Influences of Tropicamide on Anterior Segment Parameters with Pentacam in Healthy Individuals

Abstract

Background:

This study aims to investigate the effects of tropicamide 1% on the main numerical parameters of anterior segment with the Pentacam rotating Scheimpflug camera in healthy individuals.

Methods:

Pentacam measurements of 50 (25 female and 25 male) healthy individuals before and after 25 min of tropicamide 1% instillation were performed and compared. For comparison of the test parameters, paired t-test was used in the groups.

Results:

Mean age in the study group was 28.40±4.58 years (range 18–35 years). Measurements between 2 sessions were significantly different for the parameters of anterior chamber depth (ACD) and anterior chamber volume (ACV) (P<0.05).

Conclusions:

Tropicamide 1% instillation leads to a significant increment in ACD and ACV measurements. Effects of tropicamide on these parameters for Pentacam measurements should be considered to ensure exact clinical interpretation in ophthalmologic practice.

Introduction

Evaluation of anterior segment parameters is an important component of ophthalmic examination. Imaging of the anterior segment has traditionally been carried out with slit-lamp biomicroscopy, but objective quantitative assessment of anterior segment parameters was limited. Also direct visualization of the anterior chamber angle (ACA) could only be carried out with the help of diagnostic contact lenses. However, new developed devices such as the Pentacam rotating Scheimpflug camera (Oculus Optikgeräte GmbH, Wetzlar, Germany) promises quantitative information and qualitative imaging of the anterior and posterior surfaces of the cornea, anterior chamber depth (ACD), ACA, iris, and lens.¹

The assessment of the anterior segment parameters may enable important information that helps our knowledge and understanding of ocular pharmacokinetics, aqueous humor dynamics, primary open-angle glaucoma, and pigmentary glaucoma. Additionally, quantitative documentation of alterations in anterior segment parameters may provide useful information for accurate intraocular lens (IOL) power calculation, piggyback IOL implantation, and IOL exchange surgeries.

Tropicamide is a medication that is almost routinely used in ophthalmologic examination to provide temporary midriasis. It is a tropic acid derivative endowed with short duration of antimuscarinic activity. It is available in 0.5% and 1% ophthalmic solutions. Its maximum effect is achieved in about 20–25 min and lasts about 20 min, with complete recovery being in ∼6 h.^2,3 The effects of tropicamide on corneal thickness in myopic patients, the effects of intraocular pressure, and anterior segment parameters in children were studied earlier.^4,5

In this prospective study, we aimed to investigate the influences of tropicamide 1% instillation on ACD, anterior chamber volume (ACV), ACA width, central corneal thickness (CCT), mean astigmatism, and keratometry in healthy individuals. To the best of our knowledge, the alterations in these parameters in healthy adult population have not been previously reported.

Methods

A total of 50 healthy individuals (25 male and 25 female) with no refractive errors (emetropic) with the mean age of 28.40±4.58 years (range 18–35 years) were enrolled. None of the individuals had corneal pathology, glaucoma, uveitis, posterior segment pathology, history of previous eye surgery or trauma, history of using topical/systemic medications or systemic diseases, which could interfere with the eye structure. None of the individuals had the history of contact lens use for any reasons (refractive, cosmetic, etc.).

All cases were evaluated before and 30 min after instillation of one drop of tropicamide 1% with the Pentacam. The drops were administered by an ophthalmic technician, and all Pentacam analysis was performed by the same ophthalmologist. All measurements were obtained under standart dim light conditions. The technique of Pentacam analysis has been described previously.^6,7 The Pentacam system CES system is based on a 180° rotating Scheimpflug camera that can take 12–50 single images to reconstruct the anterior chamber. In this study, anterior segment reconstructions were produced with 25 single captures. After completing a scan, Pentacam software constructs the 3-dimensional image of the anterior segment and calculates the anterior chamber parameters. This imaging provides measurements of ACD, ACV, ACA width, CCT, pupil size, and keratometry.

Statistical analysis was performed with spss for Windows Version 12.0 (SPPS Inc., Chicago, IL). All data were reported as averages±standard deviations (SD). A paired t-test was used to compare variables between the pre- and post-tropicamide conditions. A value of P<0.05 was considered statistically significant. Repeatability analysis of study parameters measured with Pentacam was evaluated with coefficient of variation (CV). CV is defined as the ratio of the SD to the mean: \documentclass{aastex}\usepackage{amsbsy}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{bm}\usepackage{mathrsfs}\usepackage{pifont}\usepackage{stmaryrd}\usepackage{textcomp}\usepackage{portland, xspace}\usepackage{amsmath, amsxtra}\pagestyle{empty}\DeclareMathSizes{10}{9}{7}{6}\begin{document} \begin{align*}C_v = \frac { \sigma } { \mu } \end{align*} \end{document}

For CV calculation of study parameters measured by Pentacam, 10 consequential measurements were performed by the same operator to the same adult volunteer's same eye with a period of 2 min.

