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Spatial compression produced by a stationary low-vision telescope.

Tran G, Sedgwick HA

Illinois College of Optometry, Chicago, Illinois, USA.

PURPOSE: Geometrical analysis of the monocular information for visual space perception predicts that the magnification produced by a low-vision telescope will compress the depth dimension of space. To test this prediction we measured the compression in depth of perceived shape while looking through a stationary telescope. To control for the other aspects of telescopic viewing, apart from magnification, we also measured perception while looking through a plain tube having the same field of view. METHODS: A 2.75x Keplarian telescope was mounted 40 cm above a tabletop patterned with receding stripes. The 11.6 degrees field of view was centered on a series of rectangular stimulus cards lying flat on the table at a distance of 100 cm. Participants monocularly viewed each card through the telescope, or through a tube having the same field of view, and verbally judged the card's perceived length (in depth) relative to its width (in the frontal plane). RESULTS: Perceptual compression of shape was calculated by dividing the perceived proportion (length/width) by the actual proportion. The telescope and the tube both produced significant perceptual compression, but perception was significantly more compressed through the telescope (0.43) than through the tube (0.52). CONCLUSIONS: The magnification produced by a stationary low-vision telescope can result in a compression of perceived depth. In addition, other aspects of telescopic viewing, such as monocular vision, restricted head movements, and a restricted field of view, can together contribute substantially to such compression. Further research is needed to assess the clinical implications of these results.

Published 4 January 2008 in Optom Vis Sci, 85(1): 54-62.
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