[Normal accommodative convergence excess--long-term follow-up of conservative therapy with bifocal eyeglasses]

In patients with normaccommodative convergence excess it is possible to reduce or eliminate the excess of accommodative convergence by adding plus lenses. The resulting reduction of near deviation can lead to an improvement in the quality of binocular vision at near, and also to a better compensation of an esophoria at near. The aim of the paper was to study long term results in patients with small angle esotropia and esophoria and accommodative convergence excess treated by bifocals.

Clinical data of 91 patients were analysed retrospectively. Among them were 13 patients with esophoria, 32 patients with microesotropia and 46 with microesotropia and a phoric component. An orthoptic status was performed every three months and at every examination it was tried to reduce the added plus lenses. The mean follow up was 5.6 +/- 2.4 years (range: 1.1-13.2).

The mean onset of strabismus was similar in all groups: i.e. 2.5 (+/- 1.7) years. The patients received their first bifocals on average 3.4 (+/- 1.9) years later. In 40 of the 91 patients the near addition could be stopped because of sufficient decrease of accommodative convergence excess during the follow-up period. The convergence excess decreased continuously in all patients with esophoria and microesotropia and the additional plus lenses could be stopped on average after 6.4 (3.5-8.4) years (esophoria) and 5.0 (2.6-8.1) years (microesotropia) respectively. In patients with microesotropia and an additional phoric deviation bifocals were only partly successful to reduce the convergence excess. The basic angle decompensated in more than half of the patients (27 out of 46) and was operated in 14 cases by unilateral resection/recession procedure. After the operation the convergence excess decreased rapidly and the bifocals could be stopped after 4.4 (3.4-7.4) years. In the remaining 19 cases it was possible to reduced the convergence excess with bifocals in 8 patients after about 8.1 (4.1-9.3) years and in some of the remaining 11 cases a Fadenoperation has been suggested.

While wearing bifocals the accommodative convergence excess decreased completely in patients with esophoria and microesotropia. In the condition with markedly reduced binocular vision and a large phoric component at far and near, the convergence excess decreased only in some of the patients while wearing bifocals. Conventional strabismus surgery to reduce the basic angle has a positive influence. A Fadenoperation is only necessary in a few cases.