Ablate / Ablation
The vaporization of tissue with a laser.

Ablation zone
The area or zone of tissue that is removed during laser surgery.

Accommodation
Accommodation is the natural ability of the human lens to change power and adjust focus from near to far. The deterioration of the lens accommodation begins to be noticeable some time after age 40, when presbyopia begins.

Acuity
Measure of an eye's ability to distinguish object details and shape. Usually specified by the smallest identifiable object that can be seen at 20 ft. for distance vision and 16 in. for near vision.

Add Powers
In bifocal or multifocal lenses, the power difference between the distance and near zones of the lens.

ALK (Automated Lamellar Keratoplasty)
A surgical procedure in which a device called a microkeratome is used to remove a very thin slice of the cornea to reshape it for corrected vision. A version of this procedure has been performed since 1949.

Aniseikonia
A difference in imaging size between two eyes.

Anisometropia
A difference in refractive power between two eyes, in which the variance is at least one diopter.

Anterior chamber
The fluid-filled area between the cornea and the lens.

Aqueous
Clear watery fluid that fills the space between the back surface of the cornea and the front surface of the vitreous, bathing the lens. Aqueous is produced by the ciliary processes.

Astigmatism
A condition where the eye (cornea, lens, and/or retina) is irregularly shaped, causing distorted vision at both near and distance. Glasses, rigid contacts or toric, soft contact lenses are used to correct astigmatism. Small amounts of astigmatism may be correctable with regular soft lenses or oxygen permeable lenses.

Autorefractor
A computerized screening device designed to detect abnormalities of vision (i.e., nearsightedness, farsightedness, astigmatism).

Axis
In correcting for astigmatism, the cylinder power determines how much correction and the axis determines the direction.

Base Curve
The front curve on a lens.

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

Biomicroscope
A microscope (slit lamp) used for closely examining the cornea, lens, and membranes of the eye in layer-by-layer detail. This microscope allows for detection of degenerative changes in the cornea and is also useful in routine contact lens evaluation.

Bridge
The area of the frame-front that rests on the wearer's nose.

Bifocal
A type of spectacle or contact lens design that includes two focal areas: one for near, one for distance.

Bowman's Layer or Bowman's membrane
Bowman's layer is one of the layers of corneal tissues, immediately underneath the eye's protective epithelium. This non-regenerative layer of tissue is between the epithelium and the stroma (5-10 microns thick - .005 to .01 millimeters).

Broad beam laser
A medical instrument that produces a powerful beam of light that is focused at close range to remove corneal tissue. A broad beam laser uses a relatively large beam diameter (from 6.0 to 8.0 millimeters) which can be manipulated to ablate the cornea.

Cataract
A condition characterized by clouding of the eye's the natural lens. The cause is usually unknown but can result from exposure to ultraviolet light, injury, heredity, disease and advancing age. Some medical treatments include surgical replacement of the natural lens with an artificial lens. Cataracts are usually treated on an outpatient basis.

Center islands
A manageable complication of laser vision correction related to ablation. The incidence of center islands has been greatly reduced as more ophthalmic research has been devoted to its contributing factors.

Choroid
The choroid is a vascular layer of the eye that lies between the retina and the sclera. The choroid provides nourishment to the outer layers of the retina and forms part of the uvea, along with the ciliary body and iris. Tumors and inflammation can damage this layer resulting in diminished vision.

Ciliary Body
Circumferential tissue inside the eye composed of the ciliary muscle (involved in lens accommodation and control of intraocular pressure) and 70 ciliary processes that produce aqueous.

Cleaning solution
When cleaning contact lenses, the first step is often to apply a few drops of cleaning solution to the surface and rub gently for about 20 seconds. The solution and the lens rubbing work together to loosen debris, which is then rinsed off with saline solution. The next steps are disinfect ion and storage.

Conjunctiva
The conjunctiva is the thin transparent mucous membrane that covers the outer surface of the eye (except the cornea) and lines the inner surface of the eyelids.

Conjunctivitis
Inflammation of the conjunctiva. Conjunctivitis can be characterized by discharge, grittiness, redness, and swelling. The many forms of conjunctivitis include allergic, bacterial, viral, etc. conjunctivitis. Often called "pink eye".

