View source for Strabismus fixus

{{Article
|Authors=Gunjan.Saluja
|Category=Pediatric Ophthalmology/Strabismus
|Assigned editor=Donny.Suh
|Reviewer=Donny.Suh
|Date reviewed=September 10, 2019
|Article status=Up to Date
}}
= Disease Entity  =

Strabismus fixus convergens was first documented as a type of retraction syndrome<ref name="aebli1">Aebli R : (1933) Retraction syndrome, Arch Ophthalmol 10:602=610.  </ref><ref name="bielschowsky2"> Bielschowsky.A : (1939) Lectures on motor anomalies, Am J. Ophthalmol 22:357-367.</ref>and was thought to be a congenital structural anomaly (fibrosis of the medial rectus). It was Villascca who first described this condition as different from retraction syndrome and documented it in one of his cases which acquired it at a later age.<ref name="villaseca3">Villaseca A : (1959) Strabismus fixus, Am J Ophthalmol 48:761-762</ref>

== Disease  ==

Strabismus fixus can be associated with a number of conditions including congenital fibrosis, amyloidiosis and  in rare occasions, high myopic patient may develop a specific squint called“myopic strabismus fixus”(MSF).Myopic strabismus fixus is a rare strabismus disorder. This disease may progress over several years, from a small degree of esotropia with free ocular movement to the end stage of large angle fixed esotropia.  

== Etiology  ==
The underlying etiology of strabismus fixus still remains unclear . 

Yokoyama et al<ref name="yokoyama4">Yokoyama T, Tabuchi H, Ataka S, Shiraki K, Miki T, Mochizuki K. The mechanism of development in progressive esotropia with high myopia. In: de Faber JT, editor. Transactions of the 26 th Meeting European Strabismological Association Barcelona, Spain, September 2000. Lisse, Netherland: Swets and Zeitlinger Publishers; 2000. p. 218-21.</ref> provided the most recent explanation that the enlarged globe in high myopia herniates superotemporally and retroequatorially through the muscle cone 

Other etiologies include congential, fibrosis of extraocular muscle secondary to myositis or myopahties and infiltration of extraocular muscle by amyloid.

== Pathophysiology  ==

# Congenital : Congenital strabismus fixus is believed to be caused by fibrosis which explains loss of elasticity of medial rectus
# Lateral rectus palsy: Lateral rectus palsy causes the secondary contracture  and fibrosis of medial rectus
#Patients with high myopia have a weak intermuscular septa especially  between superior rectus and medial rectus and lateral rectus and inferior rectus which causes superior rectus to slip   medially towards medial rectus and lateral rectus to slip inferiorly, thus fixing the eye medially and down, esotropia and hypotropia, also termed as heavy eye syndrome
# Amyloidosis: Infiltration of extraocular muscle by amyloid  causes the loss of elasticity of extraocular muscle
# Unspecific, progressive fibrosis, myopahty and myositis is thought to be cause of strabismus fixus occuring in convergent form.


Mechanical
 
== General Pathology  ==
Histologic studies have demonstrated the  disappearance of myofibrils in the external recti of highly myopic eyes, with added tissue changes of homogenization, acidophilia pyknosis and karyolysis. These findings suggest involvement of the external recti in some myopathic process in pathological myopia as hypothesised earlier. But it is still controversial as to which muscle is primarily affected in pathological myopia resulting in such ocular imbalances.

= Diagnosis =
== Symptoms  ==

Patients are usually old aged, with high myopia , althogh few cases of strabismus fixus even in the absence of high myopia have been described

Patients typically complain of there eyes being fixed and there inability to move the eyes outward

== Signs  ==

===Extraocular movements===
[[File:Untitled.jpg|thumb|Nine gaze picture showing Strabismus fixus in a high myope patient]]
As a rule the eyes are anchored in a position of extreme adduction and is fixed in this position there is limitation of extraocular movements laterally.
Divergent form of strabismus fixus not accompained by ptosis or generalised fibrosis of extraocular muscle is unusual
===Visual acuity===
Patients with bilateral strabismus fixus are severely handicapped, one usually is preferred for vision and immobility of eye necessitates an extreme degree of head turn in such patients

== Diagnostic procedures  ==

Forced duction test

Done under topical anaesthesia with the help of Pierce Hoskin forcep, will further confirm the immobility of eye and associated fibrosis and loss of elasticity.

== Differential diagnosis  ==
Acquired bilateral sixth nerve palsy. 

Congenital bilateral sixth nerve palsy resembles cross fixation and sometimes it may become impossible to decide whether the origin is myogenic or neurogenic. 

Acquired bilateral sixth nerve palsy is commonly seen in middle aged individuals with history of diabetes, head injury or increased intracranial pressure symptoms. At a later stage, when secondary changes have set in, it may be difficult to differentiate it from strabismus fixus.

==Investigations==
[[File:CT Scan Coronal section of a patient of strabismus fixus.jpeg|thumb|CT Scan Coronal section of a patient of strabismus fixus]]
Computed tomography orbit

C..T. scan of orbit can demonstrate  relative localisation of extra ocular muscle in respect to globe  and presence of any slippage of extra ocular muscle in patient of myopic strabismus fixus 

MRI Scan : In cases of congenital strabismus fixus, adherences among the extraocular muscles, posterior Tenon's capsule, and the globe within the muscle cone on MRI will be seen.

= Management  =

Treatment is mainly surgical. For convergent form of strabismus fixus, complete disinsertion of medial rectus is done. In addition to this lateral rectus resection with recession of conjunctiva and tenons should be done, even though abduction beyond midline will not be possible after surgery , but will help in cosmetic and functional improvement.

Loop Myopexy  for myopic strabismus fixus
The procedure proposed by Yamaguchi et al<ref name="yamaguchi5">Yamaguchi M, Yokoyama T, Shiraki K. Surgical procedure for correcting globe dislocation in highly myopic strabismus. Am J Ophthalmol 2010;149:341-6.e2.</ref> unites  LR and SR muscle with nonabsorbable suture 15 mm behind the limbus. This procedure normalizes the vector force of these muscles and eliminates the mechanical disturbance in eye movement. It can be combined with MR muscle recession in cases of contracture as demonstrated by a positive forced duction test. 
The disadvantage of suture myopexy includes muscle strangulation, which may affect anterior ciliary circulation and may rarely cause cheese-wiring of the muscle.

= References  =
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