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T.L. Nunn, G.R. Jackson, C. Owsley; Evaluation of the Scotopic Sensitivity Tester-1 (SST-1) Dark Adaptometer . Invest. Ophthalmol. Vis. Sci. 2003;44(13):5004.
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Purpose:The SST-1 is a commercially available, portable, inexpensive dark adaptometer that may be useful in the clinic to screen for early age-related maculopathy (ARM). Previous studies have shown that when using elaborate dark adaptation (DA) protocols on custom-built dark adaptometers, the older population takes longer to adapt to the dark than the younger population. Furthermore, early ARM patients exhibit severely impaired DA functions compared to old normals. The SST-1 may be useful in the clinical setting if similar abnormalities of DA are found in the populations of interest.Methods:The sample consisted of 4 young normals (mean 24 years), 12 old normals (mean 66 years), and 10 early ARM participants (mean 72 years). All participants had visual acuity of 20/25 or better. The test eye was dilated, and the participant adapted to the dark for thirty minutes. Baseline scotopic sensitivity was measured prior to dark adaptometry. The test eye was bleached with a continuous background of achromatic light (100cd/m2) for 1 minute. The target stimulus was a full-field green LED (lmax = 572 nm) that varied in intensity over 3 log units. Thresholds were estimated using the method of ascending limits. Threshold measurements ceased when sensitivity recovered to within 0.3 log units of the previously measured baseline sensitivity. Each individual’s DA function was fit by a double exponential model using nonlinear regression to estimate the following parameters: the rod-cone break (RCB), duration, baseline sensitivity, the rod time constant (RTC), and the cone time constants (CTC).Results:There were significant differences in the RCB among the three groups (p< 0.001) and duration (p= 0.001). The CTC (p= 0.873), RTC, (p= 0.174) and baseline sensitivity (p= 0.589) were insignificant throughout the three groups. Duration in the early ARM group, on average, took 3 minutes more than the older group (p= 0.331) and 12 minutes more than the younger group (p= 0.001). Duration in the older group, on average, took 8 more minutes than the younger group (p=0.019). To reach RCB, the early ARM group took 4 additional minutes than the older group (p= 0.001) and 7 more minutes than the younger group (p= 0.001). The older group took 3 more minutes, on average, to reach RCB (p=0.116). Conclusions: The SST-1 can detect some abnormalities of DA parameters. It allows group differences to be found in the RCB and duration of DA, but not in baseline sensitivity, the RTC, or the CTC. The SST-1 is not completely sensitive to aging-related impairments. Depending on the DA parameters and the population of interest, the STT-1 may be a suitable alternative to more elaborateDA protocols.
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