Abstract
Purpose:
Albinism is a congenital disorder of melanin synthesis associated with a number of abnormalities in the visual pathway. Optical coherence tomography (OCT) has been used to describe in vivo foveal abnormalities in albinism, however this technique has not been used to systematically investigate the structure of the optic nerve. Our study uses high-resolution OCT to identify and quantify optic nerve abnormalities in albinism.
Methods:
High-resolution spectral domain OCT device (axial resolution = 3μm, SOCT Copernicus HR, Optopol Technology S.A.) was used to obtain 3-dimensional cross-sectional images of the optic nerve head of both eyes in 58 patients with albinism (mean age = 33.1 years) and 30 healthy controls (mean age = 35.7). The participants with albinism also underwent dilated fundus photography. ImageJ was used to correct nystagmus associated motion artefacts through alignment of optic nerve and retinal vascular contours assisted by fundus photographs. SOCT Copernicus Software (version 4.2, Optopol Technology S.A.) was used calculate the cup, disc and rim dimensions including diameters, areas and volumes.
Results:
Visual inspection of the scans revealed small optic cup in albinism patients with 24 patients (41%) having no cup at all in at least one eye. This was confirmed by quantitative analysis which showed that the median optic cup area in the albinism group (median = 0.105 mm2, range = 0.00 to 1.22 mm2) was 22.3% of the size cup areas in the control group (median=0.470mm2, range = 0.115 to 1.55 mm2) (Mann Whitney: p<0.0001). The median optic disc area was also slightly smaller (96% of controls) but the rim slightly larger (122% of controls) in the albinism group compared to controls although these differences were not significant (p>0.05). Retinal nerve fibre layer thickness was significantly thinner in the temporal quadrant of retina immediately adjacent to the optic nerve head (p<0.0001).
Conclusions:
Using high resolution OCT, we have been able to describe abnormalities in the optic nerve topography of individuals with albinism for the first time. Our findings indicate that in albinism, ocular maldevelopment is not just limited to the retina but also involves the optic nerve. The reduced optic cup size appears to be the result of an accumulation of neural tissue in the optic nerve rim of individuals with albinism.
Keywords: 627 optic disc •
613 neuro-ophthalmology: optic nerve •
698 retinal development