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.
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.
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. 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. 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, 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), a corneal disorder (such as keratitis), or an eye injury. It may also be due to meningitis (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 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) and dry eyes 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. 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. (See also Keratoconjunctivitis Sicca.) 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.
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.
The eyelids may droop (ptosis). Ptosis may occur in people who have myasthenia gravis and disorders that cause nerve damage.
People with these symptoms require an eye examination and a general medical evaluation. Treatment is directed at the cause.