Resources:Glossary

Resources

Glossary
Table of Contents

Ablation

The process of removing tissue by applying energy pulses from the excimer laser onto the surface of the cornea, thus reshaping the focusing surface of the eye.

Accommodation

This is the process that enables the eye to change focus from distance to near and allows us to read. It involves muscular activity within the eye as well as a change in the shape of the eye's natural lens. This process weakens with age and the result is the need to wear reading glasses starting in our 40's. See Presbyopia.

Accommodative IOL

This is an intraocular lens designed to be placed inside the eye after the natural lens is removed and attempts to recreate the eye's more youthful ability to change focus from near to far by shifting position within the eye in response to muscular activity.

Algorithm

Formula used by the computer manufacturers to control the pattern delivered by the laser to reshape the cornea.

Astigmatic Keratotomy

A procedure used to reduce astigmatism by placing small incisions, by hand, in the cornea.

Astigmatism

A condition in which the cornea is "out of round". The surface is not spherical like the surface of a standard ball but more angular like the surface of a football.

BCVA (Best Corrected Visual Acuity)

Usually refers to the best a person can see on the standard eye chart with their most accurate refraction in glasses or the phoropter testing equipment.

Contrast Sensitivity

Contrast sensitivity is a measure of how faded or washed out an image can be before it becomes indistinguishable from a uniform field. A reduction of contrast sensitivity may be related to diminished night vision. Contrast sensitivity oftens drops temporarily after conventional laser treatments, less with wavefront-guided treatments.

Cornea

The transparent front of the eye through which light enters. It is similar to the crystal on the front of a watch.

Corneal Abrasion

A surface defect involving the most superficial layer of the cornea, known as the epithelium. These defects can be caused by contact lenses, fingernails, tree branches, etc., or induced surgically, as in the PRK and LASEK procedures. Corneal abrasions typically heal spontaneously over the next few hours or days, as the epithelium has the ability to regenerate.

Corneal Flap

A layer of tissue created by a microkeratome, under which the laser treatment is placed in the LASIK procedure.

Emmetropia

The term applied to the vision status of an individual when the eye is properly shaped and has "perfect" distance vision without correction.

Enhancement

A term used to describe a re-operation or re-treatment in refractive surgery. Primarily used in association with incisional surgeries, such as radial keratotomy and astigmatic keratotomy, it is used when there is still correction needed after the initial operation.

Epithelial Erosion

Temporary loss of surface corneal cells, usually related to dryness or trauma.

Excimer Laser

An ultraviolet-based laser that generates energy pulses that when directed by computer control can be used to reshape the surface of the cornea. This technology was originally designed for etching computer chips. It was approved by the FDA for use in the correction of nearsightedness in 1995.

Fluctuating Vision

A transient condition following most refractive surgery in which the patientÕs vision may vary a bit, day to day, until stabilization. In LASIK this is usually about two weeks.

Foreign Body Sensation

A scratchy feeling that occurs whenever the corneal surface is temporarily disturbed, as in injuries or surgical procedures.

Haze

A type of healing reaction that causes cloudiness in the cornea following PRK or LASEK. It is related to the loss of BowmanÕs Layer in these procedures.

Higher Order Aberrations

Aberrations are imperfections in the shaping of individual components of the eye. Imperfections can arise in the cornea, the lens, and even the vitreous and retina. Aberrations can be broken into lower-order (sphere and cylinder) and higher-order (spherical aberration, coma, trefoil, secondary astigmatism, and others). When these higher-order aberrations are left uncorrected or worsened, patients may complain of poor night vision, glare, halos, or ghosting of images. Until recently, we have not been able to accuracy measure these higher-order aberrations. It has been shown that conventional (non-wavefront guided) laser treatments have a tendency to increase the higher-order aberrations while reducing nearsightedness, farsightedness, etc. But the new wavefront systems are capable of measuring these aberrations and consequently help us construct treatments that are designed to either reduce these aberrations or, at least, cause minimal increases.

Hyperopia (Farsightedness)

Refractive error related to either a flat cornea or short eye length. The optical effect is that distant objects tend to be clearer than near objects.

Intracorneal Rings

Approved by the FDA in April 1999, these small acrylic arc-shaped implants are fed into tunnels created in the cornea, affecting a shape change in the cornea. Currently, they are used for mild degrees of nearsightedness only. In case of complication, they are theoretically reversible.

IntraLasik

A name given to the Lasik procedure when performed with the Intralase femtosecond laser. This procedure employs two different wavelengths of light to accomplish the procedure, an infrared wavelength to create the flap and an ultra-violet wavelength to reshape the cornea. No blade ever touches the eye.

Introcular Lenses (IOL's)

Small lenses made of silicone, plastic, or acrylic material that are placed inside the eye following cataract removal. Some newer forms of these lenses are under FDA investigation for use in highly nearsighted and highly farsighted patients.

Laser In-Situ Keratomileusis (LASIK)

A surgical procedure in which a microkeratome is used to create a surface layer of corneal tissue (flap) that can be reflected out of the way so that a laser re-surfacing treatment may be applied underneath. The flap is returned to its original position and heals very quickly.

