Abstract
Purpose :
The definition of the centre of the fovea is ambiguous, and it has been shown that the preferred retinal locus of fixation (PRL) is not positioned directly aligned with the anatomical foveal centre. Using OCT, the centre of the fovea can be identified as the PRL at the time of acquisition (foveal reflex) or the point at which photoreceptor elongation is greatest (peak ellipsoid zone). This study investigates the relationship between these loci, their offset, foveal architecture, and variations between ethnicities.
Methods :
Spectralis OCT (Heidelberg, Germany) high-resolution 20°x10° volume scans (including 97 B-scans) were acquired for 224 eyes of 76 white, 78 South Asian and 70 black healthy volunteers (mean age 24 ± 6 years). Two investigators manually obtained retinal thickness at the peak of the ellipsoid zone (RTez) and the centre of the foveal reflex (RTfr). Variations in offset (x,y) distances between PRL and the ellipsoid zone (EZ) were correlated with RT, foveal width (FW) and foveal base width (FBW), and compared between ethnicities.
Results :
PRL and peak EZ were axially aligned in only 21 eyes (9.4%). Distance between PRL and peak EZ was significantly increased in South Asians (94 ± 61μm) compared to whites (51 ± 37) and blacks (62 ± 49; P<0.0005) while offset direction did not significantly vary between ethnicities (P>0.05). Decreased RTez were associated with wider FW (rho=-0.359; n=224; P<0.0005) and larger FBW (rho=-0.294; P<0.0005). RTez was significantly increased and FW significantly decreased in whites compared to South Asians and blacks (P<0.0005). FBW was significantly decreased in whites when compared to South Asian only (P=0.001). Increased distance between loci were related to wider FBW only (rho=0.307; P<0.0005), and most commonly presented a superior-temporal directional offset (P<0.0005) independent of ethnicity (P=0.41).
Conclusions :
The position of the assumed PRL during OCT acquisition indicates that over 90% of healthy subjects use eccentric fixation away from EZ. Preferred retinal location, but not direction, significantly varies between ethnicities. In addition, we report significant variation in foveal morphology (base width and slope angle) between ethnicities. Those with a wider foveal base present an increased offset between their foveal reflex and the position where photoreceptor elongation is greatest.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.