Visual function assessment of Chinese cataract patients after individual aspheric intraocular lens implantation according to preoperative cornea spherical aberration

Abstract

BACKGROUND:

Aspheric intraocular lens (IOLs) implantation has been widely applied in cataract surgery. However, there is no consensus on the optimal guidance for the operations in IOLs implantation.

OBJECTIVE:

This study evaluated the visual function of Chinese cataract patients six months after cataract surgery with two different guiding ideologies.

METHODS:

We evaluated 50 patients (61 eyes) with implantation of different aspheric IOLs (SN60WF IOLs, ZCB00 IOLs, PY-60AD IOLs, AO IOLs) 6 months after cataract surgery. Twenty-four patients (30 eyes) under individual implantation were ascribed to group 1 and 26 patients (31 eyes) with randomized implantation were ascribed to the control group (group 2). Postoperatively parameters included monocular best-corrected visual acuity (BCVA), contrast sensitivity (CS), total spherical aberration Z (4, 0) at 5 mm pupil size, and patient satisfaction. The quality of life after operation was assessed through the National Eye Institute Visual Function Questionnaire-25 (NEI VFQ-25).

RESULTS:

Six months after cataract operation, the contrast sensitivity with glare of group 1 at 2.5 ${}^{\circ}$ was 0.697 $\pm$ 0.027, and 0.532 $\pm$ 0.049 in group 2. Besides, there was no significant difference at any other special frequency. The mean spherical aberration Z (4, 0) at 5 mm pupil size in group 1 was 0.015 $\pm$ 0.028 um, and in group 2 was 0.043 $\pm$ 0.109 um, with a significant difference ( $p<$ 0.01). The mean scores obtained from NEI VFQ-25 were not significantly different.

CONCLUSION:

It is effective to implant aspheric IOLs individually according to preoperative corneal spherical aberration. Patients obtained better contrast sensitivity with glare at 2.5 ${}^{\circ}$ , but there was no significant difference in BCVA, contrast sensitivity at other special frequency, and subjective visual function.

Keywords

Visual function cataract aspheric intraocular lens implantation best-corrected visual acuity contrast sensitivity

1. Introduction

There is a negative spherical aberration in crystalline lens and a positive spherical aberration in cornea. As time goes on, the crystalline lens becomes progressively more positive in spherical aberration while the cornea remains, resulting in a gradual loss of balance between cornea and lens. That is the base of developing aspheric intraocular lensues (IOLs) with a negative or free spherical aberration to counter balance the positive spherical aberration of the cornea [1].

A previous study showed that the mean spherical aberration of Caucasian cornea is $+$ 0.27 um [2]. According to this data, there are different types of negative aspheric IOLs used in the clinic, e.g. AcrySof IQ (Alcon, Fort Worth, TX, USA) with $-$ 0.20 um, Akreos AO (Bausch & Lomb, Clearwater, FL, USA) with 0 aberration, Tecnis ZCB00 (AMO Inc., Santa Ana, CA, USA) with $-$ 0.27 um, HOYA PY60-AD (Shinjuku-ku, Tokyo Japan) with $-$ 0.18 um.

Aspheric IOLs have been widely applied in current cataract surgery as a basal dioptrical lens nowadays. Patients and surgeons are both eager to get not only good visual acuity but also good visual quality, which lead up to the phrase: functional vision. There are different ways to evaluate objective and subjective visual acuity such as BCVA, contrast sensitivity, wavefront aberration, subjective visual symptoms, and patient satisfaction.

Nevertheless, although many previous studies demonstrated that aspheric IOLs provided better outcomes compared with conventional spherical IOLs [3, 4, 5] there is no gold standard to choose a particular guide on the scheme of aspheric IOL operations. In one study, the performance of implantation of A1-UV and SN60WF aspheric intraocular lens is comparable [6]. Another study demonstrated that aspheric diffractive multifocal IOL can provide patients with better vision and can effectively alleviate the high order aberrations and spherical aberration [7]. Apart from the choice of the lens, other factors such as patient’s age also affect the adaptation to novel IOL [8], and there is tendency of personalized scheme of aspheric IOL implantation based on corneal spherical aberration [9, 10].

