Changes in central retinal artery blood flow after ocular warming and cooling in healthy subjects.

Context: Retinal perfusion variability impacts ocular disease and physiology.

Aim: To evaluate the response of central retinal artery (CRA) blood flow to temperature alterations in 20 healthy volunteers.

Setting And Design: Non-interventional experimental human study.

Materials And Methods: Baseline data recorded: Ocular surface temperature (OST) in degrees C (thermo-anemometer), CRA peak systolic velocity (PSV) and end diastolic velocity (EDV) in cm/s using Color Doppler. Ocular laterality and temperature alteration (warming by electric lamp/cooling by ice-gel pack) were randomly assigned. Primary outcomes recorded were: OST and intraocular pressure (IOP) immediately after warming or cooling and ten minutes later; CRA-PSV and EDV at three, six and nine minutes warming or cooling.

Statistical Analysis: Repeated measures ANOVA.

Results: (n = 20; mu+/-SD): Pre-warming values were; OST: 34.5+/-1.02 degrees C, CRA-PSV: 9.3+/-2.33 cm/s, CRA-EDV: 4.6+/-1.27 cm/s. OST significantly increased by 1.96 degrees C (95% CI: 1.54 to 2.37) after warming, but returned to baseline ten minutes later. Only at three minutes, the PSV significantly rose by 1.21 cm/s (95% CI: 0.51 to 1.91). Pre-cooling values were: OST: 34.5+/-0.96 degrees C, CRA-PSV: 9.7+/-2.45 cm/s, CRA-EDV: 4.7+/-1.12 cm/s. OST significantly decreased by 2.81 degrees C (95% CI: -2.30 to -3.37) after cooling, and returned to baseline at ten minutes. There was a significant drop in CRA-PSV by 1.10 cm/s (95% CI: -2.05 to -0.15) and CRA-EDV by 0.81 (95% CI: -1.47 to -0.14) at three minutes. At six minutes both PSV (95% CI: -1.38 to -0.03) and EDV (95% CI: -1.26 to -0.02) were significantly lower. All values at ten minutes were comparable to baseline. The IOP showed insignificant alteration on warming (95% CI of difference: -0.17 to 1.57 mmHg), but was significantly lower after cooling (95% CI: -2.95 to -4.30 mm Hg). After ten minutes, IOP had returned to baseline.

Conclusion: This study confirms that CRA flow significantly increases on warming and decreases on cooling, the latter despite a significant lowering of IOP.