Influence of optic disc size in retinal nerve fiber analysis by OCT : could a customizable circular algorithm help to solve the problem?

Abstract

Abstract Purpose: To investigate the correlation between two different type of optical coherence tomography circular scan algorithms for retinal nerve fiber layer (RNFL) analysis and optic nerve head (ONH) size in normal subjects. Methods: 94 eyes of 94 healthy subjects (60 females, 34 males) underwent ONH analysis performed by StratusOCT(Zeiss Meditec), with six radial scans centered on the optic disc (Fast Optic Disc scan).RNFL thickness was analyzed with two different type of circular scan: a 3.4 mm fixed‐diameter ring (Stratus OCT, RNFL Thickness 3.4 scan) and a circular scan protocol which analysis a ring 2.27 mm far from a inner circle with a customizable diameter (Stratus OCT, RNFL Thickness 2.27 x disc scan).Correlation between RNFL thickness and optic disc size data was calculated for each algorithm . Results: Analysis performed by 3.4 scan showed a significant (p<0.01 ) correlation with the optic disc area(OPD) (R= 0.47) and the vertical(VD) and horizontal(HD) disc diameters of the ONH (R = 0.51, ), (R = 0.45).Analysis performed by 2.27 x disc scan showed R value of 0.15, 0.21 and 0.17 for OPD, VD and HD respectively that are not statistically relevant (p> 0.05) Conclusions: RNFL thickness measurements obtained by StratusOCT with 3.4 scan increase significantly with optic disc size, vertical and horizontal diameter. This relationship is not verified with 2.27 x disc algorithm that seems to be less influenced by optic disc size.It is not clear if eyes with large ONHs show a thicker RNFL as a result of shorter distance between the circular scan and the optic disc edge or an increased amount of nerve fibers.