Response of retinal vessel diameters to flicker stimulation in patients with early open angle glaucoma

Diffuse luminance flicker increases retinal vessel diameters in animals and humans, indicating the ability of the retina to adapt to different metabolic demands. The current study seeks to clarify whether flicker-induced vasodilatation of retinal vessels is diminished in glaucoma patients.

Thirty-one patients with early stage glaucoma (washout for antiglaucoma medication) and 31 age- and sex- matched healthy volunteers were included in the study. Retinal vessel diameters were measured continuously with a Retinal Vessel Analyzer. During these measurements three episodes of square wave flicker stimulation periods (16, 32, and 64 secs; 8 Hz) were applied through the illumination pathway of the retinal vessel analyser.

Flicker-induced vasodilatation in retinal veins was significantly diminished in glaucoma patients as compared with healthy volunteers (ANOVA, P < 0.01). In healthy volunteers, retinal venous vessel diameters increased by 1.1 +/- 1.8% (16 seconds, P < 0.001), 2.0 +/- 2.6 (32 seconds, P < 0.001), and 2.1 +/- 2.1% (64 seconds, P < 0.001) during flicker stimulation. In glaucoma patients, venous vessel diameters increased by 0.2 +/- 1.7% (16 seconds, P < 0.6), 1.1 +/- 2.1% (32 seconds, P < 0.01), and 0.8 +/- 2.5 (64 seconds, P < 0.09). In retinal arteries, no significant difference in flicker response was noticed between the two groups (ANOVA, P < 0.6). In healthy controls, flicker stimulation increased retinal arterial vessel diameters by 1.0 +/- 2.4% (P < 0.03), 1.6 +/-3.2% (P < 0.004) and 2.4 +/- 2.6% (P < 0.001) during 16, 32, and 64 seconds of flicker, respectively. In glaucoma patients, flickering light changed arterial vessel diameters by 0.3 +/-2.6% (16 seconds, P = 0.4), 1.3 +/-3.1% (32 seconds, P = 0.03), and 1.8 +/- 3.8% (64 seconds, P = 0.005).

Flicker-induced vasodilatation of retinal veins is significantly diminished in patients with glaucoma compared with healthy volunteers. This indicates that regulation of retinal vascular tone is impaired in patients with early glaucoma, independently of antiglaucoma medication.