Vision therapy treatment for strabismus: the Ludlam Study

A landmark study on the vision therapy treatment of strabismus, but not the first such study, was conducted by Dr. William Ludlam on the vision therapy treatment of strabismus. Over a four year period, Ludlam identified all the strabismus cases that were seen at the Optometric Centre of New York - a total of 284 patients. Of these, 149 met the criteria for inclusion in the study. Those criteria were:

• The patient had strabismus, i.e. he or she manifested a binocular deviation (misalignment of the eyes), either constant, intermittent or periodic.
• The deviation was not capable of correction with lenses.
• No surgical intervention had previously taken place.
• There was no evidence of paresis or paralysis in the primary and secondary position of gaze.
• The patient attended at least eight sessions of orthoptic training (one month).
• The patient terminated regular clinical training.

If the patient met the above six criteria, he or she was included in the study. The authors had no prior knowledge of the results the patients had achieved with vision therapy training. A total of 135 cases were not included in the study for the following reasons:

• 19 patients were post-surgical cases whose surgery did not fully correct their ocular misalignment and they were undergoing vision therapy to fully correct the misalignment.
• Eight patients had non-comitant strabismus with either paresis or paralysis of one or more of the extra-ocular muscles.
• Nine patients were accomodative esotropes who were fully corrected with special eye-glasses and several vision therapy sessions.
• 48 patients dropped out of training after seven or fewer visits (21 of these dropped out after the first workup visit.
• 51 patients were still undergoing vision therapy and had not yet concluded their course.

The results of the study were as follows:

The study's criteria for a "functional cure" were stringent: the patient was required to have clear, comfortable, single binocular vision at all distances up to the near point of convergence, which is normal itself; there must be stereopsis and normal ranges of motor fusion; a occasional turning of the eyes may occur (up to 1% of the time) providing diplopia is experienced whenever this happens; correction lenses and small amounts of prism (up to five prism diopters) may be worn if necessary.

The "almost cured" category were those that may lack stereopsis, may exhibit strabismus with diplopia no more than 5% of the time, and may need larger amounts of prism to maintain comfortable binocular vision. In all other respects the patient must meet the criteria for "functional cure."

The "moderate improvement" and "slight improvement" categories were adopted for those patients for whom the main improvement was, respectively, in more than one or in only one of the defects associated with the strabismus. The category of "no improvement" caught those patients for whom there was no significant improvement in the strabismus or its associated defects.

Ludlam summarized the results as follows: "combining the functional and almost cured groups and adding four patients whose eyes ware straight ... but are listed as 'moderately improved' because of the the technical requirements of the 'cured' categories (2 subnormal ranges of motor fusion, 1 with a 7" N.P.C. rather than the required 4", and 1 with frequent asthenopia, headaches and accomodative spasm), we may state that a total of 113 (76%) of the patients in the sample had binocular vision with straight eyes 95% of the time or more at dismissal from teh regular clinic training sessions. The other 36 patients had residual deviations occurring more often than 5% of the time, and were classified as orthoptic failures. Of these, 8 of the "moderate improvement" group dropped out when quite near the "almost cured" category, i.e. with their eyes straight well over half the time and possessing all of the technical factors necessary for a cure with several moths of additional stabilization work."

The results of the study are amazingly good. They look better still when one considers - as Ludlam himself points out in the study - that the results were obtained under relatively poor clinical conditions such as the following:

• Group therapy was conducted with the patient receiving a limited amount of individual care.
• Patients were seen by different clinicians with different personalities and philosophies of training.
• Control and management of each case was relatively poor.

Ludlam notes, and subsequent studies have shown, that the absence of these unfavourable factors should yield even better results on a similar sample of strabismic patients.  A subsequent study has shown an 87% sucess rate when treating strabismus patients in a private practice optometric clinic where each patients recieves individualized, one-on-one care.

Source: Ludlam WM. Orthoptic treatment of strabismus. Am J Optom Arch Am Acad Optom 1961;38:369-88.