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Tiffany Arango, William H Seiple, Meesa Maeng, Janet P Szlyk; Comparisons of MAIA and Optos Microperimeters. Invest. Ophthalmol. Vis. Sci. 2016;57(12):5183.
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© ARVO (1962-2015); The Authors (2016-present)
Instruments that allow fundus-guided microperimetry (MP) are valuable for assessing visual function in patients with low vision. Although these instruments report sensitivities in decibels (dB), it is difficult to compare results among them due to differences in maximum light and in background levels. We compared the MAIA (MA) and optos (OP) microperimeters using the absolute luminance values for each machine.
6 control subjects and 10 low-vision patients were tested on the MA and OP using the same pattern of test points and the same threshold algorithm. Repeatability was assessed for controls by testing both instruments on three separate days. To compare equivalent units, dB thresholds were converted to light increments in apostilbs (asb), and then to delta increment intensities (ΔI) relative to the background luminance of each instrument.
The maximum stimulus intensity of the MA is 1,000 asb, and the minimum is 0.25 asb, equivalent to ΔIs of 322 and 0.08 above the 3.1-asb background, respectively. The maximum intensity of the OP is 439 asb, and the minimum is 5.2 asb, equivalent to ΔIs of 31.6 and 0.16 above the 31.4-asb background. When comparing across repeated tests, there was a significant effect for test day: average ΔI thresholds were 0.37 on Day 1 and 0.29 on Day 3. For patients, there were significant effects for instrument and subject. To test the gain associated with the larger ΔIs of the MA, we examined points where 0-dB thresholds were recorded on either instrument. 56% of these points had a 0-dB threshold on both instruments, 29.3% had measureable MA thresholds when the OP reported 0-dB thresholds, and 14.7% showed >0-dB thresholds on the OP when the MA had 0-dB thresholds. We also examined the benefit from the MA’s smaller ΔIs. Test points (in ΔI) at the smallest ΔIs produced by the OP (18-20 dB) were compared to the corresponding MA ΔI values. For 47.3% of these points, the MA recorded lower ΔI thresholds than the OP; for 52.7%, the MA recorded higher thresholds.
The background luminance of the MA is a log unit dimmer than the OP, which, in part, allows brighter and dimmer stimulus increments to be presented. However, this extended stimulus range only provided additional information in a small number of cases. Additionally, using a mesopic background level in the MA instrument confounds cone and rod contributions to thresholds.
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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