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CONGENITAL ESOTROPIA
Definition
The term congenital esotropia is a confusing one. Few children
who are eventually diagnosed with this disorder are actually born
with an esotropia. Parents often give a history of their child's
eyes crossing since birth. However, upon further questioning they
rarely remember seeing the deviation in the newborn nursery and
will often deny seeing it during the first few months of life.
Ophthalmologists have also rarely found infants with esodeviations
to have been born with the condition. In a prospective study of
3324 infants, only three children developed findings characteristic
of congenital esotropia. All of these children were either orthotropic
or exotropic at birth. Most reports in the literature have therefore
considered infants with confirmed onset earlier than 6 months
as having the same condition, which some observers have redesignated
"infantile" or congenital-infantile esotropia. The differentiation
between these terms may be important. A child born with a "later
onset" congenital esotropia may have a better prognosis for
the development of binocular vision than a child with a true "congenital"
deviation as he/she would have had an early period of ocular alignment
which could provide a stimulus for the early formation of binocular
development.
Epidemiology
Congenital esotropia represents the most common form of strabismus,
with an incidence of 1 to 2 per cent, in most series. The sex
distribution of congenital esotropia is equal. Transmission in
many families seems to be as an irregular autosomal dominant trait;
in others it may be recessive. Waardenburg reported concordance
in monozygous twins to be 81 per cent, compared with 9 per cent
in dizygous twins. Others have found different results, and the
reported incidence of affected family members has varied widely.
It is common to find a history of strabismus in the parents or
siblings of affected patients. Reduced binocular function has
been reported in parents of patients with congenital esotropia
and may represent a subthreshold effect of the "gene(s)"
that cause this disorder. The incidence of congenital esotropia
is higher in patients with cerebral palsy, hydrocephalus and other
neurologic disorders. Maternal cigarette smoking and low birth
rate have also been linked to the development of esotropia.
Pathogenesis
Much clinical literature in this century has focused on the implications of two conflicting theories of pathogenesis for congenital esotropia. Worth's "sensory" concept was that congenital esotropia resulted from a deficit in a purported fusion center in the brain. According to his theory, the goal of restoring binocularity was considered hopeless, since therewas no way to provide this congenitally absent neural function. Until the 1960s, results of surgical treatment almost universally supported this pessimistic. Burke reported that not one of his 34 patients achieved binocularity. Data on these patients was obtained at a time when surgery was rarely performed before 2 years of age.
Chavasse disagreed with Worth's theory. He suggested that
normal binocular vision may be achieved through facilitation of
conditioned reflexes that depend on early ocular alignment. To
Chavasse, the primary problem was mechanical. In this view, most
congenital esotropes were potentially curable if the deviation
could be fully eliminated in infancy. Only theoretical support
was available for this "motor" theory, until Costenbader,
Taylor, and Ing, Costenbader and Parks began to report favorable
binocular results in some infants operated on between 6 months
and 2 years of age. These encouraging results became the basis
for the theory of early surgery for patients with congenital esotropia.
Even advocates of early surgery have generally found imperfect
binocularity in their postoperative patients. Von Noorden summarized
the sensory results obtained by most investigators using various
tests of binocularity by cautioning that "subnormal binocular
vision must be considered an optimal result." Parks defined
the monofixation syndrome, in which "peripheral" fusion
and vergence amplitudes capable of maintaining alignment within
approximately 10 prism diopters may exist, despite deficient stereopsis
and a central suppression scotoma in one eye during binocular
viewing. Many strabismus surgeons accept this sensory state as
the goal of treatment (see Treatment below). In one extensive
and well-controlled study, Ing used the Worth 4 Dot system and
a gross test of stereopsis to compare the binocularity of 106
patients successfully aligned at various stages in infancy. His
results, indicated that alignment earlier than age 2 years was
associated with fusion or stereopsis in 93 per cent, as opposed
to 31 per cent after age 2.
