[The value of the prism adaptation test in determining the degree of squint surgery]

The angle of squint deviation was measured preoperatively before and after a prism adaptation of 1 day's duration in 50 esotropic and 45 exotropic patients. All had a deviation of 17 degrees or more under prismatic correction and were operated on by a recess-resect procedure of 10 mm on one eye. Postoperative measurements were done about 4 days and 6 weeks after surgery. In 58% of the esotropic and 37% of the exotropic patients, the initial deviation increased under prisms. This was found most often when normal retinal correspondence was present. There was a correlation between the effect of surgery with the change of deviation under prisms, particularly in normosensory esotropia and intermittent exotropia. Accordingly, the standard deviation of the surgical effect was smaller in this group, when it was calculated from the deviation under prisms in comparison to a calculation from the primarily measured angle. The influence of the preoperative deviation on the effect of a 10-mm recess-resect procedure was also found for the deviation under prisms and must therefore additionally be mentioned in the dosage of surgery. This retrospective study shows that preoperative prism adaptation improves predictability of the effect in squint surgery, at least in normosensory esotropia and intermittent exotropia. In patients with early-onset strabismus prism adaptation does not improve predictability, but higher dosage seems to be useful in cases with increased deviation under prisms and did not lead to over corrections. In this group the test represents an additional method for evaluation of the binocular sensory status.