Title Retinal Nerve Fiber Layer Thickness

The purpose of this study was to investigate the peripapillary retinal nerve fiber layer (RNFL) thickness in myopic, emmetropic, and hyperopic children using optical coherence tomography. Two-hundred one right eyes of subjects aged 4 to 18 years were divided into 3 groups based on their postcycloplegic spherical equivalent: myopes (< 1.0 D), emmetropes ( 1.0 to þ1.0 D), and hyperopes (>þ1.0 D). The RNFL was correlated with age, spherical equivalent, and axial length. The RNFL was compared between the 3 groups before and after age adjustment. The RNFL was thickest in the hyperopic group (107.2 10.13mm, n1⁄4 73), followed by the emmetropic group (102.5 9.2mm, n1⁄4 61), and then the myopic group (95.7 10.3, n1⁄4 67) (all P< 0.0001). The myopic group (9.6 3.9 years) was significantly older than the emmetropic (6.9 2.7 years) and hyperopic (6.5 1.9 years) groups (both P< 0.0001). When adjusted for age, myopes had a thinner RNFL than the other 2 groups (all P< 0.0001), but there was no RNFL thickness difference between the emmetropic and hyperopic groups (P> 0.05). A thinner RNFL was associated with an older age (r1⁄4 0.4, P< 0.0001), a more myopic spherical equivalent (r1⁄4 0.5, P< 0.0001), and a longer axial length (r1⁄4 0.4, P< 0.0001) on Pearson correlation analysis. The apparently thicker RNFL in hyperopic and emmetropic children was attributed to their younger age as compared with their myopic counterparts. When adjusted for age, only myopia was associated with a thinner RNFL, with emmetropic and hyperopic children having equal RNFL thicknesses. Advancing age, a more myopic spherical equivalent, and a longer axial length were associated with a thinner RNFL in children. (Medicine 94(12):e699) Abbreviation: RNFL = retinal nerve fiber layer. INTRODUCTION Ed, Tiffany T.Y. W ris W.F. Yick, hthHK, and Jimmy S.M. Lai, MD continue to decrease with advancing age. Understanding the determinants that affect the RNFL reserve in childhood helps us in the diagnosis and monitoring of optic nerve diseases. Previous studies have found that white race, lower birth weight, longer axial length, and myopia have been associated with a thinner RNFL. On the contrary, optic disc tilting and Asian or Hispanic race have been associated with a thicker RNFL. Refractive errors are common in childhood with the World Health Organization estimating that 153 million people worldwide have visual impairment caused by uncorrected refractive errors. The prevalence of myopia ranges from 22.7% to 38.7% based on large population studies, with a higher prevalence in East Asian regions. With age, the refractive status often changes from hyperopia to myopia; hence, the progressive RNFL thinning that comes with age can either be a result of age-related ganglion cell loss or due to the stretching of RNFL from the axial myopic shift in childhood. The purpose of this study was to investigate the influence of refractive errors on RNFL thickness by comparing the differences in children with myopia, emmetropia, and hyperopia. PATIENTS AND METHODS The study was conducted in accordance with the Declaration of Helsinki and no patient’s personal data was disclosed in the study. Study approval was obtained from the institutional review board of the Hospital Authority of Hong Kong. Informed consent was obtained from the parents or legal guardians of the subjects. The authors declare no financial or proprietary interests. This was a nonfunded study. This cross-sectional study recruited consecutive cases of pediatric subjects aged 4 to 18 years, attending the ophthalmology specialist outpatient clinic of Caritas Medical Centre in Hong Kong Special Administrative Region, China, from 2013 to 2014. Subjects with only eye, ocular tumors, congenital glaucoma, congenital cataract, congenital nystagmus, microphthalmos, optic nerve or retinal disease, active cornea infections, corneal scars, and severe visual impairment of any cause (Snellen best corrected visual acuity 0.1) were excluded. To increase the generalizability of the study, there were no exclusions based on the refractive errors or axial length of subjects. All subjects underwent a complete ophthalmological examination including ocular alignment and motility assessments as well as anterior and posterior segment examinations after pupil dilatation with a tropicamide 1% and phenylephrine hydrochloride 2.5% ophthalmic solution (Mydrin-P; Santen Pharmaceutical, Osaka, Japan). Spherical Equivalent and Axial Length All subjects received cycloplegic refraction with 3 drops of hloride 1% (Bausch & Lomb, Rochester, nutes apart to relieve all accommodative least 30 minutes, postcycloplegic www.md-journal.com | 1 autorefraction with a keratorefractometer (Topcon KR-8900; Topcon Europe Medical B.V., Capelle aan den IJssel, The Netherlands) was performed by an optometrist with at least 5 years of experience with pediatric assessment. The spherical equivalent was calculated in diopters. Axial length measurements in millimeters were obtained with the noncontact optical biometry (IOL Master; Carl Zeiss Meditec AG, Berlin, German). Peripapillary RNFL Thickness Measurement The protocol for RNFL measurement at our institution has been previously described in earlier publications by the authors as ‘‘The Spectralis Spectral Domain OCT (Heidelberg Engineering, 1808 Aston Ave., Suite 103, Carlsbad, CA 92008, United States of America) was performed after cycloplegia, by a single, imaging technician who was masked to subjects’ clinical information. Scans were centred on the optic disc with a scanning diameter of 3.5 mm and 768 A-scans were obtained using the High Speed mode. To improve image quality, Automatic Real Time function was used to obtain multiple frames during scanning and to optimize images by noise reduction. Scans were repeated 3 times and assessed for signal strength and centration. Scans with signal strength quality 16 or poor centration were excluded. RNFL thickness was analysed with the RNFL Single Exam Report OU with fovea-to-disc technology. The RNFL thickness of each of the 4 quadrants and the global RNFL thickness were recorded in micrometers (mm).’’