(Patney, S. A. : Strabismology Desk Reference,
Chapter 41, Rajkot (India), JKAI Publications, pp.749-761).
NONPARALYTIC NONCOMITANT RESTRICTIVE STRABISMUS
CONGENITAL FIBROSIS OF EXTRAOCULAR MUSCLES
Nonparalytic, noncomitant, restrictive
strabismus is continued in this chapter. The next condition to be discussed is the rare
but important congenital disorder of extraocular muscles called "Congenital Fibrosis
of Extraocular muscles or CFEOM". It is one of the diseases affecting the extraocular
CFEOM is a rare congenital neuromuscular anomaly in
which more than one muscle, sometimes more than three or possibly all the extraocular
muscles are fibrosed. There is a ptosis in addition to hypotropia (the most common type of
deviation in the patients suffering from this disorder) and/or other types of deviation.
The characteristic features of this anomaly are:
- Compensatory head posture (elevation of chin)
- Marked ptosis
- Hypotropia due to downward fixation of one or both
- Anomalous convergent movements on attempted elevation
- Familial or sporadic
- In 1840 Baumgarten seems to be the first to describe
ptosis in association with restricted ocular motility.
- In 1879 Heuck for the first time reported a familial
occurrence and also described postmortem findings in a case.
- In 1950 Brown1 named the condition of
fibrosis of three or more extraocular muscles as "General fibrosis syndrome".
Incidence and distribution
- Prevalence of the fibrosis syndrome in general or
strabismic populations has not been reported.
- Cases have been reported from all over the world and
- From all communities and races.
- It seems that the generalized form of fibrosis
syndrome is most common.
- But I think there is a possibility that cases in
which there is fibrosis of a single isolated muscle it may not be recognized for what it
is. Thus the case may get grouped under some other type of condition. For example, a mild
form of inferior rectus fibrosis may be diagnosed as a contracture of the muscle secondary
to congenital superior rectus palsy. The same thing happens when a bilateral case with
severe involvement of one eye and only slight involvement of the other eye gets labeled as
a unilateral case.
There are various theories about the causation of
CFEOM but the following are more popular:
The neurogenic theory
- The myogenic theory
The neurogenic theory has more support and the
neurologic cause is considered to be primary. The changes in the muscles that are found in
cases of CFEOM are supposed to be secondary to the primary neurologic defect. Absence of
superior division of oculomotor nerve and its alpha motoneurons was discovered in a case
and generalized muscle fibrosis was found in the other three. In the latter there was a
possibility of a primary myologic anomaly7. It has been suggested that in CFEOM
a primary developmental defect rules out normal neuronal connections8.
According to the classification by Harley et al2
CFEOM is divided in to following types:
- Generalized fibrosis of extraocular muscles
- Fibrosis of inferior rectus with blepheroptosis
- Strabismus fixus
- Vertical retraction syndrome
- Congenital unilateral fibrosis
There are several names given to this condition by
various authors at various times. Some of them are: generalized fibrosis of extraocular
muscles, congenital ocular fibrosis, congenital ocular fibrosis syndrome,
congenital fibrosis syndrome, syndrome of generalized fibrosis, congenital
ophthalmoplegia, ophthalmoplegia imperfecta, hereditary congenital ophthalmoplegia,
abiotrophic ophthalmoplegia externa, congenital external ophthalmoplegia with
co-contraction and autosomal dominant congenital ophthalmoplegia.
Heredity and genetics
- Mode of transmission is often autosomal dominant3
but in my experience and others4 sporadic cases are more common.
- The gene for autosomal dominant CFEOM was mapped to
chromosome 12 by Engle et al5, 6 but the gene has not been isolated so far and
its function remains obscure.
- Evidence has been found that its gene may be involved
in the development of the neurons of the III CN nucleus and probably also of other cranial
- The expression of the gene is quite variable leading
to a phenotype that is more severe and symmetric in some family members than in others.
The resulting clinical picture may be quite variable with some cases being mild, some
moderate and others severe in the same family. Also some may have symmetric anomalies in
both eyes and others asymmetric.
- No chromosomal anomalies have been reported
- Autosomal recessive modes of transmission have also
been reported4 with the anomaly affecting siblings and cousins in three Saudi
Arabian families. The parents of affected individuals have consanguineous marriages and
are themselves normal.
