Correlation between retinal nerve fibre layer thickness and retinal sensitivity

To evaluate the relationship between retinal nerve fibre layer (RNFL) thickness measured by optical coherence tomography (OCT) and light threshold values obtained with the Micro Perimeter 1 (MP1).

Forty-nine normal subjects and 37 glaucoma patients were included. Thickness of the RNFL around the optic disc was measured with Stratus OCT scans, and static threshold perimetry was performed with the MP1 at the same visit. Total average and mean 12-clock-hour RNFL thickness were measured with Stratus OCT. An automated 4-2-1 staircase strategy with Goldmann III stimuli was used for MP1. The correspondence between Stratus OCT and MP1 RNFL measurements in each clock-hour was best fit by a second-order polynomial.

Average RNFL thickness in the normal group was significantly higher than that in the glaucoma group in each clock hour. Comparing the normal and glaucomatous groups, retinal sensitivity differed significantly at 6, 7, 8 and 11 o'clock. In these regions, structure-function relationships were generally stronger than in other regions.

Structure-function associations may be strong when loss of nerve fibres is severe. However, significant reduction in retinal sensitivity does not emerge until the atrophy of nerve fibres is severe.