In this study, we designed two groups both with aspheric IOL implantation, but according to two different guiding ideologies. Patients in group 1 were implanted aspheric IOLs according to their preoperative cornea spherical aberrations measured by the iTrace View Function Analyzer, and the other group was stochastic. We evaluated the parameters of objective and subjective visual acuity to observe the effect.

2. Methods

Fifty patients (61 eyes) who were scheduled to undergo cataract surgery from March to October 2014 at Qianfoshan Hospital, Shandong University, China, were included in this prospective study. There were 24 patients in group 1 (iTrace guided), mean age 65.58 $\pm$ 8.29, and 26 patients in group 2 (randomized), mean age 62.65 $\pm$ 9.09. We applied sample power analysis using the online resources (www.stat.ubc.ca/ $\sim$ rollin/stats/ssize/n2) to ensure that the sample size meets the statistical power requirement.

Table 1
Patients characteristics

Characteristic	Control group	i-Trace guided group
No. of patients/No. of eyes	26/31	24/30
Male/female	12/14	10/14
Age (year)	62.65 $\pm$ 9.09 (57–82)	65.58 $\pm$ 8.29 (53–78)
IOL power (D)	21.19 $\pm$ 1.68 (17.5–25.0)	20.90 $\pm$ 2.12 (17.5–25.5)
Axial length (mm)	23.60 $\pm$ 0.95 (22.21–25.66)	23.79 $\pm$ 1.09 (21.94–25.63)
BCVA preoperational (logM)	0.79 $\pm$ 0.42 (0.30–2.00)	0.76 $\pm$ 0.30 (0.30–1.50)

The patient characteristics are shown in Table 1. Exclusion criteria were: systemic diseases receiving medications, corneal endothelial cell density less than 1500/mm ${}^{2}$ , history of previous ocular surgery, glaucoma, axial length more than 26 mm, astigmatism measured by keratometry greater than 1.5D, vitreoretinal disease, complications occurred during or after operation, moderate or severe posterior capsular opacity (PCO), refused to attend or lost to follow-up. Informed consent was obtained from all patients or their authorized agents before participation in this study. The study was approved by the ethics committee of Shandong University.

Patients were divided into two groups. Group 1 was called iTrace guided implantation group, in this group patients had aspheric IOL implantation in order to decrease their spherical aberration as far as possible according to the cornea spherical aberration measured by iTrace analyzer preoperatively, and if the spherical aberration of cornea was $+$ 0.1 um, we selected the aspheric IOL with 0 in order to maintain the depth of focus instead of choosing a $-$ 0.2 um aspheric IOL [11]. The criteria for group 1 was: preoperative cornea spherical aberration no more than 0.1 um, implanted with AO IOLs; preoperative cornea spherical aberration between 0.1 to 0.19 um, implanted with PY60 IOLs; preoperative cornea spherical aberration between 0.19 to 0.23 um, implanted with IQ IOLs; preoperative cornea spherical aberration more than 0.23 um, implanted with ZCB00 IOLs. Group 2 was the randomized implantation group. In this group patients had aspheric IOL implantation stochastically from the four types. Using Excel random number generator: random numbers from 0 to 1 were created and patients with a number inferior to 0.5 ( $n=$ 24) were included in group 1 and patients with a number superior to 0.5 ( $n=$ 26) were included in group 2. The detailed characteristics of the 4 types of aspheric IOLs are shown in Table 2.

Table 2

Detail parameters of the 4 aspheric IOL

Parameters	AcrySof IQ	Akreos AO	ZCB00	PY60-AD
Haptic
Design	1-piece	1-piece	1-piece	3-pieces
Material	Hydrophobic acrylic	Hydrophilic acrylic	Hydrophobic acrylic	PMMA
Length (mm)	13.0	10.5–11.0	13.0	12.5
Angle (degree)	0	10	0	5
Optic
Shape	biconvex	biconvex	biconvex	biconvex
Design	Aspheric posterior	Anterior and posterior	Aspheric anterior	Equilibrium curve
Material	Hydrophobic acrylic	Hydrophilic acrylic	Hydrophobic acrylic	Hydrophobic acrylic
Diameter (mm)	6.0	6.2	6.0	6.0
Refractive index	1.55	1.47	1.47	1.54
A-constant	118.7	118.4	118.8	118.4
SE (um)	$-$ 0.2	0	$-$ 0.27	$-$ 0.18

