Background: Retinal nerve fiber layer(RNFL) measurements using a fixed-diameter versus a user-defined scan-protocol of optical coherence tomography(Stratus OCT©) were compared in 32 normal, 62 glaucoma suspects and 36 glaucomatous eyes.
Methods: Peripapillary RNFL thickness was measured using the standard “Fast”RNFL scan-protocol and Proportional 2.27xdisc scan-protocol. Disc size was measured using “Fast” Optic Disc protocol. Correlation between RNFL thickness by each scan-protocol and disc size was analyzed.
Results: In normal eyes, RNFL thickness was independent of optic-disc area using the fixed-diameter protocol(p=0.92), but was inversely proportional to disc size using proportional protocol(p<0.001). In glaucoma suspects, optic disc area correlated with RNFL thickness using the fixed-diameter protocol(p<0.001). On multivariate analysis in glaucomatous eyes, RNFL thickness using the fixed-diameter protocol was significantly affected by mean deviation on visual fields but not by disc area(p<0.001and p= 0.64 respectively)
Conclusion: In normal subjects, disc size does not appear to affect RNFL measurements by OCT using the fixed-diameter protocol, indicating that RNFL thickness may be related to distance from the centre of the optic disc rather than the margin. The thicker RNFL observed in large-sized glaucomatous discs in this study may be related to the earlier stage of glaucoma, though it may not apply to the general population.