Squint refers to misalignment of the eyes. It is is also known as strabismus. When the eyes are not aligned, the images on the retina do not match and the person will experience double vision.
When this occurs in childhood, before the eyes have fully established their connections with the brain, the brain will cope with this misalignment by reducing the signal from the less dominant eye. This results in one eye they use to see (the dominant eye) and one eye they ignore (the “lazy eye”). If this is not treated, this “lazy eye” becomes progressively more disconnected from the brain and over time the problem becomes worse. This is called amblyopia.
Concomitant squints are due to differences in the control of the extra ocular muscles. The severity of the squint can vary.
Paralytic squints are rare. They are due to paralysis in one or more of the extra ocular muscles.
- Strabismus: the eyes are misaligned
- Amblyopia: the affected eye becomes passive and has reduced function compared to the other dominant eye
- Esotropia: inward positioned squint (affected eye towards the nose)
- Exotropia: outward positioned squint (affected eye towards the ear)
- Hypertropia: upward moving affected eye
- Hypotropia: downward moving affected eye
Cases of squint in otherwise healthy children are usually idiopathic, meaning there is not a specific underlying cause. Other causes of squint include:
- Cerebral palsy
- Space occupying lesions, for example retinoblastoma
- General inspection
- Eye movements
- Fundoscopy (or red reflex) to rule out retinoblastoma, cataracts and other retinal pathology
- Visual acuity
Hirschberg’s test: shine a pen-torch at the patient from 1 meter away. When they look at it, observe the reflection of the light source on their cornea. The reflection should be central and symmetrical. Deviation from the centre will indicate a squint. Make a note of the affected eye and the direction the eye deviates.
Cover test: cover one eye and ask the patient to focus on an object in front of them. Move the cover across to the opposite eye and watch the movement of the previously covered eye. If this eye moves inwards, it had drifted outwards when covered (exotropia) and if it moves outwards it means it had drifted inwards when covered (esotropia).
Up until the age of 8 years the visual fields are still developing, therefore treatment needs to start before 8 years. The earlier the better. Delayed treatment increases the risk of the squint becoming permanent.
An occlusive patch can be used to cover the good eye and force the weaker eye to develop. An alternative to the patch may involve using atropine drops in the good eye, causing vision in that eye to be blurred.
Management is coordinated by an ophthalmologist. It will be important to treat any underlying pathology, such as cataracts. Refractive errors can be corrected with corrective lenses.
Last updated January 2020