According to Laughlin9 Congenital
fibrosis syndrome consists of the following four components:
- Blepheroptosis and chin elevation
- Histopathologic evidence of fibrosis of the
- Absence of depression or elevation of the globe
with the eyes fixed in 20-30 degrees depression
- Little or no horizontal movements
- A fifth feature that has been added10 is
the absence of Bells phenomenon. It seems to be due to the mechanical restriction
Other important features are given below:
- The cases of CFEOM may be symmetrically or
asymmetrically bilateral. The asymmetry is sometimes so marked as to make the anomaly
- The degree of involvement may vary from case to case
from mild to severe.
- The number of muscles involved is also variable. In
some cases all the extraocular muscles (EOM) are involved, in others only one may be
- The patients of CFEOM are usually healthy but cases
of rare associated ocular and systemic anomalies have been reported in sporadic
- Some of the associated ocular anomalies reported are:
chorioretinal coloboma, bilateral optic hypoplasia, retraction of the eyeball due to
cocontraction, synergistic divergence due to neural misdirection, enophthalmos,
microphthalmos and oculocutaneous albinism8 and Marcus Gunn jaw-winking
- Some of the associated systemic anomalies reported
are benign ethmoidal mesenchymoma, bilateral inguinal hernias.
- Unilateral cases of CFEOM may show facial asymmetry
with the affected side of the face being smaller. Orbital anomalies may be present.
- The usual complaint is the strabismus and
ptosis resulting in bad cosmesis.
- Orthoptic examination (ocular motility
work-out) usually reveals following problems:
- Amblyopia is common in one
(strabismic/anisometropic/ametropic) or both eyes (ametropic). Upto 50% incidence of
amblyopia has been reported in these cases with a constant strabismus and/or ptosis or
- Refractive errors (hypermetropia and astigmatism)
occur in 60% cases but occasionally visual acuity of 20/20 is possible11. There
may be significant changes in refractive errors post-operatively, possibly due to a change
in the distribution of forces that are exerted on the globe by the tight fibrotic muscles11,12.
- Since the strabismus is constant in most of these
cases there is no binocular vision. However, Binocular functions are
preserved in some cases in which binocular single vision can be achieved by adopting
compensatory head posture. These are usually cases of fibrosis of a single muscle. 40
degrees of stereopsis has been reported11.
- Progressive development of A pattern strabismus
was reported in 8 patients of CFEOM13. This was explained by Traboulsi et al by
the excessive convergence being exerted in elevation probably by the adductive effect of
superior rectus muscle in elevation11.
- Ptosis with various degrees of severity is a
common feature of CFEOM. However, it may be absent occasionally or it may be partially or
totally a pseudoptosis because of hypotropia10. The false ptosis
disappears when the affected eye is made to take up fixation but in a case of inferior
rectus fibrosis the eye can not be brought to primary position as elevation function is
absent. On recessing or tenotomising the fibrosed inferior rectus the pseudoptosis
disappears. (see case report).
- Retraction of eyeball may be observed in
various directions because of the fibrosis of various muscles.
- Ophthalmologic examination:
- Complete ophthalmologic examination including
- Orthoptic examination including measurement of
deviation in various directions of gaze and assessment of binocular vision: One should
be careful because mild cases of congenital fibrosis are liable to be missed. The degree
of fibrosis may vary from case to case and from muscle to muscle.
- Forced duction test: It should be done in
every case preoperatively, intraoperatively and postoperatively. If the test is positive
the degree of tightness is assessed. In cases of severe fibrosis there is hardly any
movement of the globe in the direction of action of the direct antagonist.
- Special tests:
- CT scan (computed tomography) of orbits shows
the fibrosed IR muscle or other affected EOM. The badly affected muscles are seen as
thread like structures14. Other defects that may show up in CT scan are the
atrophy, aplasia, and anomalous insertions15. A thickened muscle may stand out
when compared with it normal counterpart.
- Histopathologic examination: Biopsy of the
tenotomized IR shows replacement of muscle fibres by fibrous tissue. Fibrous infiltration
of the muscles may be accompanied by the same in orbital tissue.
- Magnetic resonance imaging (MRI) may be more
helpful in recognizing the affected muscles.
- Genetic testing if possible to locate the
defective gene: At present this is being done only for research purposes. Engle and
associates6, 7 have done the maximum amount of productive work on the genetics
of congenital oculomotor anomalies.
