Binocular Vision &

Eye Muscle Surgery Qtrly

their own surgical guidelines or the surgical formula advocated by Parks (35).

Wide variation in surgical techniques of suture placement, surgical approaches and amounts of surgery performed may play a role in the wide variation of surgical success rates.

If the patient does not have a basic XT or a true DE type Xl’, but has another type of exodeviation such as convergence insufficiency or simulated DEXT, according to Kushner (41) (1988), von Noorden (178) (1976) and Hermann (179) (1981), alternative surgical procedures should be used.

If an A- or V-pattern exists, offsetting the horizontal recti superiorly or inferiorly will often decrease these patterns. The occurrence of vertical deviations is not uncommon as White et al (180) (1939) reported; 59.9% of his 1,955 patients had a vertical imbalance along with their divergence anomaly.

Lateral incomitance occurs in approximately 22% of X(T) patients according to Moore (65). But generally, altering the surgical approach to correct this incomitance has not been found to be necessary. Repka & Arnoldi (63) have suggested that prism measurement artifacts can be responsible for the apparent lateral incomitance. Thus true lateral incomitance is probably uncommon.

Let us now deal with the third question; what is a surgical success? Surgeons include a variety of postoperative results as “successful”, e.g., a small angle El’ or Xl’ of 10 pd or less; a Monofixation Syndrome; or total elimination of the strabismus. A “cure”, as defined by Pratt-Johnson in his recent 1992 publication (181), should meet the following criteria:

• No manifest tropia in any position of gaze or at any distance.

• No winking or closing of one eye in sunshine or bright lights.

• Stereoacuity of at least 60 sec of arc on the Titmus Test at 16 inches.

• Normal convergent and divergent fusional amplitudes with diplopia when these are exceeded.

Near point of convergence under 10 centimeters.

Central fusion with non-suppression of central controls which subtend a visual angle less than 50 on slides in a haploscopic device such as a the Troposcope or Synoptophore.

2. Intended immediate overcorrection:

Most strabismus surgeons today strive for an initial (in the first days to weeks) postoperative overcorrection to stabilize

Major Review: Intermittent Exotropia;

Basic and Divergence Excess Type

the long term results, as proposed by Cooper in 1966 (182) (“purposeful overcorrection”). Raab & Parks (183) (1969) and Jampolsky (184) (1986) have suggested that this overcorrection should be 11-20& Scott et al (185) (1978) recommended that the amount of overcorrection should be 4-14A. In 1927, Dunnington (11) had suggested 15 “prism degrees”.

Some surgeons feel that using postoperative adjustable suture techniques may create more accurate surgical results with better long term stability:

Regarding intended overcorrection and postoperative adju.stable sutures, McNeer (186) (1987) evaluated X(T) surgical results (all had bilateral lateral rectus muscle recessions) in three groups: 1) 25 non-adjustable suture patients; 2) 17 adjustable suture patients having an initial postsurgical adju.stment to 5-11k eso; and 3) 16 adjustable suture patients having an initial postsurgical adjustment to 12-20k eso.

The 25 non-adjustable group 1 patients had average preoperative near deviation of 25 pd, an immediate postoperative deviation of 0.2 pd XT which increased to 4 pd XT after two years; 12 of the 25 had a recurrent Xl’. Patients in group 2 (18% had to be adjusted to place the patient in the proper range) had a near postoperative deviation of 7 pd eso which changed to 2 pd eso within 2 years. The patients in group 3 (60% needed postoperative suture adjustments to achieve this degree of overcorrection) had an initial mean postoperative deviation of 18A esodeviation which decreased to a mild eso within 2 years. Five of the sixteen in group 3 had a large esotropia, and one had a recurrent secondary XT.

Limited immediate postoperative diplopia has been thought to be therapeutic in eliminating suppression and stimulating fusional vergence to allow for long term stability. Weston et al (187) (1991) and McNeer’s studies (186) suggest that the best immediate postsurgical position should be 5-6 pd eso.

Historically, according to Dunlap & Gaffney (188) (1963), the surgeon was unable to predictively and constantly create a specific amount of postsurgical overcorrection. Cooper (182) (1966), attempted to produce a deliberate overcorrection. He was only able to achieve this goal in 37% of the cases he operated on. I-Ie divided his presurgical patients into two groups. In the first group he attempted to create exact surgical alignment, while in the second group he tried to create a

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deliberate overcorrection. His post operative findings showed that there was no statistical difference between the groups. Von Noorden, in the most recent edition of his textbook (16), stated that the purposeful production of a small over- correction only occurs by chance. However, if an overcorrection between 10-15 pd is achieved, one should expect an

80% chance of acceptable long term binocular motor alignment. The recent efforts of McNeer, Weston et al suggest that this is possible.

These findings suggest that factors other than simple motor alignment play a role in the ultimate success.

3. Early versus late surgery:

The question of early surgery vs late surgery was addressed by Pratt- Johnson et al in 1977 (189). They separated their surgical patients into two groups. One group was under the age of four years (39 patients, average age 2.5 yrs) and the other consisted of patients older than four years (61 patients, average age 5.5 yrs.). Four patients were older than 7.

Results (their criteria for cure was that the deviation had to be less than 1O pd one year after surgery): in the under four age group 61% were cured, while only 28% achieved a cure in the over four age group. The overall cure rate was 41% with 81% being cosmetically corrected. Their study did not support the use of early postop overcorrection to effect a cure.

Amblyopia occurred in 4 patients who developed a consecutive esotropia in the under age four group.

[It is difficult to determine the results of any therapy in the young and non-communicative. Measurements and testing are often variable with unstable results. Young patients may not be able to respond to various sensory/motor tests. Thus, the determination of a cure in the young and non-communicative, with any form of treatment, suffers from measurement error.

Some postsurgical X(T) patients have improved fusional control with a diminution of the deviation. Although not ideal, it is an improvement with which prismatic therapy, or minus leases, may allow the deviation to stabilize for a long period of time. Further surgery, if necessary, may always be performed.]

Prolonged overcorrection in the very young has the possibility of dire binocular consequence, i.e., amblyopia and/or loss of stereopsis (see Pratt-Johnson (189) above). Edelman et al (190) reported in 1988 that 5 of 24 children (21%) operated upon for

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