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Comparitive study between a modified fixation disparity curve procedure and standard protocol

1 May 2005


PROCEDURE AND STANDARD PROTOCOL In this study a comparison was made between the efficacies of a standard fixation disparity curve and a fixation disparity curve created with protocol modified for speed of administration in a traditional clinical setting. The modified curve consists of five points; associated phoria (with 0 prism), three prism diopters each of base in and out, and one additional base in and base out point based on the each subject's vergence ranges. A modified curve and a standard curve were obtained from 40 subjects. Three objective, blind evaluators made assessments of the curves to allow comparisons between the associated phorias, the least amount of prism to the flat zone, prism value to the center of symmetry, curve type, and slope of these two curves. Also assessed was the comfort level of each examiner in using the data from the modified curves and standard curves in making patient care decisions. The analysis of the relationship between the associated phoria values from each curve (modified vs. standard) showed the difference between them to be 2 prism diopters (p = 0.012) indicating a significant change in the data sets. When a comparison was made between the 'least amount of prism to flat zone' with each of these methods, the insignificant average difference was -0.122 prism diopters (p = 0.792). With respect to the slopes, the relationship between the modified and standard curves showed an insignificant average difference of -0.14 (p = 0.295). The "blind" evaluators felt confident making patient care decisions with the standard curve 83% of the time versus only 25% of the time using the modified curve. The analysis of the data collected shows not only that the modified protocol failed to provide reliable data for essential elements of a fixation disparity curve such as associated phoria, least amount of prism to flat zone and curve type, but also raised questions about repeatability of the standard method of fixation disparity testing.


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