Comparison of pulsatile ocular blood flow in Indians and Europeans

Pulsatile ocular blood flow: relationship with flow velocities in vessels supplying the retina and choroid

BACKGROUND

Although ocular tonography measures a pulsatile component of the ocular perfusion, the retinal and/or choroidal components of this pulsatile flow remain undefined.

AIM

To compare ocular tonography with the assessment of flow velocities in arteries supplying the retina, choroid and entire orbit.

METHODS

22 normal eyes from 11 subjects were studied. Pulsatile ocular blood flow (POBF) was measured using the ocular blood flow tonograph, and flow velocities in the ophthalmic, central retinal (CRA) and temporal short posterior ciliary arteries (TSPCA) using colour Doppler imaging. The correlation between POBF and retrobulbar flow velocities was determined.

RESULTS

POBF correlated significantly with peak systolic velocity (PSV) of the CRA (r = 0.56, p = 0.007) and the TSPCA (r = 0.48, p = 0.02), and with the resistive index of the TSPCA (r = 0.45, p = 0.04). Additionally, pulse amplitude (PSV-end diastolic velocity) in the CRA and the TSPCA correlated significantly with POBF measurements (each p<0.05). However, POBF did not correlate with any flow velocity indices in the ophthalmic artery.

CONCLUSION

POBF is associated with systolic and pulsatile components of blood flow velocities in both the CRA and the TSPCA. This result suggests that POBF determinations are influenced by the pulsatile components of both choroidal and retinal perfusion.

Ethnicity and glaucoma: higher environmental temperatures may accelerate the onset, and increase the prevalence, of primary open-angle glaucoma

Publications on the age-related prevalence of primary open-angle glaucoma (POAG) show that African and African-descended patients and others living in warm climates present a higher prevalence of POAG than do those in temperate zones. The data have been analysed in order to discover whether temperature plays a role. The relation between AOO, the youngest age diagnosed with POAG, and prevalence has also been examined. Prevalences at the age of 70 years P(70) were calculated from logarithmic plots, and logP(70), plotted as a function of the average monthly maximum temperature T degrees C, and tested with the LINEST programme. AOO declined, but logP(70) rose, with T degrees C. The data are consistent with the view that high temperatures accelerate the onset, and increase the prevalence, of POAG. A consideration of evolution suggests that the reduced Caucasian prevalence may result from originally African tribes migrating to locations with more temperate climates: this would have caused a constriction of superficial capillaries to preserve body heat; hence the aqueous outflow channels might dilate, and reduce a predisposition for POAG. Suggestions are made for testing the hypothesis.

Effects of central corneal thickness and corneal curvature on the intraocular pressure measurement by Goldmann applanation tonometer and ocular blood flow pneumatonometer

PURPOSE

To assess the effects of central corneal thickness (CCT) and corneal curvature (CC) on the measurements of intraocular pressure (IOP) using Goldmann applanation tonometer (GAT) and the ocular blood flow pneumatonometer (OBFT).

METHODS

104 patients were recruited from a glaucoma clinic. The CCT was measured using ultrasound pachymetry and the mean radius of CC using a keratometer. The IOP of each eye was measured using both GAT and the OBFT in a random order. Right eyes only were analysed for statistical purposes.

RESULTS

The mean (+/-SD) IOP by GAT and OBFT was 18.2 mmHg (+/-4.4) and 18.2 mmHg (+/-4.0), respectively, with no statistically significant difference. IOP measurement with both instruments varied with CCT and CC. GAT showed an IOP increase of 0.40 mmHg per 10 microm increase of CCT and OBFT showed an increase of 0.38 mmHg in IOP per 10 microm increase of CCT. Multiple regression analysis showed that the effect of CCT was statistically significant (P<0.001) on IOP recorded by both the GAT and OBFT but CC did not have a statistically significant effect on IOP recordings performed by either technique.

CONCLUSION

IOP measurements by GAT and OBFT are positively correlated with CCT with both tonometers being similarly affected. There was no significant correlation between CC and IOP measured by either tonometer.