Section 20. Eye Disorders

Chapter 225. Symptoms and Diagnosis of Eye Disorders

Topics: Introduction | Symptoms | Diagnosis

Symptoms

Changes in Vision

Changes in vision may involve loss of vision or distortion of vision.

Loss of Vision: Loss of vision is a complete or nearly complete absence of sight. A person with loss of vision may see nothing whatsoever or he may be able to distinguish light from dark and may even be able to detect vague shapes. Loss of vision may involve part or all of the visual field of one or both eyes and may be temporary or permanent. Depending on the particular type of vision loss and how rapidly it develops, the person may immediately notice the problem, or it may not be discovered for some time--perhaps not until a car accident or other event prompts a thorough vision examination.

Complete loss of vision may occur in one or both eyes. Common causes include blockage of the blood supply to the retina, diabetes, optic nerve disease, glaucoma, and, in tropical areas, infections such as trachoma.

There are many types of loss of vision that involve only part of the visual field. People who have had certain kinds of strokes may not be able to see anything on one side but see normally on the other. People with a tumor of the pituitary gland (which lies just below the brain, behind a cross-over of the optic nerve fibers) may not be able to see things on either side but see normally in the middle (tunnel vision). Before a migraine headache, some people are temporarily (usually about 20 minutes) unable to see things above or below or to the right or left of their line of sight. People with macular degeneration lose the ability to see things they directly look at, but they retain their side or peripheral vision (the things seen out of the "corner of the eye"). Smaller, irregular patches of vision may be lost as a result of many disorders that damage the retina, such as diabetic retinopathy and hypertensive retinopathy. Glaucoma, if left untreated, can cause loss of part of the peripheral visual field, tunnel vision, and eventually total blindness.

See the sidebar How and Why Blindness Develops.

Distortion of Vision: Distortion of vision is an inability to see clearly and correctly. This distortion may involve a refractive error, lack of depth perception, double vision, glare or halos, flashes of light, or floaters. It may also involve color blindness.

See the figure What Is Astigmatism?

Refractive error causes objects to appear blurred and out of focus. Refractive error usually results from a mismatch between the shape of the cornea or lens and the length of the eye. If only distant objects are blurred, the person is nearsighted or myopic. If only nearby objects are blurred, the person is farsighted or hyperopic. Upon reaching middle age, most people--even those with previously excellent vision--develop difficulty focusing on nearby objects (presbyopia). Astigmatism, another type of refractive error, is caused by an irregularity in the curvature of the cornea or lens and results in slight blurring of vision. Astigmatism may occur on its own or together with any of the other types of refraction error.

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. Depth perception is reduced when one eye is blind or has an uncorrected refractive error. It also may be impaired by a failure of the brain to integrate the two images--one from each eye--into a single three-dimensional image (fusion), resulting in double vision. However, many depth perception clues come from only one eye; therefore, if a person closes one eye and looks at two objects, he can usually tell which object is closer, even with only one eye.

Double vision (diplopia) is seeing two images of one object. Double vision may result from weakness in one or more of the muscles that control eye movements, resulting in cross-eye (strabismus (see Section 23, Chapter 277)). Other causes include fatigue, alcohol intoxication, multiple sclerosis, trauma, or cataract. The sudden appearance of double vision may indicate a serious disorder of the brain or nervous system, such as a tumor, aneurysm, or blood clot.

Some people experience glare or halos around bright lights, especially when driving at night. Such symptoms are more common in older people and in those 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 or who have large pupils). When the pupil is widely dilated, light is able to pass through the peripheral part of the lens, where it is bent differently from that passing through the more central parts of the lens and therefore causes glare.

Older people frequently have difficulty seeing in low light. Such symptoms are sometimes referred to as night blindness. Most commonly this results from a cataract, although certain forms of retinal degeneration, such as retinitis pigmentosa, have night blindness as a feature.

Some people experience bright flashing or flickering lights. This sensation most commonly results from shifting of the jellylike substance that fills the back of the eye (vitreous humor) or less commonly from a detached retina or a migraine headache. Flashes of light can also result from a blow to the back of the head ("seeing stars"), probably because of stimulation of the part of the brain where vision is interpreted.

