A number of other symptoms and problems can affect the eyes, including changes in the appearance of the eyes, color blindness, dry eyes, glare and halos, impaired depth perception, itchy eyes, light sensitivity, and night blindness.
Impaired Depth Perception
Depth perception is the ability to determine the relative position of objects in space. People with impaired depth perception may have difficulty distinguishing which of two objects is closer.
The retina is the light-sensing structure at the back of the eye. It is a two-dimensional surface like a piece of film in a camera and can only produce a two-dimensional image. The brain integrates the two-dimensional images from each eye to create a sense of three dimensions (stereopsis). Stereopsis allows people intuitively to perceive depth. Disorders in which the eyes do not align properly (such as strabismus) can interfere with stereopsis.
However, stereopsis is effective only in a close range, such as within arm's reach. If objects are farther away than about 9 feet (3 meters), clues to depth perception obtained from only one eye (for example, the apparent size of objects) provide more information on relative position than stereopsis. Thus, a person who sees with only one eye will have trouble pouring a cup of tea but will have less trouble parking a car.
Glare and Halos
Some people experience glare (star bursts) or halos around bright lights, especially when driving at night. Such symptoms are more common among older people and among people who have had certain types of refractive surgery or who have certain types of cataracts Cataract . Glare and halos can also occur in people whose pupils are widely dilated (for example, those who have been given eye drops for an examination). When the pupil is widely dilated, light is able to pass through the peripheral part of the lens of the eye, where it is bent differently from light passing through the more central parts of the lens and therefore causes glare.
An eye examination is done. Sometimes symptoms can be relieved by treating the cause (for example, a cataract). Otherwise, people should take precautionary measures, such as minimizing driving at night or after receiving eye drops for an examination and avoiding looking directly at oncoming headlights while driving.
Older people frequently have difficulty seeing in low light. This is sometimes referred to as night blindness. Most commonly night blindness results from a cataract, although night blindness is a feature in certain forms of retinal degeneration, such as retinitis pigmentosa Retinitis Pigmentosa Retinitis pigmentosa is a rare, progressive degeneration of the retina (the transparent, light-sensitive structure at the back of the eye) that eventually causes moderate to severe vision loss... read more . The eyes of some older people dilate slowly and take longer to adjust to low light. An eye examination should be focused on detection of cataracts and should include an ophthalmoscopy. The cause is treated. Improving household lighting, particularly in the kitchen and around steps and other areas in which falls can occur, may improve safety.
People who have color blindness (dyschromatopsia) are unable to perceive certain colors, or they may perceive certain colors with different intensity than do people with normal color vision. For instance, in the most common form of color blindness (red-green color blindness), people are less able to distinguish dark or pastel green or red or both. At traffic lights, people with red-green color blindness can be guided by cues other than the color of the light.
Often, the changes are subtle, and many people are unaware they have color blindness.
Color blindness is usually present from birth and is nearly always due to an X-linked recessive gene X-Linked Recessive Disorders , which means that almost all affected people are men. Women, who are not usually affected themselves, can pass the gene for color blindness on to their children.
Most cases of color blindness are due to a relative deficiency or abnormality of one of the types of light-sensing retinal cells (photoreceptors). Red-green color blindness, the most common form, is one example. Blue-yellow color blindness, however, may be caused by optic nerve disease and is usually due to acquired rather than inherited disease. Color blindness is also sometimes due to a problem with how the brain interprets color (rather than a problem with the eyes).
A person may be tested for color blindness if it is known that a family member has the abnormality. Some people may be tested because they notice they have difficulty with matching colors. Other people may be unaware of any problem until they are tested for a job or need a license (such as for piloting an airplane) that requires them to be able to distinguish colors.
Color blindness cannot be treated.
Sensitivity to bright light occurs normally during extremely sunny conditions or when coming out of a dark environment into bright sunlight. Such sensitivity can also be caused by drugs used to dilate the pupils (mydriatics). However, pain resulting from bright light (photophobia) can be a symptom of a migraine headache or a number of eye disorders, for example, those that involve inflammation or infection within the front part of the eye (uveitis Uveitis Uveitis is inflammation anywhere in the pigmented inside lining of the eye, known as the uvea or uveal tract. The uveal tract may become inflamed because of infection, injury, a bodywide autoimmune... read more ), a corneal disorder (such as keratitis), or an eye injury. It may also be due to meningitis Acute Bacterial Meningitis Acute bacterial meningitis is rapidly developing inflammation of the layers of tissue that cover the brain and spinal cord (meninges) and of the fluid-filled space between the meninges (subarachnoid... read more (which is also typically accompanied by a severe headache and neck stiffness).
