Eyelid disorders
Congenital disorders of the eyelids
Congenital disorders of the eyelids
There are a number of congenital disorders (present at birth) of the eyelids that can cause keratitis (inflammation of the cornea) and scarring of the cornea due to abrasion of the cornea by the eyelashes. These include -:
- Epiblepharon, in which there is a horizontal fold of skin that pushes up the lashes.
- Distichiasis, in which an additional row of lashes grow from the eyelid margins.
- Entropion, in which the eyelid margin turns inwards.
- Ectropion, in which the eyelid margin turns outwards.
If these conditions cause significant problems surgical correction may be performed.
Ptosis
Ptosis (drooping of the eyelid) may be due to a number of causes but the most common is congenital ptosis, which is due to a weakness of the muscle that elevates the eyelid. It is usually unilateral but rarely may be bilateral, for example as part of the Ocular Fibrosis syndrome (where fibrous tissue replaces the usual, smooth tissue of the eye). Surgical treatment is the mainstay of treatment and is usually effective. It is important to check visual acuity prior to surgery in order to ensure that there is no amblyopia (lazy eye) that requires occlusion (eye patch) therapy.
Strabismus (squint)
Squint is a condition in which the eyes are not aligned correctly due to an imbalance in the muscles that move the eyes. It is common, affects up to 5% of children and accounts for many of the children dealt with by paediatric eye units. They usually appear in the first 3 years of life but can appear later.
Squints are classified according to the direction in which the eye turns -:
- Esotropia, in which the eye turns inwards.
- Exotropia, in which the eye turns outwards.
- Hypertropia, in which the eye turns upwards.
- Hypotropia, in which the eye turns downwards.
Esotropia and exotropia are more common than hypertropia and hypotropia.
Squints can either be constant (obvious at all times) or intermittent (apparent at certain times only).
In young children, a squint can result in amblyopia. Because the eyes are not aligned, the child may experience double vision. In order to prevent seeing double, the brain ignores the signals from the squinting eye (suppression) and only recognises signals from the normal eye. As the squinting eye is not being used the vision from that eye deteriorates and results in visual impairment. In older children, a squint may produce double vision but not amblyopia. This is because the brain has fully developed and it is not able to ignore signals from the squinting eye.
If it is identified that the vision in the squinting eye is poor, they may have to wear a patch over the normal eye (occlusion therapy) to encourage vision in the normal eye to develop.
Causes of squint
Squints can either be -:
- Congenital. Esotropia is more common than exotropia. Congenital Exotropia in the Caucasian population is uncommon and may signify significant pathology in the eye.
- Acquired -:
- Due to refractive error.
- Other causes (less common) include trauma, viral infections such as measles, genetic conditions like Noonan syndrome (causing a webbed neck, ptosis and short stature) and hydrocephalus (the abnormal expansion of ventricles within the brain).
Treatment of squint
A squint should be treated as early as possible in order to prevent the development or progression of amblyopia in the affected eye.
Several types of treatment are available for a squint -:
- Glasses if the child is long sighted. This may correct the squint as well as the refractive error.
- Occlusion therapy to stop development or progression of amblyopia in that eye
- Botulinum toxin injection into the muscles of the affected eye to temporarily weaken the affected muscle allowing the eyes to realign themselves. This is usually done under general anaesthetic in children.
- Eye exercises, especially for an intermittent squint.
- Surgery. If non surgical treatments are not effective, surgery is usually performed. Surgery should improve the alignment of the eyes and improve binocular vision. Surgery involves operating on the muscles of the eye to realign them. It is usually carried out as a day case under general anaesthetic. In the majority of cases surgery is highly effective. In some cases, however, binocular vision is not always fully restored. Further surgery is sometimes required if the squint is large or if it recurs.
