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.

View at publisher


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.

Impact and interest:

2 citations in Scopus
2 citations in Web of Science®
Search Google Scholar™

Citation counts are sourced monthly from Scopus and Web of Science® citation databases.

These databases contain citations from different subsets of available publications and different time periods and thus the citation count from each is usually different. Some works are not in either database and no count is displayed. Scopus includes citations from articles published in 1996 onwards, and Web of Science® generally from 1980 onwards.

Citations counts from the Google Scholar™ indexing service can be viewed at the linked Google Scholar™ search.

ID Code: 5169
Item Type: Journal Article
Refereed: Yes
Additional Information: For more information, please refer to the journal’s website (see link) or contact the author. Author contact details:
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
Deposited On: 02 Jan 2007 00:00
Last Modified: 10 Aug 2011 13:32

Export: EndNote | Dublin Core | BibTeX

Repository Staff Only: item control page