Abstract
Purpose :
Ganglion cell-inner plexiform layer (GCIPL) thickness decreases in myopia. Exact causes of this decrease are disputable. The aim of the study was to compare the influence of optical magnification and mechanical stretching of the sclera in myopic eyes on average GCIPL thickness.
Methods :
Fifty-three patients (53 eyes) over the age of 40 with myopia (spherical equivalent) -8.2±3.3 D (range -4.0 to -22.6 D) formed myopia group. Control group of 80 emmetropic subjects (80 eyes) had similar age and sex distribution. Axial length was 26.54±0.87 (25.26-29.88) mm in the myopia group and 23.52±0.50 (22.57-24.50) mm in the control group. GCIPL thickness was measured by Cirrus HD-OCT (Carl Zeiss Meditec Inc., Dublin, CA).
Results :
The authors and programmer A. Evsyukov created a computer program to correct for the optical magnification caused by the axial elongation of myopic eyes. Average GCIPL thickness was 79.0±5.3 µm in the control group and 73.9±5.2 µm in the myopia group (5.1 µm or 6.5% difference). Correction by the computer program increased average GCIPL thickness in the myopia group to 75.5±5.3 µm leaving 3.5 µm (4.4%) difference unaccounted for. This difference could be explained by the mechanical stretching of the sclera in myopic eyes. Mathematical model of prolate spheroid based on real eyes measurements (data of Atchinson et al., 2004) showed much larger increase (12%) in surface area of the average eye in the myopia group compared to controls. Presumably, GCIPL stretching is less pronounced due to uneven distribution of ganglion cells in the retina. Correcting table for average GCIPL thickness depending on axial length was calculated by the simple linear regression. Preliminary normative values for corrected average GCIPL thickness were established in the control group.
Conclusions :
Optical magnification explains only minor portion of the thinning of the GCIPL in myopic eyes. A stretching of the sclera and the retina with axial elongation is likely the main cause of the GCIPL thinning in myopic eyes. A simple method was developed for evaluation of the average GCIPL thickness in myopic eyes.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.