Preoperative evaluations included monocular best-corrected visual acuity (BCVA), intraocular pressure, axial length, corneal endothelial cell density (Topcon, Japan), A/B-scan (Aviso, France), OCT of macula, fundus photography (Cannon, Japan), corneal topography (Opticon, Italy), IOL-Master (Carl Zeiss, Germany) and the spherical aberration of cornea (iTrace, Tracey VFA, USA). Each data was collected three times by the same operator. The target refraction after operation was selected to be around $-$ 0.50D.

All operations were performed by the same surgeon (Gf. Dang) with the standard phacoemulsification procedure, included topical anesthesia, a 2.2 mm upper clear corneal incision, a 5.0 mm to 5.5 mm continuous curvilinear capsulorhexis, hydrodissection, phaco-chop, irrigation and aspiration of cortex using the single-handed micro-coaxial system on the Infinity machine (Alcon). Intraocular lenses were implanted with their respective IOL delivery systems. The incision was closed by hydration without suture. No complication occurred during all these operations and IOLs were implanted in the center of capsula lentis.

Postoperative evaluations included slit-lamp microscope examination, monocular BCVA, intra-ocular pressure, and vitro-retinal examination at 1 day, 3 days, and 1 week. After 6 months, besides the examinations above, a subjective refraction test, contrast sensitivity, wavefront aberration, and subjective quality of life were also assessed.

Patients were tested monocularly with normal pupils and full refractive correction at different spatial frequencies by the Contrast sensitivity tester CGT-1000 (Takagi Seiko, Japan) under moderate lighting condition. We assessed the patients’ wavefront aberrations by the iTrace View Function Analyzer after pharmacologic mydriasis (phenylephrine hydrochloride 0.5% and tropicamide 0.5% twice every 15 minutes). Three consecutive measurements were performed by the same operator. The spherical aberration Z (4, 0) at a 5.0-mm pupil diameter was automatically calculated by the aberrometer. Patients also completed the National Eye Institute Visual Functioning Questionnaire-25 (NEI VFQ-25) to evaluate their subjective visual quality including physical, emotional and social visual function. From 0–100, the higher the scores, the better the vision-related quality of life.

Statistical analysis was performed using SPSS 20.0. Variables were tested for normality and homogeneity of variances. Independent $t$ -test was used to compare demographic data, contrast sensitivity, spherical aberrations, and questionnaire scores between the two groups when the data showed normality. Wilcoxon rank sum test was performed to assess whether there was a difference between the two population distribution of the grade data (BCVA score). It was considered statistically significant when the $p$ value was less than 0.05.

3. Results

3.1 Preoperative spherical aberration on cornea

Mean preoperative cornea spherical aberration of all the patients in our study was 0.31 $\pm$ 0.13 um. The value was 0.30 $\pm$ 0.14 um in group 1, and 0.31 $\pm$ 0.13 um in group 2, there was no significant difference between the two groups ( $p=$ 0.981, independent $t$ -test). Figure 1 shows the data of patients’ spherical aberration on cornea in each group.

Figure 1.

The patients’ spherical aberration on cornea in each group. Mean preoperative cornea spherical aberration of all the patients in our study was 0.31 $\pm$ 0.13 um. It was 0.30 $\pm$ 0.14 um in group 1 ( $n=$ 24), and 0.31 $\pm$ 0.13 um in group 2 ( $n=$ 26) ( $p=$ 0.981).

3.2 Best corrected visual acuity (BCVA)

Both groups showed satisfactory BCVA after operation. Group 1 (iTrace guided) reached 0.03 $\pm$ 0.06 log MAR and its mean BCVA was 0.76 $\pm$ 0.30, while group 2 (randomized) had 0.05 $\pm$ 0.07 log MAR and its mean BCVA was 0.79 $\pm$ 0.42. There was no significant difference between the two groups in terms of BCVA score distribution 6 months after the operation ( $p=$ 0.272, Wilcoxon rank sum test).

