Merck Manual

Please confirm that you are not located inside the Russian Federation

honeypot link

Other Eye Symptoms


Christopher J. Brady

, MD, Wilmer Eye Institute, Retina Division, Johns Hopkins University School of Medicine

Reviewed/Revised Dec 2023
Topic Resources

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 2 objects is closer.

The retina is the light-sensing structure at the back of the eye. It is a 2-dimensional surface like a piece of film in a camera and can only produce a 2-dimensional image. The brain integrates the 2-dimensional images from each eye to create a sense of 3 dimensions (stereopsis). Stereopsis allows people intuitively to perceive depth. Disorders in which the eyes do not align properly (such as strabismus Strabismus Strabismus is an intermittent or constant misalignment of an eye so that its line of vision is not pointed at the same object as the other eye. If untreated, strabismus can cause amblyopia ... read more 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 adults 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.

Night Blindness

Older adults 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 adults 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.

Color Blindness

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 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 Overview of Optic Nerve Disorders The small photoreceptor cells of the retina (the inner surface at the back of the eye) sense light and transmit impulses to the optic nerve. The optic nerve from each eye carries impulses to... read more 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.

Light Sensitivity

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 medications 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.

Itchy Eyes

Dry Eyes

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 specializes in the evaluation and treatment—surgical and nonsurgical—of eye disorders) to make sure that it is not cancer.

People with these symptoms require an eye examination and a general medical evaluation. Treatment is directed at the cause.

Drugs Mentioned In This Article

Generic Name Select Brand Names
AK-Fluor, Bio Glo, Fluorescite, Fluorets , Fluor-I-Strip, Fluor-I-Strip A.T., Ful-Glo, Ophthalmicflur
quiz link

Test your knowledge

Take a Quiz!