Our study found that unilateral lateral rectus recession is effective in treating moderate-angle intermittent exotropia in young children. A high success rate of 86.2% was achieved with a mean postoperative angle of deviation of 3.5 PD for distance and 1.6 PD for near.
The success rate of unilateral rectus recession for intermittent exotropia differs among studies. Suh et al.10 compared the surgical outcomes of patients who underwent unilateral lateral rectus recession and patients who underwent lateral rectus recession and medial rectus resection for exotropia of 20-25 PD. The surgical success rate did not differ significantly between groups at last follow-up, with 45.9% in the lateral rectus group and 39.4% in the recession-resection group. Another report found a surgical success rate of 60.9% at an angle of 25 PD.14 We have previously reported a success rate of 69% in unilateral lateral rectus recession in moderate-angle exotropia.9 That study, as most studies in this era, included patients with diversity of ages: children, teenagers, and adults. In the present study, we included only young children (whom their surgical outcomes were not reported in the past) to investigate whether the success rate would be similar. We found a high success rate of 86.2% in the population of young children, higher than most papers published. It is unclear whether young children respond better to unilateral rectus recession than older children and adults. Differences in success rates among studies might be due to different follow-up periods, demographic variances, like age and surgeon experience.
Among the advantages of operating on 1 muscle instead of 2 muscles are shortening the general anesthesia time and diminishing the ocular risks associated with surgery on 2 muscles. Bearing in mind that the rate of residual and recurrent exotropia after the first surgery is not low, sparing of other horizontal muscle for future surgery is another positive thing to consider. Nevertheless, unilateral lateral rectus recession major advantage is the low rate of overcorrection. When overcorrection after surgery for intermittent exotropia occurs, it may result in a constant esotropia with debilitating diplopia and loss of stereopsis, necessitating another surgery of lateral rectus advancement or medial rectus recession. Suh and colleagues10 reported that postoperative overcorrection is less common in unilateral lateral rectus surgery. While in the recession-resection group, 9% of the patients showed overcorrection at final visit, no patient showed an overcorrection after surgery in the unilateral lateral rectus group.10 In the present study there were 2 cases (3.4%) of consecutive esotropia.
Our surgical approach was the same for a true divergence excess as well as for simulated divergence excess exotropia. In both cases, we performed lateral rectus recession, in an amount based on the distance angle of deviation. For this reason, we do not routinely perform a patch test in cases where the angle of deviation for distance is greater than that for near.
Performing a unilateral surgery for exodeviation of 25 PD would necessitates a large recession of the lateral rectus muscle – between 8 and 9 mm. The common recommendation in previous published studies was to perform unilateral lateral rectus surgery only in smaller angles of strabismus. Some stated that if a recession of more than 7 mm is needed, then a bilateral surgery should be done.2 However, others performed unilateral surgery with as large recession of the muscle as 11.5-12 mm.4 Lateral incomitance is a possible complication of large recession done unilaterally. This complication was found to be transient and uncommon.4-5 It is possible that lateral incomitance is more prevalent when the recession of the lateral rectus muscle is more than 8 mm.8 In our study, no lateral incomitance was observed in any of the patients, even in those in which the muscle was recessed by 9 mm. We believe that the risk for lateral incomitance should not prevent surgeons from performing lateral rectus recession of up to 9 mm, as this complication is probably rare. It is possible that lateral incomitance occurs if there is a muscle slippage after surgery, especially if in addition there is underaction of the lateral rectus.
The retrospective nature of our study is its main limitation. As in some patients follow up was only 6 months, longer follow-up may reveal lower success rate. This limitation is common to all studies in this era. The main strengths of the study are the homogeneity of patients and the relatively long mean follow-up period.