3.3 Contrast sensitivity

Six months after cataract operation, the contrast sensitivity of the iTrace guided group at 2.5 ${}^{\circ}$ was 0.697 $\pm$ 0.027, and was 0.532 $\pm$ 0.049 for the control group, the difference is significant ( $p=$ 0.001, independent $t$ -test). As shown in Fig. 2, contrast sensitivity with or without glare was not significantly different between the two groups at any other spacial frequency.

Figure 2.

The contrast sensitivity with and without glare at different spacial frequencies in each group. After cataract operation, the contrast sensitivity of group 1 ( $n=$ 24) at 2.5 ${}^{\circ}$ was 0.697 $\pm$ 0.027, and the group 2 ( $n=$ 26) was 0.532 $\pm$ 0.049 ( $p=$ 0.001).

Figure 3.

The entire spherical aberration Z (4, 0) after surgery at 5 mm pupil size in each group. The average spherical aberration Z (4, 0) was 0.015 $\pm$ 0.028 um in the group 1 ( $n=$ 24) and 0.043 $\pm$ 0.109 um in the group 2 ( $n=$ 26) ( $p=$ 0.0001).

Figure 4.

The score of the NEI VFQ-25 questionnaire in each group. The mean score in group 1 was 78.07 $\pm$ 3.36 ( $n=$ 24), and in group 2 was 76.74 $\pm$ 3.37 ( $n=$ 26) ( $p=$ 0.683).

3.4 Spherical aberration after operation

Six months after cataract surgery, the spherical aberration at 5 mm mydriatic pupil was shown in Fig. 3. The average spherical aberration Z (4, 0) was 0.015 $\pm$ 0.028 um in the iTrace guiding group and 0.043 $\pm$ 0.109 um in the random implantation group. The difference was statistically significant ( $p=$ 0.0001, independent $t$ -test).

3.5 Subjective visual quality

There was no significant statistical difference between the 2 groups on the result of the NEI VFQ-25 questionnaire, the mean score in group 1 was 78.07 $\pm$ 3.36, while it was was 76.74 $\pm$ 3.37 in group 2 ( $p=$ 0.683, independent $t$ -test), as shown in Fig. 4.

4. Discussion

There are a multitude of aspheric IOLs securable worldwide, and it has been confirmed that patients with aspheric IOLs implantation will get a splendid visual quality than those with spherical IOLs implantation repeatedly [12]. A number of ophthalmological investigators devoted into different kinds of aspheric IOLs manufacture. Accordingly, more and more doctors and patients are inclined to choose aspheric IOL implantation in their cataract surgery.

In our study, we evaluated the parameters represented the functional vision including BCVA, contrast sensitivity, spherical aberration after operation, and subjective visual acuity, to investigate whether individual aspheric IOLs (four types available in our hospital) implantation according to patients’ cornea spherical aberration before operation can lead to positive results.

Mean spherical aberration on cornea from all these Chinese individuals was 0.31 $\pm$ 0.13 $\mu$ m which was slightly greater than proverbial $+$ 0.27 $\mu$ m. This result is similar to Lim and Fam’s study in the Chinese population [13]. The minimum was 0.016 $\mu$ m, and the maximum was 0.731 $\mu$ m, proving that corneal spherical aberration in our cohort of patients distributed so widely that just a spot of types aspheric IOLs cannot satisfy all the demands.

The results showed that both groups achieved good and similar visual acuity. Monocular BCVA of 20/25 was achieved in 93.3% of eyes in the iTrace guided group and in 87.1% of eyes in the randomized group. At the mention of postoperative spherical aberration, group 1 (iTrace guided group) scored significantly lower than group 2 (randomized group) with a lot of benefit from preoperative intervention. There were several factors affect the postoperative spherical aberration such as the diameter of capsulorhexis, effective position of IOL, astigmatism incoming with incision, and the pupil center shift [14, 15]. Postoperative contrast sensitivity at 2.54 special frequency of group 1 was better than group 2, however, the disparity of contrast sensitivity at other special frequency between two groups was quite slight and did not result in any significant difference. This is similar to Srirampur’s study [16]. That is to say, although we corrected the spherical aberration as much as we can in group 1, we did not receive better contrast sensitivity. We surmise that contrast sensitivity and spherical aberration are different categories to describe functional vision. Although high spherical aberration will reduce contrast sensitivity in a measurable and meaningful manner, it does not mean tiny spherical aberration can lead to great contrast sensitivity. Contrast sensitivity measures the total visual system quality in terms of contrast, whereas wavefront aberration measures the optical quality in terms of special distortion [17]. Many complicated factors influence contrast sensitivity manifestation, retina function is the most important one of them. About two thirds studies did not report significant difference in contrast sensitivity between spherical and aspheric IOLs [18], which is similar to our result.

