Amblyopia refers to poor vision in one or both eyes due to underdeveloped neural connections between the eyeball and the visual areas of the brain. Also known as lazy eye, in the US amblyopia is thought to have a prevalence of just under 2%. No statistically significant differences have been found between amblyopia in females versus males, or across different ethnicities.
While 2% doesn’t quite count as a wildfire epidemic, if left untreated amblyopia in children can have considerable consequences – difficulties with learning at school, limitations with job options as an adult, and even legal blindness. It also means the person no longer has a so-called spare tire if injury or disease befalls the remaining good eye.
Misconceptions about Amblyopia
A few misconceptions about lazy eye exist in the public. Some think it refers to the eye feeling tired or perhaps the lid droops towards the end of the day. Others believe the term refers to one eye being worse in vision compared to the other when spectacles or contact lenses are not worn, even though with appropriate correction both eyes can achieve the same level of reasonable vision. In some cases, “lazy eye” has been used to describe poorer vision in one eye due to some sort of pathology, such as cataract.
In actual fact, it is possible for amblyopia to exist in the absence of any pathology of the eyeball itself. Similar to a lazy husband, there can be nothing wrong with the organ, just with getting it to do something helpful, such as load the dishwasher.
‘Sensory deprivation” is the culprit, meaning one eye is deprived of clear vision during development (in some unfortunate circumstances, both eyes – like having a husband who won’t do the dishes and a daughter who won’t tidy her room). Because the incoming visual signal from the other eye is so significantly stronger than the lazy eye, the brain eventually chooses to ignore the input from the weaker eye and devotes most of its cortical space to receiving and interpreting signals from the healthy eye. This critical period of visual acuity development in a human is from approximately 3 to 5 years of age but amblyopia (lazy eye) may be induced up to about 8 years old.
Causes of Amblyopia
A few situations can cause amblyopia to occur. The most common of these is what is known as “strabismus”, which refers to a misalignment of the eyes. Eyes typically move together and at the same time; if someone wants to look to the left, both eyes turn left. An exception is during convergence when the eyes both move inwards to focus on a close object. During strabismus, while one eye is fixated in a certain direction, the other eye may be pointing inwards (esotropia) or outwards (exotropia) – one toddler is trying to put the toys in the box while the other is trying to take them out. To cope with the double vision caused by two eyes looking in two different directions, the brain suppresses one eye, leading to it becoming lazy. This situation is known as strabismic amblyopia.
Anisometropic amblyopia occurs when one eye has a significantly higher refractive error compared to the other. For example, one eye may have a higher degree of long-sightedness, short-sightedness, or astigmatism. If this is not addressed with appropriate spectacles or contact lenses, the brain tunes out the blurry eye and induces amblyopia.
Deprivation amblyopia is a less common form of lazy eye. In cases of deprivation amblyopia, visual input is vastly or entirely inhibited. This may be due to congenital cataract, where an opacity of the lens inside a baby’s eye physically blocks light from entering the eye and forming a clear image. It may also be caused by congenital ptosis, a condition in which the eyelid is unable to open fully. An extreme case of a stubborn emo rock side fringe could possibly also induce deprivation amblyopia.
The ultimate goal of amblyopia treatment is to give the weaker eye a better chance at developing properly. If the situation involves deprivation by a congenital cataract then prompt surgical removal is required. In most cases of lazy eye, the first line of treatment is spectacles or contact lenses as research has shown even in strabismic amblyopia that vision can improve with the use of optical correction alone. Once the gains in vision have plateaued with spectacle-wear, other therapies or eye muscle surgery may be warranted to improve the vision further.
In the course of giving the weaker eye a fairer chance, the better eye may need to be held back in part. This may be in the form of a physical patch (like a pirate patch with a strap or an adhesive patch) over the good eye for a prescribed number of hours a day so that the brain is forced to attend to the amblyopic eye and therefore strengthens the relevant neural connections. Unsurprisingly, many young children are not enthusiastic about the idea of having their better-seeing eye obscured. Alternatives to patching include the use of pharmaceutical eye drops to blur the vision in the good eye; the benefit of eye drops is that once instilled, they cannot be ripped out by an exasperated child. Optical penalization involves putting a blurry prescription in the spectacle lens of the good eye such that the vision through the amblyopic eye is actually better than the good eye, which is now “over-corrected”, again forcing the brain to pay attention to the lazy eye.
Early detection of lazy eye in children provides the best chance of improving their vision and can have a significant lifelong impact. A formal diagnosis of amblyopia can only be made in the office of an optometrist or ophthalmologist, and treatment of lazy eye should never be done without professional recommendation and regular reviews. In some cases of inappropriate management, amblyopia can be induced in the previously stronger eye, known as reverse amblyopia.
Even if no obvious vision or eye abnormalities are noted by a parent, the current recommendation by the American Optometric Association is that a child’s first eye test be conducted at around 6 months of age, and again at 3 years of age. Lazy eye treatment is more effective the younger the child, but fortunately research has found that limited improvement may be seen even in teenage years to early adulthood, which one may like to believe also bodes well for training lazy spouses and teenagers to clean the house.
Critical Periods and Amblyopia. https://jamanetwork.com/journals/jamaophthalmology/fullarticle/262202
Amblyopia (lazy eye). http://www.allaboutvision.com/conditions/amblyopia.htm
Causes and Associations of Amblyopia in a Population-Based Sample of 6 Year Old Australian Children. https://jamanetwork.com/journals/jamaophthalmology/fullarticle/417732
Recommended Eye Examination Frequency for Pediatric Patients and Adults. https://www.aoa.org/patients-and-public/caring-for-your-vision/comprehensive-eye-and-vision-examination/recommended-examination-frequency-for-pediatric-patients-and-adults
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