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MJ Levitt, A Jain; A Novel Technique for Measuring Binocular Single Field of Vision . Invest. Ophthalmol. Vis. Sci. 2002;43(13):1476.
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Purpose: To create a test for the evaluation of binocular single field of vision in patients with limitation of extraocular motility that is quick and simple, yet accurate and easily reproducible. Background: Patients with limitation of extraocular motility, for example due to muscle entrapment resulting from orbital fractures, often experience diplopia. An accurate measurement of the angle of globe movement at which diplopia ensues is essential for baseline evaluation and at serial visits to assess progression. Resolution or progression of symptoms, if accurately assessed, can help guide therapy. The "gold standard" test is Goldman perimetry. However, this test requires a trained operator and considerable time and therefore is not commonly used. Instead, subjective physician assessment of the angle at which diplopia occurs is often substituted. This can result in large inter-trial and inter-operator variances. A reliable test that is easy to perform but correlates more accurately with Goldmann perimetry would be of considerable clinical utility. Methods: Our test requires the patient to sit with their globe at a preset height and distance from a tangent screen that is calibrated in centimeters. The patient is then asked to follow a test object until diplopia ensues. The angle of globe movement at which diplopia begins is then calculated from a simple trigonometric relationship (ArcTan function). Each of our five test subjects underwent three tests: the subjective physician assessment, Goldmann perimetry, and our test utilizing the tangent screen. Results: To examine the degree of association between both the tangent screen test and the subjective physician assessment with the Goldmann perimetry, we performed Pearson correlation analysis as well as intraclass correlation coefficients (ICC). We found that the tangent screen test correlated well with Goldmann perimetry (ICC=0.98, r=0.99, p<.0001) and was both more highly associated with and more in agreement with Goldmann perimetry than was the subjective physician assessment (ICC=0.70, r=0.77, p=0.07). Conclusions: This method of measuring binocular single field of vision utilizing a tangent screen is practical for the assessment of diplopia. It is quicker to perform than Goldmann perimetry, however, approaches its accuracy and reliability. In addition, the test correlates closer with the "gold standard" than does the more commonly used subjective physician assessment. This test can also be used for diplopia secondary to limitation of movement due to other causes. Its applicability involves initial patient assessment and the monitoring of progress before and after specific therapeutic interventions.
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