J Reinhard, D Besch, S Trauzettel-Klosinski
University Eye Hospital, II, 72076 Tübingen, Germany
Purpose. In patients with ring scotoma or concentric visual field there is often a discrepancy between visual acuity and reading performance. To assess the significance of the extent of the central seeing island it is crucial to have a reliable measure of its topography and size. We determined these parameters with high spatial resolution under fundus control by Scanning Laser Ophthalmoscope (SLO).
Methods. A special microperimetry program to detect absolute defects was developed and performed on the SLO in 27 eyes of 17 patients. During fixation of a cross, dots of 20 arcmin diameter were scanned onto the retina in the horizontal and vertical meridians and both diagonals up to an eccentricity of 9°. The spatial resolution (i.e. the distance between the dots) was 0.5°, the presentation time was 120 msec. The simultaneous recording of stimuli and retina allowed us to count only those answers of the patient where fixation was central.
Results. All patients fixated the cross stably and centrally. The seeing islands' diameter varied from 0.5° to 16° horizontally and from 0.5° to 13° vertically. The extent of the island was larger in patients with retinitis pigmentosa (mean 12.8°) and extremely small in patients with Stargardt's disease (mean 1.2°). Reading speed (mean 69, range 10 to 168 words per minute) increased with the horizontal diameter of the seeing island.
Conclusion. With our method we could determine the diameter of the seeing island with high spatial resolution. This measurement is of significance with respect to the reading performance.
Supported by German Research Council (DFG Zr 1/13-1 and Zr 1/14-1)
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