Most eye conditions, not to be confused with eye diseases, are caused by where light is focused on your eye. Myopia, hyperopia, presbyopia, and astigmatism are are some common conditions which you may be experiencing (descriptions are found on Allaboutvision.com) .
*Myopia Symptoms and Signs (Nearsighted)
If you are nearsighted, you typically will have difficulty reading road signs and seeing distant objects clearly, but will be able to see well for close-up tasks such as reading and computer use.
What Causes Myopia?
Myopia occurs when the eyeball is too long relative to the focusing power of the cornea and lens of the eye. This causes light rays to focus at a point in front of the retina, rather than directly on its surface.
Myopia typically begins in childhood and you may have a higher risk if your parents are nearsighted. In most cases, nearsightedness stabilizes in early adulthood but sometimes it continues to progress with age.
Hyperopia, or farsightedness, is a common vision problem, affecting about a fourth of the population. People with hyperopia can see distant objects very well, but have difficulty focusing on objects that are up close.
*Hyperopia Symptoms and Signs (Farsighted)
Farsighted people sometimes have headaches or eye strain and may squint or feel fatigued when performing work at close range. If you get these symptoms while wearing your eyeglasses or contact lenses, you may need an eye exam and a new prescription.
What Causes Hyperopia?
This vision problem occurs when light rays entering the eye focus behind the retina, rather than directly on it. The eyeball of a farsighted person is shorter than normal.
Many children are born with hyperopia, and some of them "outgrow" it as the eyeball lengthens with normal growth.
Sometimes people confuse hyperopia with presbyopia, which also causes near vision problems but for different reasons.
*Presbyopia Symptoms and Signs
Presbyopia usually occurs beginning at around age 40, when people experience blurred near vision when reading, sewing or working at the computer.
You can't escape presbyopia, even if you've never had a vision problem before. Even people who arenearsighted will notice that their near vision blurs when they wear their usual eyeglasses or contact lenses to correct distance vision.
When people develop presbyopia, they find they need to hold books, magazines, newspapers, menus and other reading materials at arm's length in order to focus properly. When they perform near work, such as embroidery or handwriting, they may develop headaches, eye strain or feel fatigued.
What Causes Presbyopia?
Presbyopia is caused by an age-related process. This differs from astigmatism, nearsightedness and farsightedness, which are related to the shape of the eyeball and are caused by genetic and environmental factors. Presbyopia generally is believed to stem from a gradual thickening and loss of flexibility of the natural lens inside your eye.
These age-related changes occur within the proteins in the lens, making the lens harder and less elastic over time. Age-related changes also take place in the muscle fibers surrounding the lens. With less elasticity, the eye has a harder time focusing up close. Other, less popular theories exist as well.
Astigmatism is probably the most misunderstood vision problem. For starters, it's called "astigmatism," not "stigmatism." (You don't have "a stigmatism" — you have astigmatism.)
In an eye with astigmatism, light fails to come to a single focus on the retina to produce clear vision. Instead, multiple focus points occur, either in front of the retina or behind it (or both).
*Astigmatism usually causes vision to be blurred or distorted to some degree at all distances.
*Symptoms of uncorrected astigmatism are eye strain and headaches, especially after reading or other prolonged visual tasks.
*Squinting also is a very common symptom.
What Causes Astigmatism?
Astigmatism usually is caused by an irregularly shaped cornea. Instead of the cornea having a symmetrically round shape (like a baseball), it is shaped more like a football, with one meridian being significantly more curved than the meridian perpendicular to it.
(To understand what meridians are, think of the front of the eye like the face of a clock. A line connecting the 12 and 6 is one meridian; a line connecting the 3 and 9 is another.)
The steepest and flattest meridians of an eye with astigmatism are called the principal meridians.
In some cases, astigmatism is caused by the shape of the lens inside the eye. This is called lenticular astigmatism, to differentiate it from the more common corneal astigmatism.
Glaucoma often is called the "silent thief of sight," because most types typically cause no pain and produce no symptoms until noticeable vision loss occurs.
For this reason, glaucoma often progresses undetected until the optic nerve already has been irreversibly damaged, with varying degrees of permanent vision loss.