Cornea
The cornea is the clear window that covers the iris and pupil and admits light into the eye. It has several layers all of which must remain clear and healthy for good vision. Eye diseases may affect one or all of the layers and thus degrade the quality of an image. Disorders of the cornea include corneal abrasions, ulcers, HSV keratitis and keratoconus. Contact lenses are fit to fully or partially cover the cornea.

In addition to clarity, the cornea provides focusing power for the eye. The cornea provides 70% of the eye's refractive power. The cornea is approximately 500 microns thick (.5 millimeter) and consists of 5 layers, which include the epithelium, Bowman's membrane, stroma, Descemet's membrane and endothelium.

Corneal flap
A thin slice of tissue on the surface of the cornea made with a microkeratome at the beginning of the LASIK procedure. This flap is folded back before the laser is applied to the inner layers of the cornea.

Corneal Refractive Therapy
Corneal Refractive Therapy ("CRT") is a non-surgical treatment that temporarily corrects myopia (nearsightedness) and astigmatism (out of round corneal surface) using the overnight wear of treatment lenses. The lenses gently reshape your corneas while asleep. Upon waking, and removing the lenses, you will experience clear and natural distance vision, without glasses or contact lenses throughout the day. Years ago the precursor of this procedure was called Orthokeratology or ortho-K.

Corneal Topographer
A corneal topographer is an instrument that maps the corneal surface to more precisely evaluate its elevation, shape and power. It has become an essential diagnosis and management tool for contact lens, refractive surgery, and disease / degeneration care.

Corneal Ulcer
An area on the cornea where the epithelial (surface) tissue has deteriorated. Associated with inflammatory cells in the cornea and anterior chamber. Corneal ulcers can be sterile or caused by bacterial, fungal or viral infection.

Contact Lens
Small plastic disc containing optical correction, worn on the cornea or sclera as substitute for eyeglasses.

Cylinder Power
In correcting for astigmatism, the cylinder power determines how much correction and the axis determines the direction of astigmatism correction.

Daily Wear Contact Lenses
Contact lenses worn during waking hours and removed at the end of each day for cleaning and disinfecting.

Decentration
A complication of laser vision correction caused by misplacement of the ablation zone that can usually be corrected with an enhancement procedure.

Demo Lenses
Plastic lenses inserted into frames for display purposes only.

Depth Perception
The appearance of depth is created when both eyes focus on the same plane simultaneously.

Descemet's membrane
The layer of the cornea between the stroma and endothelium. Five microns thick (.005 millimeters), this membrane provides an adhesion layer for the endothelium.

Deturgescence
The balance of hydration in the eye.

Diabetes
Diabetes or diabetes mellitus is a disease in which the body does not produce (Type 1) or properly use insulin (Type 2). Insulin is a hormone that is needed to convert sugar, starches and other food into energy needed for daily life. The cause of diabetes is a mystery, although both genetics and environmental factors such as obesity and lack of exercise appear to play roles. There are two major types of diabetes, type 1 and type2.
Type 1 diabetes is a disease in which the body does not produce any insulin, most often occurring in children and young adults. People with type 1 diabetes must take daily insulin injections to stay alive. Type 1 diabetes accounts for 5 to 10 percent of diabetes.

Type 2 diabetes is a metabolic disorder resulting from the body's inability to make enough or properly use insulin. It is the most common form of the disease. Type 2 diabetes accounts for 90 to 95 percent of diabetes. Type 2 diabetes is nearing epidemic proportions, due to an increased number of older Americans, and a greater prevalence of obesity and sedentary lifestyles. Both types of diabetes can lead to pathology of the eye and requires careful management.

Diabetic Retinopathy
Diabetic retinopathy includes a spectrum of retinal changes as the result of long standing diabetes mellitus. Common diabetic retinal changes include the growth of abnormal new blood vessels (neovascularization) and accompanying fibrous tissue.

Dilating
When eyes are dilated to provide an enhanced view of your internal eye structures, the pupils are wider than normal. This is accomplished by placing drops in your eyes. Your vision will normally be blurry for up to several hours after dilation.

Diopter
A unit of measure in lens focusing power or refractive error. Hyperopia is measured in terms of positive diopters. Myopia is measured in terms of negative diopters. The most common refractive errors ranged between +6 to -6 diopters.

Disinfectant
Agent that inhibits the growth of or destroys harmful microorganisms such as bacteria.

