within and after this time period with a rate of 33%.¹³⁹ These findings suggest the prophylactic measure may minimize the recurrence of HSV keratitis but does not completely eliminate this risk. Therefore, close follow-up examinations are required after keratoplasty for the early diagnosis of recurrence of HSV keratitis and its related complications such as corneal epithelial problems, vascularization, and graft rejection.¹³⁹ In addition, these patients should undergo routine kidney function examinations every 3 months to monitor the adverse effects of oral acyclovir.

Conclusion

Main advantage of DALK over PK is the complete absence of endothelial graft rejection which dramatically increases the graft survival. Despite this advantage, DALK transplant faces many issues, including complications related to the donor–recipient interface, graft epithelial problems, corneal neovascularization, stromal rejection, and recurrence of herpetic keratitis, which may lead to its failure postoperatively. Appropriate patient selection is vital for a successful outcome in DALK. Younger patients are more likely to experience frequent rejection episode due to their robust immune system. Therefore, in young patients with corneal pathologies sparing the endothelium such as keratoconus, stromal scars, and corneal dystrophies, DALK is clearly advantageous over PK. Active inflammation increases the risk of graft failure and must be treated before transplant. In patients with mental disabilities, such as Down’s syndrome, DALK has clear advantage over PK as it reduces the risk of rejection. In addition, it minimizes the possibility of ocular damage secondary to self-induced trauma, such as eye rubbing. Increased DALK graft survival is mainly built upon optimization of the ocular surface to provide a hospitable environment for the graft. Any predisposing factors for graft epithelial abnormalities and preexisting VKC should be identified and treated preoperatively. In addition, maintaining appropriate measures are crucial when any epithelial problems or recurrence of VKC is encountered postoperatively. Medical or surgical treatment of corneal neovascularization either preoperatively or postoperatively is critical for enhancing DALK graft survival. Prompt recognition and aggressive treatment of stromal graft rejection usually result in good results, with no detrimental effects on the anatomical and visual outcomes. In patients with a history of HSK, DALK should be performed in the inactive stage of the disease after a period of quiescence, and prophylactic oral acyclovir is recommended for at least 12 months postoperatively to reduce the recurrence of keratitis.

Footnotes

Conflict of interest statement

The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The authors received no financial support for the research, authorship, and/or publication of this article.

ORCID iD

Sepehr Feizi

References

Matthaei

Sandhaeger

Hermel

, et al. Changing indications in penetrating keratoplasty: a systematic review of 34 years of global reporting. Transplantation 2017; 101: 1387–1399.

Feizi

Javadi

Fekri

. Use of deep anterior lamellar keratoplasty (DALK) for keratoconus: indications, techniques and outcomes. Exp Rev Ophthalmol 2016; 11: 347–359.

Fogla

Padmanabhan

. Results of deep lamellar keratoplasty using the big-bubble technique in patients with keratoconus. Am J Ophthalmol 2006; 141: 254–259.

Shousha

Yoo

Kymionis

, et al. Long-term results of femtosecond laser-assisted sutureless anterior lamellar keratoplasty. Ophthalmology 2011; 118: 315–323.

Parker

van Dijk

Melles

. Treatment options for advanced keratoconus: a review. Surv Ophthalmol 2015; 60: 459–480.

Tsubota

Kaido

Monden

, et al. A new surgical technique for deep lamellar keratoplasty with single running suture adjustment. Am J Ophthalmol 1998; 126: 1–8.

Shimmura

Shimazaki

Omoto

, et al. Deep lamellar keratoplasty (DLKP) in keratoconus patients using viscoadaptive viscoelastics. Cornea 2005; 24: 178–181.

Baradaran-Rafii

Eslani

Sadoughi

, et al. Anwar versus Melles deep anterior lamellar keratoplasty for keratoconus: a prospective randomized clinical trial. Ophthalmology 2013; 120: 252–259.

Ozmen

Yesilirmak

Aydin

, et al. Prediction of descemet membrane perforation during deep anterior lamellar keratoplasty in patients with keratoconus with stromal scar. Eye Contact Lens 2018; 44(Suppl. 2): S176–S179.

10.

Sarnicola

Toro

Gentile

, et al. Descemetic DALK and predescemetic DALK: outcomes in 236 cases of keratoconus. Cornea 2010; 29: 53–59.

