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Allen Ingling, Ann E Elsner, Shirin E Hassan, Matthew S Muller, Jeffrey L Clendenon, Stephen A Burns; Pupil plane degradation of retinal imaging and visual display. Invest. Ophthalmol. Vis. Sci. 2016;57(12):5180.
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© ARVO (1962-2015); The Authors (2016-present)
Both retinal imaging and visual function assessment are negatively impacted by ocular media changes. We used uniform diffusing patches to assess the relative magnitude of degradation in the appearance of visual stimuli and image contrast in the retinal plane. We tested instruments designed to minimize the effects of light scatter: an adaptive optics scanning laser ophthalmoscope (AOSLO) and a digital light ophthalmoscope (DLO).
The Indiana AOSLO data was measured for 810 nm, with a field size of 1.6 x 2.0 deg. Confocal aperture and laser powers were varied, for model eye images at constant gain. The DLO was measured for visible wavelength illumination centered at 575 nm. Six subjects, aged 27 – 65 yrs matched contrast on a 7 point contrast scale for the 9 fixation crosses used for pseudo-color fundus imaging. Imaging conditions used a brighter cross on a background of 20 microwatts at the cornea, 38 deg, 14.3 Hz alternation of red (630 nm) and orange (580 nm) illumination. Relative retinal illumination was calibrated for both the AOSLO and the DLO. The amount of light loss, visual contrast, and image degradation were measured with Bangerter Occlusion Foils (Bernell) calibrated for 20/200 and 20/400 in the pupil plane, compared with a no diffuser control condition. The foils were single pass diffusers for visual stimuli and double pass for imaging.
The apparent contrast of the visible wavelength fixation crosses dropped significantly when viewed through the Bangerter Occlusion Foils, with median values of 1, 4, and 5 for no foil, the 20/200 foil, and the 20/400 foil, respectively (p < .0001, Friedman nonparametric analysis). For the AOSLO, the amount of light in a 64 x 64 pixel region of interest decreased by 98.6% and 99.1% for a confocal aperture of 8 microns and by 80.7% and 98.9% for a confocal aperture of 40 microns for the 20/200 and 20/400 foils, respectively. The relative retinal illumination dropped only 14% vs. 20% for visible wavelengths and 24% vs. 27% for 810 nm, for the no-foil to 20/200 and the no-foil to 20/400 foil conditions, respectively.
The apparent contrast and light captured from the retinal plane both decreased considerablywhen ocular media are degraded in the pupil plane. The results cannot be explained by the transmission loss of illumination.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
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