Amblyopia

Amblyopia (sometimes called a 'lazy' eye), named after the Greek word amblus meaning blunt and op meaning eye or vision, is a developmental reduction (or 'blunting') of vision in one or both eyes. Amblyopia occurs as a child while the brain is maturing, often because one eyepoints in the wrong direction or vision is significantly defocused due to refractive error.¹ In these cases, vision is sub-standard, and as a result the connections made from the eye to the visual cortex in the brain during development are not fully formed.¹ If untreated, this developmental barrier becomes lifelong and will affect vision permanently despite optical correction.

Our practices in Adelaide and Henley Beach are equipped with new technology and determined optometrists who are able to improve vision and often resolve amblyopia in younger patients, preventing an otherwise lifelong issue.

What causes amblyopia?

Refractive amblyopia

Refraction refers to a person’s glasses or contact lens prescription. Those with refractive error, including myopia, hyperopia and astigmatism, have blurry vision that needs to be corrected with optical aids. In amblyopia, the child’s refractive error is so high that without optical correction, the image sent to the brain is severely blu^rred.2 When this happens in one eye only (anisometropia), the brain preferentially choses to look through the eye with less refractive error because the image is clearer. At the same time, it ignores the signals being sent from the blurred eye, and as a result the pathway between this eye and the brain are weakened. This can also happen when both eyes have high refractive error (ametropia), wherein the brain does not receive strong signals from either eye due to poor image quality.²

Form-deprivation amblyopia

This is apparent in much younger patients who are born with a specific pathology that prevents a clear image beingformed.² Common causes include congenital cataract or a droopy eyelid (ptosis) that obstructs the light from reaching the back of the eye (retina).

Strabismic amblyopia

When one eye is misdirected compared to the normal eye (often called a strabismus, ‘squint’, or ‘turned eye’), the brain receives two different images that do not align because the images are being projected on different parts of the retina.2 In order to prevent confusion and double vision, the eye essentially ‘shuts down’ one eye and as a result its pathway to the visual cortex is weakened.

Can amblyopia be treated?

There is a ‘critical period’ that occurs before the age of 8-9 years where the visual cortex is much more ‘plastic’ and easier to modify.³ During this time treatment should be initiated, as the earlier treatment starts, the better the chance of improvement. However, this does not mean that therapy cannot be tried after this window. Older children have still been shown to benefit from amblyopia therapy, even if the overall improvement is less significant – any amount of amblyopia resolution is improving the child’s vision for the rest of their lives.³

In some eyes, even with treatment the amblyopic eye may not recover the same vision as the good eye. In these instances, care should be taken to protect the good eye with safety glasses in the future during physical activities like sport.

Optical correction

Treatment for amblyopia initially consists of removing the causative factor (for example, prescribing glasses or contact lenses to eliminate blur or to relax the muscles in the eye responsible for misdirection with an eye turn).³ Typically, there will be an improvement in vision when these optical aids are worn full-time for up to 4 months. If amblyopia persists after this time, then other therapies can be explored. It’s common for one therapy to ‘max out’ visual improvement after some time, at which point swapping therapies can spur another round of amblyopia resolution.³

Atropine therapy

Atropine 1% eye drops cause blurry vision and pupil dilation. These are instilled in the good eye to make the bad eye do most of the visual work. We now know that putting in these eye drops in only weekends has the same benefit as putting them in every day, meaning the drops only need to be instilled twice a week.³ These drops are only using in low-moderate levels of amblyopia.

Occlusion therapy

This therapy works in exactly the same way as atropine therapy, except it can be used for any level of amblyopia. The good eye is occluded with a patch, which forces the bad eye to take up vision and strengthen connections with the brain. Usually, patching is only required for a few hours a day and is best combined with visually stimulating tasks such as video games, reading or television programmes.² Visit our patching page for more information about this therapy.

Vivid Vision

Innovative Eye Care now offers an exciting and engaging new amblyopia treatment using virtual reality (VR). Unlike patching and to some extent atropine, which are not entirely binocular therapies (training both eyes at once), Vivid Vision uses games where the two eyes must work together and has been found to significantly improve amblyopia.4 Initially, the projection from the headset is unbalanced, with a weak signal sent to the ‘good’ eye and a strong signal sent to the ‘lazy’ eye, forcing the amblyopic eye to do more visual work and form cortical connections. Over time, the signals projected by the VR headset are balanced until the eyes learn to seamlessly work together with equal brain input.

References

1) Pai, A. S.-I., et al. (2012). AmblyopiaPrevalence and Risk Factors in Australian Preschool Children*. Ophthalmology,*119(1), 138–144*.* doi:10.1016/j.ophtha.2011.06.024

2) Gopal, S. K. S., Kelkar, J., Kelkar, A.,Pandit, A. (2019). Simplified updates on the pathophysiology and recent developments in the treatment of amblyopia: a review. Indian J Ophthalmol67(9). doi:10.4103/ijo.IJO_11_19

3) Chen, A. M., & Cotter, S. A. (2016).The Amblyopia Treatment Studies. Advances in Ophthalmology and Optometry, 1(1),287–305. doi:10.1016/j.yaoo.2016.03.007

4) Žiak, P., Holm, A., Halička, J., Mojžiš,P., & Piñero, D. P. (2017). Amblyopia treatment of adults with dichoptic training using the virtual reality oculus rift head mounted display: preliminary results. BMC Ophthalmology, 17(1). doi:10.1186/s12886-017-0501-8