What is myopia?
Myopia is the fancy name for near-sightedness. Myopia causes vision to be blurry in the distance. It is the result of light rays focusing in front of the light-sensitive tissue that lines the back of the eye (the retina) rather than on the retina. This can happen when the power of the front of the eye is too strong (refractive myopia) or when the eyeball is too long (axial myopia). Below is an illustration. A minus (concave) lens is used to focus the light rays on the retina so that images are clear. The most common type of myopia begins between the ages of 6 and 12.
A myopic eye focuses the image IN FRONT of the retina, producing a blurry image. Minus lenses are used to correct myopic eyes, putting the image ON the central retina so you can see clearly.
The prevalence of myopia has been increasing over the past decades. In 2000, 23% of the world’s population was myopic, and researchers are predicting that 50% of the world’s population will be myopic by 2050 (1). THAT’S HALF OF THE WORLD!! Higher rates of myopia, nearing 90%, occur in some Asian populations. The increase in myopia prevalence suggests that environmental factors play a role in its development, though there is certainly a genetic component as well. People with higher amounts of myopia are also at greater risk for eye health issues such as retinal detachment and myopic maculopathy (2), so the myopia “epidemic” is a public health concern. So much research is being done on how to slow nearsightedness in kids and thus reduce the risk for visual impairment- it’s exciting!
How does myopia develop?
The exact mechanism of myopia development is still unclear. The leading thought is that myopia progression is caused in large part by the elongation of the eye. Research suggests that peripheral hyperopic defocus causes elongation of the eye. In English? Light focuses BEHIND the retina in the periphery, as shown in the image below. The periphery can be blurred even if the center is clear (this is the case with traditional, single-vision glasses or contact lens correction), and this peripheral blur is not really something we notice. At near, the periphery is more out of focus than it is when looking in the distance, so near work may be implicated in the development of myopia (3). Some more recent studies have shown a greater association between myopia development and the time spent outdoors than the time spent doing near work. Translation: developing myopia may be more closely related to how little time people spend outdoors than how much time people spend reading. So minimal time spent outdoors could be a risk factor for myopia development. Recent research has identified a cell in the retina that may cause myopia when it dysfunctions. The dysfunction may be linked to the amount of time spent indoors/away from natural light (4).
A visual of traditional, single-vision myopic correction: light is focusing on the retina in the center, but behind the retina in the periphery. image: kids orthok
What are the risk factors for progression?
The Brien Holden Vision Institute has identified a few factors that increase the risk of a child developing high amounts of myopia. They include:
- age of onset 9 years old or younger
- more than -0.75/-1.00 Diopter change per year
- at least one myopic parent (risk increases further if both parents are myopic)
- East Asian ethnicity
Options that have been shown to slow the progression of myopia:
1. Orthokeratology (aka ortho-K, corneal reshaping technology, CRT)
These are customized contact lens worn only at night, temporarily changing the shape and power of the front part of your eye (the cornea). When you wake up, you take the contacts out and you can see! In some sense, ortho-K lenses are like a retainer. Ortho-K lenses involve reverse geometry, meaning the curves of the lens are structured so that the tear film beneath the lens essentially flattens the center of the cornea while steepening the midperipheral cornea. This creates peripheral myopic defocus that negates the peripheral hyperopic defocus that is linked to eyeball growth (5). Orthokeratology is FDA approved for myopia up to -6.00D and mild amounts of astigmatism (up to 1.75D). There is no minimum age; the child just has to be able to put the contacts in, take them out, and maintain them on their own. It all depends on the child’s maturity level. As with any contact lens wear, there is a small risk for infection. Studies have found that ortho-K treatment slowed the axial elongation by an average of 30-50% (6, 7). Ortho-K appears to be more effective for those with higher amounts of myopia and larger pupils. Both the LORIC and later the CRAYON study showed that ortho-K slowed the axial growth of the eye, thus reducing myopia progression (8). The SMART study is yet another recent study that supports the theory that ortho-K reduces myopia progression. At the conclusion of this 3-year study, the ortho-K group saw an average increase in myopia of 0.12D while the soft lens control group increased by an average of 1.01D (9).
2. Soft multifocal contact lenses
Multifocal contact lenses are those that correct your distance while also giving you plus power to help see up close when needed. The specific design of multifocal lenses that are used for myopia control are center distance design (see image below). Center distance means more plus power in the periphery of the lens, which decreases peripheral hyperopic defocus and induces peripheral myopic defocus, reducing axial elongation. Several study results have supported the use of distance-center soft multifocal contact lenses for myopia progression, averaging a 40% reduction in myopia progression (10, 11). The CONTROL study found a whopping 72% reduction in progression of myopia over a one year period when compared to wearing single vision soft contact lenses (12), though this study involved myopic children with a specific focusing/postural issue (eso-fixation at near).
