When it comes to myopia control, the good news is that there’s now a number of options to prevent or slow down shortsightedness. Clinical studies on both ortho-k and NaturalVue contact lenses are impressive – but which is best?
Ortho-k for myopia
Orthokeratology has been around for some time now, but lens designs have really improved over the last decade, making this option accessible for a lot more people.
Ortho-k uses rigid contact lenses (RGPs) with a special shape to remould the surface of the eye (the cornea) during sleep. When properly fitted this will temporarily correct your myopia. The lenses are removed on waking and you can enjoy clear vision all day.
This image demonstrates the principle, although it is greatly exaggerated. In a real eye the change in shape is only a fraction of a millimetre and is limited to the outer layer of the cornea.
Why change the shape?
This remoulding has a dual effect: the centre of the cornea is flattened, which corrects myopia (including low-to-moderate amounts of astigmatism) up to about -6 dioptres. (Up to -4 is very straightforward to correct in suitable eyes).
This corrects the myopia so you (or your child) can see clearly even when the lenses are removed during the day.
How does ortho-k slow myopia?
The reshaping of the cornea overnight also changes the shape of the outer cornea, and this is where the myopia-control effect comes in.
One stimulus for an eye to become more short-sighted over time (this is called myopia progression) is that the light entering the eye from the outer (peripheral) cornea doesn’t focus exactly on the back of the eye (the retina), but behind it. This drives the eyeball to ‘chase’ the clear focus that would result if it were a little longer, so it grows. But this only makes the eye more short-sighted.
It’s a vicious cycle that can lead to rapid increase of myopia over a short time.
By changing the shape of the peripheral cornea, ortho-k eliminates the stimulus for the eyeball to keep growing longer, and this slows, or even stops, the myopia from getting worse over time.
A review of the clinical studies on ortho-k has found that it slows progression of myopia by 45% compared to traditional methods of correcting distance vision only, which is great news for anyone who is short-sighted.
Multifocal soft disposable contact lenses for myopia
Multifocal contact lenses, such as the latest daily disposable lenses from NaturalVue, also show excellent results in slowing the progression of myopia, and at this stage, may progression of myopia even more than ortho-k.
These lenses are worn during the day only and replaced every day. They are thin, comfortable and hygienic. We will be closely watching comparative studies in the future.
Ortho-k v NaturalVue multifocal soft contact lenses
Both systems work off a similar principle but achieve this in different ways. The shape of the eye after wearing an ortho-k lens mimics the concentric optics of a multifocal contact lens, with clear distance vision centrally and defocus in the peripheral cornea to switch off the eye’s stimulus to grow.
But there are some differences between these two contact lens options in terms of suitability, safety, handling, comfort etc.
Wearing contact lenses poses challenges for children and teenagers and care must be taken to ensure they are mature enough to understand the importance of proper hygiene habits.
Even though both systems present a low risk of infection when worn according to your optometrist’s directions, any contact lens carries a small risk of eye infection. A lens worn overnight to reshape the cornea probably has a slightly higher risk of adverse side effects compared to a strictly daily-wear lens. That said, we’ve been fitting ortho-k lenses since 1995 and, after thousands of consultations, we can remember less than 5 cases where a serious event occurred and none of those ended up with any permanent concerns.
One rare side effect of ortho-k, and usually only seen in Asian children is 'epiblepharon', or, in-turning eyelashes. This is uncomfortable and usually means that ortho-k lenses are unsuitable for the child.
Soft daily disposable contact lenses are not risk-free, but good hygiene and compliance make them a very safe option.
Low to moderate amounts of astigmatism are probably better corrected with ortho-k, compared to the NaturalVue lens in our experience.
Neither of these are budget options! A pair of ortho-k contact lenses costs about $1400 and can last 12-24 months. NaturalVue lenses, if worn every day, work out at $1,600 per year (or about $4 per day).
Ortho-k lenses worn only during sleep and being made of rigid material can be a better option for people with dry eyes compared to any soft lens.
With children's smaller eyes, it's generally easier to insert a rigid lens than a (much larger) soft disposable lens. Parents can help of course, but it's good if kids can learn how to insert, remove and clean (if appropriate) these lenses themselves over time.
NaturalVue comes in a wide range of powers but if you’re outside that range or need a different fit, you’re out of options. It is possible to customise Ortho-k lenses for eyes that fall outside the normal range of shape or prescription.
At The Eye Practice, we are dedicated to reducing the burden of myopia by offering the full range of myopia control options to our patients. We are very pleased with the effects of both ortho-k and NaturalVue contact lenses on the progress of myopia and believe both options will have a significant impact on the everyday management of myopia.