Chapter 75 The accommodative esotropias
Accommodative esotropia describes an esotropia caused in whole, or in part, by the use of accommodation to clear vision in the presence of uncorrected hypermetropia. This association is widely attributed to Donders.1 Accommodative esotropia is one of the most common forms of childhood strabismus accounting for about a third of all strabismus patients in most studies in Europe and North America.2
The typical age of onset ranges from 2 to 5 years old, but may present earlier (“infantile accommodative esotropia”) or, less commonly, at a later age. Caregivers typically report crossing that is intermittent initially and most apparent when the child is fixing on a near object or when fatigued. With time, the crossing occurs more frequently and, without treatment, often becomes constant. Accommodative esotropia may manifest suddenly following a minor illness, trauma, or without any obvious precipitating event.
1. Fully accommodative esotropia (refractive esotropia): those patients in whom the distance and near deviation are equal and the esotropia is caused entirely by uncorrected hypermetropic refractive error. In one study, these patients had a mean age of onset of years and a mean refractive error of +4.75 D.3 They have a normal accommodative convergence to accommodation (AC/A) ratio and respond to correction of the full cycloplegic refractive error (Figs 75.1 & 75.2).
2. High AC/A ratio accommodative esotropia: those patients who have a significant near–distance disparity in the magnitude of the esotropia, with the deviation being at least 10 prism diopters (PD) more at near than at distance. They have a younger age at presentation (mean 2.7 years old),4 and a lower degree of hypermetropia, than patients with typical fully accommodative or refractive esotropia. They have a normal hyperopic refractive error for age and little or no esotropia in the distance
3. Arguably, the most common form has elements of both of the preceding types. These patients have a significant hypermetropic refractive error and some level of high AC/A ratio that leads to a deviation that is greater at near than distance by at least 10 PD.
4. “Early onset esotropia” or “infantile accommodative esotropia” refers to patients with fully accommodative esotropia presenting at a very early age. They may present with esotropia as early as 6 months of age and typically have very high hypermetropia and are more likely to have inferior oblique ove.raction.
Fig. 75.1 A 3-year-old girl presents with a new onset of left esotropia (with strong fixation preference for the right eye). The deviation is 35 PD at near and distance fixation. The cycloplegic refraction is +4.25 OD and +4.50 OS.
The accommodative convergence/accommodation ratio (AC/A) plays an important role in the development, treatment, and prognosis in accommodative esotropia. Patients with a high AC/A ratio present earlier, are more likely to require surgery, and to have a poorer prognosis for long-term binocular vision.5 There are different ways to calculate the AC/A ratio although in clinical practice this is not necessary. A clinical comparison of distance to near deviation is most commonly used to determine whether or not the AC/A ratio is high. Patients can be further classified based on the degree of near–distance disparity:
To calculate the AC/A ratio, either the gradient or heterophoric method can be used. For the gradient method, measure the deviation at a fixed distance while relaxing accommodation by introducing plus lenses as follows: