High AC/A accommodative esotropia strabismus treated with contact lenses: a single case design (N=1) study.

Background and purpose: The purpose was to determine the efficacy of two types of contact lenses (spherical disposable and aplanatic) as treatment in a patient with esotropia with a high Accommodative Convergence/Accommodation Ratio (AC/A). Due to the possibility of the appearance of accommodative insufficiency in this kind of patient, (i.e., following many years of bifocal glasses use), the elimination of the plus addition lens is advisable. Nevertheless, in some patients, this change leads to the appearance of a residual angle of esodeviation in near vision. It was expected that monofocal aplanatic contact lenses could achieve, due to their optical characteristics, an accurate and orthotropic binocular alignment, without aggravating an undesirable manifestation of the accommodative insufficiency.

Methods: An experimental design of a single case (N=1) was used in which the subject acted as his own control. With bifocal glasses the subject displayed stability in his binocular and accommodative system at every distance of vision for the past three years. We compared the efficacy of two different types of hydrophilic contact lenses to control the angle of deviation, both at distance and at near vision.

Results: Neither of the two contact lenses produced the results of stability and the correct binocular alignment that had been achieved with bifocal glasses. This subject experienced a worse manifest esodeviation in distance vision with aplanatic lenses than with the disposable ones.

Conclusions: These monofocal contact lenses did not create acceptable binocular alignment and stability in a subject with a high AC/A accommodative esotropia.