Squint Flashcards
Define squint and its types
Misalignment of the visual axis so that the eyes are not directed at an object at the same time
While one eye is directed at an object, the other may turn:
- In (esotropia)
- Out (exotropia)
- Up (hypertropia)
- Down (hypotropia
Either concomitant (imbalance in extra-ocular muscles) or paralytic (paralysis of muscles)
What is pseudo squint
the impression of misaligned eyes when no squint is actually present. For example, prominent epicanthic folds may partially cover the nasal sclera to give the appearance of a squint
What is the aetiology of squint
Lack of coordination that prevents the gaze of both eyes being focused on the same point in space
- Idiopathic
- Refractive errors in one or both eyes, especially hypermetropia (long-sightedness)
- Retinoblastoma
- Cataracts
- Ocular malformations
- Optic neuropathy
- Ambylopia (lazy eye)
- Neurodevelopmental e.g. CP, Down’s syndrome
- Congenital abnormalities of the extra-ocular muscles e.g. Brown’s syndrome, Duane’s syndrome
What are the common types of childhood squint
Congenital/infantile: convergent
Accomodative esotropia: occurs when the child is tired or concentrating on close by objects (corrected by glasses)
Non-accomodative esotropia: Intermittent esotropia, typically when the child is tired or when concentrating on objects close by → constant (cannot be corrected by refractive glasses)
What are the risk factors for squint
LBW
Prematurity
Maternal smoking in pregnancy
Anisometropia (eyes have varying or unequal refractive power)
Hypermetropia (long-sightedness)
FHx squint
What are the symptoms and signs of squint
May be identified on newborn exam
+ screen at 6-8 weeks old
Eye appears to be turning - abnormal eye position
Ocular abnormalities
Pupil asymmetry
Ptosis
Impaired abduction (esotropia)
Nystagmus
Hirschberg test/corneal light reflection test
Cover test
What is the Hirschberg test/corneal light reflection test
Have the child fixate on a light (for example a pen torch) held about 50 cm in front of their eyes.
Observe the light that reflects back from their corneas, which is normally in the same place on both corneas.
Any asymmetry of the reflected light suggests a squint.
What is the cover test
Cover one eye with card while they focus on an object 30cm away
As the cover is introduced over one eye, watch the uncovered eye for any movement. Then repeat, covering the other eye.
Demonstrates concomitant squint
What is the management for squint
Refer for ophthal review
Options:
Corrective glasses: for refractory errors (may correct the squint)
Eye exercises: for intermittent squint
Surgery: alters point of insertion of the extra-ocular muscle into the sclera
Botulinum toxin: injection into an extraocular muscle → paralysis → correct squint
± ambylopia treatment
What are the red flag features for squint and what should be done if they are present
Limited abduction
Double vision
Headaches
Nystagmus (involuntary, repetitive, side-to-side oscillation of the eyes)
→ urgent referral to ophthalmologist
What are the complications of squint
Ambylopia (lazy eye)
Loss of, or failure to develop binocular vision → poor stereopsis (perception of depth)
Compensatory head postures e.g. face turn, head tilt, chin elevated/depressed
Poor eye contact
Social and psychological: teasing or bullying in school, isolated, low-self-esteem
Describe ambylopia (lazy eye)
Decrease in visual acuity caused by blurred vision, obstructed vision (cataracts), or by one eye being ignored in a child with a squint
The visual cortex suppresses the image from the squinting eye to prevent double vision → impaired development of the visual pathways and areas in the brain responsible for vision in that eye → reduced visual acuity
Must be treated by 7yo, otherwise it can lead to permanent visual loss
What is the treatment for ambylopia
Occlusion therapy: patch/occlusive glasses to encourage use of the amblyopic eye
Penalisation therapy: deliberate blurring of the normal eye’s vision using atropine drops, forcing them to use the amblyopic eye
What is the prognosis for squint
Untreated childhood squint present after 3 months of age does not resolve without treatment
Esotropias tend to deteriorate over time, with loss of binocular vision and amblyopia development
Timely and appropriate treatment confers a good outlook + prevents/reduces severity of ambylopia
What are the causes of paralytic squint
CN III palsy S/S: ptosis, fixed/dilated pupil, ‘down and out’
- Medical: DM, MS, infarction
- Surgical (↑ ICP): cavernous sinus thrombosis, PCA aneurysm
CN IV palsy S/S: diplopia going downstairs
- Peripheral: DM (30%), trauma (30%), compression
- Central: MS, SOL, vascular
CN VI palsy S/S: diplopia in horizontal plane; Mx: botulinum toxin
- Peripheral: DM (30%), trauma (30%), compression
- Central: MS, SOL, vascular
