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A.J. Roman, T.S. Aleman, A.V. Cideciyan, S.B. Schwartz, E.A. M. Windsor, S.G. Jacobson; Full–field Stimulus Testing for Severe Retinal Degenerations: Extending the Dynamic Range . Invest. Ophthalmol. Vis. Sci. 2005;46(13):542.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: To develop further a psychophysical outcome measure for clinical trials of safety and efficacy in the most severe hereditary retinal degenerative (RD) diseases. We recently devised a full–field stimulus test (FST), based on a modified automated perimeter, and were able to quantify dark–adapted thresholds in a large RD cohort . For some severe RD patients, perception was close to the upper limit of the stimulus dynamic range and this result prompted the current advance in FST strategy. Methods: A software–only addition to an otherwise unmodified, commercial ERG system was developed to measure dark–adapted full–field psychophysical thresholds. The LED–based ganzfeld was programmed to deliver 200 ms flashes of different color and intensity. The "Full threshold" staircase algorithm with 4– and 2–dB level steps mimics that used in automated perimetry. Infrared video monitoring of the test eye occurred throughout the sessions and responses were recorded automatically. Severely affected RD patients and normals were tested with both implementations of the FST and results compared. Results: White and chromatic stimuli generated by the new FST implementation were perceived by all subjects. Intensities at threshold for all stimuli were at least 20 dB below the maximum intensity available and photoreceptor mediation was readily determined even in the most severe forms of RD. A session of three repeated measures of threshold for white and chromatic stimuli required a total of 8 minutes per eye, on average. For both patient and control groups, variability measures of the current implementation were similar to those of the previous FST. Conclusions: The new FST implementation extends the application of this outcome measure to the most severely affected RD patients who may be the earliest candidates for upcoming clinical trials. A further advantage is that psychophysical and ERG outcomes are now feasible to measure with the same instrumentation.
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