Optometry - Journal of the American Optometric Association
Volume 75, Issue 8 , Pages 496-502, August 2004

Influences of examiner position and effective prism power on nearpoint alternate cover test

  • Robb Johnson, O.D.

      Affiliations

    • Johnson R, Wynn S, Coffey B. Influences of examiner position and effective prism power on nearpoint alternate cover test. Optometry 2004;75:496-502.
    • ,
  • Shane Wynn, O.D.

      Affiliations

    • Johnson R, Wynn S, Coffey B. Influences of examiner position and effective prism power on nearpoint alternate cover test. Optometry 2004;75:496-502.
    • ,
  • Bradley Coffey, O.D.

      Affiliations

    • Johnson R, Wynn S, Coffey B. Influences of examiner position and effective prism power on nearpoint alternate cover test. Optometry 2004;75:496-502.
    • Corresponding Author InformationCorresponding author: Bradley Coffey, O.D., Pacific University, 511 SW 10th Avenue, Suite 500, Portland, Oregon 97205.

Pacific University, College of Optometry, Portland, Oregon

Article Outline

Background

This study was designed to resolve uncertainty concerning whether the position of the examiner is associated with variability in the results of the nearpoint alternate cover test (NACT). Two previous studies have shown that when the examiner is positioned to the side of the patient, rather than directly in front of the patient, the NACT shows greater exophoria in the range of 1.3 to 4.4 prism diopters. In the current study, we sought to determine if proximal cues or effective prism power might be the source of the apparent exo shift associated with examiner position.

Methods

Three conditions of the NACT were performed on 52 young adults with normal visual function. Two measurements using the method of limits were made in each condition and averaged. In all conditions, the fixation target remained on the subject's midline at a distance of 40 cm.

Results

Our results showed a small significant increase in measured exophoria when the examiner administered the NACT from a position to the side of the subject. The magnitude of the increase, 0.98 prism diopter, was less than in the previous studies, probably due to the control for proximal effect that was used. Intentionally rotating the measuring prism had a nominal effect on the measured phoria value, consistent with error induced due to effective prism power.

Discussion

It appears that examiner position does affect the outcome of the NACT, but that the magnitude of the effect is not clinically significant. A change in proximal cues may contribute to the effect.

Key words: Examinations, exophoria, nearpoint alternating cover test, testing, testing procedures

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PII: S1529-1839(04)70174-8

doi:10.1016/S1529-1839(04)70174-8

Optometry - Journal of the American Optometric Association
Volume 75, Issue 8 , Pages 496-502, August 2004

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