The influence of axial length upon the retinal ganglion cell layer of the human eye

Purpose We examined the relationship between axial length and the thickness and volume of the ganglion cell layer (GCL) of the retina, and related these measures to the size of the optic chiasm. Methods We used optical coherence tomography to measure the thickness of the GCL over a 50° extent of the horizontal meridian in 50 normally-sighted participants with a wide range of axial lengths. Using a model eye informed by individual biometry, we converted GCL thickness to tissue volume per square degree. The volume of the optic chiasm was measured for 40 participants using magnetic resonance imaging. Results While GCL thickness decreases with increasing axial length, there is a positive relationship between GCL tissue volume and axial length, leading us to conclude that increasing axial length is associated with decreased retinal ganglion cell packing, increased cell size, or both. We characterize how retinal ganglion cell tissue varies systematically in volume and spatial distribution as a function of axial length. This model allows us to remove the effect of axial length from individual difference measures of GCL volume. We find that variation in GCL volume correlates well with the size of the optic chiasm as measured using magnetic resonance imaging. Conclusions Our results provide the volume of ganglion cell tissue in the retina, adjusted for the effects of axial length upon ganglion cell size and/or packing. The resulting volume measure accounts for individual differences in the size of the optic chiasm, supporting its use to characterize the post-retinal visual pathway.