The following conditions can be confused with
congenital oculomotor fibrosis syndromes. Forced duction test must be done in all cases to
- Browns syndrome
- Double elevator palsy
- Graves ophthalmopathy
- Orbital floor fractures
- Muscle entrapment in orbital wall fractures
- Total or partial III CN palsy
- Atypical Duanes syndrome
- Mobius syndrome
- Chronic progressive external ophthalmoplegia (CPEO)
- Kearns-Sayre syndrome
- Myasthenia gravis
- Orbital periostitis
This particular type of congenital fibrosis of
extraocular muscles deserves special mention despite the fact that the condition is very
rare. In more than four decades I have seen only about 7 cases of strabismus fixus, four
of them convergent, one divergent and two verticals (one hypotropia and the other
In this condition the eye/eyes are anchored in a
certain position, e.g., in adduction (convergent position), infraduction/depression (see
case report 41-1), supraduction (elevation) or abduction (divergent position). Ocular
motility is severely restricted in all the directions.
Strabismus fixus can be of two kinds:
- Congenital type:
The congenital type of strabismus fixus is due to a congenital fibrosis of the
affected extraocular muscles. According to the direction of the deviation it can be
divided into two types:
A. Horizontal or
- Acquired type is due to
contracture/fibrosis of the direct (ipsilateral) antagonist of a palsied EOM or that of
its contralateral synergist in a longstanding case.
Congenital strabismus fixus of the horizontal
Medial rectus being the most commonly
affected muscle, the most frequent type of congenital strabismus fixus is convergent
On The main points regarding the congenital type of strabismus fixus are as follows:
- The condition can be bilateral or unilateral.
If bilateral it causes severe disability.
- A positive family history must be excluded.
- The eye/eyes are fixed (anchored) in an
extremely adducted (convergent) or rarely a divergent position.
- Divergent type of strabismus fixus has been
reported but is extremely rare20.
- Compensatory head posture is common as the eye
is almost immobile and the patient has to adjust the head so that the better eye can be
used to best advantage. An extreme degree of face turn is usually present in these
cases to make it possible for them to move about and carry on with their daily activities.
- Amblyopia is common in the worse affected eye.
- The degree of deviation depends upon the severity
of fibrosis but usually it is large. Extreme cases have been reported with eyes
being so severely deviated that the cornea disappears from the view20 (see case
- Ocular motility is severely restricted so as
to be almost absent. The only movements that may be possible are some further adduction in
convergent strabismus fixus and abduction in divergent strabismus fixus and slight
vertical movements in the anchored position on attempted horizontal movements.
- Binocular functions are almost always absent.
- A case of convergent strabismus has been reported25
in which there was ocular ischemia, central artery occlusion and optic atrophy due to due
to mechanical stretching and torsion of the optic nerve causing strangulation of the blood
supply to the eye.
- Computed tomography (CT) scan of the orbits
might show the string like fibrosed and short medial or lateral recti, as the case may be.
- The only treatment is surgical, whereby a free
tenotomy of the affected muscle is done with/without a resection of the normal antagonist.
However, if the patient is old and not too keen on treatment one should leave such cases
alone as the rate of complications is higher in them21 (see the surgical
management of CFEOM on page
- It is preferable to take a small piece of the
affected muscle for biopsy.
Congenital strabismus fixus of the vertical type
The main points are given below:
- The affected eye is fixed in a vertical position
(supraduction or infraduction) due to the fibrosis of superior rectus or inferior
rectus. The former leads to a large hypertropia and the latter causes a large
hypotropia (see case report 41-1)
- Other features are similar to those in the horizontal
- We treated one patient of the hypotropic
strabismus fixus in whom the left eye was anchored in an extremely depressed and
somewhat divergent position (see case report 41-1). The cornea could not be seen in the
palpebral aperture (figure 41-2). A free tenotomy of inferior rectus resulted in a
cosmetically acceptable result. About three decades ago we treated a case of vertical
strabismus fixus with the left eye fixed in supraduction. A free tenotomy of the affected
superior rectus resulted in an acceptable cosmetic appearance.
This type of strabismus has been reported in
association with certain conditions as elaborated below.
- Acquired type of strabismus fixus
- Martinez described a case of acquired strabismus
fixus (in 1948)21.
- Villaseca was of the opinion that the fibrosis of the
medial rectus is secondary to the paralysis of lateral rectus leading to a contracture of
the medial rectus22.
