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Jul 4, 2015 - E-mail: [email protected]yahoo.com. Submitted: 16 September 2014. Revised: 15 October 2014. Accepted for publication: 4 December 2014.

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OPTOMETRY RESEARCH PAPER

Effects of rigid contact lenses on optical coherence tomographic parameters in eyes with keratoconus Clin Exp Optom 2015; 98: 319–322 Umut Duygu Uzunel* MD Tuncay Kusbeci* MD Berna Yuce† MD Bora Yüksel* MD * Izmir Bozyaka Training and Research Hospital, Department of Ophthalmology, Izmir, Turkey † Giresun University Medical Faculty, Department of Ophthalmology, Giresun, Turkey

E-mail: [email protected]

Submitted: 16 September 2014 Revised: 15 October 2014 Accepted for publication: 4 December 2014

DOI:10.1111/cxo.12287 Background: The aim was to evaluate the effect of irregular astigmatism on the retinal nerve fibre layer (RNFL), macular thickness and ganglion cell analysis obtained by spectral domain optical coherence tomography (OCT) in eyes with keratoconus. Methods: Fifty-two eyes of 31 patients (20 females) with keratoconus that required correction of irregular astigmatism with rigid gas-permeable (RGP) contact lenses were included to this study. The average, superior, nasal, inferior, temporal and 12 clock hour sector’s RNFL, ganglion cell and macular thickness analyses before and 30 minutes after RGP contact lens (Rose K2 Menicon Z material, David Thomas Contact Lenses Ltd, Northampton, United Kingdom) wear were performed to all patients with Cirrus HD spectral domain optical coherence tomography. Results: The average thickness of the retinal nerve fibre layer, the thickness at the nasal quadrants and 1-2-3-4 o’clock hour sectors and mean signal strength were increased significantly by RGP contact lens wearing independent of the stage of keratoconus. Central sub-field thickness increased after correction with RGP contact lens (p = 0.037). After wearing RGP contact lenses, changes on ganglion cell analysis were not significant (all p values ≥ 0.111). Conclusions: OCT is a widely used device for retinal nerve fibre layer and macular thickness evaluation in patients with glaucoma and macular diseases. The study demonstrates that OCT parameters such as retinal nerve fibre layer, central sub-field thickness and mean signal strength are affected by irregular astigmatism. Correction of irregular astigmatism with RGP contact lenses should be recommended before analysing keratoconic eyes to obtain optimum results on OCT measurements.

Key words: irregular astigmatism, keratoconus, optic coherence tomography, retinal nerve fibre layer Keratoconus is a progressive, non-inflammatory process that leads to corneal thinning and affects one in 2,000 in the young, workingage population.1 It usually causes high myopia and irregular astigmatism and leads to visual impairment. Treatment options for high astigmatism and visual impairment are various in keratoconus and include both conservative methods (soft and hard contact lenses) and surgical interventions (intrastromal corneal ring segments);2,3 however, some patients need corneal transplantation for visual rehabilitation, because of profound steepening and corneal scarring.4 Keratoconus has been classified by Buxton et al5 based on the keratometric values at the apex of the cone. It is mild, if less than 45.00 D, moderate if between 45.00 and 52.00 D, advanced if between 52.00 and 62.00 D and severe if greater than 62.00 D. Measurement of the retinal nerve fibre layer (RNFL) and macular thickness is important for evaluation of glaucoma. Optical

coherence tomography (OCT) is a widely used device for RNFL and macular thickness evaluation in patients with glaucoma.6,7 Various factors such as age, ethnicity, refractive error, axial length, myopic optic disc tilt, signal strength, eccentric scan location and head tilt during the examination have been reported to affect OCT measurements.8–15 The effect of spherical refractive error on OCT measurement has been investigated by cross-sectional studies, which compare retinal nerve fibre layer thickness before and after corneal refractive surgery and analyse the thickness changes after refractive error correction by contact lenses;8–11,16–19 however, little is known about the effect of cylindrical refractive error (astigmatism) on RNFL and macular thickness measured by OCT. Retinal images can be distorted and image size can vary according to the axis in astigmatic eyes.20 This study was performed to evaluate the effect of irregular astigmatism on RNFL,

© 2015 The Authors Clinical and Experimental Optometry © 2015 Optometry Australia

macular thickness and ganglion cell analysis obtained by Cirrus HD spectral domain OCT (Cirrus HD OCT; Carl Zeiss Meditec, Dublin, California, USA) in eyes with keratoconus. According to our knowledge this is the first study reporting the effects of irregular astigmatism on OCT parameters. METHODS Fifty-two eyes of 31 patients were followed for keratoconus at Izmir Education and Research Hospital included to our study. The refractive error could not be corrected by wearing eyeglasses so rigid contact lenses were used to increase visual acuity in all patients. All subjects provided informed consent and all procedures conformed to the Declaration of Helsinki. Each subject underwent a full ophthalmic examination, including assessment of visual acuity, refractive error with autorefractokeratometer (RK-F1; Canon, Tokyo, Japan), corneal topography using Clinical and Experimental Optometry 98.4 July 2015

