Encyclopedia of Health and Medicine

eye pain 89
eye The organ of vision. The paired eyes work in
coordination to present NERVE impulses the BRAIN
interprets as dimensional (stereovisual) images.
The function of sight requires close integration
among the structures of the eye, the neurologic system,
and the muscular system. Each eye is a fluidfilled,
elongated globe of fibrous tissue, about 1 ⁄4
inch from front to back and 1 inch from top to bottom
and side to side, contained within the protective
cavity of the orbital socket in the skull. The
OPTIC NERVE, the second cranial nerve, provides a
direct pathway from the back of the eye to the
brain. Six muscles move each eye up and down,
from side to side, and in rotation. These muscles
direct the eye toward objects within the VISUAL FIELD
and hold the eyes steady.
The process of vision begins when lightwaves
enter the eye through the CORNEA, a transparent
portion of the eye’s tough outer layer, the sclera.
The cornea’s convex front surface initially refracts
the lightwaves for preliminary focusing. The
cornea is soft and flexible but fixed; it does not
adjust or move. The LENS, a transparent and flexible
convex disk behind the cornea, further refracts
the lightwaves. Tiny muscles at the edge of the
lens, the ciliary muscles, cause the lens to thicken
or flatten to adjust the degree of refraction for
optimal focus. The resulting light pattern strikes
the RETINA, activating the specialized cells that
detect color (cones) and brightness (rods). These
cells convert the light to nerve impulses that converge
at the back of the retina at the optic disk,
their portal to the optic nerve. The optic nerve
conveys the signals to the brain, which interprets
them as images.
COMMON CONDITIONS OF THE EYE
AMBLYOPIA
BLEPHARITIS
CONJUNCTIVITIS
DRY EYE SYNDROME
FLOATERS
HORDEOLUM
ISCHEMIC OPTIC NEUROPATHY
KERATOCONUS
NIGHT BLINDNESS
RETINAL DETACHMENT
RETINOPATHY
VISION IMPAIRMENT
ASTIGMATISM
CATARACT
CORNEAL INJURY
EYE STRAIN
GLAUCOMA
HYPEROPIA
KERATITIS
MYOPIA
PRESBYOPIA
RETINITIS PIGMENTOSA
STRABISMUS
For further discussion of the eye within the
context of ophthalmologic structure and function
please see the overview section “The Eyes.”
See also AGING, VISION AND EYE CHANGES THAT
OCCUR WITH; CRANIAL NERVES.
eye pain Sensations discomfort involving the EYE
and its supporting structures. Eye PAIN may vary
COMMON CAUSES OF EYE PAIN
Quality of Pain Possible Causes Medical Attention Required
itchy or scratchy sensation DRY EYE SYNDROME, ALLERGIC self-care such as artificial tears or
CONJUNCTIVITIS, dirty contact
ANTIHISTAMINE MEDICATIONS; timely doctor’s
lenses, EYE STRAIN
assessment if symptoms persist after self-care
efforts to relieve them
burning and PHOTOPHOBIA, may CONJUNCTIVITIS, HORDEOLUM, prompt doctor’s assessment; infections require
include discharge CHALAZION, BLEPHARITIS, KERATITIS, antibiotic medications
DACRYCYSTITIS, ENTROPION
burning, photophobia, excessive BULBOUS KERATOPATHY, CICATRICIAL immediate medical attention
tearing, visible blisters on surface PEMPHIGOID, corneal abrasion
of the eye
sharp, deep, or intense pain that may ORBITAL CELLULITIS, trauma to eye, medical emergency
increase with, or prevent, eye
GLAUCOMA, optic neuritis, chemical
movement
or flash BURNS