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Portia Sirinek, Reena Vaswani, Stanley Chang, George A Cioffi, Lama A Al-Aswad, Dana M Blumberg; The potential impact of glaucoma on photoreceptors. Invest. Ophthalmol. Vis. Sci. 2014;55(13):945.
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Due to the inadequate resolution of imaging modalities and limited histology, the effect of glaucoma on the outer retina has been poorly studied. Adaptive Optics (AO) is a technology that allows in-vivo imaging of the outer retinal layers. The purpose of this study is to image retinal cone photoreceptors and correlate their density with visual field loss in advanced glaucoma patients.
The macular region of five patients was imaged using the AO scanning laser ophthalmoscope (AO-SLO, Canon, Tokyo, Japan). Patients selected for imaging had dense hemi-field visual field defects, defined as an average difference >10 dB between the hemi-fields on Humphrey 24-2 visual field testing with an average dB > 20 in the better hemi-field. Two of the five patients were excluded due to non-glaucomatous retinal pathology and media opacity. Two readers, masked to the visual field defects, calculated cone density maps in a semi-automated fashion at 12 locations within the central 3 mm of the macula; 6 corresponding anatomic locations in the superior and inferior retina of each patient.
Of the patients recruited into the study, the superior and inferior visual field loss differed by approximately 20 dB on average. In the more damaged hemi-field, the average cone density was 3832 cells/mm2, while in the less damaged hemi-field the average density was 6390 cells/mm2. There was an average difference in cone density of 2559 cells/mm2 (95% CI 1454.12- 3663.83) between the two hemi-fields. A paired t-test was performed and showed this difference was statistically significant with a p value < 0.001.
This study shows that outer retinal damage occurs in glaucoma. A statistically significant lower cone density was found in regions of the macula corresponding with hemi-field loss. Previous studies have shown no significant difference in cone densities in the superior and inferior hemi-fields of normal patients. This new information might have implications for future treatment modalities.
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