Binocular Vision &

Eye Muscle Surgery Qtrs~y©

Major Review: Intermittent Exotropia;

Basic and Divergence Excess Type

Summer of 1993 Volume 8 (No.3): 185-216

both surgery and orthoptics vary tremendously from author to author.

Criteria for success in treatment are not unifornt One author considers a “cure” to be any residual strabismus less than 15 pd, while another considers a “cure” to be a 100% elimination of the deviation, with elimination of suppression, and normalization of fusional ranges and stereoacuity.

With the above in mind we will attempt to review current treatment strategies.

Traditional orthoptic therapy has been based on the concept that DEX(T) is a result of inadequate motor fusion. Historically, treatment has been directed towards improving deficient convergence amplitude ranges.

In 1914, Reber (126), one of the first to report orthoptic results, stated that 75% of his patients with DEX(T) were cured with such exercises. Bulson (127) in 1926 stressed the use of orthoptics with prolonged conscientious increasing effort. Duane (2) in 1897 had stated that surgery should be avoided until all other methods have failed.

Dunnington (11) in 1927 denied any

benefit from orthoptics but Berins, Hardy

& Stark (128) reported in 1929, 19 cases

of DEX(T) treated orthoptically; 16 were

cured or significantly improved, and only

3 showed no change.

The bulk of early therapy utilized the synoptophore and flat fusion targets to build fusional disparity vergences. Within a short period of time most DEX(1) patients showed enormous fusional convergence ranges.

Unfortunately, this ability does not always result in a permanent change in the exodeviation. Often, there is a short term reduction in the frequency or in the angle of exodeviation probably due to vergence aftereffects.

Moreover, many surgeons, fearing over- corrections, when determining the amount of surgery to perform in this condition, want to eliminate the effect of vergence exercise aftereffects, and advise the cessation of such convergence therapy for 6 weeks prior and/or patching before measuring the total deviation for surgery. One study, however, by Shippman & Veronneau-Troutman (129) demonstrated that preoperative convergence therapy had no effect on surgical outcome.

It is not surprising that convergence training by itself has a minimal effect on the deviation. As originally noted by Sugar in 1947 (9) DEX(T) cases have normal convergence fusion amplitudes. Therefore, the deviation is probably not due to a failure of fusional convergence. In hindsight, therefore, one would expect improvement of fusional convergence amplitudes to have only a minimum effect.

In the 1950s, diplopia awareness was added to convergence training to make the patient aware of the deviation (130). (Pathological) diplopia was taught by placing a red lens over the non-deviating eye while the patient viewed a “muscle light” in a darkened room. The light was first presented at near and eventually moved to distance, which resulted in the stimulus subtending a smaller angle and the retinal image of the light moving closer to the fovea. The subject was required to maintain diplopia while the room illumination was slowly increased. Then the red filter was replaced by the progressively less dense red filters of the Bagolini filter bar. The last step was to decrease the brightness of the muscle light, while maintaining diplopia awareness.

A similar red lens diplopia technique was used by Sanfilippo & Clahane (130, 131), combined with traditional techniques to improve fusional convergence. They treated 31 exotropes for 5 to 22 sessions (average 7.5 visits). Initially 81% were considered poor functionally. They reported that 84% of DEX(T) cases studied showed a significant improvement: 64.5% were cured, and 9.7% were classified as “good” and 9% “fair”.

The five year study (131) conducted by Sanfilippo & Clahane demonstrated a maintenance rate of 52% cured and 32% “improved”. Females did significantly better than males. Most of the improved cases had a pre-orthoptic treatment deviation of 20-25 pd

Similar findings were reported by Mann (132) who found 60% of her cases were cured and another 15% showed definite improvement. Durran (133) reported 20 of 40 X(T)s treated with orthoptics were cured.

Some patients showed improvement even after orthoptics was terminated. Duncan (134) reported that 10 of 20 (65%) X(T)s treated solely with orthoptics were cured. The average followup time was 19 months after cessation of orthoptics.

Cooper & Leyman (135) in 1976 reported a retrospective study with a minimum 1 year followup. They reported the fol

lowing: with occlusion treatment, 36% were classified as “good”; with surgery, 42% were classified as “good”; with surgery and orthoptics, 52% were classified as “good” (the majority of the third group had deviations greater than 25k); with orthoptics, 59% were classified as “good”. An optometrist, Duckman (136), re-evaluated Cooper and Leyman’s orthoptic results and noted that those with an exoangle greater than 25 pd were rated “good” 35% overall, while those with deviations less than 25t pd were rated “good” 68% overall.

Altzier (137), an orthoptist, in 1972 reported a comparison of 29 Xl’s (16 intermittent) treated with surgery alone to 23 XTs (13 intermittent) treated with orthoptics alone. Treatment consisted of total occlusion to eliminate suppression, followed by application of Fresnel prisms to eliminate the exodeviation; and convergence exercises. She concluded that “surgical and non-surgical treatment produced fairly equal functional results...”

Another orthoptist, Chryssanthou (138) reported in 1974 her retrospective orthoptic treatment study on 27 X(T)s. Therapy consisted of home based training including occlusion, diplopia awareness, and stereograms to increase fusional ranges. She reported that before training 85% were “poor”, 11% were “fair”, and 4% were “good”. After therapy 67% were “excellent” (phoria only with good vergences), 11% were “good” (phoria only with acceptable vergences), and 11% were “fair” (X(T)). Long term followup (6-20 months) revealed 37% were still “excellent”, 30% were “good”, and 23% were “fair”, while only 11% remained “poor”.

Daum (139) reported his results in 1984 in 18 DEXT cases (age 4-56 years) 13 of whom had an intermittent deviation. Optometric orthoptic therapy was mostly home based and was carried out for an average of 5.5 weeks (range 1-16 weeks). Elimination of the exodeviation occurred in 33% with partial success in 56%. Daum noted improved success in patients with a small deviation, low AC/A, and no vertical deviation. Daum’s treatment regimen was very brief with reliance on home therapy.

One of the current optometric treatment strategies was based on the findings of Brock (140)(1966) and developed by Flax (77,78) (1968,1963). Treatment was based upon the finding that DEX(T) cases are binocular when there is an advantage, i.e., in the presence of stereopsis, and exodeviate when disparity cues are lacking. Therapy employs operant conditioning techniques in which the stimuli used in the

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