Technically known as myopia (my-O-pe-ah) nearsightedness is a vision problem that affects over 25 per cent of adults worldwide and it is the most common vision problem in the United States. Nearsighted people experience difficulty seeing objects at a distance but can see objects at close range. Myopia occurs because the eyeball is too long as measured from front to back. As a result light focuses in front of the retina instead of directly on it causing blurred distant objects. The more myopic you are the more blurred distant objects appear.
Nearsightedness is usually first noticed in children or teenagers and it progresses during periods of growth. In most cases there is little change after the age of 20 when growth is completed and vision stabilizes. Causes of myopia include genetics and there is some evidence to suggest that intense close vision activities such as reading or computer use might cause or exacerbate the condition.
In Degenerative Myopia (also known as Pathological or Progressive Myopia) there are structural changes that occur in the eye that can result in extremely high prescriptions and possible vision loss. This condition occurs in less than 3% of the population and is thought to have a genetic component. Patients with this serious type of myopia need to be followed routinely as degenerative changes in structures of the eye can lead to retinal breaks and tears glaucoma and cataracts.
Nearsighted people have blurred vision or cannot focus on distant objects. Other symptoms include:
- Headaches or eye strain
- Needing to squint to see distant objects clearly
- Poor school performance in children as they cannot see the blackboard
A comprehensive examination by an eyecare practitioner will include a test for nearsightedness. If diagnosed with myopia the prescription level usually involves a fraction number. For example a person with 20/25 vision can see at 20 feet what a person with perfect vision sees at 25 feet. The most popular way to treat myopia is by eyeglasses or contact lenses to alter the way in which light images enter the eye. In mild cases corrective lenses might only be necessary for certain activities such as driving. Those more severely affected wear the eyewear all day.
Understanding Your Prescription
Common refractive disorders of the eye such as myopia hyperopia astigmatism and presbyopia are measured in units called diopters. Diopters represent the amount of correction you need to normalize your vision. The more nearsighted farsighted or astigmatic you are the higher your prescription in diopters.
Your prescription is composed of three numbers:
- -5.00 -1.50 x 180 represents a typical prescription
- The first number -5.00 identifies your degree of nearsightedness or farsightedness. The sign identifies whether you are nearsighted (- sign) or farsighted (+ sign)
- The second number -1.50 identifies your degree of astigmatism. The number can be written either with a (+ sign) or a (- sign)
- The third number 180 identifies the axis which indicates the direction of your astigmatism. An axis of 180 degrees for example means the astigmatism is horizontal
- Therefore a prescription of -5.00 -1.50 x 180 indicates that the patient is moderately nearsighted with a moderate degree of astigmatism in a horizontal direction