- A case was reported in which the strabismus fixus was
due to amyloidosis23.
Management of congenital fibrosis of extraocular
(1) Nonsurgical treatment of congenital fibrosis
Like that of most other types of strabismus, the
non-surgical treatment of congenital fibrosis of EOM consists of the following:
- Correction of refractive errors
- Treatment of amblyopia should be carried out
by occlusion of the eye with better visual acuity until the vision is equal in both eyes.
However if the patient is an adult this is not possible and in the absence of fusion can
result in (postoperative) diplopia.
- Proper assessment of binocular functions
- careful measurement of angle of deviation in
various diagnostic positions of gaze.
- Care of the ocular surface, especially the cornea:
Lubricants are used if there is exposure keratitis. The eye has to be covered at night to
(2) Surgical treatment of CFEOM
The following important points should be kept in
mind before deciding on surgery:
- Surgery is not required and should not be carried out
under the following circumstances:
- If the patient is old, has strabismus fixus and is
not keen about surgery, as the complication rate is higher in older people.
- If the compensatory head posture is not significant.
- If the pupil is not covered by drooping lid.
- If fusion can be obtained in one or more directions
without a significant head posture.
- The patient and his relatives should be warned about
the uncertainty of the result, particularly of the postoperative movements. One may have
to be satisfied with limited excursions because of the fibrosis of the muscles leading to
- If the surgeon is going to operate on more than one
member of a family, each case should be assessed fully and separately because of the
variability of the severity of the condition in the same family. This is due to the
expression of the phenotype being extremely variable6, 7.
- The strabismus should be corrected first before
ptosis surgery is carried out. Sometimes only a tenotomy or recession of the fibrosed
inferior rectus gets rid of ptosis also. This is because the ptosis may be a false one
(pseudoptosis due to hypotropia). In this case ptosis surgery will not be required.
- In most cases however, ptosis correction is required
after strabismus surgery is completed.
- Each and every muscle should be given individual
attention in these cases and assessed as to the degree of fibrosis and the function
(underaction and overaction).
- The type of surgery and the amount of recession and
resection to be done should be decided carefully after giving due attention to details
- Presence of binocular functions like fusion and its
- The angle of deviation in primary position and in
various directions of gaze
- The ocular motility in cardinal directions of gaze
- The result of forced duction test and
- The condition of the conjunctiva, which has to be
taken into account. If it is contracted, as is the case when there has been a large
strabismus for a long time or since birth particularly in cases of congenital fibrosis.
For instance the nasal conjunctiva will be found contracted and non-elastic if there is
In such cases the conjunctiva has to be recessed after recessing or tonotomising the
fibrosed muscle. This is especially true of cases of congenital fibrosis of EOM.
Treatment of congenital fibrosis of extraocular
muscles is basically surgical in most cases. It is difficult but careful planning and its
execution often leads to a fairly successful result as regards the cosmetic result and
improving the compensatory head posture. The aims of surgery are as follows:
- Correction of the compensatory head posture (CHP) or
at least improving it.
- Removing obstacles to the visual axes in primary
position, e.g., by ptosis correction.
- Achieving binocular single vision in primary position
with no or negligible CHP.
To accomplish the above, one or more of the
following procedures may be required:
- Total (free) tenotomy: It is advocated
in cases of severe fibrosis when the eye is anchored in one position, e.g., in strabismus
fixus with esotropia a free tenotomy of the fibrosed medial rectus is advocated16,
17, 18, 19. After the tenotomy the eye may be anchored temporarily in abduction to
keep it from going back to the adducted position. Particular indication of free tenotomy
is Strabismus Fixus.
- Recessions of the affected muscles, e.
g., of the tight and fibrosed inferior rectus, medial rectus or any other muscle: The
fibrosed muscles are non-elastic and tight. However, the degree of fibrosis may vary so
much that mild cases of congenital fibrosis may be missed.
The amount of recession mainly depends upon the angle of deviation in
primary position, the severity of fibrosis and tightness of the affected muscle as
determined by various tests particularly forced duction test.
The recession can be either (a) Conventional or (b) The hang-back type,
in which the muscle is allowed to hang back by the planned amount in mm and the sutures
are placed at the site of the original insertion.