Research in experimental animals by Hubel, Weisel, von Noorden
and Tychsen and Burkhalter among others, demonstrated that the
structural and functional integrity of binocular cells in the
lateral geniculate nucleus and visual cortex require early binocular
experience. Also, Crawford and co-workers showed that only a brief
period of binocular dissociation in infant monkeys can cause a
permanent loss of stereopsis, in spite of subsequent prolonged
periods of normal binocular visual input.
The pathogenesis of congenital esotropia remains unanswered.
Clinical Manifestations
Visual Acuity
The association of amblyopia and congenital esotropia is well
known. Amblyopia may occur in a higher precentage of patients
with congenital esotropia than was once thought. It is difficult
to ascertain the exact incidece, however, especially in preverbal
children. The incidence of amblyopia may be as high as 40-72%.
Size of Deviation
The characteristic angle of congenital esodeviations is considerably
larger than those acquired later in life.
Refractive Errors
Children with congenital esotropia tend to have cycloplegic refractions
similar to those of normal children of the same age.
Ocular Rotations
Children with congenital esotropia will often appear to exhibit
an apparent abduction deficit. This pseudoparesis is usually secondary
to the presence of cross-fixation. If the child has equal vision,
they will have no need to abduct either eye. They will use the
adducted, or crossed, eye to look to the opposite field of gaze.
In this case they will show a bilateral pseudoparesis of abduction.
If amblyopia is present, only the better seeing eye will cross
fixate, making the amblyopic eye appear to have an abduction weakness.
Associated Findings
Dissociated Vertical Deviation (DVD) This consists of a slow upward deviation of one or alternate eyes. Occasionally, excyclotorsion can be demonstrated on upward drifting of the eye and incyclotorsion on downward motion. DVD may be latent, detected only when the involved eye is covered , or manifest, occurring intermittently or constantly. It can be differentiated from a true vertical deviation, because no corresponding hypotropia occurs in the other eye on cover testing. Bielschowsky's phenomenon is another feature of DVD, characterized by downward movement of the occluded eye when filters of increasing density are placed before the fixing eye.
The incidence of DVD in patients with congenital esotropia
is high, ranging from 46 to 90 per cent. Hiles and co-workers
found DVD in 76 per cent of their congenital esotropes, with onset
greatest during the second year of life. After the third year,
this occurred at a mean rate of 10 per cent per year.
Inferior Oblique Overaction
(IOOA) The incidence of overaction of one or both inferior
oblique muscles in patients with congenital esotropia has been
reported to be as high as 78 per cent. Hiles and co-workers noted
the onset of inferior oblique overaction to be most frequent during
the second year of life, with a mean rate of 33 per cent per year;
the greatest occurrence was during the third and seventh years.
Wilson and Parks found
an incidence of IOOA of 72% in patients with a history of congenital
esotropia. The average age of onset in their study was 3.6 years.
There was no correlation between the development of IOOA and age
at surgery, time from onset of strabismus to surgery or decompensation
of ocular alignment. There was a correlation with the total number
of horizontal surgeries performed in these children.
Differential Diagnosis
During the first year of life, a number of conditions can
simulate congenital esotropia and cause diagnostic difficulty.
Because the management of these conditions may differ from the
treatment of congenital esotropia, their clinical recognition
is important. In general, a relatively small angle deviation should
raise doubt in assigning the diagnosis of congenital esotropia.
Many of these other disorders can be ruled out following a thorough
ophthalmologic evaluation. For this reason, all infants presenting
with esotropia require a full evaluation, including a dilated
funduscopic examination.
Treatment
Goals and Timing of Treatment The primary goal of treatment in congenital esotropia is to reduce the deviation at distance and near to orthotropia, or as close to it as possible. Ideally, this results in normal sight in each eye, in straight-looking eyes, and in development of at least a rudimentary form of sensory fusion that will maintain motor alignment. One measurement of long term success in these patients can be made by the evaluating the number of surgeries required to maintain cosmetically acceptable alignment.
