Eye pain may be severe and seem sharp, aching, or throbbing, or people may feel only mild irritation of the eye surface or the sensation of a foreign object in the eye (foreign body sensation). Many causes of eye pain also cause the eye to look red. Other symptoms may be present depending on the cause of eye pain. For example, people may have blurred vision, a bulging eye, or pain worsened by bright light.
 
The cornea (the clear layer in front of the iris and pupil) is highly sensitive to pain. Many disorders that affect the cornea also affect the anterior chamber (the fluid-filled space between the iris and the inner part of the cornea) and cause spasm of the muscle that controls the iris (the ciliary muscle). When such spasm is present, bright light causes muscle contraction and worsening pain.
 
An Inside Look at the Eye
 
Causes
Disorders that cause eye pain can be divided into disorders that affect primarily the cornea, disorders of other parts of the eye, and disorders of other areas of the body that cause pain to be felt in the eye.
 
Common causes
 
Corneal disorders are the most common causes of eye pain overall, particularly
 
Corneal scratches (corneal abrasions)
Foreign objects
However, most corneal disorders can cause eye pain.
 
A feeling of scratchiness or a foreign body sensation may be caused by a disorder of the conjunctiva (the thin membrane that lines the eyelid and covers the front of the eye) or of the cornea.
 
TABLE
Some Causes and Features of Eye Pain
Evaluation
Mild eye irritation or a foreign body sensation is common and not usually serious. However, true pain in the eye can be a sign of a severe, vision-threatening disorder. The following information can help people decide when to see a doctor and help them know what to expect during the evaluation.
 
Warning signs
 
In people with eye pain, certain symptoms and characteristics are cause for concern. They include
 
Vomiting
Halos around lights
Fever, chills, fatigue, or muscle aches
Decreased sharpness of vision (visual acuity)
Bulging of an eye (proptosis)
Inability to move the eye in all directions (such as right, left, up, and down)
When to see a doctor
 
People who have severe pain, eye redness, or warning signs should see a doctor right away. People with mild pain and no eye redness or warning signs can wait a day or two to see if the discomfort goes away on its own.
 
What the doctor does
 
Doctors first ask questions about the person’s symptoms and medical history. Doctors then do a physical examination. What they find during the history and physical examination often suggests a cause of the eye pain and the tests that may need to be done (see table Some Causes and Features of Eye Pain).
 
Doctors ask the person to describe the pain, including when it started, how severe it is, and whether it hurts to look in different directions or blink. They ask about whether the person has ever had eye pain and whether the person is sensitive to light, has blurred vision, or feels as if the eye contains a foreign object.
 
During the physical examination, doctors check for the presence of fever or a runny nose. They check the face for tenderness.
 
Most important is the eye examination, including the entire eye, eyelids, and the region around the eye. Doctors check
 
Whether the eyes are red or swollen
How clearly a person can see using a standard eye chart (visual acuity)
Whether the person can see in each part of the field of vision (visual field testing)
How the pupils react to light
Whether shining a light into the unaffected eye causes pain in the affected eye when the affected eye is closed (called true photophobia)
If doctors suspect a foreign object but do not see one, they turn the eyelids inside out to search for hidden foreign objects.
 
Doctors usually do a slit-lamp examination. A slit lamp is an instrument that enables a doctor to examine the eye under high magnification. Doctors place a drop of fluorescein stain on the cornea to show scratches or certain kinds of infection, including ulcers. Doctors use tonometry to measure the pressure inside the eye (intraocular pressure). They use a slit-lamp and/or an ophthalmoscope (a light with magnifying lenses that shines into the back of the eye) to examine the lens and use an ophthalmoscope to examine the vitreous humor (the jellylike substance that fills the eyeball), retina (the light-sensing structure at the back of the eye), optic nerve, and the retinal veins and arteries.
 
Sometimes findings are helpful in making a diagnosis. Particular findings or combinations may point to particular disorders.
 
Findings may also help suggest or eliminate certain types of disorders.
 
Corneal disorders, among other disorders, tend to cause eye redness, tearing, and pain. If those symptoms are absent, a corneal disorder is very unlikely.
Pain on the surface of the eye, a foreign body sensation, and pain with blinking suggest a foreign object.
People who wear contact lenses may have a corneal scratch, a corneal ulcer, or contact lens keratitis.
When measuring eye pressure, doctors put a drop of anesthetic into the eye. If pain then disappears, the cause of pain is probably a corneal disorder.
Deep, aching, throbbing pain often indicates a possibly serious disorder such as acute closed-angle glaucoma, anterior uveitis, scleritis, endophthalmitis, orbital cellulitis, or orbital pseudotumor. If, in addition, there is eyelid swelling, bulging of the eye, or inability to move the eye to look in all directions, the most likely disorders are orbital pseudotumor, orbital cellulitis, or possibly severe endophthalmitis.
Testing
 
The need for tests depends on what doctors find during the history and physical examination. Testing is usually not necessary. However, if doctors find increased intraocular pressure, they may refer the person to an ophthalmologist (a medical doctor who specializes in the evaluation and treatment—surgical and nonsurgical—of eye disorders) for gonioscopy. A gonioscope is a special lens that allows doctors to examine the drainage channels in the eye.
 
Bulging of the eye and inability of an eye to move in all directions without moving the head can indicate orbital cellulitis or orbital pseudotumor. Computed tomography (CT) or magnetic resonance imaging (MRI) is then done to check for these disorders. CT may also be done if sinusitis is suspected but the diagnosis is not otherwise clear or if complications are suspected. MRI with dye may be done if optic neuritis is suspected.
 
Doctors send a sample of fluids from inside the eye (vitreous or aqueous humor) to the laboratory if endophthalmitis seems likely. They may send a sample from the cornea or a blister if herpes simplex keratitis or herpes zoster ophthalmicus seems likely but the diagnosis is not certain. In the laboratory, technicians try to grow bacteria or viruses (culture) to confirm infections and determine the organism causing the infection.
 
Treatment
Treatment of the cause
Pain relievers, sometimes opioids
Sometimes eye drops to dilate the pupil
The best way to treat eye pain is to treat the cause of the pain. People may also need to take pain relievers (analgesics) until the pain stops. If an over-the-counter analgesic such as acetaminophen or a nonsteroidal anti-inflammatory drug is ineffective, an opioid may be necessary. Sometimes people with pain caused by anterior uveitis or corneal disorders also need to use an eye drop that prevents ciliary muscle spasm by dilating the pupil and thus reduces eye pain with light exposure. For example, cyclopentolate may be used.