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Proceedings Paper

Data acquisition time constraints in elevation mapping corneal topography
Author(s): William S. Baron; Sandra F. Baron
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Paper Abstract

Elevation mapping corneal topography instruments provide an array of x, y, z data points describing the corneal surface. An advantage of elevation mapping instruments is their ability to calculate the 3D data array strictly from the instrument's geometry and calibration data; no assumptions about the corneal surface itself are needed. However, uncompensated eye movements can affect accuracy. Longitudinal eye movements occur along the z axis, due to pulmonary and cardiac pulsations. Eye rotations due to saccades and drifts are normal occurrences, as are translational body movements. An analysis of eye and body movements at the cornea's surface indicates a nearly linear relationship between data acquisition times of less than 33 msec, and the possible change in elevation at a point referenced to an instrument axis. The proportionality constant is expected to vary by a factor of about six over the range of clinical patients, since eye and body movements are exaggerated in juvenile patients, geriatric patients, and patients with poor vision. The analysis estimates an elevation change due to rotation and longitudinal translation of the eye of up to +/- 285 micrometers in 33 msec within the clinical population. This analysis indicates that when a topographer's acquisition time is greater than 100 microsecond(s) ec (during which an apparent elevation change of up to 1.0 micrometers may occur) testing on static objects may not provide a realistic measure of an instrument's clinical performance.

Paper Details

Date Published: 26 May 1997
PDF: 10 pages
Proc. SPIE 2971, Ophthalmic Technologies VII, (26 May 1997); doi: 10.1117/12.275110
Show Author Affiliations
William S. Baron, Vision Metrics, Inc. (United States)
Sandra F. Baron, Vision Metrics, Inc. (United States)

Published in SPIE Proceedings Vol. 2971:
Ophthalmic Technologies VII
Pascal O. Rol; Karen Margaret Joos M.D.; Fabrice Manns, Editor(s)

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