Classically, it has been taught that patients with congenital
esotropia never become bifixators (i.e., do not develop stereoscopic
acuity of 40 seconds of arc), regardless of their age at surgical
alignment. Clinical evidence suggests, however, that alignment
within 10 prism diopters of orthotropia before 2 years of age
is associated with the attainment of some degree of binocular
vision and stereopsis. Recently there have been reports of patients
obtaining bifoveal fixation when operated upon at a very young
age. These reports are the basis for the theory of very early
surgery in congenital esotropia. Conversely, although the chance
of developing binocular vision decreases with the patient's age
at the time of surgical alignment, even older patients can develop
some degree of binocularity later in life once their eyes are
aligned. Morris and co-workers found that 12 adult patients with
a history of congenital esotropia, that had never been treated,
achieved peripheral fusion after surgical alignment to within
8 pd of orthotropia. Eight of these patients also developed stereopsis.
The most often found sensory result in patients successfully aligned before 2 years of age is the monofixation syndrome, as described by Parks. The purported benefit derived from the monofixation syndrome, in which the horizontal deviation is less than 10 prism diopters, is the development of peripheral normal retinal correspondence and fusional vergence amplitudes. Parks claimed that these attributes are instrumental in maintaining motor alignment in such patients for the remainder of their lives. Arthur and co-workers proved this to be true. In their study, eighty patients who had been treated for congenital esotropia were divided into two groups; those that had obtained monofixation syndrome and those that had not. Over 17.5 years, 74% of patients in the monofixation group had maintained alignment. Over 14 years, only 45% of patients without monofixation had achieved the same outcome.
Parents of children with congenital esotropia often report
improvements in their child's fine motor development and visual
function after surgery. Rogers and co-workers showed that early
alignment is associated with improved fine motor skills and other
visually directed tasks. Further studies with control groups are
necessary to confirm parental observations. The improved appearance
of the child can enhance his or her psychological acceptance by
the parents. This can be instrumental in the normal development
of the parent-child relationship.
Surgical Treatment
Various surgical techniques have been used for the correction
of congenital esotropia. Proponents of two-muscle surgery advocate
either symmetric recession of both medial rectus muscles, or monocular
medial rectus recession combined with lateral rectus resection,
regardless of the size of the preoperative deviation. Both procedures
are graded, with more millimeters of surgery performed for larger
angles. If a second procedure is required, symmetric resections
of both lateral rectus muscles or a recess-resect procedure in
the fellow eye are performed.
Post operative Management
Accommodative Esotropia Following Congenital Esotropia Accommodative esotropia may be present in children who were surgically corrected for congenital esotropia. Hiles and colleagues reported that 65 per cent of corrected congenital esotropes required spectacle correction of hypermetropia to control esotropia at some time postoperatively.
Freely and associates found that 28 per cent of 83 patients
with congenital esotropia who had been successfully aligned by
18 months of age subsequently redeveloped esotropia. In 78 per
cent of these patients the esotropia was corrected with a hyperopic
correction. In some patients this correction was as little as
+1.50 diopters. Therefore, they advised correcting hyperopia in
excess of +1.50 diopters with spectacles before considering further
surgery. These patients may be prone to the development of an
accommodative esotropia secondary to their underlying poor binocular
function.
Amblyopia The possibility of amblyopia occurring postoperatively must always be considered. Ing found a 41 per cent incidence of postoperative amblyopia in his group of 106 patients. Fixation preference testing should be performed at each postoperative visit until the visual acuity can be measured. Unfortunately, it is more difficult to recognize a fixation preference, the closer the eyes are to orthotropia.
Once recognized, amblyopia should be treated promptly with
occlusion therapy. Some patients may require maintenance occlusion
(approximately 1 to 2 hours daily) until visual maturity is reached,
and susceptibility to amblyopia is eliminated as the sensitive
period of visual development ends at age 9 years.