Disinfecting/Soaking Solution
After cleaning contact lenses and rinsing them with saline solution, fill the chambers of your storage case with enough disinfecting/soaking solution to cover the lenses. Always use fresh disinfecting solution. Allow your lenses to soak and disinfect overnight.

Disposable Contact Lens
Soft contact lenses, worn for brief periods, from one day to two weeks. The lenses are discarded and replaced with new lenses.

Dry Eye Syndrome
Dry eye usually occurs when eyes don't produce enough tears or when tears evaporate too quickly. Dry eye symptoms can occur because of environmental conditions or poor tear quality (which can be caused by age or the side effect of certain medications). Contact lens wearers, computer operators, post-menopausal women, and people with allergies are most susceptible to chronic dry eye.

Drusen
The white or yellowish deposits within the retina that commonly occur after age 60. Individuals with drusen are at increased risk of later developing abnormal blood vessels that leak and form scar tissue on the choroid.

Ectasia
A progressive thinning and bulging of the cornea.

Emmetropia
The scientific term for normal vision. When the cornea and lens of the eye focus an image directly on the retina, clear vision is the result.

Endothelium
The innermost layer of the cornea. The endothelium is one cell layer thick (5-10 microns or .005-.01 millimeters) and provides hydration balance to maintain the cornea's transparency. The endothelium serves three main purposes it regulates the stroma's water content, provides a barrier to ingress of several constituents of the aqueous humor, and actively transports glucose.

Enhancement
A secondary refractive procedure performed after the initial one in an attempt to achieve better visual acuity.

Enzyme cleaner
An extra-strength cleaner, typically used weekly, to remove stubborn deposits from contact lenses. Enzymatic cleaners contain enzymes, which break down proteins deposited on contact lenses. There are many different enzymatic cleansers for either soft or oxygen permeable rigid contact lenses.

Epithelial ingrowth
A complication of LASIK wherein epithelial cells grow underneath the corneal flap.

Epithelium
The epithelium is a very fine protective outermost layer of tissue on the front surface of the eye, covering the cornea. The epithelium regenerates itself every few days, is six cells thick (20 microns), and is the eye's first defense against infection.

Excimer Laser
The excimer laser is the laser used in many laser vision correction procedures. It is a cool laser that changes the shape of the cornea by vaporizing issue.

Extended Wear Contact Lenses
Contact lenses worn continually (24 hours a day), for up to thirty days prior to removal.

Extracapsular Cataract Extraction
Extracapsular Cataract Extraction is a surgical procedure to remove cataracts. In this procedure the surgeon removes the human lens from an eye while leaving the rear lens capsular intact. Prior to the development of Phakoemulsification, this was the preferred method of cataract surgery.

Eyewire
The section of the frame enclosing each lens.

Farsightedness
A condition where the eye is too weak (too short and/or flat) so that light rays haven't yet focused when they reach the retina. The most frequent result is difficulty seeing near objects clearly.

Fitting Triangle
The three contact points on an eyeglass wearer's head: right ear, left ear and nose

Floaters
In well-lit areas, some people may notice "floaters," which are tiny spots or specks that float across the field of vision. Floaters are also called vitreous floaters because the floaters are actually small pieces of the vitreous, which is the clear jelly-like substances that fill the inside cavity of the eye. Floaters are common and usually harmless, unless there is a sudden increase in the number, which could be a warning of certain eye problems.

Frame Width
The size of the frames from left side to right side. Frame width should usually equal the width of the wearer's head.

Fovea
The fovea is the center of the retina that provides the most sensitive area of vision. Nerve cells are more densely packed in the fovea, so images that are focused on the fovea can be seen in greater detail.

Ghosting
A distortion of an image that appears as a ghost-like haziness around the image. Ghosting can occur due to irregular healing of the corneal surface.

Glare
A complication of refractive surgery in which the patient sees additional luster around lights. Glare is a subjective experience that often decreases with time.

Glaucoma
An eye disease characterized by an increase in pressure inside the eye capable of causing damage to the optic nerve. Left untreated, this condition can lead to blindness. Glaucoma is usually treated with eye drops and medications. Severe cases may require surgical correction.

