What is myopia (Near Sightedness)?
Myopia, also known as
nearsightedness, is a common type of refractive error where close objects appear clearly, but distant objects appear blurry.
When you look at an object, light
rays reflect off that object and pass through the cornea and the lens of the eye, which bend (or refract) the light and focus it on the retina at the back of the eye. If you have perfect vision, the
rays focus directly on the surface of the retina. But in a myopic eye, the eyeball is usually too long from front to back. This causes light rays to focus at a point in front of the retina, rather
than directly on its surface. This makes distant objects blurry.
Myopia can also be the result of a
cornea that is too curved for the length of the eyeball or a lens that is too thick. For some people, their myopia may be caused by a combination of problems in the cornea, lens, and length of the
What are the symptoms of myopia?
If you have myopia, you have
trouble seeing things far away, but you can see nearby things clearly. This is why myopia is commonly called nearsightedness.
If you can see well enough to read what’s on your laptop or in a book, but you struggle to see what’s on the television or a movie screen, you may be nearsighted.
Sometimes people with undiagnosed myopia will have headaches and eyestrain from struggling to clearly see things in the distance.
Why does the eyeball grow too long?
What causes the eyeball to grow
too long isn’t completely known, but researchers are exploring a number of factors. For many people, myopia appears to be an inherited condition – in other words, if you have a parent with myopia you
are at higher risk for developing it. Researchers are also looking at the effects of sex, age, ethnicity, and environmental exposures – such as sunlight and the amount of time spent doing close-up
work – on the development of myopia. More recently, scientists have been considering the influence of circadian rhythms (sometimes referred to as our biological or body clock), which regulate systems
in the body according to the daily cycles of light and dark, as a factor in the development of myopia.
How common is myopia?
Based on a study published in
2009, experts at NIH estimate that at least 41 percent of Americans are nearsighted. According to the same study, the number of Americans with myopia has increased significantly from the 1970s to the
early 2000s. The prevalence of myopia has also been increasing in many other countries around the world. It is particularly prominent among school-aged children living in urban areas in some Asian
In the past, people thought
children might become myopic from spending too much time reading and writing, which require close-up vision, or from reading in poorly lit rooms. Recent studies, however, suggest that the increase of
myopia in children could be related to a decrease in the amount of time they spend outdoors.
What is hyperopia (Far Sightedness)?
Hyperopia, also known as
farsightedness, is a common type of refractive error where distant objects may be seen more clearly than objects that are near. However, people experience hyperopia differently. Some people may not
notice any problems with their vision, especially when they are young. For people with significant hyperopia, vision can be blurry for objects at any distance, near or far.
What is refraction?
Refraction is the bending of light
as it passes through one object to another. Vision occurs when light rays are bent (refracted) as they pass through the cornea and the lens. The light is then focused on the retina. The retina
converts the light-rays into messages that are sent through the optic nerve to the brain. The brain interprets these messages into the images we see.
What are refractive errors?
In refractive errors, the shape of
the eye prevents light from focusing on the retina. The length of the eyeball (longer or shorter), changes in the shape of the cornea, or aging of the lens can cause refractive errors.
Causes and Risk Factors
How does hyperopia develop?
Hyperopia develops in eyes that
focus images behind the retina instead of on the retina, which can result in blurred vision. This occurs when the eyeball is too short, which prevents incoming light from focusing directly on the
retina. It may also be caused by an abnormal shape of the cornea or lens.
Who is at risk for hyperopia?
Hyperopia can affect both children
and adults. It affects about 5 to 10 percent of Americans. People whose parents have hyperopia may also be more likely to get the condition.
Symptoms and Detection
What are the signs and symptoms of hyperopia?
The symptoms of hyperopia vary
from person to person. Your eye care professional can help you understand how the condition affects you.
Common signs and symptoms of
- Blurry vision, especially for close objects