Stereoacuity and depth perception decrease with increased instrument magnification: comparing a non-magnified system with lens loupes and a surgical microscope.
OBJECTIVE
To evaluate the effect of instrument magnification used in eye surgery on stereoacuity and depth perception.


METHODS
Twenty-one subjects (10 clinical ophthalmologists familiar with loupes and operating microscopes and 11 non-ophthalmologists) with normal near vision and stereoacuity were tested with the Randot Stereotest viewed unmagnified, with a 4x loupes (450 mm focal length), and with a 16x operating microscope.


RESULTS
Total scores: 8 errors in 210 test steps with the unmagnified observations, 25/210 with loupes, and 30/210 with the microscope. The statistical differences in these scores were "statistically highly significant" for all three tests (p = 0.002); and "significant" for the unmagnified versus loupe (p = 0.007) and unmagnified versus microscope (p = 0.002). Test viewing through the microscope, the greatest errors occurred (total errors = 1840 seconds of arc), less with the loupes (total 1150") and least without magnification (total 220"). Errors and scores for 10 experienced ophthalmologists were no different (p > or = 0.55, p = 1.00) from the 11 non-ophthalmologist subjects.


CONCLUSIONS
Stereoacuity and depth perception decrease when viewing a test target with loupes or with a microscope, with the effect worsening as magnification increases. Familiarity with the magnifying equipment did not improve stereoacuity.
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Edward S. Harkness Eye Institute, Columbia University, New York, NY 10032, USA. 1_dumymail_1997@yahoo.com
Wessels
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Underdahl
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Auran
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D000328:Adult; D003867:Depth Perception / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D008853:Microscopy; D008875:Middle Aged; D013508:Ophthalmologic Surgical Procedures / Q000295:instrumentation*; D055095:Optics and Photonics; D014787:Vision Tests / Q000379:methods; D015348:Vision, Binocular / Q000502:physiology*; D014792:Visual Acuity / Q000502:physiology*