February 1996
Volume 37, Issue 2
Free
Articles  |   February 1996
Influence of fixation accuracy on threshold variability in patients with open angle glaucoma.
Author Affiliations
  • D B Henson
    Department of Ophthalmology, University of Manchester, United Kingdom.
  • J Evans
    Department of Ophthalmology, University of Manchester, United Kingdom.
  • B C Chauhan
    Department of Ophthalmology, University of Manchester, United Kingdom.
  • C Lane
    Department of Ophthalmology, University of Manchester, United Kingdom.
Investigative Ophthalmology & Visual Science February 1996, Vol.37, 444-450. doi:
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    • Get Citation

      D B Henson, J Evans, B C Chauhan, C Lane; Influence of fixation accuracy on threshold variability in patients with open angle glaucoma.. Invest. Ophthalmol. Vis. Sci. 1996;37(2):444-450.

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      © ARVO (1962-2015); The Authors (2016-present)

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Abstract

PURPOSE: To evaluate the contribution that fixation errors make to the overall variability of perimetric responses in patients with glaucoma. METHODS: Frequency of seeing curves were established, with and without fixation error correction, at two locations in each of 14 patients with glaucoma and good visual acuity. One location corresponded to a relatively normal region of the visual field, whereas the second corresponded to a region in which there was a sensitivity deficit. All patients had an acuity of better than 20/63 (except one whose acuity was 20/100). The locations of the first and fourth Purkinje images of a collimated infrared source were used to give a measure of eye position, during each stimulus presentation (accuracy 10 minutes of arc). RESULTS: Considerable variation was found in patient fixation accuracy. In the worst case, fixation was within 30 minutes of the target in only 7% of presentations whereas in the best, it was within this range in more than 60%. No relationship was found between accuracy of fixation and extent of loss. The gradient of the frequency of seeing curve was found to be shallow at regions of reduced sensitivity, a finding that supports the recognized relationship between variability and sensitivity deficit. A recalculation of the frequency of seeing curves, using only those responses in which the patient's fixation was within a specified range ( < 60 minutes of arc), did not show a meaningful reduction in variability at either location. CONCLUSIONS: It is concluded that fixation errors, though contributing to variability, are not the major cause of the increased variability seen at locations with reduced sensitivity.

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