Influence of disc area on retinal nerve fiber layer thickness measurement by spectral domain optical coherence tomography

Background:

To examine the effect of optic disc area on peripapillary RNFLT (retinal nerve fiber layer thickness) measurement at circle diameter of 3.4 mm around optic nerve head using spectral OCT/SLO (Optical coherence tomography/scanning laser ophthalmoscope).

Materials and Methods:

In this prospective, cross sectional study, one hundred and two eyes of 102 normal subjects underwent RNFLT and disc area measurement using spectral OCT/SLO. Based on disc area, subjects were divided into three groups i.e., <3 mm² (32 eyes), 3-4 mm² (36 eyes) and >4 mm² (34 eyes). The effect of disc area on RNFLT parameters was analyzed using linear regression analysis.

Results:

The mean and quadrant RNFLT did not show significant correlation with disc area in subjects with disc area of <4 mm², however in eyes with disc area >4 mm², average RNFLT, superior and temporal quadrant RNFLT showed negative correlation with disc area, which was statistically significant (P = 0.004, P = 0.005 and P = 0.002, respectively)

Conclusion:

In healthy eyes of disc area <4 mm², disc size does not appear to affect peripapillary RNFLT measurement by spectral OCT/SLO. Average, superior and temporal quadrant RNFLT measurements were inversely proportional to disc area in eyes with disc area >4 mm². Hence, RNFLT measurement by OCT in eyes with optic disc area of >4 mm² should be interpreted carefully.