Glaucoma Check
Glaucoma evaluations typical involve tonometry and observation of the back of the eye. Tonometry is the measurement of intraocular pressure in millimeters of mercury (intraocular pressure is the internal eye pressure). Increased internal eye pressure is one of the signs of glaucoma.

Globe
The eyeball.

Halos
A distortion of an image in which one sees rings around lights at night. Halos are subjective experiences and can be a symptom of cataracts or a complication of refractive surgery. As a complication of refractive surgery, they often decrease with time.

Hard contact lens
Made of an inflexible plastic material called polymethylmethacrylate (PMMA), this was the first contact lens in wide use. Hard lenses had excellent optics, but because they kept oxygen from reaching the cornea, they are considered obsolete.

Hyperopia
Farsightedness

Intraocular Lens Implant
A plastic lens (IOL) that may be surgically implanted to replace the eye's natural lens.

Intraocular pressure
The pressure the fluid contained within the eye exerts on the globe.

Iris
The iris is the colored part of the eye. Muscles within the iris control the size of the pupil.

Irregular astigmatism
A refractive error caused by an irregular shape of the cornea in which the curve on one side of the meridian or axis is not symmetrical with the curve on the other side.

Keratectomy
The portion of the LASIK procedure in which the surgeon raises a thin layer of the cornea - creates a corneal flap - with an instrument called a microkeratome, to expose the layer of the cornea called the stroma.

Keratoconus
A degeneration of unknown cause, in which the cornea becomes unusually thin, irregular and excessively steep (ectasia). Eventually the cornea's irregular, cone-shape causes significant visual distortion and requires the use of custom-made, rigid gas permeable contact lenses for best vision.

Keratometer
An instrument used to measure the curvature of the cornea. This measurement enables the doctor to accurately fit contact lenses.

Keratomileusis
The surgical shaping of the cornea formerly done with a lathe and blade, now done with an excimer laser

Keratoplasty
The replacement of the cornea (corneal transplant). Keratoplasty can be lamellar (replacement of superficial layers) or penetrating (replacement of the full thickness of the cornea).

Keratotomy
A surgical incision (cut) of the cornea.

Lamellar keratoplasty
The replacement of the superficial layers of the cornea with the layers of donor corneal tissue.

Laser
An acronym for light amplification by stimulated emission of radiation. A medical instrument that produces a powerful beam of light and can produce intense heat or cool vaporization when focused at close range. Lasers are often used in surgery to remove tissue.

Laser radar tracker
This type of tracker is capable of tracking involuntary eye movements during surgery to ensure accurate laser beam placement.

LASIK
Acronym for laser-assisted in-situ keratomileusis, a surgical procedure in which a tiny flap is cut in the top of the cornea, underlying corneal tissue is removed with an excimer laser, and the flap is put back in place. The surgery corrects vision problems such as nearsightedness, farsightedness and astigmatism.

Lens
The clear lens of the human eye which rests behind the iris (colored portion of the eye) is a living, growing structure consisting of proteins that helps to focus light. Unlike the glass or plastic of a camera lens, the human lens can change thickness to allow us to see near or far objects. People who wear glasses cannot clearly focus images with their lens alone. Disorders of the lens are usually related to a cataract.

Lens Blank
An unfinished lens, which is then ground to fill a prescription and placed in a pair of spectacles.

Lens Capsule
The lens capsule of the human lens is an elastic-like bag that envelopes the lens. The capsule helps control the shape of the lens for accommodation.

Leucomas
Scars that are dense and white.

Macula
The macula is a very small, but extremely important portion of the retina. It has a large number of the cone nerve cells and, therefore, is responsible for our central vision. Macular degeneration and macular holes are causes of poor vision in adults.

Macular Degeneration
Age related macular degeneration is a group of conditions that include deterioration of the macula, resulting in a loss of sharp central vision. There are two general types of macular degeneration. One type of macular degeneration is dry, which is a disturbance of macular pigmentation with deposits of yellowish materials under the pigment epithelial (surface) layers. In the wet form of macular degeneration abnormal new blood vessels grow under the retina and leak fluid and blood to further disturb macular function. Macular degeneration is the most common cause of decreased vision in people over age 60.

Mapping
A computerized color picture of the physical features of the corneal surface; illustrates curves in the cornea and how steep or flat the cornea is.

Meibomian secretions
Oily secretions from the eyelid glands that supply the outer portion of tear film, preventing rapid tear evaporation and tear overflow.

