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Edoardo Midena, Enrica Convento, Margherita Casciano, Evelyn Longhin, Elisabetta Pilotto, Stela Vujosevic; Scotopic Microperimetry in Diabetes. Invest. Ophthalmol. Vis. Sci. 2012;53(14):2864.
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© ARVO (1962-2015); The Authors (2016-present)
To evaluate retinal threshold, quantified by scotopic microperimetry, in dark adapted eyes of diabetics without and with early nonproliferative diabetic retinopathy.
Fourty subjects were enrolled: 20 subjects were affected by diabetes mellitus and 20 normals served as controls. Moderate and severe non proliferative, and proliferative diabetic retinopathy, macular edema, previous laser photocoagulation, intraocular surgery or intravitreal injection, and refractive error higher than 6 diopters were the main exclusion criteria. Ten patients had no diabetic retinopathy (noDR group) and 10 patients had early nonproliferative DR (DR group). Full ophthalmic examination, including: BCVA, stereoscopic fundus photography, spectral domain-OCT were performed. After 20 minutes of dark adaptation, scotopic microperimetry was performed. The following parameters were used: log 2.0 filter in front of the projecting lights (original background 4 asb), Goldmann IV stimulus size, 3° ring as fixation target, 40 ms stimulus presentation, 37 stimuli grid covering 27°, centered onto the fovea. Standard mesopic microperimetry (no filter, Goldmann IV, 3° ring,40 ms, 37 points, 27°) was also performed. The sequence of examinations was randomly assigned.
No statistically significant differences were found for age among all groups and for glycemic control between diabetic gropus. Diabetes duration was statistically different between DR vs no DR group (p=.002). No statistically significant differences were detected among the three examined groups as dark adapted retinal threshold is concerned (7.4±1.1 dB vs 7.1±3.05 dB vs 7.1±2.1 dB in controls, no DR and DR groups , respectively; p=0.91). By scotopic microperimetry: all eyes (all groups) showed a central scotoma (of the same size), and fixation was always eccentric compared to the anatomic fovea, but stable; fixation was always central and stable in mesopic microperimetry. Mesopic microperimetry also showed no statistically significant retinal threshold differences among groups (p= 0.21).
The location of fixation and the presence of (physiologic) central scotoma confirm that scotopic microperimetry quantifies rods photoreceptors threshold. Diabetic subjects without clinically detectable or with early retinopathy have no signs of threshold changes when quantified by scotopic microperimetry. This study confirms that both rods and cones sensitivity thresholds are not affected in diabetes when no clinically detectable or early retinopathy is present. The presumed impact of diabetes on rods and cones photoreceptors should be revisited.
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