11.

Den

Shimmura

Tsubota

, et al. Impact of the descemet membrane perforation on surgical outcomes after deep lamellar keratoplasty. Am J Ophthalmol 2007; 143: 750–754.

12.

Senoo

Chiba

Terada

, et al. Visual acuity prognosis after anterior chamber air replacement to prevent pseudo-anterior chamber formation after deep lamellar keratoplasty. Jpn J Ophthalmol 2007; 51: 181–184.

13.

Kubaloglu

Sari

Unal

, et al. Long-term results of deep anterior lamellar keratoplasty for the treatment of keratoconus. Am J Ophthalmol 2011; 151: 760–767.e1.

14.

Leccisotti

. Descemet’s membrane perforation during deep anterior lamellar keratoplasty: prognosis. J Cataract Refract Surg 2007; 33: 825–829.

15.

Feizi

Javadi

Daryabari

. Factors influencing big-bubble formation during deep anterior lamellar keratoplasty in keratoconus. Br J Ophthalmol 2016; 100: 622–625.

16.

Arslan

Ünal

Tuncer

, et al. Deep anterior lamellar keratoplasty using big-bubble technique for treatment of corneal stromal scars. Cornea 2011; 30: 629–633.

17.

Huang

Zhang

Wang

, et al. Outcomes of deep anterior lamellar keratoplasty using the big-bubble technique in various corneal diseases. Am J Ophthalmol 2012; 154: 282–289.e1.

18.

Mohamed

Manna

Amissah-Arthur

, et al. Non-resolving Descemet folds 2 years following deep anterior lamellar keratoplasty: the impact on visual outcome. Cont Lens Anterior Eye 2009; 32: 300–302.

19.

Fontana

Parente

Sincich

, et al. Influence of graft-host interface on the quality of vision after deep anterior lamellar keratoplasty in patients with keratoconus. Cornea 2011; 30: 497–502.

20.

Feizi

Faramarzi

Javadi

, et al. Modified big-bubble deep anterior lamellar keratoplasty using peripheral air injection. Br J Ophthalmol 2014; 98: 1597–1600.

21.

Feizi

Daryabari

Najdi

, et al. Big-bubble deep anterior lamellar keratoplasty using central vs peripheral air injection: a clinical trial. Eur J Ophthalmol 2016; 26: 297–302.

22.

Ghanem

. Pachymetry-guided intrastromal air injection (‘pachy-bubble’) for deep anterior lamellar keratoplasty. Cornea 2012; 31: 1087–1091.

23.

Scorcia

Busin

Lucisano

, et al. Anterior segment optical coherence tomography-guided big-bubble technique. Ophthalmology 2013; 120: 471–476.

24.

De Benito-Llopis

Mehta

Angunawela

, et al. Intraoperative anterior segment optical coherence tomography: a novel assessment tool during deep anterior lamellar keratoplasty. Am J Ophthalmol 2014; 157: 334–341.

25.

Huang

Htoon

Chan

, et al. Incidence and outcomes of intraoperative Descemet membrane perforations during deep anterior lamellar keratoplasty. Am J Ophthalmol 2019; 199: 9–18.

26.

Feizi

Javadi

Jamali

, et al. Deep anterior lamellar keratoplasty in patients with keratoconus: big-bubble technique. Cornea 2010; 29: 177–182.

27.

Al-Torbak

Al-Motowa

Al-Assiri

, et al. Deep anterior lamellar keratoplasty for keratoconus. Cornea 2006; 25: 408–412.

28.

Fontana

Parente

Tassinari

. Clinical outcomes after deep anterior lamellar keratoplasty using the big-bubble technique in patients with keratoconus. Am J Ophthalmol 2007; 143: 117–124.

29.

Heindl

Riss

Adler

, et al. Split cornea transplantation: relationship between storage time of split donor tissue and outcome. Ophthalmology 2013; 120: 899–907.

30.

Chou

Cohen

Laibson

, et al. Factors associated with epithelial defects after penetrating keratoplasty. Ophthalmic Surg 1994; 25: 700–703.

31.

Wagoner

Al-Swailem

Sutphin

, et al. Bacterial keratitis after penetrating keratoplasty: incidence, microbiological profile, graft survival, and visual outcome. Ophthalmology 2007; 114: 1073–1079.

