Impact of simulated light scatter on the quantitative, noninvasive assessment of retinal arteriolar hemodynamics.

We determine the impact of artificial light scatter on quantitative, noninvasive assessment of retinal arteriolar hemodynamics. One eye from each of 10 healthy young subjects between the ages of 18 and 30 (23.6+/-3.4) is randomly selected. To simulate light scatter, cells comprising a plastic collar and two plano lenses are filled with solutions of differing concentration of polystyrene microspheres (Polysciences Inc., USA). We prepare 0.002, 0.004, 0.006, and 0.008% microsphere concentrations as well as distilled water only. The Canon laser blood flowmeter (CLBF) is used to noninvasively assess retinal arteriolar blood flow. After a preliminary screening to confirm subject eligibility, seven arteriolar blood flow measurements are taken by randomly placing the cells between the instrument objective lens and the subjects' cornea. To achieve a baseline, subjects are first imaged with no cell in place. Both low- and high-intensity CLBF laser settings are assessed. Our light scatter model results in an artifactual increase of retinal arteriolar diameter (p<0.0001) and thereby increased retinal blood flow (p<0.0001). The 0.006 and 0.008% microsphere concentrations produce significantly higher diameter and flow values than baseline. Centerline blood velocity, however, is not affected by light scatter. Retinal arteriolar diameter values are significantly less with the high-intensity laser than with the low-intensity laser (p=0.0007). Densitometry assessment of vessel diameter is increasingly impacted as the magnitude of artificial light scatter increases; this effect can be partially negated by increasing laser intensity. A cataract is an inevitable consequence of aging and, therefore, care must be exercised in the interpretation of studies of retinal vessel diameter that use similar densitometry techniques.