MEASUREMENT OF THE RETINAL NERVE-FIBER LAYER WITH SCANNING LASER POLARIMETRY IN PATIENTS WITH PREVIOUS DEMYELINATING OPTIC NEURITIS

Objectives-Subjective visual deficits are common after demyelinating o ptic neuritis despite the frequent return of normal visual acuity. Vis ual and electrodiagnostic tests have demonstrated evidence of these pe rsisting functional abnormalities, which are thought to be secondary t o demyelination and variable axonal loss in the optic nerve. Scanning laser polarimetry (SLP) is a new image analysis technique which uses t he polarising properties of the retinal nerve fibre layer (RNFL) to pr oduce a quantitative measure of its thickness. This study was carried out to assess the prevalence, extent, and pattern of RNFL loss after d emyelinating optic neuritis using SLP. Methods-Twenty four patients wi th a history of previous demyelinating optic neuritis were re-examined . Examination included measurement of logmar visual acuity, Pelli-Robs on contrast sensitivity, and the presence of a relative afferent pupil defect and optic atrophy. SLP was performed and a mean RNFL profile f rom a series of three images from each eye was constructed. This was c ompared with normative data from 20 age matched normal subjects. The l ower 99.9% confidence limit of the normal data was calculated and used as the cut off criterion for abnormality. Results-There were a total of 31 eyes with a history of demyelinating optic neuritis and SLP disc losed an abnormality in 29 (94%) of these. Twenty three eyes recovered an acuity of 0.0 or better, 21 of which had evidence of RNFL loss on polarimetry. Scanning laser polarimetry was the only abnormality found in nine of the 31 eyes (29%). The pattern and extent of RNFL loss was very variable and there was no significant difference in these indice s between patients with multiple sclerosis compared with those with is olated demyelinating optic neuritis. Conclusion-Scanning laser polarim etry can provide a quantitative measure of RNFL loss after demyelinati ng optic neuritis, demonstrating its occurrence in a high percentage o f patients recovering normal visual acuity.