Glossary of Terms
Clearness, as in visual acuity. The most common measure of visual acuity is the Snellen Acuity – completely normal acuity being 20/20 or 6/6 (metric version).
Abbreviation for Astigmatic Keratotomy.
Abbreviation for Automated Lamellar Keratectomy.
Any imperfection in refractive state of the eye – i.e. hyperopia, myopia, astigmatism.
A refractive abnormality where light is not focused to a point on the retina. This is often caused by the cornea or front window of the eye being elliptical (shaped more like a football) rather than spherical (shaped more like a basketball). Refractive correction includes a lens which has focusing power in one axis and no power in the opposite axis. The amount of astigmatism you have will appear in the second number of most glasses prescriptions i.e. -4.00 -1.00 x 30, or -5.00 +1.00 x 120. In both of the above cases you would have 1.00 diopter of astigmatism.
BCVA (Best Corrected Visual Acuity)
This is a measure of best corrected acuity or in other words the best acuity while wearing glasses or contact lenses – the best your eye can see.
The transparent front window of the eye. Light passes into the eye allowing vision and also out of the eye allowing the iris and pupil of the eye to be seen.
The cornea can be considered to have 5 layers:
- Corneal epithelium
- Bowman’s Layer
- Corneal stroma
- Descemets Membrane
- Corneal endothelium
An opacification or cloudiness of the normally clear cornea that occurs typically after PRK and rarely after LASIK. Any build up of inflammatory infiltrates (white blood cells), extra moisture, scar tissue, or foreign substances (like drugs) can cause a clouding of the cornea. Most types of haze will disappear with time or drug treatment but sometimes permanent haze or scars can form.
A process of mapping the surface details of the cornea with a unique camera/computer combination. Used to determine corneal slope and astigmatism for refractive correction. Also used post-operatively to measure the results.
Secondary laser treatments to refine or improve the original visual result. LASIK enhancements are performed typically 3 months following the original procedure by lifting the original flap or making a new flap. Like the original LASIK procedure, it is rapid, painless, and results in improved vision by the next day, in most cases.
Laser energy produced by several rare gas-halide mixtures. The term excimer comes from the concept of an energized molecule with two identical components or excited dimer (contracted to one word exci-mer). In PRK the term has for practical purposes become synonomous with the argon-fluoride (ArF) gas version. The wave length of an ArF excimer laser is in the far ultraviolet range at 193nm.
A refractive abnormality of the eye requiring a plus (positive or convex) lens for correction. The term originated because people who are far or distance sighted can see at distance more clearly than they can see objects which are closer. The medical term is hyperopia or hypermetropia.
A refractive abnormality of the eye requiring a plus (positive or convex) lens for correction. Synonyms: far sighted, hypermetropia. Far or distance sighted people can see at a distance more clearly than they can see objects which are closer.
An acronym for Light Amplification by the Stimulated Emission of Radiation
Laser light is different from ordinary light in that it is:
Composed of one color (wavelength) traveling in one direction and each light wave is traveling in step with the adjacent wave making the laser light more powerful by a factor of millions of times over light energy produced by non laser sources. Energy is carried by the wave in “packets’ of energy called Photons. Albert Einstein’s Quantum theory helps to explain the physics of lasers.
An acronym for Laser in Situ Keratomileusis. A surgical operation where a flap of surface cornea is cut and rolled aside in order that a laser beam can remove internal tissue from the inside (stroma or body) of the cornea. Following removal of tissue the surface layer is reattached. The amount and shape of the removed tissue is determined by the preoperative refractive error i.e. myopia, hyperopia, or astigmatism.
A refractive abnormality of the eye requiring a minus (negative or concave) lens for correction. Synonyms: near sighted or short sighted. People who are near sighted can see objects up close or at near without glasses.
A medical doctor who specializes in the eye. To become an Ophthalmologist one must first obtain a Medical Degree (M.D.) and then complete further specialty training. A medical degree typically takes 7 or 8 years university training and a specialist certification an extra 3 years in the USA or 4 years in Canada. Specialist MD's are usually divided into “medical’ and “surgical’ discipline. Some Ophthalmologists choose not to perform surgery and can be called "medical ophthalmologists".
(or doctor of optometry) is an independent primary health care provider who specializes in the examination, diagnosis, treatment, management and prevention of diseases and disorders of the visual system, the eye and associated structures as well as the diagnosis of related systemic conditions. Optometrists today most often complete a Bachelor of Science degree (with very specific requirements) followed by the four year Optometry degree program (6–8 years). Patient contact begins in the second professional year with the final year being a full 12 month internship.
A complication of PRK or LASIK where the expected amount of correction is more than desired. Overcorrection occurs in the occasional person where healing occurs less vigorously than predicted by the laser computer program, and the planned treatment “overcorrection’ persists. The overcorrection is revised by retreatment at 3 months after the initial treatment.
The “cold’ process of tissue removal which occurs with Excimer laser radiation in the 200nm wavelength range. This far-UV wavelength possess light photons so powerful that the molecular bonds of the target tissue both break down and have sufficient extra kinetic energy to fly off the surface, hence ablation. Microscopic pictures show incredibly precise cuts with no evidence of tissue burning in adjacent tissue.
“Old eye’ is a condition in which the ability to accommodate for near vision falls off because of loss of elasticity of the crystalline lens of the eye and weakness of the ciliary muscle. The individual is no longer able to read clearly and requires reading glasses.
PRK – Photo Refractive Keratectomy
Sculpting of a myopic or hyperopic lens for refractive reasons on the front surface of the eye with the use of a “cold’ laser light.
PTK – Photo Therapeutic Keratectomy
“Cold’ laser removal of surface tissue of the cornea such as scar tissue for medical or optical treatment reasons.
A surgical operation where 90% thickness cuts are made in the cornea. These cuts are made in a radial fashion and spare the visual center of the cornea. The intention is to flatten the central cornea.
A return to the original refractive state. In PRK the surface layer or epithelium is removed prior to or as part of the procedure and then the deeper the corneal stroma is reshaped with the cold laser treatment. During healing both the surface epithelium and the deeper corneal stroma can reshape and reform at different rates. Computer generated PRK treatments assume a normal “bell” curve amount of healing for both layers and thus normally “over correct’ the refractive error in order to finally heal with no refractive error and no need for glasses. A small percentage of patients will heal faster and more vigorously than expected and will thus regress or “heal’ their planned over correction back past no refractive error to their original type of error. This regression phenomenon occurs with both myopic and hyperopic corrections. It occurs more commonly with smaller ablation diameters and with abrupt transition zones at the edge of the laser treatment areas. Some surgeons have suggested that the epithelium overgrows as if nature abhors a vacuum and overreacts to fill in the space. Steroid medications can usually be used to regulate and control regression.
Abbreviation for Radial Keratotomy.
The accurate and detailed description or drawing of places or items and their surface details. Used to determine the corneal profile in order to program the computer for refractive correction as well as for post-operative corneal analysis.
UCVA – Uncorrected Visual Acuity
This is the best vision measurement taken without the use of glasses or contact lenses.
A complication of PRK or LASIK where the expected amount of correction is less than desired. Undercorrection occurs in the occasional person where healing occurs more vigorously than predicted by the laser computer program. The undercorrection is treated by further laser treatment or an enhancement at 3 months.
Manufacturer of argon floride excimer laser machines VISX 2015, VISX 2020,VISX Star, and VISX Star 2.