Scanning Laser Polarimetry Reveals Status of Retinal Nerve Fiber Layer (RNFL) Integrity in Eyes with Optic Nerve Head Swelling by OCT
Purpose OCT shows retinal nerve fiber layer (RNFL) thickening in optic nerve head (ONH) swelling, but does not provide information on acute axonal disruption. We hypothesized that scanning laser polarimetry (SLP) in comparison with OCT might reveal the status of axon integrity and visual prognosis in acute RNFL swelling. Methods We used threshold perimetry, OCT, and SLP to prospectively study eyes with papilledema (24), optic neuritis (13), NAION (21), and ONH swelling (defined as having average RNFL by OCT > 95th percentile of controls at presentation). Regional RNFL was judged reduced if the OCT or SLP measure in a quadrant was < 5th percentile of controls. Results At presentation, average RNFL by OCT was similar for eyes with papilledema and NAION (p=0.97), and less for optic neuritis. Average RNFL by SLP was less often increased, similar for papilledema and optic neuritis, but less for NAION (p=0.02) eyes. The RNFL by SLP was reduced in at least 1 quadrant in 1/24 eyes with papilledema, 1/14 eyes with optic neuritis, and in 13/21 eyes with NAION. In NAION eyes, quadrants with reduced SLP had corresponding visual field loss that did not recover at 1 or 6 months. By 1 month, eyes with NAION showed RNFL thinning by OCT (7/17 eyes) and by SLP in14/16 eyes) in contrast to optic neuritis (by OCT, 0/12; p=0.006 and by SLP, 1/12; p=0.0004). Conclusion OCT and SLP reveal different aspects of RNFL changes associated with ONH swelling. OCT reveals thickening, due to edema. SLP reveals a decrease in retardance in eyes with axonal injury associated with visual field loss, which is unlikely to recover. This study provides evidence that SLP may be predictive of regions of permanent axon dysfunction and visual field loss in eyes with optic disc edema.