Evaluation of Diurnal Variation of Ocular Vasculature in Healthy Eyes using Optical Coherence Tomography Angiography

Abstract

Purpose : To examine the diurnal variation of macula and optic nerve head vessel density assessed by optical coherence tomography angiography (OCT-A) in young healthy eyes by comparing measurements obtained in a 12-hour period.

Methods : 29 eyes of 15 subjects (8 male, 7 female) ranging from ages 23 to 40 years (mean 30.9±4.8) without history of ocular pathologies or intraocular surgery were included. Macula and optic nerve head (ONH) OCT-A imaging (AngioVue; Optovue, Fremont CA) was performed 4 times during the day (8am, 12pm, 4pm and 8pm), followed by intraocular and blood pressure measurements. The relationships between time of the day and both macula parafoveal vessel density (pfVD), ONH circumpapillary vessel density (cpVD) and ONH capillary cpVD (large vessels excluded) were assessed using linear mixed effects models with time as a fixed effect and an intercept nested within eye and patient as a random effect. Linear splines were used to model nonlinear diurnal trends observed within the macula responses. Mean ocular perfusion pressure (MOPP) was also included as a fixed effect in the analysis.

Results : Mean pfVD was 52.1±1.9% at 8am, 51.8±2.2% at 12pm, 52.1±2.0% at 4pm and 52.5±2.1% at 8pm; mean cpVD were 56.4±1.6%, 56.6±2.5%, 57.1±1.9% and 57.2±2.5%, and mean capillary cpVD were 49.6±1.9%, 49.8±2.7%, 50.3±1.9% and 50.3±2.7%, respectively. Macula pfVD showed a mean (95% CI) increase of 0.09% (0.00-0.18) in vessel density per hour after 12pm (linear spline model, P=0.048), and MOPP did not significantly affect pfVD (P=0.510). Every hour from 8am to 8pm was responsible for a mean (95% CI) increase of 0.08% (0.01-0.14) in cpVD (linear regression, P=0.021), while every mmHg increase in MOPP was responsible for a decrease of 0.10% (0.01-0.18) in cpVD (linear regression, P=0.036). When large vessels were excluded, capillary cpVD still presented an increase of 0.08% (0.01-0.14) in cpVD for every hour passed (linear regression, P=0.027). However, capillary cpVD was not significantly affected by changes in MOPP (P=0.073).

Conclusions : There is a small statistically significant increase in pfVD in the afternoon, and in cpVD throughout the day. Mean ocular perfusion pressure is significantly related to changes in cpVD only when large vessels are included, which suggests that the small capillaries may have a different response to changes in perfusion pressure.

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