A method for simultaneous assessment of retinal vascular oxygenation and diameter in response to light flicker in humans

Abstract

 

Purpose

 

Light flicker stimulation increases neural activity, thereby augmenting retinal oxygen metabolism and blood flow. Alterations in retinal vascular oxygen saturation (SO₂) and diameter, and their responses to light flicker may be used to detect abnormalities due to disease. The purpose of the study was to report an optical imaging system for combined measurements of retinal vascular SO₂ and diameter before and during light flicker stimulation in humans.

 

Methods

 

A slit lamp biomicroscope was modified for dual wavelength retinal oximetry at 570nm and 606nm. Fundus images were acquired in control subjects (Age: 39±17 years, N=7) and diabetic retinopathy (DR) subjects (Age: 50±13 years, N=7; 3 PDR, 4 NPDR) (P=0.18) before and during light flicker stimulation at 530nm. A customized software algorithm measured arterial and venous diameter (D_A and D_V) and optical density ratios (ODR). Arterial and venous oxygen saturations (SO_2A and SO_2V) were obtained from an ODR to SO₂ calibration and oxygen extraction fraction (OEF) was calculated as (SO_2A- SO_2V)/SO_2A. Repeatability and inter-subject variability were assessed in control subjects before light flicker stimulation.

 

Results

 

Repeatability of D_A, D_V, SO_2A and SO_2V were 2µm, 2µm, 2% and 3%, respectively. Inter-subject variability of D_A, D_V, SO_2A and SO_2V were 4µm, 4µm, 4% and 4%, respectively. As expected, D_V was significantly larger than D_A and SO_2A was significantly higher than SO_2V (P≤0.03). D_A, D_V, and SO_2V were similar between control and DR subjects (P≥0.20) but SO_2A was higher in DR subjects (P≤0.02). In control subjects, D_A and D_V increased significantly during light flicker stimulation (P<0.05). In DR subjects, D_V increased significantly during light flicker (P=0.002) but D_A did not (P=0.09). Light flicker stimulation did not significantly alter SO_2A, SO_2V or OEF in control or diabetic subjects (P≥0.08).

 

Conclusions

 

A retinal imaging system was established for combined quantitative assessment of retinal vascular SO₂ and diameter alterations in response to light flicker stimulation. The system detected alterations in retinal vascular oxygenation and caliber due to DR and light flicker stimulation.  

 

Retinal vascular oxygen saturation (SO₂) and diameter (D) in control and diabetic retinopathy (DR) subjects before and during light flicker stimulation.