32.

Fong

Ormerod

Kenyon

, et al. Microbial keratitis complicating penetrating keratoplasty. Ophthalmology 1988; 95: 1269–1275.

33.

Meyer

Bobb

. Corneal epithelium in penetrating keratoplasty. Am J Ophthalmol 1980; 90: 142–147.

34.

Feizi

Javadi

. Graft epithelial defects after deep anterior lamellar keratoplasty. Cornea 2014; 33: 1145–1148.

35.

Feiz

Mannis

Kandavel

, et al. Surface keratopathy after penetrating keratoplasty. Trans Am Ophthalmol Soc 2001; 99: 159–168.

36.

Machado

Mannis

Mandel

, et al. The relationship between first postoperative day epithelial status and eventual health of the ocular surface in penetrating keratoplasty. Cornea 2002; 21: 574–577.

37.

Kim

Palay

Lynn

. Donor factors associated with epithelial defects after penetrating keratoplasty. Cornea 1996; 15: 451–456.

38.

Wagoner

Gonnah

el-S

. Corneal graft survival after prolonged storage in Optisol-GS. Cornea 2005; 24: 976–979.

39.

Mannis

Zadnik

Miller

, et al. Preoperative risk factors for surface disease after penetrating keratoplasty. Cornea 1997; 16: 7–11.

40.

Deocampo

Sunga

. Studies on the epithelization of corneal grafts with methylene blue. Am J Ophthalmol 1963; 56: 801–806.

41.

Khodadoust

Silverstein

. The survival and rejection of epithelium in experimental corneal transplants. Invest Ophthalmol 1969; 8: 169–179.

42.

Feizi

Javadi

Kanavi

, et al. Effect of donor graft quality on clinical outcomes after deep anterior lamellar keratoplasty. Cornea 2014; 33: 795–800.

43.

Mathers

Lemp

. Vortex keratopathy of the corneal graft. Cornea 1991; 10: 93–99.

44.

Reed

Mannis

Hills

, et al. Corneal epithelial healing after penetrating keratoplasty using topical Healon versus balanced salt solution. Ophthalmic Surg 1987; 18: 525–528.

45.

Lemp

. The surface of the corneal graft: in vivo color specular microscopic study in the human. Trans Am Ophthalmol Soc 1989; 87: 619–657.

46.

Pflugfelder

Solomon

Stern

. The diagnosis and management of dry eye: a twenty-five-year review. Cornea 2000; 19: 644–649.

47.

Tsubota

. Ocular surface management in corneal transplantation, a review. Jpn J Ophthalmol 1999; 43: 502–508.

48.

Lambiase

Rama

Aloe

, et al. Management of neurotrophic keratopathy. Curr Opin Ophthalmol 1999; 10: 270–276.

49.

Tsubota

Goto

Shimmura

, et al. Treatment of persistent corneal epithelial defect by autologous serum application. Ophthalmology 1999; 106: 1984–1989.

50.

Cher

. Blink-related microtrauma: when the ocular surface harms itself. Clin Exp Ophthalmol 2003; 31: 183–190.

51.

Tseng

Di Pascuale

Liu

, et al. Intraoperative mitomycin C and amniotic membrane transplantation for fornix reconstruction in severe cicatricial ocular surface diseases. Ophthalmology 2005; 112: 896–903.

52.

Solomon

Espana

Tseng

. Amniotic membrane transplantation for reconstruction of the conjunctival fornices. Ophthalmology 2003; 110: 93–100.

53.

Tsubota

Satake

Shimazaki

. Treatment of severe dry eye. Lancet 1996; 348: 123.

54.

Chan

Foster

. A step-wise approach to ocular surface rehabilitation in patients with ocular inflammatory disease. Int Ophthalmol Clin 1999; 39: 83–108.

55.

Groden

White

. Porcine collagen corneal shield treatment of persistent epithelial defects following penetrating keratoplasty. CLAO J 1990; 16: 95–97.

56.

Charukamnoetkanok

. Corneal stem cells: bridging the knowledge gap. Semin Ophthalmol 2006; 21: 1–7.

57.

Jones

Downie

Korb

, et al. TFOS DEWS II management and therapy report. Ocul Surf 2017; 15: 575–628.

58.

