TYPES OF STRABISMUS

TYPES OF STRABISMUS image
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TYPES OF STRABISMUS

1. Incomitant: The angle of deviation varies in different directions of gaze.  This occurs most commonly where there is paralysis of one or more extraocular muscles.
Causes:

a. Neurological - due to lesions of 3rd, 4th, or 6th cranial nerves caused by:
  • Trauma- Tumour – (Intracranial)
  • Infection
  • Raised Intra-Cranial Pressure (6th Nerve Palsy)

b. Muscular – Direct involvement of the extraocular muscles by
  • Trauma
  • Tumour of the orbital or periorbital tissue
  • Infection
  • Muscular Anomaly – Dystrophy etc.
c. Neuro Muscular – Myasthenia Gravis

d. Congenital Conditions:
  • Duane’s Retraction Syndrome
  • Browns Syndrome
  • Moebius Syndrome
In all these states the angle of squint varies, becoming maximal when an attempt is made to gaze in the direction of action of the paralysed muscle.  In children the eyes may fail to realign following temporary paralysis and a permanent comitant squint may occur.

Duane’s Syndrome
– The involved eye is unable to abduct and on adduction is retracted into the orbit.
Brown’s Syndrome
- The inability to elevate the eye in adduction
Moebius Syndrome
– Combined 6th and 7th nerve palsies.

2.Comitant Strabismus
The angle of squint is equal in all directions of gaze. There is no abnormality of function of extra ocular muscles but instead, incorrect co- ordination of binocular muscle function is present.
Types Of Concomitant Strabismus
- Esotropia (Convergent Squint) optical axes converge (A convergent squint)
- Exotropia (Divergent Squint) optical axes diverge (A Divergent squint)
- Hypertropia – (Vertical Squint) – One optical axis is deviated vertically.
- Latent Strabismus becomes apparent only on dissociation of the vision of the eyes (eg on covering one eye) and is termed a phoria (exophoria, esophoria, hyperphoria). This may become overt with fatigue, illness, or with lack of attention.
Causes of Comitant Strabismus
Hereditary :
a familial predisposition to develop strabismus may be inherited as an autosomal dominant trait.
Sensory Deprivation
A blind eye has no incentive to remain aligned. Therefore any condition which results in markedly reduced vision may cause a squint. E.g. Corneal Scarring, Cataract, Opacity of the Refractive Media, Retinal Lesion e.g. – Retinoblastoma, Retinal Detachment, Optic Atrophy, High Refractive Error.
Secondary To Paralytic Squint
Children have a tenuous hold on single binocular vision therefore they frequently do not manage to redevelop this following a paralytic squint.
Accommodative
The close anatomical and physiological link between accommodation and convergence causes the frequent excessive convergence (esotropia) in children who are hypermetropic i.e. because these children need to accommodate excessively to obtain clear vision they often break down and develop a convergent squint.      ACCOM SQUINT        
Unknown
No cause for the occurrence of strabismus will be found in many cases.