Medical and surgical treatment of primary divergent strabismus

Abstract

PurposeTo evaluate the long-term effectiveness of different therapies applied in the past 30 years, both medical and surgical, and results, with the ultimate aim of determining which are the most appropriate criteria to indicate when and how to perform medical and surgical treatment in these patients. MethodA retrospective randomized study was conducted on 198 patients with primary divergent strabismus first seen in our clinic (IOC) in the last 36 years (1976–2012), with a mean follow-up of 8.38 years. Demographic and clinical characteristics, as well as the various treatments performed, and motor and sensory outcome were collected. They were finally divided into 3 groups of 70, 71 and 56 patients, respectively, according to their first visit, in order to compare the therapies applied. ResultsHalf (50%) of our patients debuted before 2 years of age (P50=24 months), and 26.3% had optimal binocular vision at the beginning of the study. Medical treatment was used as exclusive therapy in 29.3% of cases (occlusion therapy, applying negative lenses, botulinum toxin), and 70.7% required surgery (61.2% by double retro-insertion of lateral rectus, and 38.8% monolateral retro-resection). There was a recurrence in 26.7% of patients, and 40 re-interventions were performed (70% due to recurrence of divergent strabismus, 12.5% due to surgical over-correction, and 17.5% for other reasons). In the end, 61.1% of patients had perfect binocular vision (TNO=60″), and the proportion was higher in patients who showed proper control of their strabismus at the beginning (p=0.003). However, no differences were found in the other variables studied. When the patients were divided into 3 groups (which are demographically comparable), an increased number of patients in Group 3 were found to be treated using negative lenses and botulinum toxin (p<0.001 and p=0.003). This group was found to have had a higher proportion of bilateral surgery (p=0.032), seeking greater immediate postoperative over-correction, thus reducing the number of re-interventions from 40.5 to 19%, although it did not reach statistical significance (p=0.093). It was also found that there was a significantly increased number of injections of botulinum toxin in the middle rectum for treatment of excessive postoperative overcorrection (p=0.028). No other differences in final binocular vision were found between the 3 groups (p=0.703). ConclusionsIn cases of clear ocular dominance, occlusion therapy must be applied twice daily on the dominating eye, in order to encourage divergent strabismus control and improve sensoriality. An attempt should be made to wait until patients reach four years of age before indicating surgical treatment, except in cases of a significant worsening of motor or sensory component. Bilateral surgery on both lateral rectus should be attempted, provided that patient characteristics allow this. A slight post-surgical overcorrection should be looked for in the immediate postoperative period, as this, in our experience, reduces the total amount of re-operations. When working on the middle rectus, remember that the elasticity of this muscle is the key factor for obtaining a proper post-surgical outcome, but a reliable measurement of this still cannot be made. In cases of excessive post-surgical over-correction, an injection of botulinum toxin should be applied to these poor elasticity muscles, in order to reduce the number of re-operations.