About 2 per cent of children in the UK have a squint and 5 per cent have a lazy or amblyopic eye. Squint is commoner in children who have been born prematurely, have chromosomal disorders or cerebral palsy, have a family history of squint or who are very hyperopic.
A squint may occur within the first six months of life - early onset or infantile strabismus - or more usually at 18-36 months. Children may appear cross-eyed even though they have no squint if they have prominent epicanthic folds giving a pseudo-convergent appearance.
Observation of the light reflexes, which should be central, and a cover test can be performed to check for a squint. Vision testing can be difficult in young children but the observation that the child objects to covering of one eye more than the other suggests amblyopia.
Intermittently crossed eyes in very young babies are common and usually straighten, but any baby who still has a squint at 16 weeks should be referred as early surgery is often required. An older child with a squint should be referred to hospital for ophthalmic management.
Older children presenting with a squint will require hospital referral
A child presenting with a sudden-onset squint with diplopia requires urgent referral.
Initial assessment evaluates vision, presence of amblyopia, refractive error and excludes any structural cause for a squint. Children are managed by prescribing appropriate glasses, treating amblyopia with occlusion or atropine, and finally considering surgery to optimally align the eyes if they have not been straightened with glasses.
The outcome of amblyopia treatment depends on compliance with therapy but this is often difficult to achieve, particularly if the vision in the lazy eye is very poor and the child is understandably frightened by patching the good eye.
Trial results have shown that two hours of occlusion daily using an adhesive patch on the skin or felt patch on spectacles, with one hour a day involving detailed hand-eye coordination tasks is as effective in moderate amblyopia as six or more hours of occlusion. Atropine penalisation is as effective but takes longer to work than occlusion therapy.
The number of children in the UK requiring squint surgery has approximately halved in the past 20 years and it is thought that this is due to prescription of glasses where required.
Squint surgery is a day case procedure under general anaesthetic. It does not have a 100 per cent success rate and more than one procedure may be required. The aim is to get the eyes optimally aligned and if excellent alignment can be achieved a very small number of children can even achieve depth perception in addition to straight eyes.
Squint surgery is usually performed before a child starts school to avoid bullying and some parents report that their children's motor skills improve after surgery.
Good management of children with strabismus and amblyopia requires teamwork between hospital staff and parents who administer the patching or penalisation treatment and make the child wear glasses. Parents need support and encouragement to deal with the upset and stress of treatment but they are key to a good outcome.
Treatment gives children good vision allowing them more opportunities as a lazy eye debars them from certain occupations. It also gives them the safety of having a second seeing eye.
- Miss Adams is consultant ophthalmic surgeon at Moorfields Eye Hospital, London
Jack, a healthy two-and-a-half-year-old born 10 weeks prematurely, was referred because of a possible left wandering eye.
Jack was found to have subnormal right vision with extremely poor left vision and a left convergent squint. He had hyperopia, which was worse on the left side. It caused Jack to over-focus when viewing near objects and develop a convergent squint, with the more hyperopic eye becoming lazy.
The ophthalmologist found no corneal or lens opacities or fundal abnormalities (retinal scars, anomalous discs or retinal tumour) causing the squint. Jack was prescribed glasses full time.
Jack was not keen on wearing his glasses and kept peeping over the top of them. A check-up found the sight was worse in both eyes. Jack's ophthalmologist decided that the glasses were too strong for Jack to settle into easily and weaker spectacles were prescribed. In addition to glasses, patching the good eye for two hours a day was started with at least one hour of treatment taking place while colouring pictures or doing jigsaws.
At review, Jack's vision had improved but the squint was still noticeable and the glasses prescription was increased. The stronger glasses straightened his eyes so surgery was not needed.