Decoding the Numbers: Myopia
When it comes to optometry, one of the first pictures that comes to people’s minds is of an eye doctor turning dials on that one machine (the phoropter) and asking, “which is better, one or two” in efforts to determine the patient’s glasses prescription.
While I could dive into a lengthy explanation as to how we are trained to do much more than flip knobs and give glasses, that’s not the point of today’s post. Rather, I’m here today to dive into the numbers and help explain what your prescription means.
- Patients with myopia are commonly referred to as being “near-sighted”. This is because, even without their glasses, they are able to see clearly when looking at things up close. Their problem is with looking far away.
What causes myopia?
- All refractive errors (essentially the reason for needing glasses) are caused by a mismatch of power in the eyes. In the case of myopia, the power (created by the cornea/clear surface and intraocular lens) is too great for the length of the eye, or, conversely, the length of the eye is too long for the power of the eye. Either case means that light is focused in front of the retina (back part of the eye), resulting in a blurred image.
Why do we need lenses?
- Because of the mismatch, minus (concave) lenses are prescribed. Due to their structure (thinner in the center, thicker on the edges), concave lenses cause light to diverge (spread apart). This divergence moves the eye’s natural focus point back - putting it right on the retina, and providing a clear image.
Who gets myopia?
- Refractive errors in general are thought to be inherited. Myopia is no different. If you have two parents who are near-sighted, you definitely have a higher likelihood of being near-sighted. (I looked for specific figures on how much this increases your risk, but didn’t find any.)
- Becoming near-sighted has also been associated with an increase in near work, decreased time outdoors, and a lack of physical activity.
- Relatively recent reports suggest a potential connection between myopia and inflammation, specifically in children with inflammatory conditions (ie: diabetes mellitus, uveitis, lupus).
- Near-sightedness may also be associated with different genetic conditions, such as connective tissue disorders, Stickler’s syndrome, and Down Syndrome.
- Patients with Retinopathy of Prematurity often are extremely myopic.
When should I suspect myopia?
- Patients often start becoming near-sighted between 8 and 10 years of age. However, myopia can occur at any age.
- Some signs of being myopic are:
- Squinting when looking far away
- Holding objects close, or getting really close to objects to see them
- Complaining of being unable to see the board at school, or difficulty seeing signs
Does myopia get worse?
- Myopia often progresses, however, the rate at which it progresses is variable.
- Typically, we expect near-sightedness to worsen from the ages of 8-20, but not everyone follows this pattern.
Are there any complications with being near-sighted?
- As myopia is associated with a longer eye, near-sighted people are at a higher risk of retinal holes, tears, and detachments due to retinal stretching.
- Myopia, especially high myopia, that continues to progress rapidly after the normal years may be considered degenerative myopia. Patients with degenerative myopia are at a higher risk for complications that may significantly impair vision.
- Near-sighted patients are also at a higher risk for glaucoma.
Can myopia be treated?
- A ton of research is currently being done regarding myopia progression and potential treatment options to decrease myopic progression. I’ll talk about that some other day.
- Most often, patients are prescribed glasses or contacts to improve vision.
- Special lenses (Ortho-K) may also be worn overnight in some cases to allow people to go without their normal lenses during the day.
- Refractive surgery can be used to change the power of the eye. It’s important to remember though that correcting the power of the eye does not change your risk for complications secondary to being near-sighted.
*To read the second part of my series "Decoding the Numbers: Hyperopia" click here!*
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