• Clinical science

Ocular motility disorders and strabismus

Summary

Strabismus is a condition characterized by misalignment of the eyes when looking at an object. One eye deviates (either constantly or intermittently) from the normal visual axis, which results in the inability of the brain to fuse together the images from the right and left eye. Strabismus is classified as either concomitant (nonparalytic) or paralytic. Concomitant strabismus primarily occurs in early childhood and manifests with a constant angle of deviation, in which the misaligned eye follows the unaffected eye. Paralytic strabismus is frequently acquired and is due to the functional weakness of individual extraocular muscles, which alter the angle of deviation depending on the direction of view. Further typical features include double as well as decreased vision. Treatment at an early stage (e.g., via occlusion treatment or surgery) is essential to prevent complications such as amblyopia (decreased vision in an eye with no apparent structural abnormality) and loss of binocular vision. Further complex ocular motility disorders can result from central nervous pathologies. Internuclear ophthalmoplegia, for example, is caused by a lesion of the medial longitudinal fasciculus and causes disturbances in horizontal eye movements.

Basic terms

References:[1][2]

Muscles of the eye

See extraocular muscles in eye and orbit.

Concomitant strabismus

Definition

  • Strabismus in which the degree of deviation (angle between the visual axes of both the eyes) remains constant in all directions of gaze

Etiology

  • Genetic
  • Uncorrected refractive error (particularly hyperopia and anisometropia)
  • Unilateral visual impairment/amblyopia (e.g., organic causes, retinal disease, retinoblastoma)
  • Other: perinatal lesions (e.g., preterm birth, asphyxia), cerebral damage (e.g., trauma, encephalitis)

Types

  • Congenital or infantile concomitant strabismus
    • Evident at birth or onset within 6 months of age ; does not resolve spontaneously
    • May manifest as esotropia or exotropia
  • Latent strabismus: usually no clinical significance; the deviation is compensated by fixation (fusion); decompensation and manifestation occur in situations of physical stress.

Diagnostics

  • Hirschberg test; : a test for determining if the eyes are in alignment. A light is shone at the eyes and the location of the light reflex on the cornea is observed in reference to the pupil. Asymmetrical corneal reflections on examination of the eyes indicate that the visual axes are not aligned (strabismus).
  • Cover tests
Single cover test for heterotropia Cover-uncover test for heterophoria
Method
  • Cover one eye for 1–2 seconds
  • Observe uncovered eye for shift in fixation
  • Uncover eye and observe both eyes for refixation movements
  • Same procedure as in single cover test
  • Observe the occluded eye when uncovering it
Interpretation
  • No shift in fixation in either eye no misalignment
  • Fixation shift in the initially uncovered eye misaligned eye
  • Fixation shift in the covered eye on uncovering it → misaligned eye
  • Refixation movement of the occluded eye on being uncovered → heterophoria
  • Measurement of the angle of deviation, if necessary with the help of a tangent screen

Therapeutic options

The main goals in strabismus management are to optimize visual acuity and achieve binocularity.

  1. Correction of refractive errors
  2. Visual training therapy
    • Training to correct eye movements (e.g., in strabismus) and visual-motor deficiencies
    • Uses specialized computer and optical devices (e.g., lenses and prisms)
  3. Occlusion treatment
    • Initiate as early as possible!
    • Cover the unaffected eye using a patch (occlusion) → training of the weaker eye
    • Duration of coverage depends on the child's age
  4. Penalization therapy (cyclopentolate drop therapy): : apply cyclopentolate drops to the unaffected eye blurs vision → encourages monocular use of the affected eye
  5. Strabismus surgery
    • Transposition or repositioning of muscles
    • Tucking or advancement to tighten muscles
    • Myectomy or tenectomy to loosen extraocular muscles

Complications

  • Disturbances of binocular vision
  • Amblyopia
    • Definition: : visual decrease in one or both eyes (functional visual impairment) due to a developmental vision disorder during early childhood
    • Pathophysiology: : one or both eyes convey poor or mismatched visual information to the brain → brain suppresses information from one or both eyes → disuse of the eye lacking visual stimuli with partial underdevelopment of the visual cortex (cortical blindness)
    • Forms

Failure to detect or adequately treat strabismus may result in irreversible amblyopia!

A serious underlying condition (e.g., brain tumor) should be suspected in infants with strabismus, especially in the presence of additional ocular findings like leukocoria!

References:[3][4][5][6][7][8][9]

Paralytic strabismus

Definition

Etiology

Clinical features

Patients with poor visual acuity may not notice diplopia. Therefore, complete optical (refractory) correction must be achieved before testing for strabismus!

Diagnosis

Steps Inference Underlying principle
Step 1: Determine which eye is hypertropic in primary gaze.
  • Hypertropic right eye weakness of right eye depressors or left eye elevators
  • Hypertropic left eye weakness of right eye elevators or left eye depressors
Step 2: Determine whether hypertropia increases on the right or left gaze.
Step 3: Determine whether hypertropia increases on right or left head tilt.
  • Vertical strabismus increases on tilting the head towards the right shoulder → weakness of a right eye intorter or a left eye extorter
  • Vertical strabismus increases on lilting the head towards the left shoulder → weakness of a left eye intorter or right eye extorter
Weak extraocular muscle Step 1: Which eye is hypertropic? Step 2: Vertical strabismus increases with lateral gaze in this directon Step 3: Vertical strabismus increases with head-tilt towards this shoulder
Right superior oblique Right eye Left lateral gaze Right shoulder
Left superior oblique Left eye Right lateral gaze Left shoulder

Treatment

  • Correction of refractive errors
  • Prismatic glasses
  • Treatment of underlying cause
  • Strabismus surgery

References:[10][11]

Internuclear ophthalmoplegia (INO)

Remember that internuclear ophthalmoplegia (INO) is characterized by Impaired adduction of the eye ipsilateral to the lesion and Nystagmus on the Opposite side!

References:[13][14]

last updated 11/04/2020
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