Prism Adaptation in Decompensated Monofixation Syndrome

Abstract

Introduction:Prism adaptation has been used to predict the angle of surgery to be operated on in patients with partially accommodative esotropia, and esotropia with a distance-near disparity. We describe its use in adult patients with decompensated strabismus, and describe the association of myopia and decompensated strabismus syndrome.Methods:Four consecutive adult myopic patients presented with a history of acute diplopia. Three of the four had a lifelong history of small angle esotropia, but had never had diplopia. Prism adaptation using Fresnel prisms was done. All four patients had MRI scans of the brain. All patients underwent extraocular muscle surgery. Sensory testing was performed at the initial visit, during prism adaptation and at follow up after surgery. Follow up ranged from 1 month to 3 years.Results:Patients were between the ages of 34 and 42 years at onset of symptoms. All were myopic and slightly overcorrected. All four patients had an increase in the angle of esotropia during prism adaptation with an average increase of 15Δ. Three had normal MRI scans; one had a demyelinating lesion of the midbrain. Before prism adaptation patient #1 had 80 seconds of arc, #2 had 400 seconds of arc, patient #3 had no stereopsis and patient #4 had 200 seconds of arc. All patients had surgery for their prism adapted angle. All patients were within 10Δ of orthotropia at last follow-up and were free of diplopia. All of those tested (3/4) had improved stereopsis.Conclusion:Prism adaptation is a useful adjunct in deciding the target angle of surgery in patients with decompensated strabismus. There were two subsets of patients: those with myopia and monofixation syndrome and those with myopia and decompensated strabismus. Both subsets of patients were over-minused, in the peripresbyopic age range and both developed a manifest esotropia. We hypothesize that the need for extra-accommodation for near visual tasks may have induced an accommodative component causing a larger angle esotropia, loss of fusion, and thus diplopia.