Efficacy of conservative treatment of children with exotropia depending of the baseline status of visual and binocular functions

Abstract

Background: Exotropia is an eye misalignment in which one or both of the eyes turn outward due to congenital or acquired abnormalities of orbital structure, globe structure, extraocular muscle attachment and/or extraocular muscle location. Different treatment modalities are used in the treatment for exotropia: overminus lens therapy, prism therapy, occlusion therapy, extraocular muscle surgery, and orthoptic vision therapy.
Purpose: To assess the efficacy of conservative treatment for exotropia depending on the baseline status of visual and binocular functions.
Material and Methods: The study sample consisted of 51 patients with exotropia with their age ranging from 10 to 21 years. Of these, 24 (47.05%) had constant exotropia and 27 (52.95%) had intermittent exotropia (IXT). Of the 51 patients, 33 had a hyperopic refractive error of 0.5 to 6.5 diopters (D), and 18, a myopic refractive error of greater than −0.50 D to less than −5.5 D. Of the 51 patients, 27 had mild amblyopia, 22, moderate amblyopia, and 2, no amblyopia. The mean exotropia was 11.8 ± 3.12º by Hirschberg. Patients underwent a routine ophthalmological evaluation. In addition, the near point of convergence (NPC) was determined by the proximeter; the accommodative convergence–accommodation (AC/A) ratio was calculated by the heterophoria method (AC/A = ipd + (phoria at distance – phoria at near)/3, where ipd is the interpupillary distance in centimeters) and expressed in PD/D; fusional reserves were measured using the synoptophore; and binocular vision at distance and near, using the color test. Stereoacuity thresholds were assessed with the Lang-Stereotest II and Titmus Stereo Fly (circles and animals) tests at daylight at a viewing distance of 30 cm, and a Huvitz CCP3100 Chart Projector was used to assess whether stereopsis was present at a 5-m distance. Treatment procedures included optical correction, pleoptics, and direct occlusion in the presence of amblyopia, and orthoptic and diploptic treatment aimed at an improvement and strengthening of binocular functions (synoptophore, binocular vision training, Fialka apparatus, electric stimulation of the medial recti using Amplipuls apparatus, image fusion training using Mirage apparatus, electric stimulation of the medial recti, and computer-aided stereopsis training).
Results: The angle of deviation at near and at distance decreased significantly in the constant exotropia group (р = 0.0001 and р = 0.0065, respectively). In the IXT group, the angle of deviation at distance decreased significantly (р = 0.0001), and the angle of deviation at near, not significantly. Binocular vision restored in 38% and 70% of patients in the constant exotropia group and the IXT group, respectively. Convergence and AC/A ratio values improved, but not statistically significantly (p > 0.05). Fusional reserves improved significantly, stereo vision restored, and stereopsis at near (stereoacuity threshold as assessed by the Lang II Stereotest) improved in both groups, whereas stereopsis at distance improved only in the IXT group, and was present in 65.6% of patients in this group (р = 0.01). In the group with orthotropia after conservative treatment, there were 32/51 children (62.7%) with a deviation less than 6º (12.0 PD). The group with post-treatment exotropia included 19/51 children (37.3%) with post-treatment deviation exceeding 6º (12.0 PD); these children underwent subsequent surgery. The model of conservative treatment success was found to (1) include four variables (the NPC, fusion on the synoptophore, AC/A ratio, and stereoacuity threshold as assessed by the Lang II Stereotest) and (2) to predict the outcome of conservative treatment in 80.9% of cases (R= 0.80902535).