What is Myopia?
Myopia, or nearsightedness, is a type of refractive error. This means that light entering the eye does not focus where it is supposed to at the back of the eye thus creating blurry vision. In myopia, light rays entering the eye focus in front of the retina rather than on the retina, which is the intended target.
For people with myopia, close objects appear clearer but distant objects appear more blurred. Myopia is a progressive visual disorder, often seen in children. It is common for the level of myopia or strength of child’s prescription to increase as they get older. The prevalence of myopia is increasing and recent estimates suggest that 30% of children aged 13 in Canada are myopic.
What causes Myopia?
There are a number of contributing factors that may put people at a higher risk for developing myopia and contribute to its progression.
- Genetics or family history
- Time spent on “near work” (looking at things up close, ie. computers, tablets, books)
- Time spent indoors
- Age of onset
What in Myopia Control and why is it important?
Myopia control is a proactive approach to treating myopia progression. Rather than treating just the symptoms with optical techniques such as glasses or contacts, myopia control allows us to slow down the rate of change which would occur naturally. It is important to understand that myopia control slows the rate of increasing myopia but does not stop progression.
Children will still be myopic during this therapy and their prescription will continue to increase as they get older. The aim is to minimize this increase until they achieve stable vision, which for most people is when they enter their late teens, early twenties.
Myopia control is a long term commitment. Once initiated, it is most effective if it is not discontinued until stable vision is achieved. Additionally, it is most effective the earlier therapy is initiated.
There are three methods to achieve this goal, each with equal efficacy. All three methods provide approximately a 50% reduction in myopia progression. This is based on group date and therefore individual results may vary.
As an example, an 8-year-old with a -1.00D prescription may progress by -0.50D every year until they are 18 years old. So at the age of 18 they have a final prescription of -6.00D. If we are able to achieve a 50% reduction in progression that same 18 year old may only end up with a final prescription of -3.50D.
At first that may not seem significant, but patients with higher levels of myopia can lead to a greater risk of vision threatening eye conditions such as retinal detachments or myopic maculopathy. Also, a -3.50D myope is more functional without correction than a -6.00 D myope.
- Multifocal Soft Lenses
These are soft contact lenses used similarly to traditional soft contact lenses, but are used for myopia control.
One example is the MiSight contact lens. It is a daily disposable contact lens with specially designed optics, shown to reduce the rate of change of a child’s myopia by up to 59%. The soft multifocal lens allows the patient to see clearly while the peripheral area of the contact creates a myopic defocus outside of the macular area, providing the therapeutic effect of myopia control.
Disposable multifocal lenses are safe, easy to use and are worn for at least 6 days of the week for at least 10 hours. Some hurdles to soft multifocal lenses are training younger children to insert and remove lenses, and not all types of prescriptions can be corrected with these lenses. Health Canada has recently granted approval for the MiSight specifically for myopia control.
- Orthokeratology – Hard Lenses
Ortho-K therapy involves changing the curvature of the cornea by temporarily molding its shape using a ridged contact lens. By changing the curvature of the cornea, Ortho-K therapy refocuses light onto the retina. The hard contact lens allows the patient to see clearly while the peripheral area of the contact creates a myopic defocus outside of the macular area, providing the therapeutic effect of myopia control.
These lenses are worn at night and removed in the morning to allow patients to be free of glasses or traditional contacts during their waking hours. Some hurdles to Ortho-K therapy is that the initial fitting of the lenses can take time because the lenses need to be customized to each individual. Patients will also need to sleep in the lenses.
- Atropine Therapy – Eye Drops
Atropine is the active ingredient used in eye-drop form at a concentration of 0.01%. It is instilled once daily in each eye. It has been used as a method of controlling myopic progression for many years. It is believed that atropine inhibits the thinning or stretching of the sclera, consequently reducing myopia progression. Used at this concentration, atropine has minimal side effects on pupil dilation and ability to focus on things up close.
The biggest advantage that atropine has over lens correction is its ease of administration and can be used in younger patients who are unable to insert or remove contacts. Atropine can be prescribed in conjunction with the optical methods described above.
It is important to note that individual results may vary from patient to patient. It is important to consult with your optometrist when deciding the appropriate strategy. It is also important to follow up with your optometrist during this therapy.