• Determination of angle instability [ Time Frame: 18 weeks ] [ Designated as safety issue: No ]
  
• Estimation of misalignment [ Time Frame: 10 months ] [ Designated as safety issue: No ]
  

Approximately one third of infants with infantile esotropia (infantile ET) and a similar proportion of children with acquired non-accommodative esotropia (ANAET) will have an increasing angle within the first few months of their initial examination. In approximately two thirds of patients, the angle of misalignment remains stable and in a small proportion, the angle of esotropia decreases. The changing angle of misalignment in a significant proportion of children with esotropia raises an important question regarding the timing of surgical management of these children: should surgery be undertaken immediately or delayed until the alignment stabilizes? Early surgery may improve sensory outcomes; delayed surgery may improve surgical dosing accuracy and motor outcomes.

Children with acquired partially accommodative esotropia (APAET) may differ from those with infantile ET and ANAET in that they tend to present at an older age, are more likely to preserve high-grade stereopsis with appropriate treatment, require surgical intervention less frequently, and have more substantial hyperopic refractive errors. Little is known regarding early angle stability in this group of patients following correction of their refractive errors.

Although there is a need for a randomized trial to address the issue of timing of surgery in infantile ET, APAET, and ANAET, prior to designing such a trial, high-quality preliminary data are needed. We propose a multi-center observational study to 1) determine the duration of misalignment in infantile ET, ANAET, and APAET at study enrollment, 2) to prospectively establish the proportion of patients with angle instability in infantile ET, ANAET, and APAET, and 3) to determine recruitment potential for a randomized trial. These data will be crucial for sample size calculations for the eventual randomized trial, and will help further define the clinical characteristics of these conditions.

A concurrent and nested ancillary study will be conducted at selected centers to collect test-retest data on alignment measurements for estimating the amount of measurement variability. These test-retest data will be used to define a change in angle alignment that exceeds an amount which could reasonably be due to measurement error, which will be used in evaluating the proportion of patients with angle instability in the current study.

Eligible patients with infantile ET will be consented and enrolled at their initial visit. Infantile ET patients who need spectacles will be prescribed spectacles and will return for an Infantile ET Spectacle Baseline Visit 2 weeks later.

ANAET and APAET patients who present wearing spectacles with appropriate correction for at least 2 weeks will be consented and enrolled into the study at that initial visit.

For ANAET and APAET patients who present not wearing spectacles:

• Patients who do not need spectacles will be consented and enrolled into the study at that initial visit.
• Patients who need spectacles are prescribed appropriate correction if the investigator intends to offer the patient enrollment at a later date.

Patients are asked to return after wearing the new spectacles 2-6 weeks, at which time they may be consented and enrolled into the study.

Sample Size: The study will enroll 100 patients for each of the three esotropia types of infantile ET, ANAET, and APAET, for a total of 300 patients.