Strabismus is a visual condition in which the eyes are not directed toward the same object in space at the same time and, therefore, results in a decrement in the quality and quantity of visual information through both eyes. One eye may be deviated inward towards the nose (esotropia) or outwards away from the nose (exotropia). Other deviations include an eye directed upwards (hypertropia), downwards (hypotropia), rotated (cylcotropia), or some combination of these. Strabismus can either be caused by the brain lacking the ability to coordinate the eyes due to several circumstances, or a disorder of one or more of the extra ocular muscles. The different types of more common strabismus include esotropia, exotropia, and hypertropia.
Before treating a strabismus patient in Vision Therapy, it is crucial for the Vision Therapist to fully understand the patient’s visual profile, visual tendencies, developmental level, well as possible challenges that may occur during the course of therapy as given by the Developmental Optometrist. The therapist should understand the direction, type and degree of the deviation. We should also be aware of the presence of alternation, amblyopia, anomalous correspondence, non-concomitant deviations, possible suppression, as well as the frequency of the eye turn.
In my experience, following an examination, the doctor will brief the therapists on an individual patient before starting the patient in therapy. Depending on the doctor’s wishes for the patient, the Vision Therapy will follow one of two paths:
Path 1 – Eliminate the strabismus, amblyopia, and anomalous correspondence (if applicable) in the following sequential steps.
- Monocular work to strengthen and equalize the eyes
- Eliminate Amblyopia and/or eccentric fixation if present by way of monocular fixation in a binocular field (MFBF), keeping both eyes in the same field and “paying attention”
- Bi-ocular work which attempts to maintain simultaneous perception without a fusional demand
- Binocular work which will now attempt to achieve 1st, 2nd, and 3rd degree fusion.
Path 2 – Enhance the Strabismus, “disregard” possible anomalous correspondence, and work to improve the cosmesis and overall life performance in the following sequential steps.
- Work to build awareness of the body through bilateral integration, body map, gross motor exercise.
- Bi-nasal/temporal occlusion to work towards a straighter position
- Peripheral awareness and peripheral stereo fusion to build the possibility of peripheral alignment and possible peripheral lock. As therapy progresses, the targets can become more centrally located and oriented
Our course of treatment for Path #2 will begin with gross peripheral fusion activities and bilateral integration. Since periphery is primarily responsible for solving the “where is it” equation, working gross peripheral fusion helps patients to better understand and locate an object, or target, in space as they try to achieve a “peripheral lock” and thereby laying the groundwork for central fusion. Since the patient with esotropia normally makes sensory adaptations to prevent vision confusion and diplopia, peripheral retina is often not affected, making it easier to get our “foot in the door” and we work our way toward achieving more central binocularity. Bilateral integration becomes important because often times strabismus patients do not have an equal spatial representation on both sides of their body. Our next steps may include localization exercises to further tune the spatial localization, bi-nasal occlusion to help the patient understand how to move their eyes to achieve binocularity, an MIT (macular integrity tester) to help the patient “find” their fovea, and lastly disparity targets to work towards third degree fusion. Variations to this plan may occur if the patient has an alternating esotropia, in which case the goal would be to have the patient alternate at such a high rate of speed that they can achieve binocularity. Any non-comitancies would be treated by separating all fields of gaze into their own challenge. Our goal as therapists is to begin with the “easier” gaze (or the closest to fusion) and work our way into the more challenging gazes, always pushing the edge to work towards the goal of fusion. In this case, the doctor probably would specify no or very limited monocular work be undertaken.
The one serious concern when working with patients with esotropia is anomalous correspondence, which if handled inappropriately, can result in irreversible or intractable diplopia. This is why it becomes crucial that all Vision Therapy is monitored closely by a Developmental Optometrist.
Patients with exotropia provide a different set of challenges. Most times they are in fact intermittent and are capable of panoramic viewing when the eye is deviated, providing a certain degree of “depth”. In our office, the course of treatment is somewhat opposite of the aforementioned esotropia treatment. We will begin with third degree targets, working back into second and first degree. Generally speaking, patients with exotropia have an easier time with convergence than patients with esotropia have with divergence because stimulation of vergence is easier than relaxation. Continued treatment will include bilateral integration, spatial awareness, and body mapping activities.
As with any strabismus patient, the Vision Therapist should always be guided by a Developmental Optometrist as to the how, where, and the whys of Vision Therapy. Any abnormalities reported by the patient should be reported to the doctor immediately. The primary concern for a Vision Therapist when working with any patient, but especially so with a strabismic patient, is to be in good communication with the doctor as to the prognosis and progress of the patient. Because of the many complications that can arise with strabismus, it is vitally important that the Vision Therapy is done slowly, carefully, and under the close supervision of a doctor to ensure that the patient can have a positive outcome.
As a Vision Therapy provider, working with a patient with strabismus can be one of the most challenging, yet rewarding experiences. For me, personally, the key has always been to prepare well and to not guess; rather, when we come upon a situation or finding we’re not prepared for, or something which looks or sounds different than we were expecting, it’s imperative to ask for the doctor’s insights. As Vision Therapists, we should never fear asking too many questions!