What is myopia?
Myopia is commonly referred to as “near-sightedness”. People who are myopic (or near-sighted) have blurry vision for far-away objects but can see close objects clearly. The more myopic you are, the closer to your eye your natural focal point is. A person who is mildly myopic may be able to see objects up to a meter away quite clearly, but a person who is significantly myopic might have to hold an object only a few inches from their face in order for it to be in focus.
How does myopia develop?
We need light to focus on the retina (back of the eye) in order to provide the brain with a clear picture. In myopic eyes, there is a mismatch: light focuses in front of the retina, instead of on it. Generally, myopia is due to the eye being “too long” in relationship to the focusing power of the cornea (the front of the eye). Myopia typically progresses the fastest during childhood and adolescence, because the body (and the eyes) are actively growing. If the eye grows “too long”, myopia results.
In order to correct for the improper focal point of light in relation to the retina, concave (minus) lenses are used to change the refraction (bending) of light entering the eye. These lenses decrease the overall focusing power of the eye and move the focal point farther away from the cornea (towards the back of the eye). By adjusting the power of the lens, the focal point can be moved to the retina, creating a clear, in-focus image for the brain.
Why is myopia control needed?
It’s more than just thinner glasses…although that is a benefit! Higher myopia is linked with higher risk of retinal detachment, glaucoma, and myopic maculopathy, which can all lead to permanent vision loss. The increase in risk is proportional to the increase in myopia. Therefore, the more we reduce myopia, the more we reduce the risk of vision-threatening problems.
What are the risk factors for developing myopia?
There are several risk factors for developing myopia. Some of them, like genetic predisposition, we can’t do much about. Children whose biological parents are both myopic are 40% more likely to develop myopia.
Other risk factors are modifiable; we can manipulate these things to help decrease the chance of developing myopia, or slow the progression down once it has started. Studies have identified decreased time spent outdoors and a significant amount of near work (think reading and computer/device use) as a contributing factor to myopia development and progression. (Keep in mind, however, that this doesn’t mean that computers or electronic devices have “wrecked” our eyes- it is the near work that is the driving force behind these changes. Generations ago, our ancestors needed good distance vision, and our bodies evolved to have that advantage. Now, most of our day is spent on near tasks. Our body is trying to “help us out” by becoming myopic, to decrease the amount of focusing/strain we have to do for near tasks.)
Another contributing factor to myopia progression is peripheral defocus, which some people seem to be more susceptible to than others. With regular glasses and contact lenses, the lens moves the light to the retina in a linear way. The central focal point is in the correct spot, but the other focal points are behind the eye. The eye tries to grow longer to have these points in focus, too.
New technologies in glasses and contact lenses try to manipulate the focal points in such a way that there is less peripheral defocus, thereby reducing the stimulus for the eye to become more myopic.
What is myopia control?
Myopia control is the manipulation of modifiable risk factors to help decrease the rate of progression (or age of onset) of myopia. It is important to note that we cannot stop or prevent myopia, we can only slow it down.
What are the different options for myopia control?
Contrary to what you may have heard, your eyes don’t get “weaker” because you wear glasses. Wearing a “weaker” prescription will NOT stop your child’s eyes from changing.* Wearing the appropriate distance prescription is important, as it will allow your child to have clear vision for distance tasks.
*In some cases, your optometrist may recommend using a “weaker” prescription for near tasks (or taking glasses off for near tasks). This moves the focal point closer, which reduces the stress on the visual system when performing near tasks. However, it will always be a strategy that is used with the appropriate distance prescription for far tasks. This effect may be achieved with separate distance and near glasses, a bifocal lens, or a progressive lens. Typically, this strategy is utilized when there is obvious near stress with the distance prescription for near tasks. As a myopia control measure, it is moderately effective, having a range of 11-51% reduction in myopia progression.
There are four main strategies that can be used for myopia control: glasses with Defocus Incorporated Multiple Segments Technology (DIMS Technology), contact lenses that modify peripheral defocus, Orthokeratology, and low-dose Atropine.
MiYOSMART spectacle lenses use DIMS Technology and has been shown to decrease myopia progression by 60%. When you look at a DIMS lens, you will notice that the area of the lens right in front of the pupil (the line of sight) looks clear. Surrounding this area is a concentric area of DIMS segments. These segments are not readily noticeable, but can be appreciated in certain lighting when the lens is held at a certain angle. (In other words, no one will be able to see the DIMS segments when they look at your child, but if you try hard enough you’ll be able to tell that they are there.) These DIMS segments help control peripheral defocus, without causing blur to vision. Proper fit is important, as the clear portion of the lens needs to line up with the line of sight. More recently, Stellest lenses have been released which use similar technology as DIMS (HALT - Highly Aspherical Lenslet Target).
MiSight contact lenses also modify peripheral defocus. They are the only contact lens approved by Health Canada for myopia control. Studies have shown that wearing the contact lenses for a minimum of 10 hours/day, 6 days/week can slow myopia progression by 59%. There are no increased risks with MiSight contact lenses as compared to other daily contact lenses. Multifocal contact lenses may also be used to help control peripheral defocus, although these have not been specifically approved by Health Canada for this purpose. (This is called an “off-label” use.) Multifocal contact lenses have a wider range of parameters than the MiSight lenses, and may be a good option when using the MiSight lenses is not possible.
Orthokeratology involves changing the shape of the cornea (the front of the eye) by wearing a specially-designed rigid contact lens overnight. The effects are long-lasting but not permanent. It can be challenging to have a back-up pair of glasses with orthokeratology, as the prescription is more prone to fluctuations.
Low-dose atropine involves putting cycloplegic drops in your child regularly. (These are similar to the dilating or cycloplegic drops that are used in-office, but are a lower concentration.) As the concentration of atropine needed for myopia control is not readily commercially available, it must be compounded by the pharmacy. Not all pharmacies are compounding pharmacies, and supply issues can affect availability.
How do we monitor myopia control?
There are a couple factors that we can monitor to see how effective myopia control is. One is monitoring the change to the glasses prescription over time. Although we don't know what the prescription would be without myopia control, we can watch for less change in prescription over time.
Another factor that we can now measure in our clinic is axial length. The axial length is the overall length of the eye. With a new piece of equipment we are able to take this measurement which can then be used with statistical information to determine what percentile a patient lands in and their likelihood of becoming myopic or highly myopic. With myopia control, we can monitor the axial length and the treatments should slow the change.