Convergence excess esotropia: a proposed new classification and the effect of monocular occlusion on the Ac/A ratio.

BACKGROUND

Convergence excess esotropia defines an esotropia on accommodation at near fixation with binocular single vision and motor fusion at distance fixation associated with a high accommodative convergence: accommodation (Ac/A) ratio. The effect of occlusion on exotropia has been well described and is known to alter the Ac/A ratio. This study examines the effect of monocular occlusion on convergence excess esotropia.

METHODS

The Ac/A ratio was measured using the gradient method at 1/3 and 6 m in 10 patients with convergence excess esotropia immediately prior to and following a 30-minute period of monocular occlusion.

RESULTS

Clinically and statistically significant differences to the angle of deviation and the Ac/A ratio were found in some patients following occlusion.

CONCLUSION

Ac/A ratio measurement in convergence excess esotropia is influenced by fusional tenacity. Disrupting this fusion with a period of monocular occlusion results in changes to the angle of deviation in some patients, suggesting subcategorization of this condition into true and simulated convergence excess esotropia. Measurements of the Ac/A ratio are influenced by fixation distance.