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Inverse stimuli in perimetric performance reveal larger visual field defects: Implications for vision restoration

Issue title: Visual Plasticity, Restoration and Rehabilitation

Article type: Research Article

Authors: Kasten, Erich | Guenther, Tobias | Sabel, Bernhard A.

Affiliations: Institute of Medical Psychology, Medical Faculty, Otto-von-Guericke-University of Magdeburg, Leipziger Str. 44, D-39120 Magdeburg, Germany

Note: [] Corresponding author: B.A. Sabel, Institute of Medical Psychology, Medical Faculty, Otto-von-Guericke-University of Magdeburg, Leipziger Str. 44, D-39120 Magdeburg, Germany. Tel.: +49 391 611 7100; Fax: +49 391 611 7103; E-mail: [email protected]

Keywords: Perimetry, vision, visual field, ophthalmoloscope

Journal: Restorative Neurology and Neuroscience, vol. 26, no. 4-5, pp. 355-364, 2008

Received 24 October 2008
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Accepted 24 October 2008
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Published: 2008
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Abstract

Purpose: When studying the efficacy of vision restoration training (VRT), near-threshold and super-threshold perimetry revealed visual field enlargements whereas the Scanning Laser Ophthalmoscope (SLO) did not. Because the SLO procedure differs in many parameters from the other perimetric tests (task difficulty, inability to reveal relative defects, inverse stimulus presentation, bright red background) the question arises which of these parameters might be responsible for such discrepancies in outcome. We have therefore simulated with a computer-based campimetry test some of the SLO parameters and compared performance with that in standard perimetry.

Methods: A 46-year old female patient was evaluated with computer-based high resolution perimetry (HRP) using detection tasks of "positive" (bright) stimuli on grey background. Performance was compared with an SLO-like task using "inverse" black target stimuli on red background.

Results: Detection rate was 89% when the stimuli were positive (HRP) but dropped to 79.6% and 80.4% in the SLO-like "inverse" stimulation mode with red background, and striped red background, respectively. The number of false positives increased from 8.5 when a grey background was used, to 9.8 and 9.5 for plain red and striped red background, respectively. Reaction times were prolonged from 384 ms using a grey background to 412 ms and 391 ms using a plain red and striped red background, respectively. Thus, visual fields tested with SLO-like "inverse" stimuli showed larger scotomata and prolonged reaction time.

Conclusions: Inverse stimulus detection on red background is apparently a more difficult task for hemianopic patients than standard perimetric protocols (such as those used in Tuebinger Automatic Perimetry or HRP). The difference in stimulus features might explain why VRT-induced visual field enlargements could not be observed with the SLO. Our findings also suggest that vision restoration training does not improve all aspects of vision, such as inverse, chromatic stimulus detection.

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