Myopia (nearsightedness) is the ability to see well at near but the inability to see well at distance without corrective help, such as glasses. Myopia is primarily caused by “axial elongation” (an eyeball that grows to long). Myopia is considered an optical condition of the eye, not a medial condition, and therefore treatment is not usually covered by medical insurances. However, there are socio-economic as well as ocular health implications of myopia. For example, myopic children without easy or cost effective access to eye care providers may perform at levels below their non-myopic peers in school due to the inability to see the board well. For adults, wearing glasses at work may pose a safety concern. Contact lenses or LASIK are not always medically or financially possible. In rare cases, the physical lengthening of the eye that occurs in high levels of myopia may make a person more at risk for secondary medial issues, such as retinal detachments, which can be sight threatening.
Although myopia for most individuals is more of an inconvenience than a sight threatening condition, for these above mentioned reasons there has been research to determine what causes myopia and how to limit its progression.
Cause of Myopia
The debate as to what causes myopia is a classic example of nature versus nurture. Meaning is it genetic or is it caused by a person’s environment. The case for it being genetic comes from studies that show children born to parents who are both myopic are twice as likely to be myopic than those born to non-myopic parents. Also, genes have also been discovered linking a person to high degrees of nearsightedness.
Alternatively, environment causes of myopia have been discovered from studies that show those who spend the most time reading are more likely to be nearsighted than those who spend the fewest hours reading. For example, a study from China found the prevalence of myopia in the most rural areas with the lowest literacy rates to be 1% compared to 38% in more industrialized parts where the school year and study times are longer. Near point activities such as reading cause a measurable and immediate increase in “axial elongation” (the length of the eye). Although discontinuing reading causes the eye to quickly return to is normal shape, it is believed that this repeated lengthening, many times over the course of years, causes a permanent elongation to occur.
These studies lend themselves to further questions. For example, are the apparent genetic links being found not actually a result of genetics at all, but rather the home environment through book-loving myopic parents encouraging greater reading time in their children? Although still debated, most researches currently believe that myopia is a combination of genetic and environmental factors.
Controlling the Progression of Myopia
Obviously we cannot control our genes or the amount of homework our children are given, but there are several methods proven to slow myopia’s long-term progression. However, none of the methods stop myopia progression and certainly none reverse myopia. As a result, it is important to discuss with your doctor whether the commitment of long term therapy is worth the difference in outcome. With or without treatment, your myopic child will still be myopic. So it becomes a question not only about helping a child become less myopic than they would otherwise have become, but also whether the slowed progression will be enough to meaningfully improve their quality of life.
1. Outdoor time
Several studies have pointed to time spent outdoors being correlated with lower rates of myopia progression. Research from Taiwan showed the prevalence of myopia in group of children exposed to an additional 80 minutes of sunlight daily for 2 years was half that found in a control group of children without the intentional extra daily sunlight. Of the kids in either group who were myopic at the end of the study, the total amount of myopia in the “extra sunlight” group was about 1.00 diopter less than the control group. This would typically be a noticeable amount to a child in a classroom.
Although the mechanism is not yet understood, it is believed dopamine released during sunlight exposure reduces axial elongation. Additionally, more leisure time spent outdoors means less time on the phone or tablet, which we know from earlier, causes a lengthening of the eye. So although we cannot control the amount of homework our children have, we can control the types of activities they are doing when homework is complete. Studies show outdoor activities may be the type of activities we want to encourage in order to slow the progression of myopia. Cost: Free.
Atropine is similar to the dilating drops you have likely received during an eye exam. The goal of atropine is to inhibit the ability of the focusing muscles in the eye from flexing during near activities. Why might this be beneficial? Because when we paralyze the focusing muscle inside the eye the eye cannot elongate during reading activities. Since the focusing muscle is paralyzed, reading glasses may be needed during treatment for near activities. However, a very low dose is used and most children in the study were able to still read without the use of reading glasses.
A 2-year study of Atropine drops used nightly showed children’s myopia progressed 0.28 diopters over 2 years as compared to 1.20 diopters for children on a placebo. Both groups of children at the study completion still needed glasses for best vision, but the prescription was about 1 diopter less for those who used the drops nightly. This study showed results similar to spending an additional 80 minutes per day outdoors. 1.00 diopter less myopia would make a noticeable difference in a classroom for a child with a relatively mild amount of myopia. Cost: About $30 per month.
~David McCleary, OD
California Optometric Association