Written informed consent was obtained from all patients. The study protocol was reviewed and approved by the appropriate institutional ethics committees and health authorities and was conducted in accordance with the Declaration of Helsinki.

Results

Mean ACD measurements of the right and the left eyes were 3.06±0.37 mm (range 2.30–3.76 mm) pretropicamide and 3.16±0.33 mm (range 2.53–3.85 mm) post-tropicamide, and 3.11±0.38 mm (range 2.33–3.80 mm) pretropicamide and 3.19±0.34 mm (range 2.53–3.90 mm) post-tropicamide, respectively (Table 1). The increments in ACD in both eyes were significant (P<0.0001; paired t-test).

Table 1.

The Measured Values of Keratometry, Astigmatism, CCT, ACD, ACV, ACA, and Pupil Diameter in the Study Group

	Pretropicamide	Post-tropicamide	Mean difference	SD of the difference	P value
R Mean keratometry	43.40	43.41	0.01	0.10	0.842
R Mean astigmatism	0.890	0.884	0.06	0.21	0.845
R CCT	556.18	555.60	0.58	20.35	0.841
R ACD	3.06	3.16	−0.10	0.08	0.000^a
R ACV	171.86	181.44	−9.58	15.85	0.000^a
R ACA	36.40	34.28	2.12	9.15	0.107
R Pupil diameter	3.22	5.96	0.66	0.09	0.000^a
L Mean keratometry	43.41	43.42	0.01	0.12	0.830
L Mean astigmatism	0.860	0.800	0.06	0.42	0.344
L CCT	558.46	557.96	0.50	23.74	0.882
L ACD	3.11	3.19	−0.08	0.11	0.000^a
L ACV	173.96	179.04	−5.08	17.69	0.048^a
L ACA	38.85	33.39	5.46	7.74	0.000^a
L Pupil diameter	3.18	5.89	−2.72	0.73	0.000^a

P<0.05 (paired t-test).

R, right; L, left; CCT, central corneal thickness (μm); ACD, anterior chamber depth (mm); ACV, anterior chamber volume (mm³); ACA, anterior chamber angle (degree); SD, standard deviation.

Mean pre- and post-tropicamide measurements of the ACV in the right eyes were 171.86±38.13 mm³ (range 92.00–251.00 mm³) and 181.44±35.91 mm³ (range 112.00–254.00 mm³), and the left eyes were 173.96±40.56 mm³ (range 101.00–288.00 mm³) and 179.04±35.07 mm³ (range 104.00–258.00 mm³), respectively. The difference in the right and the left eyes were both statistically significant (P<0.0001 and P<0.05, respectively; paired t-test).

Mean ACA measurements of the right and the left eyes were 36.40°±5.64° (range 23.50°–49.10°) pretropicamide and 34.27°±10.30° (range 18.00°–58.80°) post-tropicamide, and 38.85°±6.05° (range 22.70°–50.10°) pretropicamide and 33.39°±9.77° (range 11.90°–52.20°) post-tropicamide, respectively. The difference between pre- and post-tropicamide ACA measurements were not significant in the right eyes, but significant in the left eyes (P=0.107 and P<0.05, respectively; paired t-test).

Mean CCT measurements of the right and the left eyes were 556.18±34.28 μm (range 470–635 μm) pretropicamide and 545.76±84.82 μm (range 469.00–642.00 μm) post-tropicamide, and 558.46±36.51 μm (range 473.00–641.00 μm) pretropicamide and 548.26±84.87 μm (range 474.00–639.00 μm) post-tropicamide, respectively. The decrements in both eyes were statistically insignificant (P>0.05; paired t-test).

Mean pupil size measurements of the right and the left eyes were 3.21±0.62 mm (range 1.98–4.90 mm) pretropicamide and 5.96±0.83 mm (range 3.47–7.91 mm) post-ropicamide, and 3.17±0.60 mm (range 2.11–4.89 mm) pretropicamide and 5.89±0.86 mm (range 4.06–7.80 mm) post-tropicamide, respectively. The difference between pre- and post-tropicamide pupil sizes were statistically significant as expected (P<0.001; paired t-test).

Mean keratometric values of the right eyes were 43.40±1.66 D (range 38.85–48.00 D) pretropicamide and 43.40±1.66 D (range 39.05–47.75 D) post-tropicamide, and the left eyes were 43.41±1.72 D (range 39.10–47.65 D) pretropicamide and 43.50±1.74 D (range 38.95–47.80 D) post-tropicamide. The difference between pre- and post-tropicamide measurements in the both eyes were statistically insignificant (P>0.05; paired t-test).

