Aberration -Visual error caused by the eye lens resulting in imperfect image

Aberrometer - An instrument to measure the aberration

Ablation - Surgical removal of eye tissue to correct a refractive error

Accommodation - A process of the eye's lens altering its focal point to bring distant and closer objects into focus.

AK - A simple modification of RK to correct astigmatism. Incisions are placed on the steepest curves instead of placing them uniformly on the cornea in a radial pattern. The steep areas relax and the cornea heals into a more spherical shape. This allows light to focus more precisely on the retina. AK can be performed alone or in conjunction with other refractive procedures.

Ametropia - Occurs when eyes with vision defects such as astigmatism, myopia, and Hyperopia are unable to properly focus light rays into a clear image. Eyes with ametropia typically require corrective lenses or eye surgery.

Amsler's grid - It is a diagnostic tool that aids in the detection of visual disturbances caused by changes in the retina, particularly the macula (e.g. macular degeneration)

Aqueous - The space between the lens and the cornea is filled with a clear watery fluid called aqueous humour.

Binocularity - The ability to focus upon an object with both eyes and create a single stereoscopic image.

Cataract - It is any opacity, which develops in the crystalline lens of the eye or in its envelope.

Contours - represent the vertical, or third, dimension on a topographic map. They show the shape and size of physical features such as mountains, hills and valleys

Cornea - The clear and strong part at the front of the eye that allows light in.

Dioptres - A measurement of refractive error. Hyperopia is measured in terms of positive dioptres. Myopia is measured in terms of negative dioptres.

Emmetropia - is the ideal state of the eye in which no refractive error is present

Epithelium - the outermost layer of cells of the cornea and the eye's first defence against infection

Excimer Laser - Type of laser used in all laser refractive surgical procedures in order to reduce refractive error.

Halos - are rings around lights due to optical imperfections in or in front of the eye

Intraocular lens (or IOL ) - an implanted lens in the eye, usually replacing the existing crystalline lens because it has been clouded over by a cataract. They usually consist of a plastic lens with plastic side struts called haptics to hold the lens in place within the capsular bag.

Keratomileusis - carving of the cornea to reshape it.

Meibomian glands - Glands in the conjunctiva of upper and lower eyelids. Produce the components of the oily, outermost layer of tear film

Microkeratome - a surgical device that is affixed to the eye by use of a vacuum ring. When secured, a very sharp blade cuts a layer of the cornea at a predetermined depth.

Phakic - the state of an eye that still has its natural (crystalline) lens intact.

Retina - light- sensitive layer of cells

Stroma - the middle, thickest layer of tissue in the cornea

20/20 Vision - the ability to correctly perceive an object or letter of a designated size from a distance of 20 feet; normal visual acuity. I f you have 20/20 vision your vision is "normal". If you have 20/40 vision, it means that when you stand 20 feet away from the chart you can see what a normal human can see when standing 40 feet from the chart. A person with 20/10 vision can see at 20 feet what a normal person can see when standing 10 feet away from the chart.