A multifocal lens with a center-distance design
image: Review of Optometry
The MiSight® lens is a dual-focus lens, utilizing ActivControl™ Technology. It is a concentric ring design with alternating vision correction and treatment zones. The two correction zones correct the child’s vision and provide clear vision, while the two treatment zones create 2 diopters of myopic defocus to slow the progression of myopia.
MiSight® 1 day is a daily wear, single use contact lens that has been clinically proven and FDA-approved to slow the progression of myopia (nearsightedness) when initially prescribed for children 8-12 years old.
Over a three-year period, comparing MiSight 1 Day to Proclear 1 day (a single vision lens), the MiSight group saw a 59% reduction in refractive error (aka prescription) and a 52% slowing in axial length (13).
3. Low-dose atropine
This method is different from the above two because it is not about changing the stimulus that contributes to eye elongation, but rather interfering with a biochemical pathway. How does it work? We don’t really know for sure. But it is thought to act on the white part of the eye (the sclera) or the tissue that lines the back of the eye (the retina) to prevent the sclera from thinning or stretching (14). Because atropine appears to involve a different mechanism of action, it can be used in conjunction with the other myopia control options discussed above. If you have had your eyes dilated during an eye exam, the doctor likely used tropicamide. Atropine is in the same family of drugs, but the effects are stronger. The effectiveness of atropine in controlling myopia progression is dose-dependent; higher concentrations produce greater myopia control, but come with greater side effects. One study found that after two years of treatment, patients on atropine 1% showed a nearly 80% reduction in myopia progression compared to non-atropine patients, and essentially no increase in axial length when compared to baseline (15). The downside: blurry near vision, light sensitivity, and large pupils. Other studies have shown comparable results using lower concentrations of atropine, which produce less side effects. Atropine 0.01% has been shown to slow myopia progression by roughly 50% (16, 17). Most recently, the LAMP study concluded that 0.05% atropine was most effective (compared to 0.025% and 0.01%) in controlling myopia progression and axial length elongation over a period of 1 year (18). Pirenzepine has also been tested, showing slightly less efficacy (44%), but with fewer side effects. Unfortunately, it’s not commercially available as an eyedrop or gel in the US.
4. Spectacles
Multifocal spectacles include bifocal lenses (the ones with a line across the lens) and “no-line bifocals,” or progressive addition lenses (PALs). These lenses feature a distance prescription at the top and a near prescription at the bottom. Many people over the age of 40-ish wear these to help them see clearly at all distances. There have been some studies to show efficacy in myopia control (especially in those patients with focusing or eye teaming issues), but multifocal spectacles are generally not considered as effective as the other 3 options mentioned above. Certainly, they are better than nothing, but for the purposes of myopia control, they’re not a top option. The COMET study found a small, statistically significant decrease in myopia progression in children wearing PALs vs children wearing regular, single-vision lenses, but only in the first year (19). There has only been one study done on myopia control with executive bifocal lenses, and the results showed a decrease in progression of 39-51% (20) . So the conclusion: yes, multifocal lenses produce a decrease in myopia progression, but I would use this option as a primary method of myopia control only if all other methods were taken off the table.
Beyond multifocal lenses, we will soon see specially designed lenses specifically for myopia management. Hoya’s MiyoSmart lens and Essilor’s Stellest lens are two spectacle lenses for myopia management that I discuss elsewhere on the blog.
Options that are NOT GREAT for slowing the progression of myopia:
1. Undercorrection of myopia
I’ve had some parents specifically ask me to give their child less powerful glasses in hopes that that would make the child need glasses less. There is no validity to this claim; actually, the undercorrection of myopia has been shown to INCREASE its progression (21, 22, 23).
2. Single vision spectacles
These are just “regular” glasses that correct for the distance prescription. While these do a great job of correcting myopia and clearing up central vision, they do not play any significant role in slowing myopia progression.
3. Spherical soft contact lenses or rigid gas-permeable (RGP) contact lenses (aka regular distance vision contacts).
These two choices are excellent forms of vision correction, but they have shown little value in terms of controlling myopia progression. The CLAMP study showed some reduction in myopia with RGPs in year 1 in comparison to soft contact lenses; however, it was not clinically significant because it didn’t change axial length and was likely due to the flattening of the cornea, which is not permanent (24).
| CliffsNotes: Regular glasses and regular contact lenses don’t help slow myopia progression. Undercorrection of myopia doesn’t help either; it actually makes it worse. Atropine therapy, orthokeratology, and multifocal soft contact lenses have been shown to be most effective in controlling myopia progression. Ask your optometrist for more information! |
Additional recommended resources for parents:
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