By Dr Robert Daniel, Allison Powell & Byron-Mahieu van der Linde
One in five children have underlying vision abnormalities that may lead to lazy eye, or Amblyopia. Of these, around 30% of the children will eventually develop Amblyopia: an incurable condition that is a major cause of blindness in children worldwide. With over a million children born in South Africa each year, more than 50,000 children will unnecessarily lose their vision in one or both eyes. Instrument based vision screening is one of the only ways to detect underlying risk factors for Amblyopia in children younger than three-years-old.
What is Amblyopia?
Amblyopia – commonly referred to as lazy eye – is a condition resulting from vision loss in children before the age of four and which is mostly preventable. However, as it can be quite difficult to test the eyes of children so young, Amblyopia is often left undiagnosed. Children are also masterful at masking shortcomings in their vision by adapting to their environment, whether unwittingly or wilfully, to cope. It is, thus, not always evident to an observer that there is an underlying vision problem. Conventional eye examinations are very difficult in pre-verbal children and this is where early vision screening devices play an invaluable role.
Children are not born with 20/20 vision: it develops from birth. The neural retina – the nerve layer at the back of the eye, responsible for vision that receives light and codes it into neural messages sent to the brain – develops rapidly in response to visual stimuli from birth until the ages of two to three years, where after its development rapidly decreases until the age of around eight years.
If this window of development is hindered, the ability to interpret visual images may be irreparably damaged, leading to Amblyopia. The affected person would thus suffer life-long vision loss, including possible blindness.
One or both eyes may become amblyopic when vision in the affected eye does not develop naturally as a result of some interference in the development of the neural pathway between the eyes and brain.
After the age of eight years it is near impossible to reverse vision loss caused by Amblyopia. However, if the cause of vision loss is addressed at the critical development phase, by means of a suitable intervention method, vision development may continue in a normal way.
Examples of such interventions include:
- issuing of spectacles, which result in clear images being received by the brain, or
- surgical removal of possible cataracts, which would remove the obstruction to light being received by the retinal layer at the back of the eye.
Early detection of vision abnormalities
Of course, intervention is subject to the underlying vision abnormality first being detected. This is no easy task in the pre-literate and pre-verbal age demographic. Consequently, children younger than three years of age – especially in South Africa – do not undergo regular vision screening, in contradiction of the American Academy of Paediatrics (AAP). This highly esteemed professional body released a policy statement and clinical report in 2016, stating that examination of the eyes and visual system should begin at nursery school level and continue throughout childhood. The AAP highly recommend regular early vision screening of all children.
Instrument-based vision screening technology has been shown to be the most effective and accurate way of detecting and diagnosing underlying risk factors that may lead to Amblyopia in young children. German medical devices manufacturer Plusoptix GmbH has developed the gold standard in this early vision screening technology. Its line of vision screeners are among the few mobile auto refractors available worldwide that are both FDA approved and CE marked.
The range of award-winning, user-friendly Plusoptix vision screening devices can be operated by anybody, from specialist ophthalmologists through primary healthcare workers and even laypersons. The compact, mobile design allows the user to perform an accurate vision screening anywhere. It is therefore perfectly suited to the need for making sight-saving technology available to all children in South Africa. Moreover, the vision screening is performed one metre away from the child and can be completed in a couple of seconds. This is one of the most effective and safest medical screenings in the age of COVID-19 physical distancing.
Vision abnormalities that may lead to Amblyopia
Refractive errors: Vision focusing errors, such as short sightedness, farsightedness or astigmatism (misshapen cornea) could lead to Amblyopia – especially when the error is greater in one eye. This causes the brain to receive two different sized images from each eye, which the brain will not be able to reconcile. The eye that produces distorted images will eventually be suppressed, resulting in stymied development of the neural pathway and functional blindness in the affected eye.
Strabismus: Squinting – referred to as strabismus – may also lead to Amblyopia. It is more easily recognisable than refractive errors. Strabismus is often caused by one eye turning in or out; and less commonly caused by an eye squinting up or down, or even obliquely. The brain receives two spatially separated images that it cannot fuse and the image from the deviating eye is then suppressed, eventually leading to functional blindness, as in the case of undiagnosed refractive errors.
Pathological conditions: A less common cause of Amblyopia is ‘deprivation Amblyopia’. It is brought about when the visual pathway in one eye is physically obscured, either by an obstruction, such as a corneal scar, eyelid tumour, retinoblastoma (tumour of the retina inside the eye), cataract, droopy eyelid, or as a result of medical conditions, such as paediatric glaucoma.
Amblyopia is a childhood disease that develops rapidly and unnoticeably. Most instances of Amblyopia are completely asymptomatic! Many parents assume their child has adequate vision, but the reality may be vastly different.
Early vision screening is essential to ensure that your child has every opportunity to develop healthy vision. It is also completely compatible with COVID-19 physical distancing regulations.