Success of Prisms in the Management of Diplopia Due to Fourth Nerve Palsy

To analyze the success of prism use in alleviating diplopia in patients with fourth nerve palsy and to provide recommendations for prism prescription.In this retrospective cohort study, the medical records of 83 patients who were prescribed prisms for symptomatic diplopia due to fourth nerve palsy were analyzed. Data on the nature and duration of diplopia, motility and alignment findings, and amount and type of prism prescribed were recorded. The success of prescribed prismatic correction was assessed by the patient's self-reporting of satisfaction with prism use and follow-up records. The main outcome measure was the satisfaction rate associated with the use of prisms (satisfaction score 1 or 2) in patients with fourth nerve palsy.There were 69 patients with congenital fourth nerve palsy and 14 patients with acquired fourth nerve palsy who received prisms. The mean primary position (SD) deviation in this group was 7.8 (4.6) prism diopters (PD). The mean prism prescription was 6 (2.9) PD. Overall, 92% of patients were satisfied with the use of prisms. During the length of follow-up, which ranged from 2 months to more than 6 years (median: 18 months), 86% of the cohort continued using prisms while 14% of patients underwent strabismus surgery. Among 15 patients who had primary position deviation greater than 15 PD, 80% of the patients reported satisfaction with prisms, and in the 11 patients who received 10 PD or more of prismatic correction, 82% were satisfied.Prisms are an effective modality for the management of patients with symptomatic diplopia due to fourth nerve palsy. Even in patients with larger deviations including those who were prescribed greater than 10 PD of correction, the success rate of prisms in alleviating diplopia was high. Prisms should be considered as initial therapy in symptomatic patients with fourth nerve palsy