Generally, occlusion or ‘patching’ therapy in children is used to improve poor vision in one eye (amblyopia).
If glasses are also required to be worn, occlusion therapy would usually begin once the child is successfully wearing them all the time.
To understand the use of occlusion therapy for retinoblastoma, it is important to first understand its use when the poorly seeing eye is otherwise healthy and not affected by retinoblastoma.
What Causes Amblyopia?
The most common causes of amblyopia are a turned eye (strabismus/squint) or a difference in the focussing ability between the eyes (anisometropia), and glasses do not improve the vision fully. In some children, amblyopia can be caused by a combination of both these problems.
Some children will have very mild amblyopia (a difference of only several lines on a vision chart). In others, it can be quite severe. This will depend on the cause of the amblyopia, how long that cause has been present, and the child’s age when the amblyopia is diagnosed. Early diagnosis and treatment offers greater potential to improve vision to as close to normal as possible.
A child’s vision is continually developing until about 7 or 8 years of age, so amblyopia is most successfully treated in children before this time. However, there are several reports of children responding to treatment beyond this age, so patching may be worth attempting in an older child.
In a very small number of children, a significant pathology inside the eye also contributes to their vision loss, as with retinoblastoma. While efforts can be made to achieve early diagnosis and prompt treatment, doctors cannot control where on the retina the tumours arise, nor collateral damage to healthy retinal cells in the process of trying to treat the disease. This includes all types of treatment.
Laser and cryotherapy will invariably damage some healthy retinal cells close to the tumour. Any chemotherapy – delivered intra-arterially, intravitreally or intravenously – will also be toxic to healthy cells, just as it is to the cancer cells.
What Is The Aim Of Occlusion Therapy?
Occlusion therapy aims to improve vision to the very best possible level. Ideally, this would be at least to the minimum level required to drive a car. Thus, should something happen to the child’s good seeing eye in the future, it wouldn’t prevent them from driving. Unfortunately, accidents do happen that can affect the good seeing eye, as do adult eye diseases such as macular degeneration.
In a child with retinoblastoma, either the tumours themselves or the treatment used to control them can have a significant impact on vision. Because this occurs when the child’s visual system is still developing, it can be difficult to know whether their vision could be any better. Often, your eye doctor will not know whether patching will lead to any improvement until it is tried.
When Should We Try Occlusion Therapy?
The decision will be made by you, together with your treating eye specialist (ophthalmologist). The most critical factor to consider is whether the part of the retina used for the sharpest vision – the fovea and macula – are clear of disease in your child’s worst-seeing eye.
If this area is significantly damaged, no amount of occlusion treatment will improve vision.
When the disease is very close to the fovea or macula, a trial of occlusion may determine whether it is worthwhile or not.
