Flashcards in Strabismus: Childhood Deck (21)
What is strabismus?
Also known as a squint, it refers to the misalignment of the two eyes.
What is the 'sensitive' period of visual development, and why is this significant?
Up to 7-8 years of age. If strabismus develops during this time, the brain responds by refusing to see the image from the deviating eye (visual cortex).
This prevents double vision but leads to a condition known as amblyopia - lazy eye.
Onset of strabismus after the sensitive period will usually result in what?
The deviating eye may drift in any direction, though certain patter,s (particularly horizontal) are more common.
Strabismus may be constant or intermittent.
What is a latent deviation vs a manifest deviation, and what are their respective suffixes?
Latent deviation is controlled by subconscious effort: in certain situations, such as fatigue, control is lost and the deviation becomes 'manifest'.
What are concomitant and incomitant squints?
Concomitant = when the angle of the squint is the same in all directions.
Incomitant = not the same in all directions.
When the eyes are convergent, the deviation of squint is (1)?
When the eyes are divergent, the deviation of squint is (2)?
What are the prefixes for vertical deviation (3)?
3. Hypo- or hyper-
Eso-, exo-, hypo- and hyper- deviations may be manifest (-tropia) or latent (-phoria). Torsion (twisting of the eye) occurs rarely.
Childhood squints are usually what (when considering angle of squint and position of the eyed looking straight ahead)?
Usually concomitant, and eso- deviations predominate over exo- .
What is amblyopia characterised by?
Reduced visual acuity (despite full correction of any refractive error) in the absence of any other organic explanation for reduced vision. Amblyopia is usually unilateral.
The diagnosis is one of exclusion: an explanation for visual loss should always be sought.
What are the causes of amblyopia?
1. Most commonly due to squint.
2. Refractive error, particular if asymmetrical (anisometropia) is a common cause, and amblyopia will follow even reversible visual deprivation (eg. cataract) during the sensitive period.
What does binocular vision enable?
More than simply seeing equally well with each eye, binocular vision at its highest level enables stereopsis: an advanced form of 3D sight.
Incomitant deviations are often compensated for by the involuntary adoption of what?
Abnormal head posture.
In this position, the angle of deviation is least and binocular vision may be achieved.
History of strabismus should consider which three things?
1. Age of onset
2. Causative factors (maternal infection, birth trauma, illness, family hx)
3. Neurological disease ( incl. raised ICP) should be considered.
Presence of strabismus is confirmed by which test?
The angle of deviation is measured by cover test and prisms. Examination of eyes in different positions of gaze helps to demonstrate abnormalities of ocular movement. Refraction, usually under cycloplegia (paralysis of accommodation) is essential.
All children presenting with a squint should undergo a retinal examination with the pupils dilated.
4 principles of strabismus management?
1. Correct any refractive error (usually with full-time glasses).
2. Reverse the amblyopia (part-time occlusion of the better eye).
3. Orthoptic management (orthoptists doing stuff).
4. Surgery (only for satisfactory cosmesis; altering the pull of extraocular muscles cannot improve vision or reverse amblyopia. Relief of an abnormal head posture is the next most common reason).
What are the two types of surgical procedures for strabismus?
Most operations are weakening procedures (recession), which turn the eye away from the muscle, or strengthening procedures (resection) which pull the eye towards the muscle.
What are the 4 causes of childhood squint?
2. Refractive error
3. Visual loss
4. Central or peripheral neurological deficit
What are the 3 main consequences of childhood strabismus?
2. Lack of normal binocular vision
3. Poor cosmesis
What are the three types of convergent squint?
1. Early-onset (non-refractive)
2. Later-onset (usually with hypermetropia)
3. Rarely, sixth nerve palsy and Duane's syndrome (failure of adduction - occasionally of abduction - with retraction of the globe).
What are three causes of divergent strabismus?
3. Secondary to visual loss
True or false: many of the 'adult' causes of strabismus, such as myaesthenia gravis, orbital fracture, myopathy and nerve palsy, may also occur in children.