Purpose. To determine whether the HRF retinal blood flow values, under normal conditions, are in the saturated range of the instrument so that it cannot register a moderate increase in blood flow. The HRF is a new instrument and it is uncertain whether its upper cutoff frequency (2 KHz) is below the Doppler shifted frequencies caused by normal blood flow. Methods. We used 10 Hz flicker stimulation to induce an increase in retinal blood flow (Riva, et al. Neurosci. Lett., 1991). We captured 5 HRF images of the papillomacular area of 4 subjects under mesopic conditions with no flicker and 5 images with flicker. The 10 Hz flicker (Grass PS22 flash filtered by a "green" bandpass and an infrared (K G3) filter) was diffusely or specularly reflected at the point of fixation which was slightly nasal to the final ocular. Blood flow values were measured in either two or three 200X200 μm frames in a 2.5X10° window centered about 5° from the optic disk. The instrument calculates the the blood flow values from power spectra of the beat frequencies resulting from the Doppler shifts caused by the reflection of 780 nm laser radiation from moving blood cells. Results. Blood flow values increased during flicker at all sites measured except for 2 sites in the retest of one subject. Analysis of data from the most robustly responding site of each subject revealed a mean 37% (±9.5% sd) increase (p=0.017 two-tailed paired t test). In the 3 subjects retested, the same sites showed a 40% (test) and a 29% (retest) increase in blood flow value. Conclusions. These observations indicate that HRF retinal blood flow values are not saturated in the normal range and that the HRF can detect modest increases in blood flow when the eye is exposed to 10 Hz flicker.
|Original language||English (US)|
|Journal||Investigative Ophthalmology and Visual Science|
|State||Published - Feb 15 1996|
ASJC Scopus subject areas
- Sensory Systems
- Cellular and Molecular Neuroscience