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Errors in determining the direction of the visual axis in the presence of defocus

Atchison, David A., Smith, George, & Charman, William N. (1998) Errors in determining the direction of the visual axis in the presence of defocus. Ophthalmic and Physiological Optics, 18(5), pp. 463-467.

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Abstract

The visual axis is the ray path from the fixation point to the fovea by way of the nodal points. Such a ray path does not exist in unaccommodated vision when the fixation point does not coincide with the far point of the eye because of induced or natural defocus. Nevertheless an approximation to the visual axis can be obtained by the position of a small pupil close to the cornea for which a bichromatic vernier target appears correctly aligned. When the visual axis is determined, an eye rotation from the usual fixation position must occur, which is reversed upon removing the small pupil. Upon engaging in any experiment for which the visual axis is then used as a reference, there is an error in this reference position. We develop simple paraxial equations to estimate this error. We show that these equations have good accuracy. The error associated with locating the visual axis at the cornea is 0.002 mm per dioptre of defocus, which is small enough to be ignored.

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2 citations in Web of Science®

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ID Code: 5169
Item Type: Journal Article
Additional Information: For more information, please refer to the journal’s website (see link) or contact the author. Author contact details: d.atchison@qut.edu.au
Keywords: visual axis, defocus, nodal points, ray path
DOI: 10.1046/j.1475-1313.1998.00379.x
ISSN: 0275-5408
Subjects: Australian and New Zealand Standard Research Classification > MEDICAL AND HEALTH SCIENCES (110000) > OPTOMETRY AND OPHTHALMOLOGY (111300)
Divisions: Current > QUT Faculties and Divisions > Faculty of Health
Current > Institutes > Institute of Health and Biomedical Innovation
Copyright Owner: Copyright 1998 Blackwell Publishing
Copyright Statement: The definitive version is available at www.blackwell-synergy.com
Deposited On: 02 Jan 2007
Last Modified: 10 Aug 2011 23:32

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