Strabismus |
CONGENITAL strabismus syndromes— such as congenital esotropia, congenital exotropia, congenital nerve palsies, Duane syndrome and Brown syndrome— will be evident in the first year of life. Variable, intermittent strabismus is very common in newborns up until the age of 16 weeks. Thereafter, any form of strabismus is not normal and should be assessed by an ophthalmologist. |
Esotropia. |
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Congenital esotropia Congenital esotropia is a constant, large-angle convergent strabismus, which starts before six months of age. Children with this condition will often‘ crossfixate’. They will use their convergent right eye to look at objects on their left and their convergent left eye to look at objects on their right. This alternation of fixation between their right and left eyes may protect them from developing amblyopia.
Treatment is primarily surgical and usually involves recessing each medial rectus muscle posterior to its original insertion( to weaken its action) between the ages of 12 and 24 months. Because of the large angle, up to 30 % of children require a second operation to fully correct the strabismus. Occasionally, spectacles and part-time occlusion therapy are also used.
Pseudo-esotropia This is a common differential diagnosis of a true esotropia in early childhood. In pseudo-esotropia, the ocular alignment is intact, but the shape of the face and eyelids gives the appearance of an esotropia. This is common in young children because, compared with older children, they have flatter nasal bridges and wider epicanthic folds, giving the impression of a convergent squint.
The proof is in a cover test—
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VARIABLE, INTERMITTENT STRABISMUS IS VERY COMMON IN NEWBORNS UP UNTIL THE AGE OF 16 WEEKS. |
a truly deviated eye will move to take up fixation; in contrast, it will stay steady in a pseudo-esotropia. A positive stereopsis test result( which measures depth perception) proves good ocular alignment.
Cover and stereopsis tests are difficult to perform in young children, and given the potential for a poor outcome if a true strabismus is dismissed or missed, it is always appropriate to refer these children for a complete ophthalmic assessment. Given the incidence of a true esotropia is higher in children previously diagnosed with a pseudo-esotropia, it is my practice to examine these children on two separate occasions, unless I can prove they have stereopsis.
Congenital exotropia This is an uncommon condition. It is a large angle, constant divergent squint, which starts before six months of age. It is generally associated with ocular and systemic conditions including prematurity, cerebral palsy, seizure disorders and chromosomal anomalies.
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Congenital nerve palsy The most common congenital nerve palsy affects the trochlear( fourth) nerve. This nerve supplies |
the superior oblique muscle, which is responsible for elevating the eye when it is in the adducted position. A palsy of this nerve causes the affected eye to become hypertropic, especially when it is the adducted position, and also causes the eye to excyclotort( where the‘ 12 o’ clock position’ of the eye rotates towards the temple).
In order to avoid double vision and to continue using both eyes together, children with this condition may develop a head tilt or head turn away from the affected side. This will become apparent only after the child learns to sit up independently.
Duane syndrome Duane syndrome is a cranial misinervation syndrome in which the sixth cranial nerve fails to develop properly and cannot innervate the lateral rectus muscle. It instead receives an anomalous branch of the third cranial nerve. The affected eye cannot move fully in all directions and some movements will cause the globe to retract and a ptosis to be induced. Strangely, the left eye is affected much more frequently than the right.
Surgery is occasionally useful if the condition is associated with
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a strabismus in the primary position, a significantly altered head posture, or if the globe retraction is troublesome. In the absence of surgery, any associated refractive error and amblyopia is managed, and children will often develop compensatory head postures to give themselves better binocular function and to improve the cosmesis of their ocular alignment.
Brown’ s syndrome This may be congenital or acquired and is rare in the first year of life. It is caused by a mechanical restriction of the superior oblique muscle through the trochlea, a bony and tendinous pulley in the superonasal orbit. The eye cannot elevate in adduction.
Children will compensate for this by lifting their chin and turning their head away from the affected side. This will only become apparent when they have learned to sit up independently. Surgery is only occasionally performed for this condition.
Treatment is usually not required unless the onset is sudden( acquired). In those circumstances, oral NSAIDs and peritrochlear steroids can be trialled.
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Retinoblastoma |
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WHILE rare, retinoblastoma is the most common malignant ocular tumour of childhood, caused by a mutation in the RB1 gene( a tumour suppressor gene).
In familial / hereditary cases, the child is born with a mutation in one copy of the RB1 gene. A mutation in the second copy of the RB1 gene in an immature retina cell results in the development of a retinoblastoma. Because the second mutation is a relatively common event, the usual pattern is for multiple tumours to develop in both eyes.
Familial cases often present within the first year of life and tumours may even be present before birth.
Because children with a hereditary or germline RB1 mutation have the mutation in every cell of their body, they are at high risk of developing other tumours, such as sarcomas, breast cancer, lung cancer and lymphoma. For this reason, radiation in the form of CT scans or X-rays to any part of the body should be avoided in these patients. MRI and ultrasound are
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the preferred imaging modalities.
In non-hereditary cases, a single cell needs to undergo a mutation in both of its RB1 genes. Because this is a relatively rare event, non-hereditary cases tend to be unilateral and tend to present after the first year of life, but usually before the age of 3-5.
The most common presenting sign of retinoblastoma is leukocoria or photoleukocoria( a white pupil or asymmetry of the red reflex on flash photography or ophthalmoscopy)( see figure 6), followed by strabismus. Any sign suggestive of retinoblastoma should be referred urgently to an ophthalmologist.
Retinoblastoma is managed with a multidisciplinary approach and treatment may include enucleation, laser or cryotherapy to intraocular tumours, local and systemic chemotherapy. Genetic counselling, nursing support, social work and play therapy are essential components of the multidisciplinary approach. cont’ d next page
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Figure 6. Retinoblastoma. Source: Meilahti Hospital, Department of Ophthalmology bit. ly / 2qrXjdd |