Hyperopia

 

People with hyperopia have difficulty seeing objects up close.  This disorder is more commonly known as far-sightedness and is caused by a defect in the eye.  Blurred vision, inability to focus on near objects, eye strain and headaches are symptomatic of this condition.  Through comprehensive vision screenings, it can be detected.  Far-sightedness can be corrected by wearing eyeglasses or contact lenses.

 

Myopia

 

Myopia, or near-sightedness, describes the condition which prevents a person from seeing objects at a distance caused by a long eyeball or a cornea that is too steep.  Near-sightedness may be hereditary or can develop over time.  Like hyperopia, it can be treated through prescription eyeglasses or contact lenses.  It can also be treated through Lasik surgery which involves the use of a laser beam of light to reshape the cornea.

 

Astigmatism

 

Astigmatism is caused by an abnormally shaped cornea or lens and is a very common eye disorder.   It may occur in conjunction with far sightedness or near-sightedness.  A small astigmatism does not require treatment and typically does not affect one’ ability to see clearly.  However, larger amounts can cause blurred vision.  Headaches are common with people who experience a large amount of astigmatism.

Vision impairment can be caused by damage to the eye itself that affects its ability to receive or process visual information.  Impairment can also be due to the eye being shaped incorrectly, which can make it harder to focus on things.  Vision impairment can also occur if the brain does not process visual information correctly.  Vision impairment can occur anytime during a person's life, even before birth. 
 
The most common causes of vision impairment among adults in the United States are age-related macular degeneraion, diabetic retinopathy, glaucoma and cataracts.
 
Age-related macular degeneration affects the part of the retina that is responsible for sharp central vision. Central vision is needed for common tasks such as reading. Risk factors for age-related macular degeneration include obesity, smoking, and family history.

Retinopathy or diabetic eye disease  is a serious problem that can lead to loss of sight. There’s a lot you can do to take charge and prevent such problems. A recent study shows that keeping your blood glucose level closer to normal can prevent or delay the onset of diabetic eye disease. Keeping your blood pressure under control is also important. Finding and treating eye problems early can help save sight.

Since diabetic eye disease may be developing even when your sight is good, regular dilated eye exams are important for finding problems early. Some people may notice signs of vision changes. If you’re having trouble reading, if your vision is blurred, or if you’re seeing rings around lights, dark spots, or flashing lights, you may have eye problems. Be sure to tell your health care team or eye doctor about any eye problems you may have.

 

The optic nerve is the part of the eye that transmits visual information from the retina to the brain. Glaucoma is a disease that occurs when the optic nerve is damaged and if left untreated can cause vision loss and blindness.  The optic nerve can be damaged by increased pressure caused by a build-up of fluid in the eye.  Symptoms of glaucoma are not immediate but over time patients will experience decreased frontal and peripheral vision. If detected early, glaucoma can be controlled and treated through medication or surgery.

A cataract refers to the clouding of the lens of the eye and generally affects older people.  Some of the symptoms include blurred vision, double vision, glare and poor night vision.  A cataract can occur in one or both of the eyes and may be corrected by new eyeglasses, brighter lighting, or surgery depending on the severity of the condition.

Vision impairment means that a person's eyesight cannot be corrected to a "normal" level.  Vision impairment may be caused by a loss of visual acuity, where the eye does not see objects as clearly as usual.  It may also be caused by a loss of visual field, where the eye cannot see as wide an area as usual without moving the eyes or turning the head.

There are different ways of describing how severe a person's vision loss is.  The World Health Organization defines "low vision" as visual acuity between 20/70 and 20/400, with the best possible correction, or a visual field of 20 degrees or less.  "Blindness" is defined as a visual acuity worse than 20/400, with the best possible correction, or a visual field of 10 degrees or less.  Someone with a visual acuity of 20/70 can see at 20 feet what someone with normal sight can see at 70 feet.  Someone with a visual acuity of 20/400 can see at 20 feet what someone with normal sight can see at 400 feet.  A normal visual field is about 160-170 degrees horizontally. 

Vision impairment severity may be categorized differently for certain purposes.  In the United States, for example, we use the term "legal blindness" to indicate that a person is eligible for certain education or federal programs.  Legal blindness is defined as a visual acuity of 20/200 or worse, with the best possible correction, or a visual field of 20 degrees or less. 

Visual acuity alone cannot tell you how much a person's life will be affected by their vision loss. It is important to also assess how well a person uses the vision they have.  Two people may have the same visual acuity, but one may be able to use his or her vision better to do everyday tasks.  Most people who are "blind" have at least some usable vision that can help them move around in their environment and do things in their daily lives.  A person's functional vision can be evaluated by observing them in different settings to see how they use their vision.  A functional vision evaluation can answer questions such as these:

• Can the person scan a room to find someone or something?
• What lighting is best for the person to do different tasks?
• How does the person use his or her vision to move around in a room or outside?