What is it?
Orthokeratology contact lenses, sometimes also referred to as ‘night lenses’, is a novel way of correcting vision whereby a specially designed contact lens is worn overnight while asleep and then removed in the morning, allowing the wearer to achieve clear and comfortable vision all day without the need to wear spectacles or conventional ‘day’ contact lenses. Orthokeratology lenses have also been shown to be effective in slowing the progression of myopia in children, which has become a growing area of research in current times.
How does it work?
Orthokeratology lenses work by gently reshaping the outermost layer of the cornea, the clear tissue at the front of the eye, as shown in the diagram below. In myopia, the eye is focussing too strongly making images in the distance appear blurry, while an eye with astigmatism has an irregularly shaped cornea, meaning vision may appear distorted. The orthokeratology lens can correct both issues by reshaping the cornea into a flatter and smoother surface, providing clearer sight.
The changes take approximately 7-10 days to take full effect and, unlike laser eye surgery, are completely reversible after ceasing lens wear for 7-10 days.
Is it safe?
While it is true that sleeping in a contact lens that has been worn all day is unhealthy, orthokeratology lenses are specifically designed to be worn overnight. To reduce the risk of infection, lenses must be stored immediately after removal in an appropriate contact lens solution for at least 6 hours to disinfect, clean, and condition the lenses before being worn again at night. The lenses are made from highly breathable materials allowing enough oxygen to reach the cornea even while asleep to maintain corneal health. Wearing any type of contact lens increases your risk of developing corneal infections, however the risk associated with orthokeratology lenses is low and equivalent to wearing a soft daily disposable contact lens.
Who is suitable for orthokeratology?
Orthokeratology can be used to correct up to -5.50 dioptres of myopia, and up to -2.50 dioptres of astigmatism. Patients with prescriptions higher than this are unlikely to achieve full correction, and the lenses are currently not suitable for correction of hyperopia (long-sighted ‘plus’ prescriptions). Myopic patients with presbyopia (age related loss of near focus) who require either multifocal spectacles or removal of their distance glasses to see up close, may still be suitable for orthokeratology using the concept of ‘monovision’ where only one eye is fully corrected for the distance, while the other eye is left corrected for near, a technique that has often been employed successfully for many years with soft contact lenses.
This technology requires a healthy cornea to work effectively, so unfortunately patients with corneal conditions such as keratoconus, previous corneal surgery including refractive laser surgery, or any previous history of corneal infections or trauma, would not be suitable.
What are the benefits of using Orthokeratology?
The main benefit of orthokeratology lenses is relief from the burden of wearing spectacles and contact lenses during the day. Activities such as sports, cycling, and swimming where spectacle or contact lens wear may be prohibitive or even dangerous can be practiced safely with clarity of vision using orthokeratology lenses overnight. Orthokeratology can free a patient from the annoyance of having to regularly clean spectacle lenses, or lenses fogging up in cold weather, becoming wet in the rain, or worrying about scratches on the lens surface. Patients currently wearing soft contact lenses may have issues with discomfort and dry eye particularly towards the end of the day, but since orthokeratology lenses are only worn overnight, contact lens related dry eye and discomfort issues can also be remedied.
There is a secondary benefit to using these lenses in children who are showing signs of becoming myopic, typically from the age of 6+ years old. The development and progression of myopia in children is a growing area of research, with half the world predicted to be myopic by 2050. Orthokeratology has been shown in studies to be effective in slowing down the rate of progression of myopia in children. This is due to effect orthokeratology lenses have on the way light is focussed on the peripheral retina, which appears to limit axial growth of the eyeball, one of the main causes of myopic progression.
Finally, these lenses are better for the environment as they will only need replacing every 6 months. This means a patient can achieve daily correction of their vision requiring no more than a total of 4 lenses per year, in comparison to the material plastic waste of 24 monthly reusable lenses, or 730 daily disposable lenses per year.
In summary, orthokeratology provides a safe and effective way of correcting myopia, while also slowing myopic progression in children. If you are interested in learning more about what orthokeratology lenses could do for you, then book an appointment to speak to an optometrist at Monnow Eyecare.
By Scott Cox