Reproducibility of pixel-by-pixel analysis of Heidelberg retinal flowmetry images: the Thessaloniki Eye Study

Basic technique and anatomically imposed limitations of confocal scanning laser Doppler flowmetry at the optic nerve head level

Many studies have suggested an association between blood flow dysregulation and glaucomatous damage to the optic nerve. Confocal scanning laser Doppler flowmetry (CSLDF) is a technique that measures the capillary blood flow of the retina and optic nerve head and provides a two-dimensional map of ocular perfusion in these areas. This review discusses the anatomy of the anterior optic nerve vasculature and the capabilities and limitations of the CSLDF. Methods to minimize error and to acquire more reliable measurements of capillary blood flow are also outlined.

Ocular blood flow and oxygen delivery to the retina in primary open-angle glaucoma patients: the addition of dorzolamide to timolol monotherapy

PURPOSE

To assess the effects of adding dorzolamide to timolol monotherapy on ocular haemodynamics and retinal oxygen saturation in patients with primary open-angle glaucoma (POAG).

METHODS

Twenty-four patients (12 healthy, 12 with POAG) were treated with dorzolamide/timolol combination (DT) versus timolol maleate 0.5% twice daily in a randomized, crossover, double-blind study conducted over a period of 18 months. Patients received each treatment for 8 months then crossed over to the other treatment after a 1-month washout and second baseline. Goldmann applanation tonometry, Heidelberg retinal flowmetry (HRF), colour Doppler imaging (CDI) and retinal photographic oximetry were performed at each visit.

RESULTS

DT significantly reduced intraocular pressure (IOP) in both glaucomatous [right eye (OD) -13.15%, left eye (OS) -14.43%; p < 0.036] and non-glaucomatous (OD -12.4%, OS -13.88%; p < 0.039) patients compared to timolol after 8 months of treatment. DT significantly reduced the number of zero blood flow pixels in the superior (-39.72%; p < 0.014) and inferior (-51.44%; p < 0.008) retina in the non-glaucomatous group and inferior retina in the glaucomatous group (-55.38%, p < 0.006). The continuation of timolol monotherapy from baseline did not change (p < 0.05) any measured parameter and neither treatment had a significant effect (p < 0.05) on retinal oximetry or CDI parameters.

CONCLUSION

The addition of dorzolamide to timolol monotherapy decreases IOP and increases retinal blood flow in the superficial retinal vasculature in both glaucomatous and healthy patients following 8 months of treatment. The combination of increased retinal blood flow with consistent oxygen saturation may potentially increase oxygen delivery to the retina.

Twelve-hour reproducibility of retinal and optic nerve blood flow parameters in healthy individuals

PURPOSE

The aim of the present study was to investigate the reproducibility and potential diurnal variation of optic nerve head and retinal blood flow parameters in healthy individuals over a period of 12 hr.

METHODS

We measured optic nerve head and retinal blood flow parameters in 16 healthy male non-smoking individuals at five time-points during the day (08:00, 11:00, 14:00, 17:00 and 20:00 hr). Outcome parameters were perimacular white blood cell flux (as assessed with the blue field entoptic technique), blood velocities in retinal veins (as assessed with bi-directional laser Doppler velocimetry), retinal arterial and venous diameters (as assessed with the retinal vessel analyser), optic nerve head blood flow, volume and velocity (as assessed with single point and scanning laser Doppler flowmetry) and blood velocities in the central retinal artery (as assessed with colour Doppler imaging). The coefficient of variation and the maximum change from baseline in an individual were calculated for each outcome parameter.

RESULTS

No diurnal variation in optic nerve head or retinal blood flow was observed with any of the techniques employed. Coefficients of variation were between 1.6% and 18.5% for all outcome parameters. The maximum change from baseline in an individual was much higher, ranging from 3.7% to 78.2%.

CONCLUSION

Our data indicate that in healthy individuals the selected techniques provide adequate reproducibility to be used in clinical studies. However, in patients with eye diseases and reduced vision the reproducibility may be considerably worse.