General Eye Terms

Use this glossary of general eye terms for a better understanding of overall eye care.

Monofocal intraocular lenses (IOLs) that change power in response to your eyes' own muscles, providing greater range of vision.
Treating a patient for a condition with two or more medications at one time.1
An eye condition in which the macula—the part of the retina that provides sharp, central vision—is progressively damaged. This is a leading cause of vision loss in Americans over age 65.
Inflammation of the whites of the eyes (conjunctivae), with itching, redness, and tearing, due to allergy.
The compartment in the eye between the cornea and the iris.3
Also called aqueous humor, a transparent fluid that is produced in the anterior chamber and flows through the drainage angle of the eye.2
An uneven or irregular shape of your cornea, the front surface of your eye, or your lens, the part of the eye that focuses light onto your retina.
Also referred to as toric lenses, these advanced technology IOLs are designed to correct your astigmatism.
A cloudiness in the natural lens of the eye that obstructs or scatters light as it passes through the eye to the retina. Cataracts develop naturally with age, and as they progress they can cloud your vision and interfere with daily activities such as driving or reading.
A procedure in which the cataract is removed and replaced with a clear artificial intraocular lens implant (IOL) to improve vision.
Light-sensing nerve cells in the eye’s retina that provide clear central vision and detect colors and fine details in bright light.
A thin, clear, moist membrane that coats the inner surfaces of the eyelids (palpebral conjunctiva) and the outer surface of the eye (ocular, or bulbar conjunctiva). Inflammation of the conjunctiva is called conjunctivitis (pinkeye).
The transparent outer front surface of the eye. It is clear and focuses light rays that pass through the pupil onto the retina.
Dry Eye is a condition caused by changes in the quantity or quality of your tears. Tears are composed of three main layers that work together to keep your eyes comfortable and protected. If anything affects the balance of these elements, your tears may evaporate too quickly, causing your eyes to feel dry and irritated.4
The place within the eye where all entering light rays are focused. For clear vision to occur, the focal point must fall directly in the light-sensitive retina. Common focusing errors occur when the focal point falls in front of or behind the retina.5
An eye disease that causes damage to the optic nerve, the nerve that transmits visual information to the brain. In many cases, the damage results from increased pressure in the eye.6
Farsightedness, a refractive error of the eye that causes near objects to appear blurred, and as the patient ages, far objects as well.
An artificial lens implanted within the eye during eye surgery. It replaces the eye's natural lens that is removed during cataract surgery. IOLs can also be placed in front of the natural lens to correct myopia, hyperopia and other conditions.
The pressure inside the eye that keeps it firm and round. Also referred to as IOP, intraocular tension or, simply, eye pressure.7
A method of cataract removal in which many of the manual aspects are performed with a laser rather than a hand-held tool for improved accuracy and precision.
Corrective eye surgery that uses lasers to reshape the cornea. It can help reduce or eliminate nearsightedness, farsightedness and/or astigmatism.
Part of the retina that provides sharp, central and color vision needed for seeing objects clearly.
The most frequently utilized intraocular lens implants, these artificial lenses provide clear vision at one distance: far, intermediate or near.
A method of cataract surgery that gives one eye the ability to see near or intermediate objects and the other eye the ability to see distant objects—creating a greater range of vision.
Considered an advanced technology IOL, these lens implants create two or more focal points, improving uncorrected vision at far, intermediate and near distances with the goal of reducing the need for glasses or contact lenses.
Nearsightedness, a refractive error that causes distant objects to appear blurred.
A common form of open-angle glaucoma,8 though differs in that the optic nerve is damaged even though the patient’s eye pressure is in a “normal” range.9
Eye pressure that is above the normal range but with no evident changes in vision or damage to the optic nerve.10 This is considered a risk factor for glaucoma.11
The ocular (eye) surface includes two major territories: the cornea and the conjunctiva, bordered by upper and lower lids. Unlike the skin covering the rest of the body, the ocular surface is covered by a thin layer of tear film. A stable tear film present when the eye is open helps to maintain a healthy ocular surface.
Open-angle Glaucoma, also called primary open-angle glaucoma, is the most common type of glaucoma. It may result from increased eye pressure caused by a slow clogging of the drainage canals, resulting in damage to the optic nerve.12 Though open-angle glaucoma may result from high eye pressure, it’s not always the case.
The nerve that transmits visual signals from the retina to the brain.
When the correction of the original refractive error was larger than intended after eye surgery.13
What you see on the side when you’re looking straight ahead. Also called side vision.14
A surgical technique for cataract removal where the cataract is broken up and removed through a small incision using an ultrasonic probe. This is done before the artificial intraocular lens (IOL) is implanted.
The natural hardening of the eye's lens, which creates an inability to focus on nearby objects beginning for most people in their 40s.
Sometimes called “no-line bifocals” or “trifocals,” they provide a gradual progression of powers for all viewing distances.15,16
The round, central opening in the iris of your eye that light enters through.
Optical imperfections that prevent the eye from properly focusing light, causing blurred vision. The four most common kinds are myopia, hyperopia, astigmatism and presbyopia.
The innermost layer on the back of the eye. It contains millions of light-sensing nerve cells that convert light images into electrical impulses that the brain uses to create images.
Retinopathy is a common complication of diabetes where the blood vessels of the retina can swell, leak or grow abnormally. Symptoms may not be present at first but it can worsen to the point of being a leading cause of blindness in adults. Diabetic retinopathy generally affects both eyes.17
Light-sensing nerve cells in the eye’s retina that provide peripheral or side vision, allow the eyes to detect motion, and help you see in dim light and at night.
Basic contact lenses typically used to correct myopia (nearsightedness) and hyperopia (farsightedness).
Strabismus, or crossed eyes, occurs when the eye muscles or the nerves that control them don’t function properly. It can lead to an imbalance in eye movement, or the eyes not looking at the same spot at the same time. This misalignment of the eyes may be caused by severe farsightedness or poor eye muscle control.18
Every time you blink, a thin layer of tears is spread across the cornea. This layer of moisture, or tear film, forms a protective coat, lubricating your eyes and washing away any foreign bodies that might cause harm or obscure your vision.
A test used to measure intraocular pressure (IOP), or eye pressure.19
The mesh-like drainage canals between the iris and the cornea.20
When the original refractive error was improved but not completely eliminated after eye surgery.21