Micron
A unit of measure equal to one thousandth of a millimeter, or about the size of three blood cells.

Microkeratome
A microkeratome is a surgical instrument, (often automated) which uses a blade to create a very thin flap of corneal tissue as the initial step in certain refractive surgery procedures such as LASIK.

Misaligned flap
A condition in which the flap created with the microkeratome during LASIK has not returned to its correct position after the procedure is complete. It is sometimes possible to reposition the flap.

Mixed astigmatism
A condition of the eye that results in blurred distance and near vision. The cornea and lens focus the light rays at different points with one point focused in front of the retina and the other point focused behind the retina. Clear vision requires that all focus points be directly on the retina.

Monovision
This is a contact lens fitting technique that is an alternative to bifocal glasses, bifocal contacts or reading glasses. It may be used with either soft or oxygen permeable rigid contacts. One eye is fit with a contact lens for distance vision, and the other eye is fit for near vision. Although it is an effective technique, it does have disadvantages. For example, many people who use monovision report compromised depth perception. Due to the success of monovision contact lenses many surgeons offer monovision as an option for refractive surgery patients who require correction for both distance and near.

Multifocal Lens
A lens with more than one optical center (i.e., a bifocal with two, a trifocal with three, a progressive with many).

Myopia
Nearsightedness.

Nearsightedness
A condition where the eye is too strong (the eyeball is too long and steep), so that light rays focus before they reach the retina. The result is difficulty in seeing distant objects clearly.

Nebulas
Scars that are translucent.

Nomogram
A surgeon's adjustment to the laser's computer calculation to further refine his or her own results.

Off label use
The permissible use of an approved drug or instrument in a way that has not been specifically sanctioned by the Food and Drug Administration (FDA).

Ophthalmologist
Ophthalmologists are medical doctors (M.D.) or osteopathic doctors (D.O.) who specialize in the eye. They perform eye examinations, treat disease, and perform surgery.

Ophthalmoscope
This hand-held, lighted instrument helps detect a wide range of systemic and vision problems by giving the doctor a close-up view of the retina and other important parts of the eye.

Optic Atrophy
A pathological condition in which the optic nerve degenerates and results in loss of vision.

Optical Center
The spot on the eyeglass lens where light passes through without bending (refracting). This point is normally placed in front of the pupil.

Optic Nerve
This large yellow structure gathers the nerve impulses from the retina and transmits them to the specialized visual portions of the brain. Visual information is organized very precisely as it is directed from our eyes to the occipital cortex in the back of the head just above the neck. Glaucoma and optic neuritis are examples of eye diseases in this portion of the eye.

Optician
Opticians are certified to fit glasses and contact lenses. Opticians usually work in optometric or medical offices, working as a team with an O.D., D.O., or M.D. to fit contact lenses and glasses.

Optometrist
Doctors of optometry (O.D.) complete four years of post-graduate optometry school. Optometrists examine eyes for both vision and health problems, diagnose and treat eye disease, prescribe glasses, and fit contact lenses. They can prescribe many ophthalmic medications and often participate in pre- and post-operative surgical care.

Overcorrection
The result achieved when the change to refractive error exceeds the attempted correction.

Oxygen Permeable Contact Lens
Also known as an RGP (rigid gas permeable), this contact lens is made of breathable plastic that has been custom fit to the shape of the cornea. Oxygen permeables are long lasting, comfortable, easy to clean, and healthy for the eyes.

Pachymetry
The process of measuring corneal thickness, usually using an ultrasonic probe.

Phakoemulsification
Phakoemulsification is a surgical technique used to remove cataracts. The procedure is performed using a special irrigation-aspiration instrument. With this instrument, the surgeon first breaks up a cataract with ultrasonic (sound) vibration and then removes the particles via aspiration (fluid and suction). This technique revolutionized cataract surgery, allowing the surgeon to perform the entire surgery through a very tiny incision in a much short time than old fashioned (extracapsular) method.

Phoroptor
Instrument used by the doctor to determine the final lens prescription and alignment of the eye. This is the instrument use during the "which is better, one of two" procedure.

Photorefractive Keratectomy
A surgical procedure in which an excimer laser removes surface corneal tissue (epithelium) to reshape the stroma and correct vision problems such as myopia. The acronym for photorefractive keratectomy is (PRK).

