Myopia – (Nearsightedness)
Myopia is the medical term for nearsightedness. Nearsighted eyes are good at seeing objects that are up close but have trouble seeing objects that are far away. This is due to a refractive error in the eye.
Refraction is the bending of light. When a light wave enters the eye, it is bent by the cornea as it makes its way through to land on the retina. There are two different factors that can contribute to myopia: the curvature of the cornea and the length of the eye. If the curvature of the cornea is too great, the light beam lands on the wrong part of the eye. Similarly, if the length of the eye is too long, the light will land in front of instead of on top of the retina. Either way, the result is that far away objects become blurry and out of focus.
Myopia is not an eye disease, but an eye disorder. Because of the role refraction plays in this type of nearsightedness, myopia is known as a refractive disorder.
Myopia is often inherited from the parents. Chances are, if your parents wore glasses, you will need glasses too.
There is also some evidence that an increased amount of close work may cause myopia. Close work is any kind of work that involves looking at objects close up, such as typing, reading or sewing.
Other causes include being born premature with a low birth weight, having an eye disease that is seen along with myopia or having a condition that causes the eyes to grow larger than is normal.
Onset and Treatment
Myopia appears in children between the ages of eight and twelve and may worsen as the body grows throughout the teenage years.
Between the ages of 20 and 40, there may be little or no change in vision. After 40, vision may begin deteriorating again. The onset of myopia may be slow and gradual, or rapid and sudden. Every case is unique to the patient.
The first signs of myopia often become noticeable when a child has a difficult time reading a chalkboard, or seeing the teacher clearly but has no trouble reading his textbook.
Other signs are the decreased clarity of a distant TV screen, problems driving at night or blurred vision at the cinema. Squinting is an outward sign that a child may need to be examined for myopia.
They might also sit closer to the television, rub their eyes frequently or hold a book very close to their face. It is important to have your child tested for myopia as there are educational and social consequences they may suffer due to decreased vision that remains uncorrected.
A child may be too embarrassed to complain of vision problems or they might be unaware of the changes in their vision, emphasizing the need for regular eye exams for children. Every one to two years in school age children helps catch vision problems early on before they have a chance to affect the child’s schoolwork or their social life.
Common options for treatment are the use of glasses or contact lenses. There are other options for myopia which include:
• Orthokeratology, also known as corneal refractive therapy: a re-shaping of the cornea using rigid gas-permeable contacts. These contacts rest on the surface of the eye and gently re-shape the cornea. Altering the curvature of the cornea restores proper vision in the eye.
• Laser eye surgery: A surgical procedure where vision is corrected by removing a small part of the eye with a laser. Using a highly focused laser beam, a specialist cuts away a bit of eye tissue, flattening the cornea and correcting the focus.
In particularly bad cases of myopia, known as high myopia, surgery may be necessary. There are some refractive surgery procedures that can correct vision in extreme cases of myopia.
• Phakic intraocular lenses: These are thin lenses that are implanted into the eye, eliminating the need for contacts or glasses. They sit right in front of the natural lens and help the eye focus light onto the retina, which allows far away objects to be seen clearly.
• Intraocular lens transplant with clear lens extraction: A surgical procedure where the eye’s natural lens is replaced by an implant. The natural lens is removed, and a synthetic lens is put in its place. This allows most people to achieve 20/40 vision or better over time.
A diagnosis of myopia can be made by taking a classic vision test under the supervision of an optometrist or ophthalmologist. A person who is nearsighted will have an easy time reading the letters on a Jaeger eye chart (the close objects chart) but a hard time with a Snellen chart (the far objects chart).
If a problem in the patient’s vision is detected during the eye chart test, the retina may be examined using a retinoscope. This device shines light on the patient’s retina so the doctor can examine it and find the issue causing problems with the patient’s vision.
When other causes of nearsightedness, such as eye disease, are ruled out and the problem with vision is determined to be a refractive error, the doctor will use a phoropter. This is the machine that allows the doctor to show a series of lenses to a patient, switching back and forth between them to determine the best fit for corrective lenses.
People with myopia are at a higher risk for glaucoma and cataracts.
They also have a higher than average chance of having a detached retina. If you notice a sudden change in vision, a loss of central vision, a large increase in the amount of floaters (squiggly, transparent shapes that “float” across the eye), or sense a feeling of heaviness in one eye, this could be a sign of a detached retina. Immediately seek treatment from a medical professional. Early treatment could prevent further complications.