Using two different stimuli, a pure red and a pure green illuminance ßicker, the coefÞcient of variation of the Flow responses was 26% (n = 5 trials) and 12% (n = 4).

The CVs of SFCH Vel, Vol, and Flow were reported to be 14%, 25%, and 18%, respectively, in subjects with AMD, and 8%, 18%, and 13%, respectively, in normal controls. No statistically signiÞcant differences were observed between these CVs for subjects with AMD and those for normal controls [83]. Another study in eyes with AMD of increasing severity provided a CV(Flow) of 10.3% ± 7.2% (n = 3 trials) [84].

With the confocal choroidal ßowmeter (Fig. 7.13), the sensitivity of SFCH Flow, calculated based on measurements in 10 subjects, was between 7.5% and 17.5% for Vel, 14.5Ð 37.8% for Vol, and 19.2Ð31.6% for the Flow [85]. Intrasubject variability was less than 8% for Vel and Vol and less than 18% for Flow, and the sensitivity of the measurements (21 subjects) was 3.3% for Vel, 7.1% for Vol, and 7.4% for Flow [86].

7.3.6Applications of LDF

Continuous, real-time LDF because of its high spatial and temporal resolution appears most suitable for the investigation of the regulatory processes of blood ßow in response to various physiological stimuli. The following investigations illustrate some of the applications. Regrettably, because of space limitation, it is not possible to mention all the important studies performed until now.

LDF investigations of ONH blood ßow in humans include the responses to: (1) changes in ocular perfusion pressure (increase and decrease) [75, 87, 88]; (2) hyperoxia, breathing carbogen, and mixtures of O2 and CO2 [89]; and (3) increased neuronal activity [90].

They also include a number of clinical studies, such as ONH blood ßow and its regulation in response to various stimuli in normal, ocular hypertensive, and glaucomatous eyes [91Ð97] and in children with cerebral malaria [98, 99].

LDF measurements of subfoveal choroidal blood ßow in humans are recent and include studies of the effect of (1) increases and decreases of ocular perfusion pressure [100Ð104]; (2) Valsalva maneuvers [105]; (3) breathing of various gas mixtures (pure O2, various mixtures of O2 and CO2) [86]; and (4) the effect of light [106Ð108]. Investigations of the effect of aging, age-related macular degeneration, and choroidal neovascularization have been reported [83, 84, 109Ð111].

7.4Summary for the Clinician

The LDV/LDF techniques have been applied over a number of years in normal subjects and patients with various ocular and systemic diseases. They provide a noninvasive means of investigating changes in blood ßow in the retina, ONH, and subfoveal choroid. Both techniques have a high sensitivity and a temporal response fast enough to reveal the changes in blood ßow during the cardiac cycle and in response to acute changes in various physiological stimuli. Their limitations include dilatation of the pupil, particularly for bidirectional LDV, good subject collaboration in terms of target Þxation, and head stability as well as clear media. These techniques open new avenues in the investigation of the regulation of blood ßow in the vascular tissues of the eye fundus in response to various physiological stimuli and the effect of a number of treatments on the ocular circulation.

Acknowledgement The author thanks the ÒFondazione Cassa di Risparmio in Bologna, ItalyÓ for its generous Þnancial support.

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