Driver

Lemp

. Meibomian gland dysfunction. Surv Ophthalmol 1996; 40: 343–367.

59.

Shimazaki

Sakata

Tsubota

. Ocular surface changes and discomfort in patients with meibomian gland dysfunction. Arch Ophthalmol 1995; 113: 1266–1270.

60.

Yao

Zhang

Zhou

, et al. Autologous limbal grafting combined with deep lamellar keratoplasty in unilateral eye with severe chemical or thermal burn at late stage. Ophthalmology 2002; 109: 2011–2017.

61.

Fogla

Padmanabhan

. Deep anterior lamellar keratoplasty combined with autologous limbal stem cell transplantation in unilateral severe chemical injury. Cornea 2005; 24: 421–425.

62.

Gobbels

Spitznas

. Influence of artificial tears on corneal epithelium in dry-eye syndrome. Graefes Arch Clin Exp Ophthalmol 1989; 227: 139–141.

63.

Shore

Foster

Westfall

, et al. Results of buccal mucosal grafting for patients with medically controlled ocular cicatricial pemphigoid. Ophthalmology 1992; 99: 383–395.

64.

Calonge

. The treatment of dry eye. Surv Ophthalmol 2001; 45: S227–S239.

65.

Tai

Cosar

Cohen

, et al. The clinical efficacy of silicone punctal plug therapy. Cornea 2002; 21: 135–139.

66.

Lim-Bon-Siong

Valluri

Gordon

, et al. Efficacy and safety of the ProTek (Vifilcon A) therapeutic soft contact lens after photorefractive keratectomy. Am J Ophthalmol 1998; 125: 169–176.

67.

Cherry

Tutton

Adhikary

, et al. The treatment of pain following photorefractive keratectomy. J Refract Corneal Surg 1994; 10(Suppl. 2): S222–S225.

68.

Romero-Rangel

Stavrou

Cotter

, et al. Gas-permeable scleral contact lens therapy in ocular surface disease. Am J Ophthalmol 2000; 130: 25–32.

69.

Rosenthal

Cotter

Baum

. Treatment of persistent corneal epithelial defect with extended wear of a fluid-ventilated gas-permeable scleral contact lens. Am J Ophthalmol 2000; 130: 33–41.

70.

Matsumoto

Dogru

Goto

, et al. Autologous serum application in the treatment of neurotrophic keratopathy. Ophthalmology 2004; 111: 1115–1120.

71.

Tsubota

Goto

Fujita

, et al. Treatment of dry eye by autologous serum application in Sjögren’s syndrome. Br J Ophthalmol 1999; 83: 390–395.

72.

Versura

Buzzi

Giannaccare

, et al. Targeting growth factor supply in keratopathy treatment: comparison between maternal peripheral blood and cord blood as sources for the preparation of topical eye drops. Blood Transfus 2016; 14: 145–151.

73.

Versura

Buzzi

Giannaccare

, et al. Cord blood serum-based eye drops: the impact of donor haematological and obstetric factors on the variability of epidermal growth factor levels. Blood Transfus 2014; 12(Suppl. 1): S44–S50.

74.

Cosar

Cohen

Rapuano

, et al. Tarsorrhaphy: clinical experience from a cornea practice. Cornea 2001; 20: 787–791.

75.

Anderson

Ellies

Pires

, et al. Amniotic membrane transplantation for partial limbal stem cell deficiency. Br J Ophthalmol 2001; 85: 567–575.

76.

Barabino

Rolando

Bentivoglio

, et al. Role of amniotic membrane transplantation for conjunctival reconstruction in ocular-cicatricial pemphigoid. Ophthalmology 2003; 110: 474–480.

77.

Tabbara

. Ocular complications of vernal keratoconjunctivitis. Can J Ophthalmol 1999; 34: 88–92.

78.

Bonini

. Atopic keratoconjunctivitis. Allergy 2004; 59: S71–S73.

79.

Leonardi

De Dominicis

Motterle

. Immunopathogenesis of ocular allergy: a schematic approach to different clinical entities. Curr Opin Allergy Clin Immunol 2007; 7: 429–435.

80.

Wagoner

Ba-Abbad

and King Khaled Eye Specialist Hospital Cornea Transplant Study Group. Penetrating keratoplasty for keratoconus with or without vernal keratoconjunctivitis. Cornea 2009; 28: 14–18.

