Relationships between axial length, retinal vessel calibres, density and oxygen saturation in otherwise healthy individuals

Abstract

Purpose : Current research has shown that retinal vessel calibres and density is decreased in individuals with longer eyes. We hypothesised that such changes in vessel dimensions could potentially impact on retinal vessel oxygen saturation.

Methods : We included 74 healthy participants (40 males) with an age range of 16 to 51 years. All participants underwent a full ocular examination including axial length (AL) measurements (range: 21.45-28.20 mm, IOL-Master), 50 degree retinal photography (FF450) and retinal vessel oxygen saturation measurements using a dual wavelength technique (ImedosSystems UG). Retinal vessel calibres CRAE (Central Retinal Artery Equivalent), CRVE (Central Retinal Vein Equivalent) and retinal fractal dimesion (Df) were calculated using semi-automated software. Oxygen saturation was determined seperately for arteries (A SO2) and veins (V SO2) by analysing arteries and veins crossing through a concentric annulus around the optic nerve head. Arterial minus venous (A-V) saturation was calculated as a surrogate for retinal oxygen consumption. Relationships between retinal vessel calibres, density, oxygen saturation and axial length were sought by univariate and multivariate regression analysis.

Results : Univariate analysis showed a strong relationship of vessel calibres with AL, despite correction for ocular magnification (CRAE R²=0.29, p<0.001 and CRAE R²=0.42, p<0.001). Other associations included an increase in V SO2 (R²=0.34, p<0.001) and a reduction in A-V saturation (R²=0.42, p<0.001) with increasing age. There were no relationships between vessel calibres, AL and SO2 with retinal vessel density (Df). In multivariate analysis only age (p<0.001) and AL (p=0.032) remained a significant relationship with retinal V SO2.

Conclusions : While longer eyes show narrower vessels , they did not have a reduction in A-V SO2. Surprisingly, Df was neither linked with AL, vessel calibres nor retinal vessel SO2. An explanation for this result could be that all included participants were healthy and none of the highly myopic individuals showed any sign of myopic degeneration at the time of the study. This finding however does not rule out the possibility that those with the narrowest calibres and lowest fractal dimension might not go on to develop retinal pathology in the future however.

This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.