Sixth Cranial Nerve Palsies

DEFINITION:

A paralytic/paretic strabismus in which partial or complete innervation to the extra-ocular muscles innervated by the sixth cranial nerve has been impaired.

SIGNS AND SYMPTOMS:

The signs and symptoms associated with sixth cranial nerve palsies may include, but are not limited to, the following:

1. eye turn, deviation (ICD:H51.9); sensation of monocular viewing; head turn
2. defective stereopsis and inaccurate/inconsistent depth judgment
3. general fatigue after sustained task
4. diplopia (ICD: 2)
5. inaccurate eye-hand coordination
6. reduced efficiency and productivity/diminished accuracy/inconsistent work product
7. asthenopia and diminished performance with increased task time
8. abnormal postural adaptation/abnormal working distance (ICD: 3)
9. spatial disorientation/incoordination/clumsiness (ICD: 8)
10. decrease in visual acuity

DIAGNOSTIC FACTORS:

Sixth cranial nerve palsies are characterized by one or more of the following findings:

1. sudden onset diplopia
2. secondary deviation greater than primary deviation
3. gradual progression of deviation through stages (i.e. deviation in primary gaze, over-action of antagonist muscle leading to contracture of deviation, and, finally, spread of comitance of the deviation)
4. eye is deviated inward

THERAPEUTIC MANAGEMENT CONSIDERATIONS:

The doctor of optometry determines appropriate diagnostic and therapeutic modalities, and frequency of evaluation and follow-up, based on the urgency and nature of the patient’s conditions and unique needs. Vision disorders that are not totally cured through vision therapy may still be ameliorated with significant improvement in visual function and quality of life. In cases of paralytic strabismus such as sixth nerve palsies, co-management with medicine (i.e. internists, neuro-ophthalmology and/or ophthalmology) is often in order due to systemic complications. The management of the case and duration of treatment would be affected by:

1. the severity of symptoms and diagnostic factors, including onset and duration of the problem
2. the complications of associated visual conditions
3. implications of patient’s general health, cognitive development, physical development, and effects of medications taken
4. etiological factors
5. extent of visual demands placed upon the individual
6. patient compliance and involvement in the prescribed therapy regimen
7. type, scope, and results of prior interventions

PRESCRIBED TREATMENT REGIMEN:

Some cases are successfully managed by the prescription of therapeutic lenses and/or prisms. Many sixth cranial nerve palsy cases benefit from optometric vision therapy, which incorporates the prescription of specific treatments in order to:

1. develop adequate fusional vergence ranges and stability in all positions of gaze at distance and near
2. enhance accommodative/convergence relationships
3. enhance depth judgments and/or stereopsis
4. integrate binocular function with information processing
5. enhance fusional vergence facility and flexibility
6. integrate binocular skills with accurate motor responses
7. integrate binocular skills with other sensory skills (vestibular, kinesthetic, tactile, and auditory)
8. increase visual stamina/integrate newly established skills with information processing

 

DURATION OF TREATMENT:

The following treatment ranges are provided as a guide. Treatment duration will depend upon the particular patient’s condition and associated factors. When duration of treatment beyond these ranges is required, documentation of the medical necessity for additional treatment services may be warranted for third-party claims processing and review purposes.

1. Full treatment requires resolution of associated visual
2. The most commonly encountered cases of sixth cranial nerve palsy usually require 30 to 40 hours of office therapy.
3. Associated factors such as cerebral vascular accident, head trauma, and/or systemic conditions may warrant an increase in treatment

 

FOLLOW-UP CARE:

At the conclusion of the active treatment regimen, periodic follow-up evaluation is required. Should signs, symptoms, or other diagnostic factors recur, further therapy may be medically necessary.

Therapeutic lenses may be prescribed during or at the conclusion of active vision therapy to assist in the maintenance of long-term stability.