Glossary
A - D E - H I - L M - P Q - T U – Z
A
Astigmatism – A refractive error caused by the eye being an irregular shape. With astigmatism, the eye ball is shaped more like a football instead of a soccer ball. This type of refractive error is measured in diopters and cyclinder axis.
C
Closed Loop Tracking – A system of tracking eye movement by sampling eye position thousands of times per second. In the case of laser vision correction, closed loop tracking provides continuous feedback to the laser about the position of the eye, and where the eye will be at the time the laser beam makes contact with the eye. The laser can then adjust the beam to compensate and ensure the laser is falling in the correct area. Logically this leads to improved accuracy.
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 – The clear, outermost part of the eye, that contains five layers (epithelium, Bowman’s membrane, stroma, Decemet’s membrane and endotheiluim). The cornea provides around 70% of the eye’s total refractive power.
D
Diopters – A measure of refreactive power. Hypermetropia is measured in positive diopters, myopia is measured in minus diopters. i.e. +3.50 or -3.50
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 stabilized.
Epithelium – The outer most layer of the cornea. In PRK the epithielium is pushed aside so the excimer laser can treat the underlying corneal tissue. The epithelium then regenerates within 48hours as it was pre-procedure. In LASIK, the flap that is created contains the epithelium, and adhere’s back onto the eye to cover the underlying tissue that has been treated.
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 is a small beam laser only 0.8mm wide, ensuring precise removal of tissue.
F
Farsightedness – See Hypermetropia.
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. Customised treatments, such as CustomCornea are able to measure and in a majority of cases, minimize the effect of higher order aberrations on the eventual outcome of LVC.
Hypertropes – People who have a hypermetropic refractive error.
Hypermetropia – A refractive error where the light rays entering the eye are not bent rapidly enough, theoretically resulting in the light rays coming to a focus behind the retina, instead of on it.
L
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 = 1 meter).
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 dependancey on an optical correction ie. Glasses or contact lenses.
M
Microkeratome – 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 – A refractive error where the light rays entering the eye are bent too quickly, resulting in the light rays coming to a focus infront the retina, instead of on it.
N
Nearsightedness – See Myopia
O
Open loop tracking – A type of eye tracking employed by some laser systems that do not detect or compensate for involuntary eye movements made during surgery. These types of tracking devices generally only are used for safety, with the laser shutting off if an eye movement takes the eye outside a designated zone. This type of tracking does not contribute to improved accuracy.
Overcorrection – 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 pushing aside 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
R
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.
U
Undercorrection - 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. |