81.

Egrilmez

Sahin

Yagci

. The effect of vernal keratoconjunctivitis on clinical outcomes of penetrating keratoplasty for keratoconus. Can J Ophthalmol 2004; 39: 772–777.

82.

Thomas

Guel

Thomas

, et al. The role of atopy in corneal graft survival in keratoconus. Cornea 2011; 30: 1088–1097.

83.

Feizi

Javadi

, et al. Deep anterior lamellar keratoplasty in keratoconic patients with versus without vernal keratoconjunctivitis. J Ophthalmic Vis Res 2015; 10: 112–117.

84.

Arora

Jain

, et al. Results of deep anterior lamellar keratoplasty for advanced keratoconus in children less than 18 years. Am J Ophthalmol 2016; 162: 191–198.e2.

85.

Leonardi

. Management of vernal keratoconjunctivitis. Ophthalmol Ther 2013; 2: 73–88.

86.

Costa

AXD

Gomes

JÁP

Marculino

LGC

, et al. Supratarsal injection of triamcinolone for severe vernal keratoconjunctivitis in children. Arq Bras Oftalmol 2017; 80: 186–188.

87.

Avunduk

Kapicioglu

, et al. Mechanisms and comparison of anti-allergic efficacy of topical lodoxamide and cromolyn sodium treatment in vernal keratoconjunctivitis. Ophthalmology 2000; 107: 1333–1337.

88.

Hida

Nogueira

Schaefer

, et al. [Comparative study between 0.025% ketotifen fumarate and 0.1% olopatadine hydrochloride in the treatment of vernal keratoconjunctivitis]. Arq Bras Oftalmol 2006; 69: 851–856.

89.

D’Angelo

Lambiase

Cortes

, et al. Preservative-free diclofenac sodium 0.1% for vernal keratoconjunctivitis. Graefes Arch Clin Exp Ophthalmol 2003; 241: 192–195.

90.

Sharma

Gupta

Ram

, et al. Topical ketorolac 0.5% solution for the treatment of vernal keratoconjunctivitis. Indian J Ophthalmol 1997; 45: 177–180.

91.

Kosrirukvongs

Luengchaichawange

. Topical cyclosporine 0.5 per cent and preservative-free ketorolac tromethamine 0.5 per cent in vernal keratoconjunctivitis. J Med Assoc Thai 2004; 87: 190–197.

92.

Leonardi

Bogacka

Fauquert

, et al. Ocular allergy: recognizing and diagnosing hypersensitivity disorders of the ocular surface. Allergy 2012; 67: 1327–1337.

93.

Yücel

Ulus

. Efficacy and safety of topical cyclosporine A 0.05% in vernal keratoconjunctivitis. Singapore Med J 2016; 57: 507–510.

94.

Oray

Toker

. Tear cytokine levels in vernal keratoconjunctivitis: the effect of topical 0.05% cyclosporine a therapy. Cornea 2013; 32: 1149–1154.

95.

Daniell

Constantinou

, et al. Randomised controlled trial of topical ciclosporin A in steroid dependent allergic conjunctivitis. Br J Ophthalmol 2006; 90: 461–464.

96.

Akpek

Dart

Watson

, et al. A randomized trial of topical cyclosporin 0.05% in topical steroid-resistant atopic keratoconjunctivitis. Ophthalmology 2004; 111: 476–482.

97.

Ebihara

Ohashi

Uchio

, et al. A large prospective observational study of novel cyclosporine 0.1% aqueous ophthalmic solution in the treatment of severe allergic conjunctivitis. J Ocul Pharmacol Ther 2009; 25: 365–372.

98.

Pucci

Caputo

Mori

, et al. Long-term safety and efficacy of topical cyclosporine in 156 children with vernal keratoconjunctivitis. Int J Immunopathol Pharmacol 2010; 23: 865–871.

99.

Tesse

Spadavecchia

Fanelli

, et al. Treatment of severe vernal keratoconjunctivitis with 1% topical cyclosporine in an Italian cohort of 197 children. Pediatr Allergy Immunol 2010; 21: 330–335.

100.

Kiliç

Gurler

. Topical 2% cyclosporine A in preservative-free artificial tears for the treatment of vernal keratoconjunctivitis. Can J Ophthalmol 2006; 41: 693–698.