1. Schmier JK, Covert DW. Characteristics of respondents with glaucoma and dry eye in a national panel survey. Clinical Ophthalmology. 2009:3 645–650. Available through Accessed February 18, 2013

2. Encyclopedia Britannica Online: Aqueous humor. Accessed March 12, 2013.

3. Merriam Webster Medical Dictionary: Anterior chamber. Accessed February 20, 2013

4. National Eye Institute. Dry Eye. Accessed December 2, 2013.


6. Medline Plus. Glaucoma. Accessed February 20, 2013

7. Merriam Webster Medical Dictionary: Intraocular pressure. pressure. Accessed February 20, 2013

8. Shields, BM. Normal-tension glaucoma: is it different from primary open-angle glaucoma?, Current Opinion in Ophthalmology, 2008, 19:85-88. Accessed March 12, 2013.

9. Glaucoma Research Foundation, Normal-Tension Glaucoma, Accessed March 12, 2013.

10. American Optometric Association. Ocular hypertension. Accessed February 20, 2013

11. Glaucoma Research Foundation. High Eye Pressure and Glaucoma. Accessed February 11, 2013

12. National Eye Institute. Facts About Glaucoma. - a. Accessed March 6, 2013.

13. Eye Surgery Education Council. Surgery Options: LASIK Surgery: Post-Op Care and recovery. (glossary entries) Accessed February 22, 2013.

14. Glaucoma Research Foundation. Other Types of Glaucoma. . Accessed February 20, 2013

15. American Academy of Ophthalmology. EyeSmart: Eyeglasses for Vision Correction. Accessed February 16, 2013.

16. All About Vision. Heiting G, Mattisson-Shupnick M. Progressive Lenses Replace Bifocals for Age-Defying Appearance. Accessed February 16, 2013

17. National Eye Institute. Facts About Diabetic Retinopathy. Accessed February 21, 2013

18. American Optometric Association. Strabismus (Crossed Eyes). Accessed March 12, 2013.

19. Glaucoma Research Foundation. Glossary: Tonometry. Accessed February 20, 2013

20. Glaucoma Research Foundation. Glossary: Trabecular Meshwork. Accessed February 20, 2013

21. Eye Surgery Education Council. Surgery Options: LASIK Surgery: Post-Op Care and recovery. (glossary entries) Accessed February 22, 2013.

22. American Optometric Association. How The Eyes Work. Accessed October 7, 2013.