Diagnosis-related factors favoring the success of exotropia surgery

Aim of the study
To identify factors favoring the success of surgery for exotropia.

Material and methods
Fifty-nine patients with mostly bilateral exotropia were enrolled, 33 with basic constant exotropia (group 1) and 26 with intermittent exotropia (group 2). Patient age ranged from 10 years to 21 years, the mean corrected visual acuity was 0.8 ±0.3, and the mean refractive error was 0.61 ±2.3 D (range, –5.0 D to 7.0 D). The ocular motor and sensory system was assessed through eye examination and orthoptic methods. Success of surgery was defined as orthotropia of 10 prism diopters (PD) or less. Analysis of variance with the Newman-Keuls multiple comparisons test and the chi-square test were used for group comparisons. A multiple regression analysis was used to determine the relationships between the preoperative characteristics of the ocular motor and sensory systems and the outcome of surgery.

Results
Our comparison of the surgery success group to the surgery failure group for preoperative values of accommodative convergence–accommodation (AC/A) ratio, near point of convergence (NPC) and state of stereopsis showed that near-normal preoperative levels of AC/A ratio (4.0 ±1.65 PD/D) and NPC (8.03 ±3.02 cm), the preoperative presence of distance stereopsis, near stereopsis of 200 seconds of arc, and the absence of medial rectus muscle hypofunction were characteristic for the former group. The multiple regression model developed confirmed that the NPC and the presence of distance stereopsis can be used as predictors of the success of exotropia surgery.   

Conclusions
NPC and the presence of distance stereopsis can be used as predictors of the success of exotropia surgery.