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Torsten Strasser, Hana Langrová, Anne Kurtenbach, Ditta Zobor, Dominic Hillerkuss, Eberhart Zrenner; Quick and easy light sensitivity assessment of the dark adapted eye: The Tuebingen Scotopic Threshold Test (TSTT). Invest. Ophthalmol. Vis. Sci. 2013;54(15):3015.
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Light sensitivity of the dark-adapted eye is a valuable indicator of retinal function. Changes in light sensitivity are observed in many retinal disorders like Retinitis pigmentosa, CSNB, or in vitamin A deficiency. Light sensitivity is usually tested using dark adaptometry: after transient exposition to bright light the dark-adaptation curve and the final threshold are measured. This procedure is time-consuming and uncomfortable, especially for children. Within the EU-project TREATRUSH, we developed a test for assessing the scotopic threshold for early detection of Usher's syndrome.
The TSTT has 2 panels for scotopic and photopic stimulation. Each panel has a size of 7×10cm, consisting of 35 individually addressable LED bars, thus allowing to use various stimulus shapes. The centerpiece of the TTST is a microcontroller (ATmega8515, Atmel Corp.), running a self-developed software. Stimulus luminance is tuned by pulse-width modulation and adjustable in 100 steps between -3 to -1 log cd/m2. Using filters, this can be extended from -8 to -1 log cd/m2. The luminance gradually increases until a perception is indicated. The patient names the shape and the examiner confirms or discards the response, thus discriminating correct answers from false-positives. If confirmed, the luminance is decreased and the procedure is repeated. Feasibility and repeatability were tested in 11 subjects (10-68yrs). Monocular and binocular presentation were compared, as well as results obtained with natural or dilated pupil.
All subjects completed the test successfully. Binocular presentation reduced threshold by ~0.15 log units. Intra-subject repeatability was >90%. We found no difference in the results obtained with natural or dilated pupils. A flickering stimulus did not show advantages over a constant presentation.
The Tuebingen Scotopic Threshold Test allows for quick and easy assessment of the sensitivity of the dark-adapted eye. The recording takes only 5 minutes (w/o dark adaptation), can be done with natural pupils and is comfortable for the patient. Results obtained with the TSTT show a high correlation to similar tests. This makes the TSTT to a well suited tool for testing children. This project and study is supported through TREATRUSH (HEALTH-F2-2010-242013), a European Collaborative project - supported by the European Commission under the 7th Framework Program.
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