In most cases, glaucoma is associated with higher-than-normal pressure inside the eye — a condition called ocular hypertension. But it also can occur when intraocular pressure (IOP) is normal. If untreated or uncontrolled, glaucoma first causes peripheral vision loss and eventually can lead to blindness.
*Cataract Symptoms and Signs
A cataract is a clouding of the eye's natural lens, which lies behind the iris and the pupil. It starts out small and at first has little effect on your vision. You may notice that your vision is blurred a little, like looking through a cloudy piece of glass or viewing an impressionist painting.
A cataract may make light from the sun or a lamp seem too bright or glaring. Or you may notice when you drive at night that the oncoming headlights cause more glare than before. Colors may not appear as bright as they once did.
What Causes Cataracts?
The lens is mostly made of water and protein. The protein is arranged in a precise way that keeps the lens clear and lets light pass through it.
But as we age, some of the protein may clump together and start to cloud a small area of the lens. This is a cataract, and over time, it may grow larger and cloud more of the lens, making it harder to see.
*Age-Related Macular Degeneration Symptoms and Signs
Age-Related Macular Degeneration (AMD) is degeneration of the macula, which is the part of the retina responsible for the sharp, central vision needed to read or drive. Because the macula primarily is affected in AMD, central vision loss may occur.
Age-related macular degeneration usually produces a slow, painless loss of vision. In rare cases, however, vision loss can be sudden. Early signs of vision loss from AMD include shadowy areas in your central vision or unusually fuzzy or distorted vision.
AMD is the leading cause of vision loss and blindness among Americans who are age 65 and older. Because people in this group are an increasingly larger percentage of the general population, vision loss from macular degeneration is a growing problem.
What Causes Macular Degeneration?
Though macular degeneration is associated with aging, research suggests there also is a genetic component to the disease. Duke University and other researchers have noted a strong association between development of AMD and presence of a variant of a gene known as complement factor H (CFH). This gene deficiency is associated with almost half of all potentially blinding cases of macular degeneration.
*Dry Eye Symptoms
Dry eye syndrome is caused by a chronic lack of sufficient lubrication and moisture on the surface of the eye. Consequences of dry eyes range from subtle but constant eye irritation to significant inflammation and even scarring of the front surface of the eye. Symptoms of dry eyes and dry eye syndrome include:
Photophobia (light sensitivity)
What Causes Dry Eyes?
An adequate and consistent layer of tears on the surface of the eye is essential to keep your eyes healthy, comfortable and seeing well. Tears bathe the eye's surface to keep it moist and wash away dust, debris and microorganisms that could damage the cornea and lead to an eye infection.
A normal tear film consists of three important components:
- An oily (lipid) component
- A watery (aqueous) component
- A mucous-like (mucin) component
Each component of the tear film serves a critical purpose. For example, tear lipids help keep the tear film from evaporating too quickly and increase lubrication, while mucin helps anchor and spread the tears across the surface of the eye.
Each tear component is produced by different glands on or near the eye:
- The oily component is produced by meibomian glands in the eyelids.
- The watery component is produced by lacrimal glands located behind the outer aspect of the upper eyelids.
- The mucin component is produced by goblet cells in the conjunctiva that covers the white of the eye (sclera).
A problem with any of these sources of tear film components can result in tear instability and dry eyes, and there are different categories of dry eyes, depending on which component is affected.
*How Does Diabetes Cause Diabetic Retinopathy?
Diabetic retinopathy — vision-threatening damage to the retina of the eye caused by diabetes — is the leading cause of blindness among working-age Americans, according to the U.S. National Institutes of Health (NIH). Yet, many cases could be prevented with regular eye exams and appropriate treatment. Diabetes mellitus (DM) causes abnormal changes in the blood sugar (glucose) that your body ordinarily converts into energy to fuel different bodily functions.
Uncontrolled diabetes allows unusually high levels of blood sugar (hyperglycemia) to accumulate in blood vessels, causing damage that hampers or alters blood flow to your body's organs — including your eyes.
Symptoms of Diabetic Retinopathy and
Other Diabetes-Related Eye Problems
You first may notice diabetic retinopathy (DR) or other eye problems related to diabetes when you have symptoms such as: