The effect of myelination on perimetry and retinal nerve fibre analysis.
BACKGROUND: Myelinated retinal nerve fibres around the optic nerve head can lead to an enlargement of blind spot with kinetic perimetry. Presumably extensive myelination will also decrease the visual sensitivity with static perimetry. This study reports the effect of myelination on static perimetry in several patients. Scanning laser polarimetry can measure the retinal nerve fibre layer thickness around the optic nerve head in vivo. This technique was applied at the myelination to investigate its effect on retinal nerve fibre layer thickness determination. METHODS: Four eyes of three subjects with myelination around the optic nerve head were tested with Bjerrum screen at one metre to measure the blind spot size. They were followed by Humphrey Visual Field Analyser with a custom pattern to quantify the threshold level at the blind spot region. A GDx Nerve Fiber Analyser was used to measure the retinal nerve fibre layer thickness around the optic nerve head. RESULTS: All the patients demonstrated an enlargement of the blind spot, with different extents, corresponding to the area of myelination. Threshold testing revealed a depression in the myelinated regions. The results for retinal nerve fibre layer were not conclusive with two eyes demonstrating thickening and two eyes showing no effect from myelination. CONCLUSIONS: A static field test with a modern visual field analyser may help to quantify the effect of myelination on visual sensitivity. More studies on the effect of myelination on retinal nerve fibre layer thickness measurement are suggested with more subjects involved.
Lam
Andrew KC
AK
Department of Optometry and Radiography, Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong.
Pang
Peter CK
PC