101.

Zhai

Yuan

, et al. Tacrolimus in the treatment of ocular diseases. Biodrugs 2011; 25: 89–103.

102.

Chatterjee

Agrawal

. Tacrolimus in corticosteroid-refractory vernal keratoconjunctivitis. Cornea 2016; 35: 1444–1448.

103.

Miyazaki

Fukushima

Ohashi

, et al. Steroid-sparing effect of 0.1% Tacrolimus eye drop for treatment of shield ulcer and corneal epitheliopathy in refractory allergic ocular diseases. Ophthalmology 2017; 124: 287–294.

104.

Occasi

Duse

Nebbioso

, et al. Vernal keratoconjunctivitis treated with omalizumab: a case series. Pediatr Allergy Immunol 2017; 28: 503–505.

105.

Mahdy

Nada

Marei

. Subcutaneous allergen-specific immunotherapy versus topical treatment in vernal keratoconjunctivitis. Cornea 2012; 31: 525–528.

106.

Chang

Gabison

Kato

, et al. Corneal neovascularization. Curr Opin Ophthalmol 2001; 12: 242–249.

107.

Cursiefen

Küchle

Naumann

. Angiogenesis in corneal diseases: histopathologic evaluation of 254 human corneal buttons with neovascularization. Cornea 1998; 17: 611–613.

108.

Lee

Chung

. The effect of subconjunctival suramin on corneal neovascularization in rabbits. Cornea 2010; 29: 86–92.

109.

Awadein

. Subconjunctival bevacizumab for vascularized rejected corneal graft. J Cataract Refract Surg 2007; 33: 1991–1993.

110.

Dana

Schaumberg

Kowal

, et al. Corneal neovascularization after penetrating keratoplasty. Cornea 1995; 14: 604–609.

111.

Al-Torbak

Al-Amri

Wagoner

. Deep corneal neovascularization after implantation with intrastromal corneal ring segments. Am J Ophthalmol 2005; 140: 926–927.

112.

Cursiefen

Wenkel

Martus

, et al. Impact of short-term versus long-term topical steroids on corneal neovascularization after non-high-risk keratoplasty. Graefes Arch Clin Exp Ophthalmol 2001; 239: 514–521.

113.

Manzano

Peyman

Khan

, et al. Inhibition of experimental corneal neovascularisation by bevacizumab (Avastin). Br J Ophthalmol 2007; 91: 804–807.

114.

Hosseini

Nejabat

Mehryar

, et al. Bevacizumab inhibits corneal neovascularization in an alkali burn induced model of corneal angiogenesis. Clin Exp Ophthalmol 2007; 35: 745–748.

115.

Erdurmus

Totan

. Subconjunctival bevacizumab for corneal neovascularization. Graefes Arch Clin Exp Ophthalmol 2007; 245: 1577–1579.

116.

Foroutan

Fariba

Pejman

, et al. Perilimbal bevacizumab injection for interface neovascularization after deep anterior lamellar keratoplasty. Cornea 2010; 29: 1268–1272.

117.

Feizi

Azari

Safapour

. Therapeutic approaches for corneal neovascularization. Eye Vis (Lond) 2017; 4: 28.

118.

Baer

Foster

. Corneal laser photocoagulation for treatment of neovascularization. Efficacy of 577 nm yellow dye laser. Ophthalmology 1992; 99: 173–179.

119.

L’Esperance

Jr . Clinical photocoagulation with the organic dye laser. A preliminary communication. Arch Ophthalmol 1985; 103: 1312–1316.

120.

Marsh

. Argon laser treatment of lipid keratopathy. Br J Ophthalmol 1988; 72: 900–904.

121.

Faraj

Elalfy

Said

, et al. Fine needle diathermy occlusion of corneal vessels. Br J Ophthalmol 2014; 98: 1287–1290.

122.

Kamiya

Hori

Kagaya

, et al. Preservation of donor cornea prevents corneal allograft rejection by inhibiting induction of alloimmunity. Exp Eye Res 2000; 70: 737–743.

123.

Sharma

Kandar

Singh Titiyal

. Stromal rejection after big bubble deep anterior lamellar keratoplasty: case series and review of literature. Eye Contact Lens 2013; 39: 194–198.

124.