Piggyback contact lenses
This is the combined use of soft and rigid gas permeable lenses. The soft lenses promote comfort and stable positioning of the rigid lenses. The rigid lenses, worn over the soft lenses, are used to promote maximum vision. This technique is used in unusual cases when rigid gas permeable lenses can not be tolerated because of discomfort.

Plano
No refractive error or zero (0) diopters of correction.

Presbyopia
With aging, the eye's lens looses its ability to change power and adjust focus from near to far. This results in blurred vision at reading distance, as well as eyestrain. Presbyopes may wear reading glasses, or multifocal contact lenses or glasses. Most often, presbyopia begins some time after the age of 40.

Polarized Lenses
Lenses that contain a polarized filter specifically designed to reduce glare. Those who work or drive in bright conditions and those who play snow or water sports would benefit from polarized lenses.

Polycarbonate
A synthetic, light material used to create impact-resistant spectacle lenses.

PRK
Since it was first developed in 1987, over 1,000,000 Photorefractive Keratectomy (PRK) procedures have been performed. PRK uses an excimer laser to gently reshape the surface of the cornea. Because the excimer laser is a cold laser, it does not burn the tissue. It produces a gentle beam of light, which removes microscopic corneal layers, usually only 10-15% of the cornea's total thickness. This process, known as photoablation, changes the shape of the cornea, resulting in an image, which is more finely focused on the retina, restoring clearer vision.

Progressive Addition Lenses
Like bifocals and trifocals, progressive lenses provide clear vision at all distances: near, intermediate, and far. The difference is that the viewing zones gradually blend into each other. This gradual transition offers a lens power for virtually all viewing distances and provides the cosmetic advantage of no visible bifocal line.

Ptosis
Drooping of upper eyelid.

Pupil
The small dark portion in the center of the eye, the pupil opens and closes to regulate the amount of light, and thus the amount of visual information, the retina receives.

Pupillary Distance
The distance, in millimeters, from one pupil center to the other. PD measurement is used to ensure proper lens placement.

Radial Keratotomy
A surgical procedure in which incisions (cuts) are made in the cornea in a radial pattern, to flatten the cornea and correct myopia. The acronym for radial keratotomy is RK.

Refraction
The procedure used to determine the presence or level of refractive errors (myopia, hyperopia, astigmatism, presbyopia). A refraction is needed to generate the prescription for glasses or contact lenses.

Refractive Error
Optical defect where parallel light rays are not brought to a sharp focus on the retina, producing a blurred retinal image. Common refractive errors include myopia, hyperopia and astigmatism.

Refractive Index
The ability of a lens to bend light. Materials that bend the most light have the highest refractive index (RI).

Refractive Surgery
Any type of surgery, whether performed with a blade, laser, or waterjet, that corrects visual acuity. Refractive surgeries includes Radial Keratotomy (RK), Photorefractve Keratectomy (PRK), LASIK (laser-assisted in-situ keratomileusis), PT, etc.

Regression
A backwards shift from the initial visual outcome.

Regular astigmatism
A refractive error caused by an irregular shape of the cornea (usually a football shape) in which the curvature is symmetrical across one or more meridians or axes.

Retina
The retina is a thin tissue in the back of the eye that receives light formed by the lens (similar to the film in a camera) into an image. The retina contains multiple layers and specialized nerve cells called rods and cones, which transmit light and convert the image to electrical impulses, which are then carried by the optic nerve to the brain. Retinal detachment and diabetic retinopathy are common diseases of the retina.

Retinal detachment
Retinal detachment is a condition in which the sensory retina separates from the underlying pigment epithelium (surface). The detachment disrupts visual cell structure and disturbs vision. Detachment is usually caused by a retinal tear and requires immediate surgical repair.

Retinitis pigmentosa
Retinitis pigmentosa is a type of retinal degeneration, which progresses over many years to tunnel vision and finally blindness.

Rewetting solution
Drops that contact lens wearers can use if needed to keep the eye moist and their lenses comfortable.

Rigid gas permeable lens
Same as oxygen permeable lens. The acronym for rigid gas permeable is RGP.

Saline solution
Sterile salt solution used to care for, primarily, soft contact lenses.