- Recession of the conjunctiva covering the
fibrosed muscle: It is not only a good idea but it is quite important to recess
the conjunctiva after recessing or tenotomising the fibrosed tight muscles otherwise the
desired result will not be achieved (see case report 41-2). Usual amount of recession is 4
mm. The sclera in this area is left bare.
|Case report 41-1 (see figure 41-2)
An adult male patient came to us with severe vertical strabismus fixus of left eye.
The cornea was not visible in the palpebral aperture. The eye was anchored in extreme
depression and mid-abduction. He was in his thirties and had not been able to get married
because of the weird look produced by the condition.
There was severe amblyopia in left eye as expected and complete absence of binocular
Total tenotomy of the short and fibrotic inferior rectus was done, which resulted in good
He was thrilled by the result. On discharge from the hospital on the 8th day of
surgery he was asked to report after 6 weeks as per our routine but he never turned up
|Case report 41-2 (see
figure 41-1) An adult male patient came with a bilateral severe strabismus fixus
convergens. He was keen on improving his appearance. Bilateral free tenotomy of medial
recti muscles was done. The conjunctiva was sutured in the usual way. To our surprise the
eye went back to convergent position. The conjunctival suturing was undone and the
conjunctiva was recessed by 4 mm. This resulted in the improved appearance that had been
achieved before conjunctival suturing.
His appearance improved considerably but a moderate esotropia was still there. He however,
was satisfied and did not want to have any more surgery. The second stage surgery was to
be lateral rectus resection in the more convergent eye.
Remark: He did not have fusion therefore there was no postoperative diplopia and no reason
to insist on further surgery to achieve orthotropia in primary position.
- Resection of the direct antagonist of the affected
muscle along with recession/free tenotomy of the affected muscle has to be done in
many cases. Many surgeons do it at the same sitting but I prefer to do it as a second
stage procedure. This is because the result of the recession/free tenotomy can not be
predicted with any certainty and one can plan the amount of resection of the antagonist
better after assessing the result of the previous surgery.
- Ptosis correction should only be done
if it is severe and then one aims at under-correcting it because of the risk of exposure
keratitis. The latter has to be kept in mind while correcting ptosis. An undercorrection
is preferable, just sufficient to expose the pupil. Any of the frontalis suspension
methods can be used. The material for the frontalis sling can be according to the
surgeons choice, fascia lata being the most popular at present. However, I used
retinal silicone bands in two patients years ago and the results were good.
Use of lubricants is advised in the postoperative period even if the exposure
is not much. In bad cases the lids should be taped at night.
Some important points concerning surgical
management and postoperative care are given below:
- Forced duction test is a good indicator of the
severity of fibrosis and should be performed preoperatively, intraoperatively and
- During surgery if the muscle is found to be
particularly stiff two hooks can be used to facilitate the placing of the sutures.
- Thorough dissection of the muscle fascia,
tenons membrane and intermuscular septum is a must otherwise even well planned
surgery can fail. This is because the fascia is often not normal in these cases. It may be
short and non-elastic and may pull the recessed muscle with it to an undesirable position.
Even the tenotomized muscle may go on having an attachment that acts as its insertion.
- It is possible to find anomalous insertions in these
cases, particularly in the case of SR and SO26. The muscle must be disinserted
from all its insertions for the operation to be effective.
- If more than two recti have been operated upon one
should look for signs of anterior segment ischemia in the postoperative period.
- Postoperative orthoptic exercises are a must in all
strabismus cases, particularly in CFEOM. Ocular movements should be exercised on a regular
basis for several weeks.
- Regular follow-up for at least a year is important.
- Patient must be made to understand the importance of
always protecting the cornea in cases of exposure after ptosis surgery.
- Overcorrection of ptosis can cause severe exposure
keratitis. Lubricants must be used in such cases. Taping of the lids done at night helps.
- Even without overcorrection of ptosis there may be
incomplete closing of the lids leading to exposure keratitis. Absence of Bells
phenomenon plays an important role. Night exposure is particularly to be prevented as
- Anterior segment ischemia may occur if more than two
rectus muscles are operated upon.
- Operation may fail if all the insertions are not
included in the procedures.
- Failure to severe old fascial attachments and
intermuscular septa may also lead to an unsatisfactory result.
- Free tenotomy of medial recti may result in
- Too much resection of the antagonist may exacerbate
the often-present look of slight enophthalmos in some cases.
- Brown, H.W.: Congenital structural muscle anomalies.
