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Noah C. Benson, Dwight Stambolian, David H. Brainard; Contrast Sensitivity At Soft Drusen In Early Age-related Macular Degeneration Using Fine-detail Perimetry. Invest. Ophthalmol. Vis. Sci. 2012;53(14):4382.
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Age-related macular degeneration (AMD) is the most common cause of blindness in the Western world, yet functional characterization of the disease in its early stages remains difficult. Previous work has demonstrated a relationship between advanced AMD-related large soft drusen and a reduction in contrast sensitivity (CS) near such drusen. Less evidence supports a similar reduction near early-stage AMD-related small and intermediate drusen. To clarify, and to allow correlation of functional changes with information obtained using genetic and high-resolution retinal imaging, we are developing psychophysical procedures that can measure functional changes at a fine spatial scale near small early-stage drusen.
Fundus photos were acquired for each subject, and the fundus, optic disc, and perimetry targets corresponding to drusen (for experimental subjects) and blood vessels (for controls and experimental subjects) were marked in each. Perimetry was performed using a 19" cathode ray tube (CRT) monitor with 14-bit control over contrast provided by a Bits++ box (Cambridge Research Systems). Gaze position was monitored using an Eyelink 1000 eye tracker (SR Research). Perimetry target locations were mapped from the fundus photo onto the screen by aligning the subject’s blind spot, measured psychophysically, with the optic disk. CS measurements were made by flashing small Gaussian blobs and recording the fraction seen at each target location. The size and contrast of the blobs were chosen for each subject to maximize sensitivity.
Six control and two experimental subjects have been studied. A statistically significant dip in CS is observed near the blood vessel of each control subject (p < 0.05) with an average distance between the location of the measured dip in CS and the blood vessel of 0.26º. Of the two experimental subjects, one showed a small but significant dip in CS (p < 0.05) across a series of small drusen while the other showed a larger dip in CS over a single larger druse and a smaller dip across a blood vessel (p < 0.05).
CS measurements in the vicinity of small soft drusen appear feasible with our procedures.
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