Sir,

Patients with symptomatic unilateral right inferior oblique overaction/superior oblique underaction may describe diplopia that is initially confined to levo-elevation or levo-depression, and eventually can progress into primary position. The goal of surgery is to achieve as large a field of diplopia-free vision as is functionally possible without the need to assume a compensatory head position. Ideally, this surgical outcome should not then recede with time.

One of the interesting observations noted in the subgroup of patients with preoperative moderate/marked inferior oblique overaction and binocular single vision, was the observed trend in postoperative inferior oblique muscle overaction in the inferior oblique recession and inferior oblique myectomy groups between 2 months and 12 months postoperatively.1 There was a greater likelihood of a recurrence of some inferior oblique muscle overaction in patients who underwent an inferior oblique muscle recession. Should this trend continue, then this could lead to not only a clinical but a functionally different long-term outcome between these two procedures in this subgroup of patients with overacting inferior obliques. The anatomical differences between the described myectomy and recession procedures may well be one explanation for this observational difference.

We fully agree with Shankar and Thompson that a difference of 1.25 prism dioptres, while statistically significant, is not likely to be clinically significant in this group of patients who are expected to have normal/supranormal vertical fusion ranges.

The statistically significant differences between the two groups, as a whole, is very much more likely to be genuine rather than attributable to small changes in head positioning as all the measurements in the three gaze positions for the recession and myectomy patients were carried out under the same clinical conditions by the same experienced orthoptist. None of the patients in either group were unhappy postoperatively.

While Table 2 indicated that a single case had a measurable but functionally asymptomatic contralateral inferior oblique muscle underaction, Table 3 reflected the changes that occurred in the hyperdeviation after the immediate postoperative period, namely from 2 weeks to 12 months postoperatively. This table demonstrated the variability in the range of primary position and contralateral gaze measurements in the myectomy and recession groups. These data do not support the view that recessions are more predictable. Accordingly, we disagree with Shanker and Thompson: our conclusions have not been overstated.