Characterisation of Abnormal Optic Nerve Head Morphology in Albinism Using Optical Coherence Tomography

Purpose: To characterise abnormalities in three-dimensional optic nerve head (ONH) morphology in people with albinism (PWA) using spectral domain optical coherence tomography (SD-OCT) and to determine whether ONH abnormalities relate to other retinal and clinical abnormalities. Methods: SD-OCT was used to obtain 3-dimensional images from 56 PWA and 60 age- and gender-matched control subjects. B-scans were corrected for nystagmus associated motion artefacts. Disc, cup and rim ONH dimensions and peripapillary retinal nerve fibre layer (ppRNFL) thickness were calculated using Copernicus and ImageJ software. Results: Median disc areas were similar in PWA (median=1.65mm2) and controls (1.71mm2, p=0.128) although discs were significantly elongated horizontally in PWA (p<0.001). In contrast, median optic cup area in PWA (0.088mm2) was 23.7% of that in controls (0.373mm2, p<0.001) with 39.4% of eyes in PWA not demonstrating a measurable optic cup. This led to significantly smaller cup: disc ratios in PWA (p<0.001). Median rim volume in PWA (0.273mm3) was 136.6% of that in controls (0.200mm3). ppRNFL was significantly thinner in PWA compared to controls (p<0.001), especially in the temporal quadrant. In PWA ppRNFL thickness was correlated to ganglion cell thickness at the central fovea (p=0.007). Several ONH abnormalities such as cup/disc ratio were related to higher refractive errors in PWA. Conclusions: In PWA ocular maldevelopment is not just limited to the retina but also involves the ONH. Reduced ppRNFL thickness is consistent with previous reports of reduced ganglion cell numbers in PWA. The thicker rim volumes may be a result of incomplete maturation of the ONH.