Laser Sub-Epithelial Keratomileusis (LASEK)

A surface laser procedure in which the epithelial layers are loosened as a single sheet, moved to the side, and the laser treatment is placed immediately on the underlying surface (Bowman's membrane). The epithelial layer is then repositioned to facilitate in the healing process. Also known as Advanced Surface Ablation (ASA) or Epi-LASEK.

Lower Order Aberrations

These are the imperfections in the shape of the ocular system that result in the conditions we know as nearsightedness, farsightedness, and astigmatism. These more simple problems are what we traditionally treat with glasses, contact lenses, and conventional laser treatments.

Microkeratome

A surgical instrument used to cut the corneal flap in the LASIK procedure. There are several manufacturers and different methods by which they work. The latest development in microkeratome technology is the ultra-fast femtosecond laser system which uses infrared light to create the corneal flap, thus, no blade touches the eye.

Monovision

The process of treating one eye (mono) for distance and leaving one eye somewhat nearsighted for reading. This allows the greatest freedom from glasses use but also has the negative of reduced depth perception and the reduction of acuity that comes from two eyes adding image information together.

Myopia (Nearsightedness)

Refractive error related to either a steep, or pointed cornea, or an eye of greater than usual length. The optical effect is that near objects are clearer than distance ones.

Night Vision Problems

Many individuals complain of poor vision in the dark. This is essentially normal since the human eye is not designed for high acuity night acuity. However, some of us have worse night vision than others. Unusual enlargement of the pupil in the dark, in some people, may contribute to this problem.

Nomograms

Tables created by surgeons to adjust the laser for individual patient treatments. Based on the major variables of age and amount of correction required.

Off-Label Use

When drugs or devices that have been approved by the FDA for a specific purpose are used in a fashion outside of the official labeling guidelines, that use is considered "Off-Label". This allows a physician to apply a treatment that he feels will benefit a patient even though it has not been specifically investigated and approved by the FDA for that use, as long as the drug or the device itself has been proven to be safe and effective in certain settings. This is often apply to laser treatments that may be somewhat outside of the tested range of treatments, and often applies to drugs that have been shown to have a side benefit that was not tested in the original FDA studies. This falls under the category of what the physician and patient feel is the best Practice of Medicine and, therefore, should always be done with the patients' knowledge.

On-Label Use

When drugs and devices are approved by the FDA, they are designed to be applied in a very specific way as indicated in the Use Guidelines. As long as these guidelines are followed properly that use is considered "On-Label."

Overcorrections

The term applied to the situation when a refractive surgery treatment produces a change that is larger than that planned. This can happen in treatments for nearsightedness, farsightedness or astigmatism. Overcorrections are related to unusual healing responses, errors in preoperative measurements or nomogram use. Overcorrections can usually be remedied by the application of another, reversing type treatment.

Phakic IOL

This is an intraocular implant (IOL) that is placed in the eye without the removal of the eye's natural lens (phakos). Therefore, the eye would have two lenses within it at the same time. The FDA approved the first lens for the correction of nearsightedness in late 2004 and lenses for farsightedness and astigmatism are currently under investigation.

Photorefractive Keratectomy (PRK)

A surgical procedure using the excimer laser to reshape the front surface of the eye, the cornea, to correct refractive errors. In this procedure, the laser pulses are applied directly through the surface of the cornea after removing the most superficial layer, the epithelium, which then regenerates to cover the treated area over the next few days.

Presbyopia

This is the condition, faced by all of us as we age, that causes us to require reading glasses for near focus. This is due to the progressive weakening of our focusing muscles, which begins in our youth and culminates in reading glasses, typically in our forties.

Pseudo-Accommodative IOL

Many intraocular lenses, due to complex optical properties, seem to have some ability to provide some accommodative effect even though they are not designed to specifically change position within the eye (see Accommodative IOL).

Radial Keratotomy (RK)

A surgical procedure used to correct mild degrees of nearsightedness and astigmatism. This procedure involves making a series of small incisions in the cornea with a diamond knife to cause the cornea to change shape. RK has largely been abandoned in the United States.

Regression

This is the term applied to the situation when, following surgery for a refractive error, there is a tendency for the eye to shift somewhat back towards its original condition during the healing process. It is usually a relatively minor shift and can be adjusted with a re-treatment procedure.

Retina

The lining of the back of the eye upon which the images focused by the front of the eye fall. It is very specialized and serves as a "living film" to process the light impulses into the images that we "see".

Re-treatment

A term equivalent to "enhancement" but usually reserved for secondary treatments in laser corrections.

Surface Laser Ablation

A category of vision correction surgery including PRK and LASEK.

Topography

A digital image processing device used to measure the surface contour of the cornea. It is used before refractive surgeries to identify certain individuals with conditions making refractive surgery an unacceptably unpredictable undertaking. It can also be used after surgery to identify unusual cornea shapes during the healing process.

Undercorrection

The term applied to the situation when a refractive surgery treatment produces a change that is less than that planned. This can happen in treatments for nearsightedness, farsightedness or astigmatism. Undercorrections are related to unusual healing responses, errors in pre-operative measurements or nomogram use. Undercorrections can usually be remedied by the re-treatment process.

Wavefront Sensing

A technology designed to improve the optical quality of lens elements used in astronomical telescopes. A new addition to vision correction surgery used to attempt to reduce the aberrations present in the human eye.
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