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 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; SD): Pre-warming values were; OST: 34.51.02C, CRA-PSV: 9.32.33cm/s, CRA-EDV: 4.61.27cm/s. OST significantly increased by 1.96C (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 1.21cm/s (95 CI: 0.51to1.91). Pre-cooling values were: OST: 34.50.96C, CRA-PSV: 9.72.45 cm/s, CRA-EDV: 4.71.12cm/s. OST significantly decreased by 2.81C (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 1.10cm/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 1.57mmHg), but was significantly lower after cooling (95 CI: -2.95 to -4.30mmHg). 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.