Binocular Vision &

Eye Muscle Surgery Qtriy°

XT between the ages of 2 and 4 years, developed a consecutive esotropia requiring surgery. Twenty-nine percent of them had a reduction of stereoacuity. Nine percent of those who had XT surgery between 4-6 years of age developed amblyopia and 20% of these had a reduction in stereoacuity. However, after age 6 years no child developed amblyopia or lost stereoacuity.

Richards & Parks (191) noted in 1983 that 12% of patients under 3 years of age were (finally) overcorrected while only 3% over 3 years were (finally) overcorrected.

Care must be exercised in balancing the desire for a “real cure” apparently more readily achieved with early surgery versus the potential complications of microtropia, amblyopia and loss of stereopsis in the young, visually developing child.

Von Noorden (16) recommends that surgery be delayed until at least 4 years of age. Prior to age 4, binocular vision can be reinforced with minus lenses, patching, base in prisms and TV trainers. He has noted that surgical correction for deviations greater than 20 pd rarely results in a consecutive esotropia.

4. Management of consecutive esotropia:

At some point in time, the aforementioned desireable intended purposeful immediate and early postoperative esodeviating overcorrection becomes no longer acceptable. This is usually around three to four weeks postop. This esodeviation then becomes (or is redefined to be) a consecutive esotropia.

Consecutive esotropia which occurs in 6-20% of surgically treated X(T)s (192-

194) may be initially handled by either judicious observation or the application of base out prisms. If the esodeviation does not change after a few additional weeks, some groups advocate limited alternate patching.

The amount of prism should be the least amount which eliminates the deviation in all gazes at both distance and near. Thin plastic press-on Fresnel prisms are advantageous when large amounts of prism are used and/or when frequent changes are made. However, they have more chromatic aberration and thus reduce vision more than “ground-in” full thickness glass prisms.

Anticholinesterase miotics and/or bifocals may also be useful here.

The goal is to stimulate slow vergence, to reduce the apparent deviation, by slowly reducing the miotics, bifocals, or prism (2 to 5 pd at a time). Orthoptics designed to improve divergence may be helpful in

Major Review: Intermittent Exosropia; Basic and Divergence Excess Type

stimulating fusional divergence and slow vergence. The elimination of prism with orthoptic therapy is a slow process and requires good patient, parent, physician rapport.

If no change occurs within approximately 6 months, an (additional) surgical procedure may be indicated. This is usually bilateral medial rectus muscle recession or a recession-resection on one eye depending on the clinical findings. According to Moore et al (65), 61% who developed a consecutive esotropia required such additional ET surgery (or by calculation, approximately 5-10% of all patients undergoing XT surgery).

5. Bilateral lateral rectus recession versus recession-resections for the initial XT surgery:

Burian (195) (1958) stated that different surgical procedures should be performed on true DEXT and simulated DEXT /basic XT For true DEXT, he advocated recession of the lateral recti, while for simulated DEXT and basic XT he advocated monocular recession of the lateral rectus and resection of the medial rectus

Summer of 1993

Volume 8 (No.3): 185-216

in the non-dominant eye (“recess-resect”).

Burian believed that a bilateral lateral rectus recession resulted in a greater reduction in the distance exodeviation than the near, while recess-resect procedures were more apt to result in an equal correction at distance and near.

Von Noorden (39)(1969), evaluated Burian’s hypothesis. He compared results in two surgical groups: one in which both simulated and true DEXT received bilateral lateral rectus recessions; while the second group of simulated and true DEXT was subdivided for surgery according to Burian. In this group 70% were simulated DEXT and were surgically treated by Burian’s criteria with “recess- resect”, while the other 30% were diagnosed as true DEXT and had bilateral lateral rectus recessions.

Table II below is a summary of von Noorden’s data. The data indicate that the surgical success rate improves when true DEXTs have bilateral rectus recessions and simulated DEX(T)s have unilateral recess-resect, confirming Burian’s hypothesis.

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