Glossary

A

Astigmatism – The term used when the surface of the eye is oval rather than spherical. This can be corrected with the laser.

C

Conventional LVC – A term used to describe all types of laser vision correction whereby the calculations for how much corneal tissue to be removed is manually entered into a laser system by the surgeon.

Cornea – This is the clear curved window at the front of the eye. The eye is like a camera and the cornea acts as the light focusing system at the front of the eye and provides most of the eye’s focus.

D

Diopters – This is the optical measure of refractive power in glasses or contact lenses. It is measured as a positive, e.g. +3.50, if you are Hyperopic (long- sighted) and as a negative, e.g. -3.50, if you are Myopic (short-sighted). The larger the number the greater the refractive error.

E

Enhancement – A LVC procedure that may be undertaken to improve the visual outcome after LVC. Enhancements are usually done once the initial procedure has stabilised.

Epithelium – The outer most layer of the cornea. In PRK the epithelium is removed, usually with the laser in the T-PRK method so the laser can then treat the underlying corneal tissue. The epithelium then regenerates within about 4 days to its pre-procedure state. 

Excimer Laser – Is a high energy, cold laser that is used to reshape corneal tissue in LVC by emitting a pulsating beam of ultraviolet light that removes corneal tissue to a precise depth. Our excimer laser uses dual small laser beams each 0.65mm wide, ensuring precise removal of tissue.  

F

Farsightedness – See Hypermetropia or Hyperopia.

G

Glare – A common complication of a LVC procedure where a patient may see additional luster around lights. It is often a subjective phenomena that usually decrease over time.

H

Haze – Usually caused by the eye’s reaction to excimer laser, haze is unnoticed by most patients, but a surgeon may be able to measure the presence of haze on a microscopic level. For more information see the section on Risks and Complications. 

Haloes – A common complication of a LVC procedure where a patient may notice concentric light rings around light sources in low levels of light. Like glare, haloes are a subjective phenomena that usually decrease over time.

Higher Order Aberrations – Until recently these particular type of aberrations where unmeasureable by conventional means. They refer to optical factors that may affect the overall visual outcome of LVC, and may contribute to glare and haloes experienced by some people after the procedure. The customised treatments delivered by our laser minimize the effect of higher order aberrations on the eventual outcome of LVC.

Hyperopia – This is the optical term for long-sightedness. In long-sightedness the cornea is too flat therefore bringing the light rays to a focus point that would be behind the retina rather than on it causing problems with distance and reading vision. To treat this the cornea needs to be steepened at the centre. Currently the most predictable and stable treatment is with the Excimer Laser.

Hypertropes – People who have a hyperopic refractive error, i.e are long-sighted.

Hypermetropia – Another word for hyperopia or long-sightedness.

I

Laser – An acronym  for Light Amplification by Stimulated emission of radiation. Lasers produce a powerful beam of light that are often used in many types of surgery to remove tissue.

LASIK – An acronym for Laser Assisted in Situ Keratomileusis. This terms refers to the process of using an excimer laser to reshape the cornea without disrupting other corneal cells. For more information on LASIK, see the section on Laser Vision Procedures.

Level of your vision – This term refers to the measurement on a common eye chart, of which line can be read. Normal vision is denoted by 6/6, meaning that a person can see at six meters, what a normal person with no refractive error can see at six meters. Better than normal vision hence would be for example, 6/4 meaning at six meters a person can see what a normal person would see at four meters. 20/20 vision is also a common term that is used, and refers to the same concept, but is measured in feet (20 feet = 6 meters approximately).

Lower Order Aberrations – These are the optical or refractive errors that can be corrected by conventional means, ie. Glasses, contacts or conventional laser vision corrective treatments. They are measurable, and can be fully revealed by a normal test for a refractive error such as a test for a glasses prescription.

LVC – An acronym for Laser Vision Correction, the term used to describe any surgical procedure that uses a excimer laser to reshape the cornea to reduce or eliminate the dependancy on an optical correction ie. Glasses or contact lenses.

M

Micro-Keratome – The intrsument used by a surgeon only in the LASIK procedure to create the flap on the outermost layer of the eye to enable the underlying tissue to be treated with the excimer laser.

Monovision – The intentional correction of one eye to be used for near vision, and the other to be used for distance. This can be accomplished by either corrective lenses or incorporated into the planning of a LVC procedure.

Myopes – People who have a myopic refractive error.

Myopia – this is the optical term for short-sightedness. In short-sightedness the cornea is too steep therefore bringing light rays to a point of focus in front of the retina rather than on it causing problems with distance vision. To treat this the most predictable method involves the Excimer Laser.

N

Nearsightedness – See Myopia.

O

Over Correction – A term used to describe the result when the change to the refractive error exceeds the attempted correction. This is less less common in LVC.

P

Presbyopia – The age related natural deterioration of near vision, resulting from the loss of elasticity of the lens as the eye ages.

PRK – The acronym for Photorefractive Keratotomy. This procedure involves removing the outermost layer of the cornea (the epithelium) and using an excimer laser to treat the underlying corneal tissue. To read more about PRK, see the section on Laser Vision Procedures.

QT

Refractive Surgery – Any surgical procedure that is undertaken to affect the overall refractive power of the eye and it’s optical system.

Regression – A complication with LVC that refers to the eye to move back towards it’s orginal refractive error after LVC. For more information, see the section on Risks and Complications.

UZ

Under Correction - A term used to describe the result when the change to refractive error does not fully achieve the attempted correction. This is more common than overcorrection, and can be altered with enhancements.

W

Wavefront Device – A machine used to reveal both lower and higher order aberrations and customize laser treatment plans to individual eyes.

Wavefront Map – A virtual map created by a wavefront device loaded into a laser system that allows a laser to customize treatment based on the individual optical error values of an eye.