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Does operating on the flat portion of the forced fixation disparity curve eliminate near asthenopia?

16 February 1982


Sheedy and Saladin have stated that near point asthenopia may be relieved by prescribing prism to allow the patient to operate on the flat portion of the forced fixation disparity curve. This study determined the level of success attainable using this criterion by prescribing two sets of lenses for comparison purposes. One set of lenses contained · the subjective to best visual acuity (SBVA) findings and the other set of lenses contained prism to put the subject on the flat portion of the forced fixation disparity curve (SBVA and prism). Individual comparisons between each set of lenses were conducted - ~~ on eight subjects (five male and three female) between the ages of twenty and thirty. A relative decrease in the asthenopia index scores occurred in six of the eight cases when SBVA and prism lenses were compared to the SBVA lenses. In the remaining two cases the asthenopia index scores increased in one subject and were of a variable nature in the other. Sheedy and Saladin's criterion has limitations in its usage which are dependent on whether a forced fixation disparity curve can be attained and, onc e attained~ that a flat portion of the curve is present. However , it did detect oculomot or imbalances missed by Sheard and Percival's criteria. Additionally , it allowed for the prescribing of more practical prism adds as compared to Sheard and Percival's .


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