Vision Diseases, Disorders & Definitions

# A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

L Definitions


Acronym for Light Amplification by Stimulated Emission of Radiation. High energy light source to cut, burn, or dissolve tissues for various clinical purposes: in the retina, to treat diabetic retinopathy and macular degeneration by destroying leaking and new blood vessels (neovascularization); on the iris or trabecular meshwork, to decrease pressure in glaucoma; after extracapsular cataract extraction, to open the posterior lens capsule.


Acronym for Laser in Situ Keratomileusis. Type of refractive surgery in which the cornea is reshaped to change its optical power. A disc of cornea is raised as a flap, and then an excimer laser is used to reshape the middle layer of corneal tissue, producing surgical flattening. Used for correcting myopia, hyperopia, and astigmatism.

Lazy eye:

The brain and the eye work together to produce vision. Light enters the eye and is changed into nerve signals that travel along the optic nerve to the brain. Amblyopia is the medical term used when the vision in one of the eyes is reduced because the eye and the brain are not working together properly. The eye itself looks normal, but it is not being used normally because the brain is favoring the other eye. This condition is also sometimes called lazy eye.

How common is amblyopia?

Amblyopia is the most common cause of visual impairment in childhood. The condition affects approximately 2 to 3 out of every 100 children. Unless it is successfully treated in early childhood, amblyopia usually persists into adulthood, and is the most common cause of monocular (one eye) visual impairment among children and young and middle-aged adults.

What causes amblyopia?

Amblyopia may be caused by any condition that affects normal visual development or use of the eyes. Amblyopia can be caused by strabismus, an imbalance in the positioning of the two eyes. Strabismus can cause the eyes to cross in (esotropia) or turn out (exotropia). Sometimes amblyopia is caused when one eye is more nearsighted, farsighted, or astigmatic than the other eye. Occasionally, amblyopia is caused by other eye conditions such as cataract.

Learn more about Amblyopia

Lens, crystalline lens:

The eye's natural lens. Transparent, biconvex-shaped tissue that helps bring rays of light to a focus on the retina.

Lenticular Lenses (plus):

Prior to the use of surgical implant lenses after cataract removal, the lenticular lens was used in eyeglasses to offset the visual effect of having no lens behind the pupil to focus on objects both near and far. To do this a "high plus" trifocal eyeglass lens of approximately 10 to 15 diopters was required. A "high plus" lens is a lens that is very thick in the center and thin at the edges.

Lenticular Lenses (minus):

"High minus" lenticular lenses, although still available today as a benefit, are also not often used. A "high minus" lenticular lens is a lens that is very thick at the edges and very thin in the center. The lens design is used for those who typically must wear prescriptions of approximately minus10 diopters and higher. The "high minus" lenticular lens makes the eye of the wearer, from an observer's stand point, appear to be about twice as small as actual. The lens has the appearance of being "dished-out" in the center. The minus lenticular lens design has for all intents and purposes been replaced by lenses made of "high index" materials.

Low vision:

Low vision means that even with regular glasses, contact lenses, medicine, or surgery, people find everyday tasks difficult to do. Reading the mail, shopping, cooking, seeing the TV, and writing can seem challenging.

Millions of Americans lose some of their vision every year. Irreversible vision loss is most common among people over age 65.

Is losing vision just part of getting older?

No. Some normal changes in our eyes and vision occur as we get older. However, these changes usually don't lead to low vision.

Most people develop low vision because of eye diseases and health conditions like macular degeneration, cataract, glaucoma, and diabetes. A few people develop vision loss after eye injuries or from birth defects. While vision that's lost usually cannot be restored, many people can make the most of the vision they have.

Your eye care professional can tell the difference between normal changes in the aging eye and those caused by eye diseases.

How do I know if I have low vision?

There are many signs that can signal vision loss. For example, even with your regular glasses, do you have difficulty:

  • Recognizing faces of friends and relatives?
  • Doing things that require you to see well up close, like reading, cooking, sewing, or fixing things around the house?
  • Picking out and matching the color of your clothes?
  • Doing things at work or home because lights seem dimmer than they used to?
  • Reading street and bus signs or the names of stores?

Vision changes like these could be early warning signs of eye disease. Usually, the earlier your problem is diagnosed, the better the chance of successful treatment and keeping your remaining vision.

How do I know when to get an eye exam?

Regular dilated eye exams should be part of your routine health care. However, if you believe your vision has recently changed, you should see your eye care professional as soon as possible.

Learn more about Low Vision

Low vision aids:

Instruments such as magnifiers, prisms, print and audio materials, and computer programs to allow people with low vision to read and perform other tasks. Help is available even for people who have lost much of their vision.


Portions of this page are excerpted from Dictionary of Eye Terminology, copyright 1990-2006 by Barbara Cassin and Triad Communications. Reprinted with permission.

Some of the information above is reprinted from the National Eye Institute, National Institutes of Health, and is for educational purposes only. Superior Vision strongly recommends eye exams as the best way to diagnose eye conditions and learn more about potential vision problems.