I. Introduction: Closed head injuries or stroke victims survive at increasing rates. They recover medically, then, too often, are released without adaptive or rehabilitative consults. This is particularly true for vision problems in patients with ABI (acquired brain injury). Often, they face:

  • -non-comitant strabismus -diplopia

    -paretic EOM(s) -oculomotor dysfunction

    -visual hypersensitivity -fixation difficulty

    -vision perception problems -visual attention

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    II. General Trends and Fun Facts About Paretic Strabismus:

    A. Incidence for each cranial nerve (Younge, 1981) IN A HOSPITAL SETTING:
    i. VI cranial nerve (42%)

    ii. III cranial nerve (29%)

    iii. IV cranial nerve (17%)

    iv. multiple nerves (12%)

    - it is important to note here, that clinical experience outside a hospital will have a higher incidence of IV cranial nerve paresis. This is usually secondary to more "minor" causes, so the patient may not be hospitalized

    B. Most of these cases were adult onset IN A HOSPITAL SETTING:
    i. 26% were idiopathic

    ii. 20% were secondary to head trauma

    iii. 17% were vascular (including diabetes)

    - it is once again important to note that in a typical optometric setting, the relative frequency of paretic strabismus may be more heavily distributed towards the ischemic neuropathies (usually diabetic).

     

    III. Traditional Passive Therapy For A Paretic Strabismus:

    A. Full, constant patching of the paretic eye

    B. Prism application (to gain fusion in primary gaze)

    1. BO prism for LR paresis

    2. BD for IR paresis

  • C. Surgery to regain alignment (and fusion in primary gaze). It is not considered a method of choice for an adult onset strabismus.
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    IV. Occlusion Therapy For Paretic Strabismus: uses very clever twists on the three themes listed above and offers the patient more comfort and increased function. After passive, "relieving" therapy has begun, it may be possible to increase EOM function; this is the hallmark of optometric therapy

  • A. When patching to relive a patient of initial symptoms of an acquired non-comitancy, the traditional approach is constant patching of the paretic eye.
    1. This is fine for initial relief from diplopia, but does nothing to increase function of the paretic muscle

    2. In fact, constant wear of the patch on the affected eye will lead to contracture of the ipsilateral antagonist

    B. Another approach is to patch the non-paretic eye (i.e. like direct patching for an amblyope). This forces the paretic eye to work.

    1. This may not be practical when attempting to drive!

    2. This is easily "cheated" on with a simple head turn (patient education is a must here)

    3. Constant wear of the patch on the non-affected eye will lead to contracture of the contralateral synergist (by Hering's Law)

    C. To avoid the above problems, it may be advisable to alternate the occlusion regimen.

  • 1. Patch paretic eye when driving or performing tasks that rely on effective eye movements

    2. Patch non-paretic eye when "futzing around"

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    D. In general, it may be better to use any patching regimen intermittently to avoid unwanted contracture of EOMs.

    E. Those special patching cases: the use of sectional occlusion.

    1. If you have a patient WITH A LR PARESIS who is actively working on increasing oculomotility ranges (abduction), it may be beneficial to use binasal occlusion. This, if used properly will eliminate cross-fixational patterns.
    a. assume the pt. has a right LR paresis, the binasal wedge will
    i. force O.D. to abduct as a visual stimulus passes into the temporal regions the right hemifield (avoiding contracture of the ipsilateral MR)

    ii. force O.S. to abduct as a visual stimulus passes into the temporal regions the left hemifield (avoiding contracture of the contralateral MR)

    b. the pt. must be properly educated and learn to avoid head movements that diminish the effect of the sectional occlusion

    2. If you have a pt. with a long term non-comitant deviation, and contracture of the ipsilateral antagonist has already occurred: a sectional occlusion can be placed so that occlusion of the paretic eye only takes place as gaze is directed into the paretic muscle's diagnostic action field

    a. assume the pt. has a right LR paresis, the sectional occlusion should be placed over the temporal half of the right lens

    b. allows normal binocular vision on primary and left conjugate gaze

    c. occludes right eye on right gaze (to avoid diplopia)

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    V. Use of Prism In the Non-Comitant Strabismic Patient

    A. Use of prisms when binocularity is present in some gaze positions:
    1. Yoked prisms: either base left or base right. Prescribe to avoid gaze into the paretic diagnostic action field (i.e. Base Right for a right LR paresis, Base Left for a right MR paresis).

    2. If there is significant binocularity except for significant excursions into the paretic eye field, sectional prisms may work quite well. This is particularly true for diabetic neuropathy, which resolves slowly over time.

    a. sectional prisms are designed to allow fusion while actually looking into the paretic diagnostic action field

    b. for a right LR paresis: Base Out prism in the right half of the right eye (usually put most of the prism over the paretic eye)

    c. for a right SO paresis: Base Down prism over the left lower quadrant of the right lens

    3. It is far better to use prism in the lowest amount possible. Patient acceptance is usually much better.

    a. just enough power to achieve fusion over a small range into the paretic muscle's diagnostic action field

    b. prism application should accompany at least limited vision therapy to increase motility and fusional ranges

    B. Use of prism on monocular/amblyopic patients: When the "only good eye" acquires a paresis secondary to injury or disease, it is very traumatic for the patient. In general, it is very important to AVOID GAZE INTO THE PARETIC FIELD! the base of the correcting prism should accomplish this goal.

  • 1. A patient should be educated regarding the distorting nature of prisms (especially for press on variety).
  • a. BD: makes objects appear farther away/larger

    b. BU: makes objects appear closer/smaller

    c. BI: increased curvature of field (pin cushion distortion)

    d. BO: increased "flatness" of the field (barrel distortion)

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    2. Prisms will not only allow fusion in more gaze positions, it may also:

  • a. Change/improve posture

    b. Improve vergence ranges in primary gaze

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    VI. Basic Vision Therapy and Surgical Options For ABI Cases:

    A. General scheme for patching/prism/therapy for non-comitancy
    1. Full occlusion for a short period of time (1-2 weeks) for relief from symptoms.
  • 2. Alternate occlusion with some simple fixation and monocular motility work (thumb pursuits).

    3. More advanced therapy: VOR motilities, pegboard rotator, Marsden ball.

    4. Rx sectional or yoked prism (or binasal wedge if LR paresis).

    5. Train compensatory head position to avoid diplopia.

    6. Surgical intervention for non-comitancy: wait at least six months to allow the paresis to stabilize. Many cases of ischemic mono-neuropathies will self resolve in that time frame.

    a. Waiting may be useful in youngsters as well.

    b. Surgery may be called for if over 15 prism diopters of prism are required to maintain fusion in primary gaze.

    c. Don't forget that the age and general health of the patient must be considered before surgery.

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    B. Therapy for visual imperception:

    1. Yoked prisms:
  • 2. Fixation games (work towards neglected field)
  • a. Versions (toward neglected field): Marsden ball, Acuvision 1000

    b. Bisection of lines (work towards field of neglect

    c. Evaluate for true field loss

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  • C. Therapy for visual hypersensitivity:
    1. Fixation/ pursuits : gradually add peripheral "noise"

    2. Peripheral awareness training: MacDonald forms

    3. After-image work: align with fixation target

    4. Etch mark on back surface of lens to line up with fixation

    D. Therapy for perceptual difficulties: Same as for any perceptual case…just remember that they are adults!!!

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