Amblyopia
Amblyopia is a condition where an eye with otherwise normal structure has poor vision. Amblyopia is the leading cause of vision loss amongst children. It occurs when vision develops abnormally in a child’s eye in infancy or early childhood. It usually occurs in one eye, but can occur in both.
When children are born, their vision is not fully developed. The brain needs to learn how to interpret the images that are relayed to it. In order for this to occur, certain conditions need to exist. For example, the eyes need to be correctly aligned and any refractive error that may exist needs to be corrected. Some opacities can also sometimes cause amblyopia, such as droopy eyelids or other pathology. Vision develops in children in approximately the first 7-8 years of life but sometimes it can continue to develop until a child is a little older. The best prognosis is achieved by starting treatment when a child is as young as possible.
Treatment for amblyopia can involve prescribing glasses to correct any refractive error and occlusion therapy (patching) to ‘force’ the eye with poor vision to be utilised. This is so that the visual pathways between the eye and the brain can develop. Sometimes glasses and patching are both used simultaneously, or sometimes the treatment options are used individually, depending on the individual patient's needs.
Occlusion Treatment / Patching:
When a child is diagnosed with amblyopia in one eye, occlusion therapy is usually advised. When patching an eye, we may recommend that you use something similar to a felt patch, which can be placed over one lens of the child’s glasses by slipping it along the arm of the glasses. Other forms of patching may include placing clear contact over one lens of the child’s glasses, or using skin-coloured, stick-on patches for the eye which can be purchased from your local pharmacy.
If occlusion therapy is recommended for your child, you will be advised to patch the good eye for a certain number of hours per day and to return to the clinic in a particular number of weeks to reassess your child’s visual acuity at that point. Whilst your child is wearing their patch, their vision may be restricted, especially at the beginning of intervention, so they should be monitored. It is best if your child spends time doing tasks that help promote visual development whilst wearing their patch such as reading, writing, or drawing.
When a child is receiving occlusion treatment, it is very important that their vision (visual acuity) is monitored closely and regularly. This is to ensure that the vision in the poor eye continues to develop and that the vision in the good eye does not regress.
The most reliable means of testing a child’s vision is to assess what they are able to read on a vision chart (if they can read alphabet letters). For some children who are not able to recognise or match letters of the alphabet or numbers, we use pictures to assess their visual acuity. When a child is still learning to recognise pictures, we may give you a copy of some pictures to take home. This is so that you can practise recognising the pictures with your child at home, as knowing the names of the pictures will help us assess your child’s vision more accurately at the following visit.
Refractive error
Refractive error is the term used to describe an eye not correctly focussing the rays of light entering the eye and landing on the retina, which results in the patient seeing a blurred image. Refractive errors include long-sightedness (hypermetropia), short-sightedness (myopia) and astigmatism.
Hypermetropia
(Long-sightedness)
Hypermetropia (also called hyperopia) is the name given to a refractive error in which the focal point of light rays from a distant object come to a focal point behind the retina. This is usually a result of the eye being shorter than average in length. Convex (plus) lenses are prescribed to correct hypermetropia.
Myopia
(Short-sightedness)
Myopia is the name given to a refractive error in which the focal point of light rays from a distant object come to a focus in front of the retina. This is usually a result of an eye being longer than average in length. Concave (minus) lenses are prescribed to correct myopia. The onset of myopia usually occurs in childhood and gradually progresses until early adulthood.
Atropine (Low dose)
One treatment option for paediatric patients that are diagnosed with myopia, other than wearing spectacles or contact lenses, is to regularly instil Atropine drops to control the progression of their myopia. This treatment regime is usually considered when children are diagnosed with myopia between the ages of 4 and 12 and can usually be utilised for up to 3 years. Myopia can progress rapidly in children hence controlling progression where possible at this age is very important. Increasing daylight outdoor activity and reducing excessive near-vision tasks are important measures needed to reduce the rate of progression of myopia in children.
Astigmatism
Astigmatism occurs when the cornea is shaped asymmetrically, more like a football than a soccer ball, and hence the light rays do not enter the eye evenly, causing the patient to see a blurred image.
Strabismus/ turned eyes
There are many of different types of strabismus (also sometimes referred to as a squint). Strabismus can be broadly classified into 3 categories; these are esotropia, exotropia and hypertropia/hypotropia.
Esotropia is also known as convergent strabismus. It occurs when one eye turns inwards towards the nose and is the most common type. It commonly has onset in infancy or early childhood and may be associated with long sightedness.
Exotropia is also known as divergent strabismus. It occurs when one eye turns outwards away from the nose. Up to 10% of the normal population may have a small divergence.
Hyper/Hypotropia occurs when one eye turns to be higher or lower than the other eye.
It is important to exclude a neurological cause for a turned eye and also for associated amblyopia (“lazy eye”).