Impact of Simulated Light Scatter on Canon Laser Blood Flow Meter

Abstract

Abstract: : Purpose: To determine the impact of artificial light scatter on quantitative measurements of retinal arteriolar blood flow acquired with the Canon Laser Blood Flow Meter (CLBF). Methods: One eye of 6 normal subjects (mean age 27.3 years, SD 1.1) was randomly selected. All subjects were free from lens opacity and any other ocular disease and had a logMAR visual acuity of 0.0 or better. Polystyrene microspheres (Polybead Polysciences Inc., USA) of 500 micron diameter were dissolved in distilled water. Solutions of 0.002%, 0.005% and 0.008% microsphere concentration, plus distilled water only, were prepared and injected into optically clear cells to simulate light scatter. Each volunteer underwent quantiative retinal arteriolar blood flow measurement using the CLBF with no cell in place as a baseline to optimize and set the instrument focus and position. Retinal blood flow measurements were then acquired at the same arteriolar site with the various light scatter cells placed in front of the subjects’ eye in random order. Seven separate measurements of retinal blood flow were acquired for each condition. Repeated measures Analysis of Variance (ANOVA) was used to determine the relationship between CLBF measurements of retinal arteriolar diameter, centreline blood velocity and flow and microsphere concentration. Results: The laser tracking system consistently failed to lock the diameter laser on to the retinal arteriole when the 0.008% concentration was used. Group mean arteriolar diameter significantly increased (ANOVA, p<0.0001) with increase of microsphere concentration; however, centreline blood velocity was not significantly effected. Tukey HSD post hoc test revealed that the 0.002% and 0.005% concentration cells produced significantly higher diameter values (p=0.001 and p=0.0001, respectively) than both the baseline and distilled water conditions. Retinal arteriolar blood flow was also significantly increased with increase of microsphere concentration (ANOVA, p<0.001). Conclusions: CLBF derived retinal arteriolar diameter significantly increased with increase in simulated light scatter, whereas centreline blood velocity was not significantly effected. Caution has to be exercised in the interpretation of CLBF quantitaitive retinal blood flow measurements in situations with existing, or changing, light scatter status.

Keywords: imaging/image analysis: non-clinical • retina • blood supply