Sclera
The tough protective layer of the eye is the sclera. It is the white of the eye. Inflammation of this layer is known as scleritis.

Slit lamp
A microscope (Biomicroscope) used for closely examining the cornea, lens, and membranes of the eye in layer-by-layer detail. This microscope allows for detection of degenerative changes in the cornea and is also useful in routine contact lens evaluation.

Small-spot beam
At less than 1 mm in width, this type of beam allows a LASIK specialist to perform corneal shaping in fine, gradual, precise increments.

Snellen Chart
The eye test chart for assessing visual acuity (i.e. 20/20 to 20/400).

Soft Contact Lens
Made of gel-like plastic (also called hydrogel or hydrophillic), soft contact lenses contain varying amounts of water. They provide good initial comfort for first-time wearers but must be replaced often.

Sphere Power
The first number in a prescription for corrective lenses, which indicates the amount of myopia or hyperopia correction.

Spot scanning laser
A medical instrument that produces a powerful beam of light that is focused at close range to remove corneal tissue. Spot scanning lasers use radar technology to track the eye's movement.

Starbursts
Flares of light seen around a lighted object that may appear like a star. This symptom is similar to halos and may occur after surgery.

Sterile interface inflammation
An inflammatory reaction underneath the corneal flap after LASIK surgery that is not due to bacteria. This condition may result in vision loss.

Stromal Tissue
Stromal tissue refers to the central layers of the cornea. It comprises the majority or thickest part of the corneal structure (450-600 microns - approximately .5 millimeters). It is located between Bowman's and Decemet's membranes.

Symmetry of refractive error
This occurs when the refractive error of both eyes are close to the same value.

Tear Film
Tears are extremely important for good vision and eye health. The tear film nourishes and lubricates the front of the eye and contains three components, oil, aqueous (water), and lipid (fat). All of these components must be present in the proper quantities to properly lubricate the outer surface of the eye. Disorders of the tear film include dry eye.

Tonometry
Tonometry is the measurement of intraocular pressure in millimeters of mercury (intraocular pressure is the internal eye pressure). Increased internal eye pressure is one of the signs of glaucoma.

Topical proparacain hydrochloride
An anaesthetic eye drops.

Toric lens
A spectacle or contact lens designed to correct for astigmatism.

Transition Zone
The area of progressive eyeglass lenses where the distance vision power gradually changes into the near-vision power.

Trial or diagnostic contact lens
This is a lens, often disposable, that is worn on a trial or diagnostic basis to determine its effectiveness and safety.

Trifocal lens
A type of spectacle or contact lens design that includes three focal areas: usually a reading lens, a lens for faraway viewing, and a lens for mid-distance viewing.

Uncorrected visual acuity
A person's vision without corrective lenses measured in terms of Snellen lines on an eye chart. Acronym is UCVA.

Undercorrection
The result achieved when desired change in refractive error is not fully achieved.

Ultraviolet (UV) Protection
The degree to which a lens or its coating protects the wearer's eye from the sun's harmful rays.

Uvea
The uvea consists of the pigmented (colored) layers of the eye including the iris, ciliary body and choroid.

Uveitis
Inflammation of any of the structures of the uvea: iris, ciliary body, or choroid.

Vaporization
The process by which the laser breaks the bonds of chemicals between individual molecules with little or no damage to surrounding cells. This process is also called photoablation.

Visual acuity
Another phrase for visual clarity, it refers to how clearly a person can see. Visual acuity is often measured with a traditional eye chart.

Visual Fields Test
This test is used to detect deficiencies in central or peripheral vision and is often computerized.

Visual Therapy
Vision therapy is the process of educating the visual system to function more effectively through specialized treatment, therapeutic exercise and home treatments. Visual therapy is often prescribed to improve near focusing, accommodation or binocularity.

Vitreous or Vitreous humor
Vitreous fluid fills the cavity of the eye. It is a clear gel-like substance that supports the growth of the eye during development. As we age, the vitreous becomes more water-like in consistency and bits of the vitreous may break off and float around. Vitreous floaters are common and generally inconsequential. Uveitis is a serious disease involving the vitreous.

Wetting solution
When placing an oxygen permeable contact on your eye, first put a drop or two of wetting solution on the bowl of the lens. This helps the lens adhere to your eye better. Wetting solution may also be used to relieve dryness after several hours of lens wear.