Eye pain can originate in the eye, its surrounding structures or in other parts of the head or body. It can range from gritty or dull to burning or stabbing, or may feel as if a foreign body is lodged in the eye.

The eye is one of the most sensitive organs in the body. Parts of the eyes are covered with pain receptors, which are designed to protect these vital organs. The number and sensitivity of these pain receptors can cause them to react and send pain signals to the brain from such minor changes as a gust of cold air or a grain of sand.

The eyes rest in sockets in the skull called the orbits. An optic nerve and other nerves connect each eye to the brain. The eye is a sphere, held in place by muscles. The sphere has a bulge near the front, which is the visible portion of the eye. Most of the outer layer of the eye is the white portion, called the sclera. The remainder of the outer layer is the cornea, a sensitive clear tissue that covers the front of the eye.

The next layer under the cornea and sclera is the uvea or uveal tract. The uvea includes the iris (colored part of eye) under the cornea, the choroid (a membrane that supplies blood to the retina) and the ciliary body, a muscular area that controls the lens and intraocular pressure under the sclera. The pupil is the dark opening at the center of the iris that expands and contracts to allow light inside the eye.

The eyelids cover the eyes. Above and behind the sides of the eyelids are lacrimal glands, which produce tears that lubricate the eyes. After bathing the eyes, tears empty into the lacrimal sacs, along the bridge of the nose. A thin membrane called the conjunctiva covers the sclera and the inside of the eyelids.

Several other factors make the eye susceptible to pain. The complexity of the structure – a fluid–filled body partially enclosed by bones – exposes it to injury. The fact that the eye is one of the few body parts with an exposed mucous membrane makes it susceptible to infection.

The eyes are working during all of a person’s waking hours, which can result in overuse and eyestrain. Trauma can also cause eye pain. Finally, the eye’s proximity to other pain sites is also a factor. For instance, migraines and other types of headaches can produce referred pain to the eyes.