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Optical coherence tomography in keratoconus Uzunel, Kusbeci, Yuce and Yüksel

Keratograph (Oculus, Wetzlar, Germany), pachimetry using PacScan 300p (Sonomed Inc, USA), optic nerve head evaluation and fundus examination with a 90 D lens and measurement of peripapillary RNFL and macular thickness using Cirrus HD OCT. Age, gender, mean keratometric values, visual acuity, retinal nerve fibre layer, ganglion cell and macular thickness analyses before and 30 minutes after contact lens wearing were recorded. Rose K2 lenses (David Thomas Contact Lenses Ltd, Northampton, United Kingdom) were used for correcting irregular astigmatism. Contact lenses were chosen between the two keratometric readings or a steep trial lens was fitted over the irregular cornea. Fluorescein was used for lens fitting and apical touch was permitted. Adequate tear exchange was estimated by fluorescein drainage. After finalisation of the base curve, over refraction was done through the same contact lens to determine the power. Patients with scarring or hydrops were excluded from the study. A 200 by 200 cube ‘optic disc scan’ was obtained using Cirrus HD OCT (software version 6.0.2.81) at the baseline state and improved astigmatic states by wearing hard contact lenses. For measurements of the baseline state (without contact lens), subjects were seated at the proper position. Scanning laser images were then focused. Using the iris and fundus viewports, the alignment was properly positioned to the optic nerve head in the centre of the scan. Once the optic nerve head was centred on the live scanning laser image, a 6.0 by 6.0 mm square of data was captured. After measurement of RNFL thickness, macular cube 512 by 128-scans and ganglion cell analyses were obtained for both eyes. The average, superior, nasal, inferior, temporal and 12 clock hour RNFL thickness parameters were obtained by using the Glaucoma OU Analysis mode of Cirrus HD OCT. The average cube thickness, macular cube volume, central subfield thickness (defined as the average thickness in the central 1.0-mm sub-field centred at the fovea) were obtained in the Macula Thickness Analysis mode of Cirrus HD OCT. In the Ganglion Cell Layer Analysis mode of Cirrus HD OCT, superior, superonasal, inferonasal, inferior, inferotemporal, superotemporal, average ganglion cell and minimal ganglion cell scores were obtained. All the scans had signal strength of at least 5 and all measurements were performed by the same, welltrained examiner. Clinical and Experimental Optometry 98.4 July 2015

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In this study, data were analysed using the statistical package SSPS v.15.0. Paired samples student t-test was used for statistical analyses and a p-value of less than 0.05 was considered statistically significance. RESULTS Twenty patients (64.5 per cent) were female. Twenty-three study eyes (44 per cent) were right while 29 were left. Mean age was 32.2 ± 9.4 years (range: 15 to 54 years). Mean keratometry was 49.8 ± 5.3 D (range: 42.94 to 76.85 D). Mean central corneal thickness was 436.6 ± 36.9 μm (range: 348 to 498 μm). Mean radius was 6.70 mm, mean diameter was 8.80 mm and mean refractive power was -5.75 D for Rose K2 contact lenses. Mean visual acuity before contact lens wearing was 0.63 ± 0.65 logMAR (range: 0.1 to 3) and 0.12 ± 0.11 logMAR (range: 0.5 to 0) after wearing contact lenses. The increase on visual acuity obtained by wearing contact lenses was statistically significant (p < 0.001). Results of comparison of RNFL thickness between with and without RGP contact lenses are listed in Table 1. After wearing RGP contact lenses, RNFL thicknesses of average,

nasal areas and 1, 2, 3, 4, 7, 10, 11 and 12 o’clock hour sectors increased (p = 0.001, p < 0.001, p < 0.001, p = 0.001, p = 0.004, p < 0.001, p = 0.024, p = 0.035, p = 0.018, p = 0.039, respectively). These results were highly correlated with Pearson’s correlation analysis values (all p values were ≤ 0.007). We observed that contact lens wearing affected the values of superior quadrants analyses markedly. Results of comparison of macular thickness analysis between with and without RGP contact lenses are listed in Table 2. After wearing RGP contact lenses, central sub-field thickness increased (p = 0.037). After wearing RGP contact lenses, mean signal strength increased from 7.0 to 8.7 (p < 0.001). Comparisons of ganglion cell analyses with and without RGP contact lenses are listed in Table 3. After wearing RGP contact lenses, changes on ganglion cell analysis were not significant (all p values ≥ 0.111). Study eyes were divided into subgroups according to mean keratometric values. Thirty-eight eyes with mild or moderate keratoconus (keratometric value less than 52 D) and 14 eyes with advanced or severe keratoconus (keratometric value greater than

Before wearing RGP contact lens

After wearing RGP contact lens

Average

85.8 ± 15.1

91.4 ± 12.4

Superior

100.3 ± 28.6

110.5 ± 16.9

65 ± 14.1

72 ± 14.1

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