Javadi

Feizi

Jamali

, et al. Deep anterior lamellar keratoplasty using the big-bubble technique in keratoconus. J Ophthalmic Vis Res 2009; 4: 8–13.

125.

Borderie

Guilbert

Touzeau

, et al. Graft rejection and graft failure after anterior lamellar versus penetrating keratoplasty. Am J Ophthalmol 2011; 151: 1024–1029.e1.

126.

Olson

Basti

. Stromal rejection following deep anterior lamellar keratoplasty: implications for postoperative care. Cornea 2012; 31: 969–973.

127.

Tullo

. Pathogenesis and management of herpes simplex virus keratitis. Eye (Lond) 2003; 17: 919–922.

128.

Watson

Tuft

Dart

. Patterns of rejection after deep lamellar keratoplasty. Ophthalmology 2006; 113: 556–560.

129.

Roberts

Maycock

O’Brart

. Late stromal rejection in deep anterior lamellar keratoplasty: a case series. Cornea 2016; 35: 1179–1181.

130.

Giannaccare

Weiss

Sapigni

, et al. Immunologic stromal rejection after deep anterior lamellar keratoplasty with grafts of a larger size (9 mm) for various stromal diseases. Cornea 2018; 37: 967–972.

131.

Gonzalez

Price

Feng

, et al. Immunologic rejection episodes after deep anterior lamellar keratoplasty: incidence and risk factors. Cornea 2017; 36: 1076–1082.

132.

Javadi

Feizi

Javadi

, et al. Deep anterior lamellar keratoplasty using fresh versus cryopreserved corneas. Ophthalmology 2014; 121: 610–611.

133.

Guilbert

Bullet

Sandali

, et al. Long-term rejection incidence and reversibility after penetrating and lamellar keratoplasty. Am J Ophthalmol 2013; 155: 560–569.e2.

134.

Cheng

Visser

Schouten

, et al. Endothelial cell loss and visual outcome of deep anterior lamellar keratoplasty versus penetrating keratoplasty: a randomized multicenter clinical trial. Ophthalmology 2011; 118: 302–309.

135.

Kornmann

Gedde

. Glaucoma management after corneal transplantation surgeries. Curr Opin Ophthalmol 2016; 27: 132–139.

136.

Liesegang

Melton

3rd Daly

, et al. Epidemiology of ocular herpes simplex. Incidence in Rochester, Minn, 1950 through 1982. Arch Ophthalmol 1989; 107: 1155–1159.

137.

Hamrah

Cruzat

Dastjerdi

, et al. Corneal sensation and subbasal nerve alterations in patients with herpes simplex keratitis: an in vivo confocal microscopy study. Ophthalmology 2010; 117: 1930–1936.

138.

Liu

Zhou

Huang

, et al. Clinical evaluation of deep anterior lamellar keratoplasty using glycerol-cryopreserved corneal tissues for refractory herpetic stromal keratitis: an observational study. Medicine (Baltimore) 2016; 95: e4892.

139.

Lyall

Tarafdar

Gilhooly

, et al. Long term visual outcomes, graft survival and complications of deep anterior lamellar keratoplasty in patients with herpes simplex related corneal scarring. Br J Ophthalmol 2012; 96: 1200–1203.

140.

Zhou

Zhang

, et al. Long-term comparison of full-bed deep lamellar keratoplasty with penetrating keratoplasty in treating corneal leucoma caused by herpes simplex keratitis. Am J Ophthalmol 2012; 153: 291–299.e2.

141.

Halberstadt

Machens

Gahlenbek

, et al. The outcome of corneal grafting in patients with stromal keratitis of herpetic and non-herpetic origin. Br J Ophthalmol 2002; 86: 646–652.

142.

Ficker

Kirkness

Rice

, et al. Longterm prognosis for corneal grafting in herpes simplex keratitis. Eye (Lond) 1988; 2: 400–408.

143.

Goodfellow

Nabili

Jones

, et al. Antiviral treatment following penetrating keratoplasty for herpetic keratitis. Eye (Lond) 2011; 25: 470–474.

144.

Awan

Roberts

Hegarty

, et al. The outcome of deep anterior lamellar keratoplasty in herpes simplex virus-related corneal scarring, complications and graft survival. Br J Ophthalmol 2010; 94: 1300–1303.