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The production of tears, especially in excess.
The inability to close the eyelids completely.

An acronym meaning "LASER In situ KERATOMILEUSIS". It is a method of correcting the eye to decrease dependence on glasses and contact lenses. LASIK uses a combination of sophisticated microsurgery and a laser to reshape the cornea. Reshaping the cornea alters the focusing power of the eye allowing the subject to become less dependent on glasses or contact lenses. It differs from standard laser surgery (PRK) in the rate of restoration of vision, which tends to be more rapid; it is painless; and fine-tuning of vision can be done earlier. There is also a larger range of correction available.


Lazy Eye
A condition in which visual acuity is reduced and not completely correctable by refractive methods. If vision is 20/30 or less, or if it is less than that of the other eye, it is clinically diagnosed as lazy eye, or Amblyopia.


A crystalline structure responsible for focusing light onto the retina. It changes shape slightly to allow us to change focus between objects that are near and those that are far in a younger person. In an older person, it may not be adjustable. In this case, reading glasses or bifocals may be used.


Lens Coatings
  • Scratch Protection Coating
    Light weight hard resin lenses can be more easily scratched than glass lenses. Special coatings have been developed to help protect lenses for normal scratching. The modest additional cost for such scratch coating is usually a prudent investment.
  • TD2 Hard Coating
    This new scratch coating is the ultimate anti-scratch protection for hard resin lenses. It is so effective that it has a two year guarantee against scratches.
  • Anti-Reflection Coating
    Special anti-reflective coatings are now available for spectacle lenses, much like those used for fine camera lenses. These coatings are particularly effective for reducing eye fatigue for computer operators and anyone driving at night. And, of course, anti-reflection coatings on lenses enhance appearance by removing all distracting reflections.
  • Crizal (integrates an Anti-Reflection Coating & Hard Coating)
    Time spent in front of computer screens and in harsh fluorescent lighting situations produces eye fatigue and stress from glare. By reducing glare, Crizal lenses make you feel more comfortable in your work environment. In fact, Crizal lenses have been proven in clinical studies to dramatically reduce eye fatigue caused by unwanted light reflections that create glare. Also, studies have shown that Crizal lenses allow your eyes to recover more quickly from glare caused by bright oncoming headlights when driving at night.

(contributed by H. Frank Storey, OD)

Lens Tinting Options

lens tint display

Photogray Tint
This is a tint that is clear indoors and due to the amount of sunlight darkens like sunglasses outdoors. The Photogray tint is only available in glass lenses. This tint does not work well in a car because most cars have tinted windows.

Transition Tint
This tint is available in light weight plastic lenses. Because it darkens when outdoors and lightens indoors it provides both comfort and versatility. The tint also give protection for the UV rays. One should not consider these as sunglasses for driving because they do not tint well in a car because of tinted car windows.

Standard Sunglasses
Quality sunglasses filter about 80% of the visible light spectrum and all the UV and infrared rays. The best colors for sunglasses are gray, green or brown. These tints filter more evenly across the visible light spectrum. Quality sun lenses are ground and polished to be free of distortions and imperfections. They are perfectly matched in color and absorption. Standard tinted lenses are available in glass and plastic. Sunglasses are designed for outdoor daytime wear only.

Polarized Sunglasses
When light strikes a surface like water it becomes scattered and travels in all directions like a child's sparkler. This is what is commonly know as glare. This glare produces eyestrain and discomfort. Standard sunglasses filter out 80% of the light, but cannot block glare. A polarized lens acts like a filter or lattice which allows the useful light traveling from an object to reach the eye, while blocking all the glare caused by the scattered light traveling in many different random directions. Objects then appear sharper and colors are seen more vividly. Therefore, Polarized Sunglasses combine the advantage of "standard sunglasses" with a polarized lens. These lenses are particularly effective around water, snow, sand, or simply driving down the highway. Polarized sun lenses are made by a special process which places an ultra-thin sheet of polarizing film within the lens itself. This protects the film from any damage, allows the lens to be ground to any prescription, and to be tinted.

(article contributed by H. Frank Storey, OD)

The conical projections of the anterior or posterior surface of the lens.
The globular projection of the anterior or posterior surface of the lens.
The lightening of the pupil reflection so that it looks white to tan rather than almost black.
A white corneal opacity; adherent leukoma - iris adherent to cornea.
The Eye Encyclopedia is a collection of eye care terminology created by practicing optometrists and ophthalmologists. The information provided is not intended to be a substitute for regular medical care or to diagnose or treat any medical condition, and should be used only as a supplemental source of information. Please consult your doctor if you have any questions or concerns about your eye health.