Doctors first try to differentiate light sensitivity from photophobia. The cause of light sensitivity or photophobia can usually be determined by the person's symptoms and an eye examination. A slit-lamp examination Slit-Lamp Examination A person who has eye symptoms should be checked by a doctor. However, some eye disorders cause few or no symptoms in their early stages, so the eyes should be checked regularly (every 1 to 2... read more is particularly useful for detecting disorders that cause photophobia. Light sensitivity and photophobia can be minimized by protecting the eyes from light (for example, by wearing sunglasses). When photophobia is the result of inflammation within the eye, dilating eye drops can help to relieve pain.
Itching may result from allergy and is usually accompanied by watering of the eyes (tearing). Inflammation of the eyelids (blepharitis Blepharitis Blepharitis is inflammation of the edges of the eyelids, possibly with thickening scales, crusts, shallow ulcers, or redness and swelling at the edges of the eyelids. The inflammation is caused... read more ) and dry eyes Dry Eyes A number of other symptoms and problems can affect the eyes, including changes in the appearance of the eyes, color blindness, dry eyes, glare and halos, impaired depth perception, itchy eyes... read more may also cause itching. Much less commonly, itching may result from infection or infestation with lice or other parasites. Abnormalities that cause itching can usually be diagnosed by a slit-lamp examination Slit-Lamp Examination A person who has eye symptoms should be checked by a doctor. However, some eye disorders cause few or no symptoms in their early stages, so the eyes should be checked regularly (every 1 to 2... read more . Until the cause of itching is relieved, applying a cool washcloth may provide some relief.
The sensation of dryness of the eyes can be caused by a variety of conditions, including inadequate tear production, accelerated tear evaporation, or, less commonly, refractive surgery,vitamin A deficiency (rare in developed nations), or Sjögren syndrome Sjögren Syndrome Sjögren syndrome is a common autoimmune connective tissue disorder and is characterized by excessive dryness of the eyes, mouth, and other mucous membranes. White blood cells can infiltrate... read more . (See also Keratoconjunctivitis Sicca Keratoconjunctivitis Sicca Keratoconjunctivitis sicca is dryness of the conjunctiva (the membrane that lines the eyelids and covers the white of the eye) and cornea (the clear layer in front of the iris and pupil). Too... read more .) Dry eyes may also be a result of aging.
Tear production may be measured, particularly if Sjögren syndrome is suspected. Doctors may also try to determine whether tears evaporate too quickly. They place a tiny amount of yellow dye (fluorescein) in an open eye and measure how long it takes for tears to evaporate. During the day, dry eyes can be relieved with the use of eye drops that substitute for a person's tears (artificial tears). At night, an ointment can be used before bed to relieve morning dryness.
Changes in the Appearance of the Eyes
Dark (pigmented) spots can appear on the iris or conjunctiva. Some are present at birth, and others may appear with age. Although often insignificant, any dark spot that grows should be evaluated by an ophthalmologist (a medical doctor who specialize in the evaluation and treatment—surgical and nonsurgical—of eye disorders) to make sure that it is not cancer.
The sclera become yellow, as does the skin, in people who have jaundice Jaundice in Adults In jaundice, the skin and whites of the eyes look yellow. Jaundice occurs when there is too much bilirubin (a yellow pigment) in the blood—a condition called hyperbilirubinemia. (See also Overview... read more .
The eyelids may droop (ptosis). Ptosis may occur in people who have myasthenia gravis Myasthenia Gravis Myasthenia gravis is an autoimmune disorder that impairs communication between nerves and muscles, resulting in episodes of muscle weakness. Myasthenia gravis results from malfunction of the... read more and disorders that cause nerve damage.
Sometimes the eyes are unusually wide open and prominent, usually because they are being pushed forward (exophthalmos Eyes, Bulging Bulging or protruding of one or both eyes is called proptosis or exophthalmos. Exophthalmos is usually used when describing bulging eyes caused by Graves disease, a disorder causing overactivity... read more ). Exophthalmos can occur in people who have Graves disease Hyperthyroidism Hyperthyroidism is overactivity of the thyroid gland that leads to high levels of thyroid hormones and speeding up of vital body functions. Graves disease is the most common cause of hyperthyroidism... read more .
People with these symptoms require an eye examination and a general medical evaluation. Treatment is directed at the cause.