Abdominal obesity linked to a longer cone-mediated dark-adaptation recovery time in healthy eyes

• Published in: Experimental eye research Vol. 181; pp. 163 - 170
• Main Authors: Puell, María Cinta, Fernandez-balbuena, Antonio Álvarez
• Format: Journal Article
• Language: English
• Published: England Elsevier Ltd 01.04.2019
• Subjects: Abdominal obesity; Adiposity; Adult; Aged; Body Mass Index; Cones; Contrast sensitivity; Contrast Sensitivity - physiology; Cross-Sectional Studies; Dark adaptation; Dark Adaptation - physiology; Female; Follow-Up Studies; Healthy eyes; Humans; Male; Middle Aged; Obesity, Abdominal - physiopathology; Photopigments; Retinal Cone Photoreceptor Cells - physiology; Risk Factors; Slit Lamp Microscopy; Time constant; Visual Acuity; Young Adult; Abdominal obesity; Cones; Healthy eyes; Adiposity; Contrast sensitivity; Dark adaptation; Photopigments; Time constant
• ISSN: 0014-4835; 1096-0007
• DOI: 10.1016/j.exer.2019.02.007

Obesity has been associated with abnormal lipid metabolism and with tissue hypoxia. Human Bruch's membrane (BrM) lipid deposits have been proposed to create a diffusion barrier to metabolic exchange between the choroid and photoreceptors, delaying the regeneration of photopigments. The speed of retinal dark adaptation (DA) is dependent on the regeneration of these photopigments. While the retina is extremely sensitive to hypoxia, the inner retina, which encodes visual contrast, is more affected by hypoxia than the outer retina. This study examines the association between adiposity measures and the time course of DA measured psychophysically through contrast detection to test the functionality of both the outer and inner retina. Cone-mediated DA recovery of contrast threshold (CT) was measured following near-total photopigment bleach for 6 min in 52 healthy eyes of 52 individuals (42.6 ± 18.3 years). Stimuli were sine-wave gratings of low-spatial frequency (1 cycle-per-degree (cpd)) and low luminance (1 cd/m2) generated at the centre of a CRT monitor. CT recovery functions were fitted to an exponential decay model to determine the time constant (τ, seconds) of cone sensitivity recovery, final cone CT (CTf) and CT elevation (CT0). Weight, height and waist circumference (WC) were measured and body mass index (BMI) and waist-to-height ratio (WHtR) calculated. Relationships were examined through Spearman correlation and through multiple linear regression using age, optical and adiposity measures as independent variables. The repeatability of cone time constant measurements was estimated by the Bland-Altman method and reported as the coefficient of repeatability (CoR). Mean ± SD of time constant and CTf were 57.3 ± 27.7 s and −1.78 ± 0.20 log10 units respectively. Cone time constant showed positive Spearman correlation with WC (p = 0.008) and WHtR (p = 0.023) but not with BMI (p = 0.058). Only WHtR emerged as an independent predictor of time constant (p = 0.001). CTf was not correlated with any adiposity measures. Mean cone time constant was 41 s slower in subjects (25%, n = 13) with abdominal obesity (WHtR≥0.5). Mean CTf was not significantly different in subjects with or without abdominal obesity. CoR for cone time constant was ±16 s. In adult subjects, greater abdominal obesity (WHtR) was related to a longer contrast recovery time for cone-mediated DA (time to dark-adapt) suggesting outer retinal dysfunction. Final contrast threshold, preferentially processed by inner retinal cells, was unaffected by abdominal obesity. •Cone-mediated dark adaptation slowed down as abdominal obesity increased.•Final contrast threshold was unaffected by abdominal obesity in healthy eyes.•Intersession repeatability of contrast sensitivity recovery time constant was good.