Imperfections in the visual or optical system that result in distortions and out-of-focus images.

Aberrations, Low-order
Also called refractive errors; includes myopia, hyperopia and astigmatism.

Aberrations, Higher-Order
Irregularities, other than refractive errors, that can cause such problems as decreased contrast sensitivity or night vision, glare and halos. Higher-order aberrations do not always affect vision.

Astigmatism is blurry vision produced by football-shaped cornea that is too steep in one place and too flat in another. Astigmatic corneas focus light in two different places in the eye, making both near and distance vision a problem.

The cornea is sometimes referred to as the ‘window of the eye.’ It provides most of the focusing power when light enters the eye. The cornea is composed of five layers of tissue. This is the part of the eye reshaped by laser vision correction.

Corneal Pachymetry
This is the measurement of your corneal thickness. This cornea is like the glass surface of your watch. It is clear and has a certain thickness. The averga thickness of a cornea is 500 to 600 microns or 0.5 to 0.6 millimeters thick.

Corneal topography
A computerized system to measure the shape and contour of the cornea. Essential is LASIK.

This occurs when the treatment area of the laser is not in line with the visual axis of the patient.

A measurement of the degree of which light converges and diverges; also a measurement of the lens refractive power.

The outer layer of the cornea that serves as the eye’s protective layer.

Excimer laser
A type of laser (light amplification of stimulated emission of radiation)-excited dimmer made from argon-fluorine gas. A dimmer is a combination molecule of two gases; in this case, argon and fluorine. It produces an invisible far ultraviolet light that vapourises the cornea with almost no damage or scarring.

This is a complication of PRK Excimer laser surgery. The cornea develops scarring and cloudiness after laser treatment. It does not occur with LASIK.

A refractive error in which you see better from a distance than close up.
Hyperopia is caused by an eyeball that is too short to focus light on the retina.

The coloured tissue behind the cornea. It is usually brown in Asians and blue in Caucasians. It controls the amount of light entering the eye. The pupil is opening in the iris. By regulating the size of the pupil, the iris controls the amount of light entering the eye.

Irregular Astigmatism
This is a condition where the irregular surface of the eye causes multiple images and scattering of light.

A disease of the cornea in which the cornea is conical-shaped, thin and bulging forward. Most patient who have keratoconus have very hight myopia and astigmatism.

The pupil is the "black circle” in your eye. The primary function of the pupil is to control the amount of light entering your eye. When you are in a bright environment, the pupil becomes smaller to allow less light to pass through. When it is dark, the pupil expands to allow more light to reach the back of your eye.

Lid Speculum
An instrument, placed in the eye before surgery, to gently hold the lids apart, eliminating the possibility of blinking.

LASIK (Laser-In-Situ Keratomileusis) is currently the most frequently performed elective procedure. In LASIK, a protective hinjed flap is created and gently lefted by the surgeon, then a computed-controlled cool beam of light from the Excimer laser reshapes gently the corneal bed, then the flap is repositioned and heased by itself.

Custom lasik is a procedure that enables the surgeon to further customize the conventional LASIK procedure to your individual eyes. Using an additional tools called wavefront analyzer and/or topography guided, we measure the way light travels through your eye, creating a 3-D map of your eye. This data is then programmed into the laser to customize your treatment.

The lens is the clear structure located behind the pupil. Its primary function is to provide fine-tuning for focusing and reading, which it accomplishes by altering its shape.

When, with vision correction, one eye is intentionally left slightly nearsighted. This allows you to maintain your ability to read after presbyopia begins. Gaining this near vision means giving up some distance sharpness.

A refractive error in which you see better close up than from a distance. Myopia is caused by an eyeball that is too long to focus light on the retina or a cornea which is too steeply curved.

Presbyopia develops as the lens of the eye loses some of the flexibility that characterizes a younger eye. Everyone experiences the effects of presbyopia, typically between the ages of 40 and 50.

PRK (Photorefractive Keratectomy)
Prior to PRK, PRK was the most common laser vision correction procedure. For the PRK procedure, the surgeon first removes the eye’s protective first layer of the cells, or epithelium, to reveal the next layer of corneal tissue. The surgeon will apply computer-controlled pulses of cool light from the excimer laser to reshape the curvature of the eye. PRK patients require about three days for the epithelium to heal and allow clearer vision.

The retina consists of fine nerve tissues that line the inside wall of the eye and acts like the film in the camera. Its primary function is to capture and transmit images.

Slit-lamp examination
A detailed examination of your cornea, eyelids, conjunctiva (the transparent lining of the white of your eye), iris and lens is done with a special instrument called the slit-lamp.
The health of your cornea, its shape and evidence of corneal disease will all be carefully examined. Scarring and irregularities of the central cornea will exclude the possibility of LASIK surgery.

The thick middle substance of the cornea. It is made mostly of collagen.

Included in the slit-lamp examination will be the measurement of your intra-ocular pressure. This will exclude glaucoma, a disease of the eye which causes vision and loss of visual field. LASIK will not help these patients.

By far, the most common complication of any refractive surgery: too little tissue is removed and insufficient correction of refractive error results.

Visual Acuity (VA)
Measurment of the visual ability and accuracy of the eye. Perfect vision is stated as 6/6 (in meters) or 20/20 (in feet).

Visual Acuity, Best corrected visual acuity (BCVA)
The best possible vision a person can achieve with corrective lenses measured in terms of Snellen lines on an eye chart.

Visual Acuity, Uncorrected visual acuity (UCVA)
The best possible vision a person can achieve without corrective lenses measured in terms of Snellen lines on an eye chart.

Wavefront Analyzer
Originally developed for use in high-powered telescopes to reduce distortions in space, now adapted for eye care. A single beam of infrared laser light is passed into the eye and focused on the retina. The light is then reflected off the retina, passed back through the eye, through a lenslet array to a sensor, and then analyzed from 200 different aspects to create a map of the eye – or fingerprint of vision. This technology uncovers unique characteristics of the eye never measured before using standard methods for glasses and contact lenses.
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