Scanning laser polarimetry of edematous and atrophic optic nerve heads

Objective: To determine if scanning laser polarimetry (SLP) measures form birefringence of the retinal nerve fiber layer (RNFL). Methods: Consecutive patients with either acute unilateral disc edema or chronic diffuse unilateral disc atrophy underwent SLP using the GDx Nerve Fiber Analyzer (Laser Diagnostic Technologies Inc, San Diego, Calif). The former group had peripapillary RNFL edema, presumably with no change in form birefringence elements, while the latter had optic nerve atrophy, presumably with a loss of birefringence elements in the RNFL. A subset of patients with acute unilateral disc edema who subsequently developed disc atrophy had repeated SLP at 6 months. Intereye and intertest comparisons of 6 SLP parameters representative of RNFL thickness were performed using the paired t test. Results: In the acute unilateral disc edema group (n = 28), none of the SLP parameters were significantly increased in affected vs fellow eyes. In the chronic unilateral disc atrophy group (n = 30), all SLP parameters were significantly decreased in affected vs fellow eyes (P<.001). Patients with disc edema who had a follow-up SLP demonstrated significant declines of all parameters in the affected eyes (P<.007) but no change in SLP parameters in unaffected eyes. Conclusion: Scanning laser polarimetry measures form birefringence properties of the RNFL, but not necessarily the RNFL thickness.