Response to “Critique of the study ‘sensory eye dominance following surgically correction for acute acquired concomitant esotropia of adulthood’”

Dear Editor,

We have read the letter from Qian et al. They had several concerns and we will address here.

In the letter, Qian et al. provided an alternative interpretation for our results. They thought that refraction change due to strabismus surgery might lead to adaptation insufficiency which in turn could cause deficits in binocular combination. We think that it is unlikely the case. In the follow-up after the treatment, all patients accepted thorough examination of refractive state and wore prescribed spectacles. We measured the sensory eye dominance at least three months after the surgery. The patients should have sufficiently adapted to the refractive change if any. Moreover, as showed in Figure 5 of our paper, the sensory eye dominance didn’t depend on the interval from the surgery to the measurement, which was consistent with the results on intermittent exotropia that post-operative binocular imbalance was sustained even for more than one years. ¹ Nevertheless, quantifying the sensory eye dominance of patients whose ocular deviation had been corrected through administration of botulinum toxin may help us to further address this issue.

In our study, we evaluated post-operative stereopsis using Titmus, which had been employed in Spierer's study defining the AACE of adulthood as a distinct type. ² The view distance required by our phase combination paradigm is difficult to match the distance available in most traditional clinical methods. Although the patients in our study did not have their stereopsis assessed at other view distance, we are still able to have some clues based on the data from our other research (data not shown). One subgroup of our patients (12/26) had undergone examination of stereopsis at the view distance of 6 metres (OPTEC 3000) about one month after the surgery. 8 of 12 patients had stereoacuity smaller than 100 arc-secs; 11 of 12 patients had stereoacuity smaller than 200 arc-secs. Given that stereopsis would become even better in long-term without reoccurrence, ³ we believe that most of them should have achieved normal stereopsis when they performed our visual task. The balance points of these patients (0.79 ± 0.04, Mean ± SE) were on average lower than that of normal controls (0.95 ± 0.01), which was significant (Mann-Whitney U test, P < 0.01). Moreover, their balance points had no relationship with their stereopsis at distance (R² = 0.346, p = 0.271). Consistently, Wang et al. conducted measurements of stereopsis and balance point at the same view distance using laboratory methods and found these two measures were independent. ⁴ Measuring stereopsis at even greater visual distances or using different methods ⁵ may yield different results. Anyway, all these work can further our understanding of recovery of binocular visual function after the surgery, which motivated us to carry out this study.

We thank Qian et al. for their letter. We believe that the study proposed by them to establish the relationship between sensory eye dominance and recurrence of AACE after botulinum toxin administration is of great value.