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M. Klein, D. G. Birch; The Diagnosys Full-Field Stimulus Threshold (d-fst) Is a Useful Tool to Assess Visual Function in Low Vision Subjects. Invest. Ophthalmol. Vis. Sci. 2009;50(13):6278.
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© ARVO (1962-2015); The Authors (2016-present)
Assessing retinal function beyond the sensitivity of electroretinography is increasingly important for new treatment trials for retinal degeneration. The FST test was developed as one useful measure that does not require fixation and produces a wide range of intensities. To date, the FST had to be custom built from modified Humphrey perimeter (FST1, Roman 2005) or as home-made software for a Ganzfeld dome (FST2, Roman 2007). Now Diagnosys LLC provides the D-FST software with the Espion ColorDomeTM system. We determined whether the D-FST is a valid new method of measuring visual function in low vision subjects and compared it to the FST2.
Twenty-five eyes of subjects ages 5 to 82 yrs (incl. 9 LP, 3 CF, 1 NLP) with severe retinal dystrophies (Retinitis Pigmentosa, Usher, Leber, Bardet-Biedl), for which ERGs were either not attempted or non-detectable, were tested with achromatic stimuli on the D-FST. A subset of 3 affected eyes and 4 normal eyes (ages 23 - 52 yrs) were tested on both the FST2 and the D-FST. After dilation and dark-adaptation, 3 trials were performed, each trial consisting of ~14 presentations for the FST2 and ~40 presentations for the D-FST. While the threshold on the FST2 was determined with a staircase-paradigm, the D-FST used a two-parameter Weibull Probability Function, weighing false positives and false negatives, to reach a threshold.
On the D-FST, a threshold could successfully be determined for 8 of the 9 LP eyes (mean -2.2 log cd.s/m2) and all 3 CF eyes (mean -4.1 log cd.s/m2). The NLP eye and one LP eye did not reach measurable thresholds. The mean full-field threshold for the normal eyes tested was -6.5 log cd.s/m2 on the D-FST and -6.9 log cd.s/m2 on the FST2. The mean threshold for the eyes with severe retinal degeneration was elevated 4.6 log units on both systems.
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