Changes in central retinal artery blood flow after ocular warming and cooling in healthy subjects.
BACKGROUND
Retinal perfusion variability impacts ocular disease and physiology.


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


METHODS
Non-interventional experimental human study.


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.


METHODS
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.


CONCLUSIONS
This study confirms that CRA flow significantly increases on warming and decreases on cooling, the latter despite a significant lowering of IOP.
Shamshad
M A
MA
Institute of Ophthalmology, JNMC, AMU, Aligarh, India.
Amitava
A K
AK
Ahmad
I
I
Wahab
S
S
D001783:Blood Flow Velocity; D005260:Female; D006801:Humans; D008297:Male; D012016:Reference Values; D012161:Retinal Artery / Q000502:physiology*; D013696:Temperature; D055815:Young Adult