Glossary of Terms
Edina Eye has put together a list of top terms and eye related words with their descriptions to answer your questions.
Parts of the Eye
A clear protective membrane that covers the cornea and lines the inside of the eyelids. The conjunctiva produces a mucus that allows tears to adhere to the eye. The mucus, along with other eye lubricants, is spread over the entire eye by blinking, and helps to keep the eye wet and clean. The blood vessels of the conjunctiva are normally invisible but can become inflamed and reddened from irritation or a disease such as conjunctivitis.
The transparent ourter shell that forms the front of the eyeball. The cornea has two main functions: it helps to focus light upon the retina, providing about 70% of the eyes refractive, or focusing power; and it shields the front of the eye, which is extremely sensitive to abrasion or injury from foreign particles. The pain produced from irritation to the cornea provides an early warning system that can prevent possible damage to the eye.
The cornea is lubricated by the lacrimal glands, the meibomian glands, and the mucus of the conjunctiva, which form a tear film over its surface. Blinking spreads the lubricants, keeping the cornea constantly wet and preventing it from becoming damaged by drying out.
The colored portion of the eye lying just behind the cornea. The iris is donut-shaped with its hollow center forming the pupil, through which light passes to the lens and the retina of the eye. In bright light, the iris contracts to allow in a lesser amount of light; in dim light, the iris expands to allow in a greater amount of light. The color of the iris is determined by the amount and distribution of pigment within it.
A clear, elastic, and convex disk which, along with the cornea, gives the eye its ability to focus. Its proper name is the crystalline lens, which is used to distinguish it from the cornea. The lens lies just behind the iris with its outer rim attached to the ciliary body by thin ligaments. The muscles of the ciliary body enable the elastic lens to expand and contract to keep objects at varying distances in focus.
When the lens grows cloudy, whether from age, trauma, disease, or other causes, the condition is called a cataract. A severe cataract may require the lens of the eye to be removed and replaced with an intraocular lens.
The small central area within the retina that enables people to see fine details clearly. Damage or breakdown of the macula results in a loss of vision in the center portion of the eye, while peripheral, or side, vision remains unaffected. Macular degeneration is a fairly common disorder of the eye. It can vary greatly in its severity, and should be evaluated immediately if suspected.
The black, circular opening in the center of the iris. The pupil allows varying amounts of light to pass through the eye. The muscles of the iris control the diameter of the pupil, widening it to allow in more light under dim conditions and narrowing it to restrict light under bright conditions. The pupil appears black only because light enters the eye through it but is not reflected back out.
A light-sensitive layer that covers the back inner surface of the eye. Light passes through the pupils and strikes the retina, where an image is reproduced and transmitted via the optic nerve to the brain. The retina has light-sensitive nerve cells called rods and cones. Rods are very sensitive to light but not color, while cones are very sensitive to color but not light. Rods and cones are most highly concentrated in the center of the retina, where they provide the greatest visual acuity for objects looked upon directly.
Conditions of the Eye
Falsely Misaligned Eyes (pseudostrabismus)
Sometimes infants appear to have crossed eyes, yet the eyes are truly straight. The cause for pseudostrabismus is presence of a wide nasal bridge or extra folds of skin between the nose and the inside of the eye that make the child have a cross-eyed appearance. Most children outgrow this problem, but you should contact your doctor for an examination. Your pediatrician can tell whether a child has misaligned eyes or just pseudostrabismus, but in some instances, a visit to an ophthalmologist is necessary for further tests.
Misaligned Eyes (strabismus)
With strabismus, the eyes are not aligned. Strabismus is quite common and occurs in about 4% of children. One eye may gaze straight ahead while the other eye turns inward, upward, downward, or outward. When an eye turns inward, the child has “crossed” eyes (esotropia). There are two common causes for esotropia. Some children are born with crossed eyes (or develop it shortly after birth), and in this situation the muscles are too tight. Treatment for this most commonly involves surgery on the eye muscles, generally performed prior to the age of 2.
The second most common cause for esotropia is excessive farsightedness. This problem can be present at birth, but most commonly occurs between the age of 2 and 6 years. This type of esotropia is corrected with glasses. When an eye turns outward, the child has exotropia. Exotropia may be present from birth, but most commonly is seen in children 2 to 7 years of age. Generally the eyes turn out on rare occasions at first but with time more frequent outward turning of the eyes is noted. Children with exotropia occasionally squint one eye when exposed to bright sunlight. The treatment for large amounts of exotropia is usually eye muscle surgery.
Children with misaligned eyes will generally turn off the vision in the turned eye so that they are not plagued with double vision. Children with strabismus should have a careful examination by an ophthalmologist because untreated strabismus may lead to a lazy eye (amblyopia) or loss of depth perception. Rarely, strabismus may indicate a more serious condition, such as cataract or eye tumor (retinoblastoma).
Lazy Eye (amblyopia)
Lazy eye is reduced vision from lack of use in an otherwise normal eye. It usually happens only in one eye. Any condition that prevents a clear image can interfere with the development of vision and result in amblyopia. Amblyopia is common, affecting about 2% of children. Some causes of amblyopia include strabismus, droopy eyelids (ptosis), cataracts, or refractive errors. Because early treatment offers the best results, your pediatrician will refer you to an ophthalmologist.
Cataract (cloudy lens)
A cataract is a clouding of the eye’s normally clear lens. The lens is located behind the pupil and helps focus images on to the back of the eye (retina). Cataracts may be present at birth or may appear later in life. Injury may also cause this condition. Early detection and treatment are crucial in infants and children so that normal visual development can occur. For this reason, most cataracts should be surgically removed soon after they are discovered. It should be noted that cataracts in infants and children are uncommon and not related to cataracts that occur in adults. Glaucoma (elevated eye pressure) Glaucoma is a condition in which the pressure inside the eye is too high. If left untreated, glaucoma will eventually lead to total blindness. Warning symptoms are extreme sensitivity to light, tearing, and persistent pain. Signs include an enlarged eye, cloudy cornea, and lid spasm. If any of these are present, your pediatrician will refer you to an ophthalmologist immediately. Glaucoma in childhood usually requires surgery to prevent blindness.
The tear duct system, which allows the tears to drain from the eyes into the nose, usually opens in the first few months of life. In some infants, however, the system remains blocked, resulting in the eyes overflowing with tears and collecting mucus. Tearing may result from other ocular conditions, the most serious of which is glaucoma (see above). If your child suffers from continued tearing or watering from the eyes, please consult your pediatrician. Gentle massage of the tear duct can occasionally assist in relieving the blockage. If massage and observation are unsuccessful, a tear duct probe or more involved surgery is occasionally required.
Ptosis (droopy eyelids)
Ptosis refers to a situation in which the eyelids are not as open as they should be. This situation is caused by a weakness of a muscle that opens the upper eyelid. When ptosis is mild, it is just a cosmetic problem. However, ptosis can interfere with vision if it is severe enough to block the vision in the eye. In infancy, it is important that ptosis be eliminated so that vision will develop normally. Correction of ptosis usually requires surgery on the eyelid(s).
Blepharitis (swollen eyelids)
Blepharitis refers to an inflammation in the oily glands of the eyelid. This usually results in swollen eyelids and excessive crusting of the eyelashes, most evident in the morning. Tenderness of the eyelids and a foreign body sensation in the eye may occur as well. Blepharitis can be treated with warm compresses and eyelid scrubs using baby shampoo. If an infection is present, antibiotics may be necessary. If any of these findings are present, please consult your pediatrician.