Aberration
An imperfection in a lens or optical system which prevents a point focus.

Anterior Chamber
The portion of the eye behind the cornea and in front of the iris which contains the aqueous fluid.

Anti-Reflective Coatings
Lens coatings that reduce reflection and glare off lenses for cosmetic improvement, and enhancement of vision.

Astigmatism
A condition when the Cornea, (sometimes the lens) curves differently in different directions (a slice through a football). This causes objects (light) to bend differently to focus on the retina. The image is thus blurred, ghosted, or blurred unless corrected by contact lenses or spectacles.

Aqueous
The liquid contained in the anterior chamber of the eye; it is produced by the ciliary body behind the iris, and flows through the pupil into the anterior chamber before draining away at the anterior chamber angle, around the periphery of the iris at its junction with the cornea.

Bandage lens
A special contact lens used to speed healing or to protect the cornea.

Beta Carotene
In the eye, beta-carotene is converted to the aldehyde form of vitamin A called retinaldehyde (or retinal for short). It becomes bound to a protein called opsin. This combined m olecule resides in the rods and cones, the photoreceptors of the retina which lines the back of the eye.

Bifocal Lenses
Eyeglasses that accommodate two viewing zones, one for seeing objects that are near and one for distance. Bifocal lenses may have a well-defined single visible line separating the two viewing zones, or be blended as in "no line" or progressive add lenses.

Binocular
The simultaneous use of the two eyes in the act of vision to produce one image.

Biocompatible
Not causing injury, toxic or immunologic reaction to living tissue.

Cataract*
While a comprehensive eye examination by an eye care practitioner can determine for certain if you have a cataract forming, there are a number of signs and symptoms which may indicate a cataract. Among them are:

• Blurred or hazy vision where colors may seem yellowed
• The appearance of dark spots or shadows that seem to move when the eye moves
• A tendency to become more nearsighted because of increasing density of the lens
• Double vision
• A gradual loss of color vision
• A stage where it is easier to see without glasses
• The feeling of having a film over the eyes
• An increased sensitivity to glare, especially at night
• The presence of a cataract does not necessarily mean you need surgery

*What is a cataract? A cataract is a clouding or darkening that develops in the normally clear lens of the eye. This prevents the lens from properly focusing light on the retina at the back of the eye, resulting in a loss of vision. A cataract is not a film that grows over the surface of the eye. A cataract may be associated with certain diseases, medicines, or normal aging.

CE Mark
A mark on contact lens and lens care product packaging showing that the products were designed, developed and manufactured using systems approved by the Regulatory Authorities of the European Union.

Choroid
The highly vascular middle coat of the eye globe lying between the sclera and retina. Its principal function is blood supply to sustain the retina.

Computer Vision Syndrome
As defined by the American Academy of Optometry, CVS is "the complex of eye and vision problems related to near work which are experienced during or related to computer use."

Cornea
The front transparent part of the outer protective layer of the eye covering the iris and pupil. Its bulging curvature provides the major refraction or focusing ability of the eye.

Corneal Abrasion
Damage or defect of the superficial layer of epithelium of the cornea.

Corneal Distortion
An irregularity of the normal corneal curvature or surface tissue or tear film, often due to the wearing of hard non-gas-permeable lenses; tends to cause blurred vision with spectacles.

Corneal Edema
Swelling of the cornea, usually due to fluid accumulation in one or more layers of the cornea it can be due to lack of oxygen (hypoxia). This causes glare and blurring. And in some cases pain.

Crystalline Lens
The natural lens of the eye, a transparent structure suspended behind the iris; focuses light rays on the retina and changes shape to change the focus of the eye from distance to near etc.

Daily Wear
Worn contact lenses during waking hours only.

Depth Perception
Ability to determine the different distances of objects in front of us. Requires binocular vision.

Diplopia
The eyes are not working together to see things at the same time. Resulting in double vision.

Disinfectant
Solution or liquid that slows or impairs the growth of organisms, bacteria, etc. Soft lenses must be stored in a disinfecting solution. Temporary storage in saline is allowed, but the lenses will have to be disinfected prior to the next use. RGP lenses can be stored in tap water in an emergency, but will need to be cleaned and con conditioned by soaking in an appropriate disinfecting solution prior to use.

Disposable Wear
Wearing a contact lens on a disposable basis; when lens is removed from eye, it is discarded; allows benefits of decreased problems from lens deposits and spoilage.

Edema
An abnormal excess accumulation of fluid in a tissue.

Emmetropia
The condition of the normal eye where light rays from distant objects are focused on the retina so that vision is sharp and clear (20/20).

Extended wear
Wearing a contact lens for any period that includes sleep, up to a maximum of seven days continuously.

Field of view
The area that is visible through the lens of an optical system.

Flare
Starburst effect observed when light rays are reflected from the edge of a lens or optic zone.

Flashes of light
These apparent bursts of light seen in the peripheral vision can be small, bright pin-point objects, sparkles, zig-zag patterns or even appear like a lightning storm. The phenomena can be vascular in origin or due to stimulation of the retinal photoreceptors or by vitreous fluid movement or tension.

Floaters
The most common type are those annoying little black specks which seem to dart away---just out of sight--as you look for them. Often these are small remnants of vitreous protein floating freely in the more jelly-like vitreous in the back of the eye. (The vitreous fills nearly the entire inside of the eye ball.)