In Allen, J.H., editor: Symposium on Strabismus: Transactions of the New Orleans Academy
of Ophthalmology, St. Louis, C.V. Mosby Company, 1950, p. 205.
- Harley, R.D. et al: Congenital fibrosis of
extraocular muscles, J. Pediatr. Ophthalmol. Strabismus 15:346, 1978.
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Management: Principles and Surgical Techniques. Editors: Rosenbaum, A.L. and Santiago,
A.P., chapter 27, 1998, Philadelphia, PA, W.B. Saunders Company, p. 363.
- Noorden, G.K. von: Congenital hereditary ptosis with
inferior rectus fibrosis, Arch. Ophthalmol. 83:378, 1970.
- Engle, E.C. et al: Mapping a gene of congenital
fibrosis of the extraocular muscles to the centrogenic region of the chromosome 12, Nat.
Genet. 7:69, 1994.
- Engle, E.C. et al: Congenital fibrosis of the
extraocular muscles (autosomal dominant congenital external ophthalmoplegia): Genetic
homogeneity, linkage refinement and physical mapping on chromosome 12, Am. J. Hum. Genet.
- Engle, E.C. et al: Oculomotor nerve and muscle
abnormalities in congenital fibrosis of the extraocular muscles, Ann. Neurol. 41:314,
- Brodsky, M.C. et al: Neural misdirection in
congenital ocular fibrosis syndrome: Implications and pathogenesis, J. Pediatr.
Ophthalmol. Strabismus 26:159, 1989.
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extraocular muscles, Am. J. Ophthalmol. 41:432, 1956.
- Jaafar, M.S. and Traboulsi, E.I.: Same as in ref. No.
3, P. 364.
- Traboulsi, E.L. et al: Congenital fibrosis of the
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management, Am. Orthopt. J. 43:45, 1993.
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blepharoptosis and enophthalmos syndrome, Ophthalmology 99:347, 1992.
- Fells, P. et al: Progressive exaggerated A-Pattern
strabismus with presumed fibrosis of the extraocular muscles. In Reinecke, R.D., editor,
Strabismus II, Proceedings of the Fourth meeting of the International Strabismological
Association, Asilomar, CA, 1982. Publisher: Grune & Stratton, 1984, Orlando, FL.,
- Jaafar, M.S. and Traboulsi, E.I.: Clinical Strabismus
Management: Principles and Surgical Techniques. Editors: Rosenbaum, A.L. and Santiago,
A.P., chapter 27, 1998, Philadelphia, PA, W.B. Saunders Company, p. 368 (fig. 27-5).
- Hupp, S.L. et al: Computerized tomography in the
diagnosis of general fibrosis syndrome, J. Clin. Neuroophthalmol. 19:135, 1990.
- Apt, L. and Axelrod, R.L.: Generalized fibrosis of
the extraocular muscles, Am J. Ophthalmol. 85: 822, 1978.
- Crawford, J.S.: Congenital fibrosis syndrome, Can. J.
Ophthalmol. 5:331, 1970.
- Letson, R.D.: Surgical management of the congenital
ocular fibrosis syndrome, Am. Orthopt. J. 30:97, 1980.
- Traboulsi, E.I. et al: Congenital fibrosis of the
extraocular muscles: Report of 24 cases illustrating clinical spectrum and surgical
management, Am. Orthopt. J. 43:45, 1993.
- Noorden, G.K. von: Binocular Vision and Ocular
motility- Theory and Management of Strabismus, 5th edition, St. Louis, 1996, Mosby-Year
Book, p. 443.
- Martinez, L.: A case of fixed strabismus, Am. J.
Ophthalmol. 31:80, 1948.
- Villsecca, A.: Strabismus fixus, Am. J. Ophthalmol.
- Sharma, P. et al: Strabismus fixus convergens
secondary to amyloidosis, J. Pediatr. Ophthalmol. Strabismus 28:236, 1991.
- Prakash, P. et al: Myopic strabismus fixus
convergens, Indian J. Ophthalmol. 37:24, 1989.
- Mansour, A.M. et al: Ocular complications in
strabismus fixus convergens, Ophthalmologica 195:161, 1987.
- Jaafar, M.S. and Traboulsi, E.I.: Clinical Strabismus
Management: Principles and Surgical Techniques, editors: Rosenbaum, A.L. and Santiago,
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