Impact of simulated light scatter on scanning laser Doppler flowmetry

Abstract

Aim: To determine the impact of simulated light scatter on scanning laser Doppler flowmetry (SLDF) assessment of retinal capillary blood flow and retinal image quality. Methods: One eye of 10 normal subjects (mean (SD) age 24 (1.7) years, range 22-27) was randomly selected. Varying concentrations of polystyrene microspheres were suspended in optically clear cells to simulate light scatter. The microsphere concentrations used were 0.05%, 0.03%, 0.02%, 0.01%, and a cell containing only water. LogMAR visual acuity and contrast sensitivity were measured both with and without cells. Optimal focus and alignment was established by acquiring three SLDF images each of the optic nerve head (ONH) and of the macula using the Heidelberg retina flowmeter (HRF) with no cell in place. SLDF images were subsequently acquired with each of the light scatter cells mounted in front of the HRF. The group mean retinal capillary blood flow was compared using repeated measures analysis of variance (reANOVA) as a function of microsphere concentration. Results: Retinal capillary blood flow increased significantly in the ONH, nasal macula, fovea, and temporal macula with increasing microsphere concentration (p,0.0001). Using Dunnett's post hoc test, retinal capillary blood flow was found to be significantly increased relative to the no cell condition for the 0.03% and 0.05% cell concentrations. Conclusions: Simulated light scatter produces an artifactual increase in retinal capillary blood flow. The impact of cataract on SLDF measurements has yet to be determined.

Preoperative and postoperative measurements of retinal vessel oxygen saturation in patients with different grades of cataracts

“…Previous studies have quantified the influence of artificial light scatter on various retinal imaging instruments (Venkataraman et al. ; Burke et al. ; Azizi et al.…”

“…Therefore, it would also be interesting to determine whether poor images attributable to severe cataracts were excluded from the analysis. Previous studies have quantified the influence of artificial light scatter on various retinal imaging instruments (Venkataraman et al 2005;Burke et al 2006;Azizi et al 2007). In vivo, Patel et al (2013) introduced an additional plano lens filled with a polybead solution that simulated light scatter to mimic the changes in lens morphology.…”

The effect of simulated cataract light scatter on retinal vessel oximetry

“…The details of the artificial light scatter model have been published elsewhere (Azizi et al, 2007, Burke et al, 2006, Venkataraman et al, 2005. In brief, cells comprising a plastic collar (inner diameter 25 mm) and two 35 mm removable CR39 plano parallel lenses (with a spacing of 4.5 mm between the lenses and a thickness of 2.04 mm each) were filled with solutions of differing concentrations of polystyrene microspheres (Polybead © Polysciences…”

“…Despite this, the impact of lens opacity on the assessment of blood oxygen saturation is unknown. Previous studies from our group have quantified the influence of artificial light scatter on various retinal imaging instruments (Azizi et al, 2007, Burke et al, 2006, Venkataraman et al, 2005. In order to mimic the change in lens morphology, we introduced an additional plano lens, filled with a polybead solution to simulate light scatter.…”

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

“…(1999) showed that the zero offset changed dramatically with the change in brightness of the background and it had a significant impact on the magnitude of HRF estimated noise. Similarly, Venkataraman et al. (2005) showed that with an increase in light scatter the image brightness and DC values decreased and the flow values increased significantly.…”