Glaucoma
An eye disease caused by impaired drainage of aqueous humor which results in increased intra ocular pressure. Finally the peripheral nerve fibers of the retina gradually die resulting in blindness of central vision to total blindness. Treatment may be medical (eye drops) or surgical. The condition may be acute (angle closure) or the more common open angle glaucoma. Sometimes it may also be associated with the use of certain medicines.

Hard Lens
Contact lens made from a material which is stiff and rigid usually PMMA plastic; lens will flex only a small amount, and will break if excessive force is applied.

High-Index Lenses
Advanced plastic lenses that are thinner and flatter than conventional plastic or glass lenses.

Hydrophilic
"Water-loving" i.e., absorbs water; term used for soft lenses; technically, any plastic with 4% or greater water content by weight.

Hyperopia
A condition (refractive state) in which images come to focus behind the retina resulting in defective vision for near objects, and sometimes distant objects. The eye may be too short or too weak in focusing ability. Correctable with glasses or contacts.

Hypoxia
Relative lack of oxygen; causes corneal physiological problems (e.g., corneal edema).

Intra ocular Lens
Abbreviated to IOL; plastic lens implanted in place of the natural crystalline lens during cataract surgery.

Laser Vision Correction
Surgical procedure to reshape the cornea with excimer laser; approved for correcting myopia, hyperopia and astigmatism. Also known as PRK or LASIK.

LASIK
Surgical procedure to reshape the cornea with excimer laser, used to correct myopia, astigmatism, and hyperopia.

Lens Intolerance
Discomfort during contact lens wear; can involve foreign body sensation, light sensitivity, blurred vision; often due to over wear of contact lenses, especially PMMA lenses.

Limbus
Anatomical location where the clear cornea and white sclera meet; contains many blood vessels and is a critical area in contact lens fitting for indicating the success or otherwise of a fit.

Low Vision
Impaired vision with a significant reduction in visual function which is not correctable with conventional glasses or contact lenses.

Monocular
Refers to only one eye.

Monovision
A correction therapy for presbyopia (loss of reading vision) using contact lenses; one eye is fitted for distance, the other for near vision.

Myopia
A condition in which images come to focus in front of the retina resulting in defective vision for distant objects. Eye may be to big or focusing too weak.

Optical Lens Prescriptions
Lens optical powers are written in a notation called diopters, which is a metric notation relating to the focal point of an image passed through the lens These numbers from your eye doctor tell the optician how to make your glasses.

Optometrist
Eye doctor who has completed optometry school, called an O.D. Licensed to examine eyes for defects of vision and disease and to prescribe for corrective lenses or therapy.

Ophthalmologist
Medical doctor specializing in the eye; has completed medical school, called a M.D. Licensed to examine eyes, treat eye diseases and perform eye surgery.

Opaque tint
Tint applied to a contact lens which blocks all light passage; allows total eye color change (e.g., from brown to blue eyes). May be used for cosmetic improvement of blindness.

Oxygen Transmission
General term referring to the passage of oxygen through a contact lens or lens material.

Peripheral vision
The outer part of the field of vision. Also called side vision.

Photochromic Lenses
Lenses that remain clear during dim light, but darken during bright light, or exposure to ultra violet light.

Planned Replacement
The scheduled replacement of contact lenses at periodic intervals as determined by the contact lens practitioner; also called programmed replacement.

Polycarbonate
Plastic lenses that are particularly durable and impact resistant.

Presbyopia
Loss of elasticity of the natural lens of the eyes which inhibits the eyes from sharply focusing on near objects.

Progressive Addition Lenses
Used for correcting presbyopia; lenses that have progressively more reading power from top to bottom. No-line bifocals.

PRK
Surgical procedure to reshape the cornea with excimer laser; approved for use in correcting myopia, hyperopia, and astigmatism. Also known as laser vision correction.

Refractive Error
Condition where light entering the eye is not clearly focused on the retina, resulting in blurred vision.

Rigid gas permeable lens (RGP)
A rigid lens that allows the passage of oxygen molecules.

Scotoma
An impairment to vision a blind spot caused by diminished or total lack of function of the retina or optic nerve in a limited area. It may be unnoticed (Mariotte's blind spot) or be seen as a black area in the visual field.

Scratch Resistant Coatings
A special hardened coating added to protect plastic lenses from scratching.

Single Vision Lenses
Eyeglass lenses used to correct a single refractive need, such as myopia or hyperopia, or distance or reading only.

Tear Pump
System by which fresh tears flow under and behind a contact lens when blinking; pressure from the eyelids and the movement of the contact lens create pressure which pushes old tears from behind the lens and pulls fresh tears under the lens to flush away any debris that might accumulate there.

Toric lens
A lens with two different optical powers at right angles to each other for the correction of astigmatism.

Trifocals
Eyeglasses that accommodate three different viewing areas to provide clear vision at near, distance and mid-range; have two well-defined visible lines separating the viewing zones.

Ultraviolet Rays
Invisible rays from sunlight and lamps; potentially harmful to eyes, especially related to the development of cataracts.

Uvea
The middle layer of the eye which consists of the choroid and extends to the ciliary body and iris.

Vitamin A
The need for vitamin A in the human vision system was identified almost 100 years ago. The biochemistry was clearly identified over fifty years ago, making vitamin A the first vitamin carefully examined; hence the reason why it is called A. Another related micro-nutrient, lutein, was discovered only months ago to be involved in the biochemistry of human vision.

Wettability
The degree to which water or other liquid will spread evenly across a surface.