Purpose: The present study aimed to determine the main cause of ganglion cell-inner plexiform layer (GCIPL) thinning in long myopic eyes.
Methods: Optical coherence tomography was performed in 53 subjects with moderate or high myopia (53 eyes; myopia group) and 20 emmetropic subjects (20 eyes; control group). All subjects were over the age of 40 years.
Results: Compared groups did not differ in age, sex, and radius of corneal curvature. Spherical equivalent in the myopia group was - 8.2 ± 3.3 D (from - 4.0 to - 22.6 D). A specialized computer program was created to study the effect of the ocular magnification on the average GCIPL thickness. Based on the data of control subjects, a mathematical model was constructed, which showed a very little effect of ocular magnification on GCIPL thickness. It was confirmed by real measurements. After correction by the program, GCIPL thickness in myopes increased only slightly (from 73.9 ± 5.2 to 75.0 ± 5.2 μm, P < 0.000) remaining much lower than in controls (79.7 ± 6.3 μm, P < 0.000). Modeling myopic eye as an ellipsoid showed a significant increase in its surface area compared with emmetropia. Retinal stretching associated with an increase in the surface area of the eyeball explained most of the thinning of GCIPL in myopia.
Conclusions: Ocular magnification is responsible for only a minor part of GCIPL thinning in myopia. Stretching of the retina in a long eye is the main cause of the GCIPL thinning. Myopic normative databases should be created to account for the GCIPL thinning in highly myopic eyes.
Keywords: Ganglion cell-inner plexiform layer; Myopia; Ocular magnification; Optical coherence tomography; Stretching of the retina.