Mean astigmatism of the right and the left eyes were 0.95±0.62 D (range 0.10–2.70 D) pretropicamide and 0.91±0.50 D (range 0.10–2.80 D) post-tropicamide, and 0.82±0.44 D (range 0.00–2.40 D) pretropicamide and 0.80±0.45 D (range 0.10–2.40 D) post-tropicamide, respectively. The difference between pre- and post-tropicamide measurements were insignificant in both eyes (P>0.05; paired t-test).

Repeatability analysis of the study parameters measured with Pentacam was calculated.⁷ The CV of K1, K2, ACD, CCT, ACV, pupil diameter, and ACA were 0.11%, 0.20%, 0.72%, 1.63%, 2.73%, 5.95%, and 6.11%, respectively. The least trustable parameters were ACA and pupil size.⁷

Discussion

Many devices, such as slit lamp, optical coherence tomography, ultrasound biomicroscopy, Orbscan scanning slit topography, the scanning peripheral ACD analyzer, and the Pentacam have been used for the qualitative and quantitative evaluation of the anterior segment.^6–16 The Pentacam is a relatively new, noncontact optical system, specifically designed to image the anterior segment of the eye. It is an easy to use anterior segment analyzer, and its high reliability and repeatability have been previously documented.¹⁷

Biometric inaccuracy is one of the leading causes of unwelcome refractive errors after cataract surgery. Correct ACD measurement is therefore very important for precise biometric evaluation. Keratometry and axial length data determine the desired IOL power. Newly developed biometric formulas such as Haigis and Holladay 2 use preoperative ACD measurement to predict effective IOL position.¹⁸ A 0.1 mm error in ACD measurement results in 0.1 D misaligned postoperative refraction. Considering that these formulas anticipate postoperative IOL position according to ACD, it is clear that precise measurement of the preoperative parameters, especially ACD.¹⁹ Recently, Tsai et al. reported that tropicamide 1% instillation in children (both emetropic and myopic) caused an increase in ACD.⁵ Our study also supports that ACD increases (∼0.1 mm in each eye) after tropicamide application. This means that if ACD is measured after instillation of one drop of tropicamide 1%, there will be an error of ∼0.1 D.

Phakic anterior chamber IOL implantation without removal of crystalline lens is a novel approach for high refractive errors.²⁰ ACD is also an important parameter for phakic anterior IOL implantation.²⁰ The pseudo-high ACD values as measured with Pentacam after tropicamide instillation might cause undesired corneal endothelial cell damage due to the closer position of the IOL with endothelium than expected.

Anterior movement and thickening of the crystalline lens in accomodative activity were previously reported.^21,22 After application of tropicamide similar to cyclopentolate hydrochloride the lens thickness decreases and the lens moves backward, which results in an increment in ACD.⁵ The increasing pupil diameter also leads to higher ACV readings.^21,22

From the standpoint of glaucoma anterior chamber parameters, such as ACD, ACA width, and CCT are important.⁹ The probability of primary angle-closure glaucoma formation increases with smaller ACD and CA width values.²³ The increment in ACD measurements after tropicamide instillation was significant in our study, similar to Tsai et al.'s findings.⁵ However, there was a discordance in the means of ACA in the right and the left eyes after tropicamide application. Although there was a decrement in ACA width in both eyes, the difference was only significant in the left eyes. Tsai et al.⁵ also reported a statistically insignificant decrease in ACA in children after tropicamide instillation. This might be explained by the help of the repeatability analysis, which proves that one of the least reliable parameters measured with Pentacam is ACA width. If the Table 1 is reviewed, one can easily see that the SD of ACA width is high, which also supports this issue. CCT is reported to affect the accuracy of the IOP readings.²⁴ Gao et al.⁴ demonstrated increment of CCT after tropicamide and saline instillation in myopic adults. However, we found no difference in CCT after tropicamide application in adults.

The effects of cyclopentolate hydrochloride in children were recently reported.⁷ The ACD and ACV were higher, and CCT was lower after cyclopentolate hydrochloride 1% application. However, there are no reports on the effects on Pentacam measurements of other midriatics, such as atropine and phenylephrine. Further studies are needed to investigate the changes on anterior segment measurements acquired with Pentacam after instillation of various midriatic agents.

In conclusion, tropicamide 1% application in healthy individuals causes significant increase both in ACD and ACV. Therefore, the effects of tropicamide 1% in the anterior segment should be considered, especially for biometric measurement and phakic IOL implantation.

Footnotes

Author Disclosure Statement

No competing financial interests exist.

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