Floating spots (floaters) are dark specks that appear to move in front of the eye. They are fast-moving or slow-moving clumps of the microscopic fibers that make up the vitreous humor. Floaters become increasingly common with aging. Floaters rarely affect vision and are generally considered normal; however, a sudden increase in the number of floaters (especially in association with flashing lights) may indicate a serious problem, such as a detached retina. A person with these symptoms should be evaluated by an ophthalmologist.

People with color blindness 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 may have a reduced ability to distinguish dark or pastel green or red or both. Often, the changes are subtle, and many people are unaware they have color blindness until they are tested.

See the sidebar What Causes Color Blindness?

Changes in the Appearance of the Eyes

The most common change in appearance is a red eye. Many conditions dilate the blood vessels in the conjunctiva, causing the white of the eye to appear red. Such conditions include fatigue, allergies, infections, abrasions or ulcers of the cornea, and foreign bodies in the eye. Sometimes, a forceful cough or a direct blow causes a blood vessel in the conjunctiva to burst, resulting in a bright red patch in the white of the eye. Sometimes the bleeding turns the whole white of the eye bright red. With a chalazion (see Section 20, Chapter 228), allergy, or a bacterial infection of the eyelids or sinuses, typically the eyelids and other tissue around the eye may become red.

In jaundice, the whites of the eyes (the sclera) become yellow, as does the skin (see Section 10, Chapter 135).

Sometimes dark spots appear on the iris or conjunctiva. Some are present at birth, and others may appear as a person ages. Often they are of no significance; however, any dark spot that grows should be evaluated by an ophthalmologist to ensure that it is not cancer.

The pupils normally are the same size; they become large (dilate) in the dark and become small (constrict) in bright light. Certain drugs used to treat eye diseases dilate or constrict the pupils. Opioid drugs, such as morphine, constrict the pupils. Amphetamines, antihistamines, cocaine, and marijuana may dilate the pupils.

Unequal pupils (one large and one small) may be caused by injury or inflammation of the eye, injury of the nerves that control the pupil, head injury, or brain tumors or by using eye drops in only one eye. People with syphilis may have small, irregularly shaped pupils (Argyll Robertson pupils). A few people are born with pupils of different sizes.

Changes may also be visible in the structures around the eye, such as the eyelids. For instance, the eyelids may droop (ptosis). This may occur in myasthenia gravis (see Section 6, Chapter 95). Sometimes the eyes are unusually wide open and prominent, usually because they are being pushed forward (exophthalmos), which can occur in Graves' disease (see Section 13, Chapter 163).

The eyelids may become swollen, due to allergy, infection, or inflammation (as in a chalazion or stye). The roots of the eyelashes may become infected, sometimes resulting in the eyelashes falling out. Allergies or infections may also lead to abnormal secretions from the eyes, which may harden (crusting) and cause difficulty in opening the eyes.

Changes in Eye Sensation

Pain may occur around the eye, in the eye, or behind the eye. Pain from the cornea tends to be sharp and is usually worsened by blinking; it may give a sensation of "something in the eye." Corneal pain may be caused by an abrasion, foreign body, dry eye, ulcer, or infection. Acute closed-angle glaucoma produces a deep, aching pain in the eye. However, most chronic glaucoma is not painful. Pain originating within the eye may occur together with tenderness of the eyeball (when gently pressed, it hurts). A deep, boring pain in the eye can be a symptom of scleritis, a potentially serious inflammation of the thick fibrous coat of the eye, or uveitis, an inflammation of the inner structures of the eye.

Sensitivity to bright light (photophobia) occurs normally during extremely sunny conditions or when coming out of a dark environment into bright sunlight. However, unusual sensitivity to light can also be a symptom of a migraine headache or a number of eye disorders, for example, due to inflammation or infection within the front part of the eye (keratitis and uveitis) or an eye injury. It may also be due to meningitis (which also results in a severe headache with neck stiffness (see Section 6, Chapter 89)). Photophobia can also be caused by the use of drugs to dilate the pupils (mydriatics).

Itching may result from allergy and is usually accompanied by watering of the eyes (tearing). Inflammation of the eyelids (blepharitis) may also cause itching. Itching may also result from infection or infestation with lice or other parasites.

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, vitamin A deficiency and Sjögren's syndrome (see Section 20, Chapter 228).