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A. Gofen, M. MacKeben; Retinal Function Testing by SLO With Gaze-Contingent Stimulus Display. Invest. Ophthalmol. Vis. Sci. 2007;48(13):3548. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
To overcome the inconvenience and unreliability of conventional software performing micro-perimetry with the Scanning Laser Ophthalmoscope (SLO).
We developed "smart micro-perimetry" (SMP) software using state-of-the-art computer technology with high processing speed and high rate of data transfer. It continuously digitizes and processes the image of the retina on-line and instantaneously corrects stimulus placement to compensate for involuntary eye movements (EMs). The program is implemented on a secondary PC with a Matrox Morphis frame-grabber board and uses low-level image tracking routines from a specialized library (MIL-8).
SMP provides gaze-contingent display of the stimulus and senses the conditions for image tracking. Stimulus placement during blinks and temporarily flawed image quality is thus actively prevented. Specialized software was used to ascertain that indeed every video frame is tracked. The time-saving aspect of SMP was tested on normally sighted subjects to control the number of unsuccessful trials. Conventional micro-perimetry was run for comparison. It was found that in 600 trials for each method, SMP took 118.8 s ± 10.54 SD, range 107 to 133s (2.38 s/trial), while the older program took 191.5 s ± 17.51 SD, range 168 to 224s (3.83 s/trial), a time saving of about 40%.When automated target placement with a pre-designed stimulus grid was used, the average trial took only 1.73 s, thus cutting the experimental time compared to conventional software in half. Custom software has demonstrated that EMs of up to 110º/sec velocity can be compensated for. According to the "main sequence" for saccadic EMs , this shows that fixational EMs of up to 3 deg amplitude can be corrected.The SMP program has also been used on 30 low vision patients and was found to be quick and reliable. Noticeable slowing of the tracking process was found only in 2 patients with large "floaters" in the media.
We have demonstrated that modern computer technology and specialized software can make true gaze-contingent stimulus display possible. This has greatly increased the precision and reliability of SLO micro-perimetry data in comparison to those obtained by older programs.
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