We assessed the subjective visual quality through the NEI VFQ-25 questionnaire, because quality of vision does not depend on central visual acuity alone, it is widely used to evaluate health-related quality of life [18]. In our study, group 1 obtained 77.07 $\pm$ 5.13 and group 2 obtained 75.77 $\pm$ 5.08. Each group included two patients with glare and halo disturbance, which might be caused due to small differences at the edge design, the refractive index, the optic diameter, and material of the IOL [19, 20, 21].

Visual function refers to the ability or function connected to visual acuity during all the human activities, such as reading, movement, orientation and self-care [22]. Another study using a subjective depth-of-focus analysis in a multivariate model found no correlation between final spherical aberration and objective quality of vision measurements [23]. Zhu et al. illustrated that a host of situations affected patients’ functional vision after cataract surgery, such as changes of reading habit, stereopsis vision, xerophthalmia after surgery, the lost of accommodation with a single focus IOL [24]. The major complaint after cataract surgery is pseudophakic dysphotopsias with positive or negative forms [25]. Positive dysphotopsias refer to bright artifacts present in only certain lighting conditions Negative dysphotopsias block light from reaching the retina, resulting in shadows or dark spots that often are in the temporal visual field [26].

In addition, a previous report suggests that intravitreal injection angle affects the subsequent ocular tissue damage [27]. Therefore, the optimal angle of IOL implantation during operation needs to be evaluated to avoid undesirable consequences. Besides, it has been shown that in keratoconus patients, piggy-back lens greatly enhances corrected visual acuity and comfort level [28]. The application of piggy-back lens in cataract patients remains to be assessed.

This study had certain limitations. First, the study setting may have been biased toward aspheric IOLs, there is currently no IOL able to correct more than 0.27 um of corneal spherical aberration, therefore, it cannot be called individual implantation. Second, in our study, there were four different kinds of aspheric IOLs, there might be some patients with different cornea spherical aberration on bilateral eyes. If these patients were assigned to group 1, they might get two different aspheric IOLs bilaterally. This may lead to variations on the results of objective visual quality and NEI VFQ-25 score. Third, although the sample size meets the requirement of statistical power analysis, a larger sample size will provide more convincing conclusions.

5. Conclusion

Individual aspheric IOLs can provide good visual outcomes for cataract patients, the patients’ spherical aberration were decreased extremely compared with randomized. However, other descriptive parameters of functional vision including the contrast sensitivity and subjective visual quality did not increase incidentally. It remains a goal to make cataract patients see more clearly and more comfortable after operation, also it is necessary to develop a new more subjective, sensitive and effective standard to evaluate Chinese function visual acuity. It is not easy to implant custom-made IOL, but maybe that is the target we should struggle for.

Funding

This study was supported by the Natural Science Foundation of Shandong Province (ZR2010HL016).

Ethics statement

All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Declaration of Helsinki and its later amendments or comparable ethical standards. The study was approved by Qianfoshan Hospital, Shandong University.

Footnotes

Acknowledgments

None to report.

Conflict of interest

None of the authors have any conflict of interest to declare.

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Visual function assessment of Chinese cataract patients after individual aspheric intraocular lens implantation according to preoperative cornea spherical aberration

Abstract

BACKGROUND:

OBJECTIVE:

METHODS:

RESULTS:

CONCLUSION:

Keywords

1. Introduction

2. Methods

Table 1 Patients characteristics

3.1 Preoperative spherical aberration on cornea

3.3 Contrast sensitivity

3.5 Subjective visual quality

4. Discussion

5. Conclusion

Funding

Ethics statement

Footnotes

Acknowledgments

Conflict of interest

References

Table 1
Patients characteristics