RETINAL NERVE-FIBER LAYER POLARIMETRY - HISTOLOGICAL AND CLINICAL COMPARISON

Aims-To compare histological thickness of the retinal nerve fibre laye r in the primate with retardation measurements obtained in vivo using the A lark II Nerve Fiber Analyzer (NFA, Laser Diagnostic Technologies , San Diego, USA). Methods-Scanning laser polarimetry was performed on both eyes of a healthy anaesthetised adult primate (Macaca mulatta). The retinal nerve fibre layer thickness was measured in the eye with t he best polarimetry image. A nerve fibre layer thickness map was scale d and aligned to a retardation map to permit correlation of retardatio n and thickness measurements. Results-Retinal nerve fibre layer thickn ess measurements could be satisfactorily aligned with corresponding re tardation values at 216 locations. The overall correlation coefficient for nerve fibre layer thickness and retardation was r = 0.70 (n = 216 , p <0.001). Regional comparison showed the best correlation (r=0.76, n = 45, p <0.001) occurred inferior to the optic disc. Less positive b ut still highly significant correlations were seen superiorly and temp orally (r=0.52, n=26, p = 0.007 and r = 0.49, n = 86, p = <0.001 respe ctively), with the lowest correlation occurring at the nasal aspect of the disc (r = 0.06, n = 67, p = 0.64). Conclusions-In the primate eye , retinal nerve fibre layer thickness shows a positive correlation wit h retardation measurements obtained with the nerve fibre analyser. How ever, since the correlation coefficient varied around the optic disc, further evaluation of the device is advised before its routine clinica l use.