A. Diabetes and vision Diabetes affects tiny blood vessels that nourish the retina, the eye’s internal projection screen. Over time, the retinal blood vessels become clogged or leak. When the retina?s blood vessels are unable to deliver enough nutrients to its light-sensitive cells, vision loss occurs. This disease is called diabetic retinopathy.
In the early stages, tiny blood vessels in the retina become blocked or damaged, cutting off the food supply to small patches of light-sensitive cells. Blood (hemorrhage) or fluid (exudate) leaks into retinal tissues, causing swelling. At first, sight is rarely affected. For that reason, this stage is called background retinopathy.
Over time, abnormal blood vessels grow into the retina and vitreous (jelly-like substance that fills the eye) in places where tiny blood vessels no longer function. These rogue vessels are fragile and rupture easily. When leaks occur, complications can cause severe vision loss if not promptly treated. This advanced stage of disease is called proliferative retinopathy.
When abnormal vessels burst, blood or fluid can collect in the retina’s central spot or macula. This spot is responsible for central vision. When it is swollen, central vision gets blurry. Fine details are lost. Reading, watching television and driving become difficult. If not treated promptly, macular edema may cause permanent vision loss.
As the body works to repair damage to the retina, scars form. Eventually, scar tissue can push the retina away from the back of the eye (retinal detachment). This detachment causes permanent loss of vision. If caught early, laser surgery may prevent or limit irreversible vision loss.
When abnormal vessels bleed into the vitreous, vision is blurred. Specks of blood may float through your field of vision. Large leaks into the vitreous can obscure sight, making it difficult to tell light from dark. The blood may clear away in a few days, months or even years. Large leaks (hemorrhages) often occur during sleep. If a lot of blood builds up in the vitreous, the eye doctor may recommend a vitrectomy. This operation replaces the cloudy vitreous with a clear solution.
Timely treatment of problems, macular edema, retinal detachment, abnormal blood vessel formation or blood- clouded vitreous, may prevent or limit permanent loss of vision in people with diabetes.
Glaucoma results from high pressure in the eye With glaucoma, what the eye sees in parts of its visual field starts to fade. This loss of vision usually is clustered in zones located around the center of focus. It most often occurs in both eyes, which explains why one symptom in advanced glaucoma is called “tunnel vision.”Areas or zones of the eye’s light receptors are not sending signals to the brain (the visual cortex).
Clusters of the nerve fibers in the retina that link with the receptors start to switch off. In glaucoma, the cornea and lens still focus the light they receive, but the nerve damage cuts off some communication channels to the brain.
Vision loss due to glaucoma is most often gradual. This, perhaps, is one reason why most glaucoma is found in people over 40 years of age. The glaucoma probably developed slowly over several years prior to being diagnosed.
A person with the first stages of glaucoma who has regular and frequent eye examinations has a better chance of having their condition diagnosed early.
The earlier glaucoma is diagnosed, the greater the likelihood that it can be slowed down or even stopped with medication, well before the tunnel-vision stage is reached.
“Lazy eye” describes a progressive loss of vision that occurs because of poor development in one or both eyes during infancy and childhood. Usually, only one eye is affected. Infants with lazy eye will make a fuss and cry if one eye is covered. Children with lazy eye may be able to see things well on one side, but have problems seeing all objects clearly and judging depth or distances.Consequently, they may try covering one eye or tilting their head to read. They may also be seen rubbing their eyes, winking or bumping into objects on the side of their weaker eye. Children with crossed-eyes often develop lazy eye. However, this degenerative condition may also develop without any very obvious signs, and the affected eye often appears perfectly normal.
Lazy eye usually develops because of an inherited condition and is experienced by children. There is very little likelihood that lazy eye would develop in an adult.
Keratoconus affects the way people see Normally, the cornea, a clear window at the front of the eye that covers the iris and pupil, is round like a dome. In people with keratoconus, the centre of the cornea thins and develops an irregular, cone-shaped bulge. The word keratoconus comes from the Greek words karato (cornea) and konos (cone).Changes in the cornea’s shape affect the way people see. In people with keratoconus, vision becomes blurred and distorted, like trying to see a road sign through a car windshield in a downpour.
Keratoconus usually begins in the late teens or early twenties. It progresses over time and usually affects both eyes. Changes tend to occur over 10 to 20 years, then stabilize on their own.
Keratoconus affects everyone’s eyes differently. Its effects on vision range from mild to severe. In the early stages, keratoconus causes:
- slight blurring
- visual distortion
- light or glare sensitivity
- tearful eyes
As keratoconus progresses, the cornea bulges more.
Visual distortion and blurriness worsen. People become increasingly nearsighted (have more difficulty seeing distant objects).
In a small number of people, keratoconus causes sudden swelling, which leads to rapid changes in vision.
Swelling occurs when tiny cracks develop in a steep, cone-shaped bulge in the central cornea.
Keratoconus is a treatable disease. While it affects the quality of vision, it does not usually cause vision loss.
Retinitus pigmentosa (RP) is a group of rare, inherited diseases affecting the retina, the layer of tissue located at the back of the eye where we “see.” The onset of symptoms can begin in early childhood with poor night vision.Peripheral vision usually deteriorates in early adulthood. By middle age, people with RP may see with limited tunnel vision only. Peripheral vision can continue to diminish and progress to blindness. However, some forms of retinitus pigmentosa begin later in life or progress more slowly, so total blindness does not occur.Retinitus pigmentosa is also associated with nearsightedness, cataracts, degenerative vitreous opacities and inherited hearing loss.
On average, people blink about 15 times per minute. When that rate slows, the eyes feel gritty, burning or tired, and become red. The eye?s protective coating of tears dries up, leaving the eye open to infection and injury. This condition is known as dry eye. Not enough blinking is only one cause of dry eye, the leading eye problem in North America. About 10 million Americans have this condition. Dry eye is more common in women, especially after menopause. About 60% of eye fatigue is caused by dry eye.Tears bathe and soothe the eye. They are important for eye health and clear vision. Dry eye occurs when tear quality is poor or not enough tears are available to protect the eye’s surface.
People with dry eye find it difficult to wear contact lenses. They may even produce fewer tears when they cry. When dry eye is serious, people may become sensitive to light or have blurry vision.
Without a protective layer of tears, the eye’s surface is easily scratched and is vulnerable to infection. Fortunately, your eye doctor can suggest many options to treat dry eye. With proper care, people with dry eye can avoid eye injury and vision loss.
Detecting dry eye
To detect dry eye, an eye doctor usually does a few simple tests during the annual eye exam. Some eye doctors use a fluorescein test. They put a droplet of yellow dye into the eye, then count the number of seconds it takes for the tear film to break up. If it takes less than 10 seconds, the person has dry eye. Sometimes, the yellow dye will temporarily stain the eye. Viewed through a slit-lamp microscope, dry eye looks like dry, cracked skin. The rose bengal test uses a reddish-purple dye to detect dry eye. During the Schirmer test, the eye doctor touches a strip of filter paper to the inner eyelid. The paper is used to measure tear production. Some people are more likely to have dry eye. Computer users, who blink less often than normal (4 versus 15 blinks per minute on average), are often bothered by dry eye. More women than men are affected. People with allergies and contact lens wearers are more likely to develop this condition.
Styes are infections of the glands around eyelashes or inside the eyelid. Redness, tenderness or pain are usually the first symptoms they cause. These are followed by swelling in some or all of the eyelid.The eye may water, feel irritated and may become sensitive to light.After a few days, eyelash styes usually come to a head and drain, thus relieving the pain. The whole process should take about a week. Eyelid styes are deeper, more painful, usually do not drain on their own and often recur.
A chalazion is a cyst that forms in a clogged oil gland in the upper or lower eyelid. The first symptoms resemble those of styes (see Styes), including tenderness, swelling and irritation.After a few days, the chalazion becomes a painless, firm, slow-growing bump in the eyelid and may blur vision. In most cases, chalazia are gone within a few months. However, one cyst may be followed by other, possibly larger cysts within two years time.
Conditions associated with chalazia include seborrhea, chronic lid inflammation, dry eye and acne.
Macula is a Latin word that means spot. In macular degeneration, a pea-sized spot in the center of the retina is permanently damaged. This spot is responsible for central vision.When the macula is injured, objects directly ahead look blurry. Details are lost. There is a fuzzy “hole” in your vision. When looking at a face, only the ears are clear. People see a picture frame clearly, but not the picture.How badly central vision is blurred depends on the amount of damage. Macular degeneration develops slowly and painlessly over time. It may affect one or both eyes.People with macular degeneration have difficulty: reading small print, street signs and distant faces or objects driving, sewing and doing close work.Side vision remains normal, so people with macular degeneration can walk and perform daily activities without help. Two kinds of macular degeneration (MD) can affect central vision:Dry MDAbout 90% of people have dry MD. Behind the retina, a membrane separates the central spot or macula from its blood supply. Over the years, this membrane ages, thins and breaks down ? exposing light-sensitive cells in the central spot to leaky or abnormal blood vessels. Cut-off from their food supply, these cells eventually stop working.There is no way to reverse this damage. Central-vision loss occurs slowly and is usually mild. Someone with dry MD in one eye may not notice any difference in their vision.
Only 10% of people have wet MD, but it accounts for 90% of MD-related vision loss. It occurs when fragile blood vessels, growing between the macula and supporting layer of tissue, leak or rupture. Leaking blood or fluid damages light-sensitive cells in this region, leading to a rapid loss of central vision over a short time.
One early warning sign is visual distortion: straight lines look wavy. This happens when blood-vessel leakage forms bumps under the macula. Or, a blind spot may appear. Prompt laser therapy can prevent or slow central-vision loss.