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Glossary of Vision Terms

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Aberrometer: A device used to identify vision errors, which measures light waves as they travel through the eye's optical system.

Ablation: A term that refers to the removal of eye tissue in regards to correcting a refractive error.

Ablation Zone: Area where ablation occurs.

Accommodation: The ability for one's eyes to change focus from one distance to another.

Accommodation disorder: Accommodation refers to the eye's ability to change focus from one distance to another. The most common accommodation disorder is Presbyopia, which occurs with age; the eyes are no longer able to switch from one distance to another.

Acuity: Clearness or sharpness of vision

AK (astigmatic keratotomy): A procedure in which the surgeon makes one or two incisions in the cornea so that it is less football-shaped, thereby reducing the astigmatism. This procedure has been, for the most part, replaced by LASIK.

Anterior chamber: The part of the eye behind the cornea and in front of the iris and lens.

Aqueous humor: This is the fluid in the front of the eye between the cornea and the iris. Produced by the ciliary body, it provides nutrients to the cornea and the lens. People suffering from glaucoma have difficulty draining this fluid away, which results in possible damage to the optic nerve and a loss of vision.

Argyll Robertson pupil: Pupils that are small, irregular and do not respond to light.

Astigmatism: This is where the cornea is asymmetrical. Instead of being spherical, the eye is shaped like a football or egg. What happens is that light rays are focused on two points of the retina rather than one, which blurs the vision.

Atopy: Type of allergy where levels of the antibody immunoglobin E are increased; atopy includes rhinitis, asthma, hay fever and eczema.



Best corrected vision: The best vision achieved with correction (glasses, contact lenses) as measured on the Snellen eye chart. It is supposed to be 20/20.

Bifocal: Type of lenses segmented for nearsight and farsight. They are used most often for people suffering from Presbyopia.

Bowman's membrane: Layer of the cornea between the epithelium and the stroma.



Cataract: A term referring to the clouding of the eye's natural lens. Symptoms include: blurred vision, glare, halos, dull colors and cloudy vision.

Central island: A complication resulting from Laser Surgery; the laser leaves an "island" of corneal tissue in the ablation zone.

For more about potential risks and complications of LASIK

Choroid: Blood vessels located between the white of the eye and the retina. They provide nourishment to the back area of the eye.

Ciliary body: Part of the eye between the iris and the choroid forming the uvea. The ciliary body's main functions are accommodation, aqueous humor production and holding the lens in place.

CK (Conductive Keratoplasty): Procedure in which a surgeon uses radio waves to shrink the cornea's periphery. This is used mainly for hyperopia and presbyopia.

Read more about CK.

Color blindness: The inability to distinguish specific colors. Color blindness is inherited, and is much more common in men than in women.

Cone: A receptor in the retina that helps you see color.

Conjunctiva: The mucous membrane that lines the visible part of the eye and the inner surface of the eyelid.

Cornea: The clear, front part of the eye, which bends or refracts the light providing most of the focusing power.

Corneal abrasion: The loss of the epithelial layer of the cornea. Symptoms include: blurred vision, grittiness, light sensitivity, discomfort and tearing.

Corneal implants: Devices placed in the eye to correct vision.

Corneal topography: The recording of the surface of the eye. This map is used for evaluations related to refractive surgery, contact lens fitting and corneal disease management. It is especially useful for measuring astigmatism.



Decentration: Complication in Laser Surgery that occurs when the laser is not centered on the pupil while removing tissue. Symptoms include: glare, double vision and halos.

Descemet's membrane: Layer of the cornea between the stroma and the endothelium.

Diopter: A measurement of refractive error. Hyperopia is measured in terms of positive diopters. Myopia is measured in terms of negative diopters. The most common refractive errors range between +6 to -6 diopters.

Dry eye: A condition resulting from the eyes' inability to produce enough tears to keep them lubricated.

Read more about potential risks and complications of LASIK.



Ectasia: The progressive thinning of the cornea.

Emmetropia: The condition of an eye with normal (perfect) vision.

Endothelium: The cornea's inner layer of cells.

Episclera: Outer layer of the eye's sclera that loosely connects it to the conjunctiva.

Epithelial ingrowth: A complication from LASIK surgery in which epithelial cells grow under the LASIK flap.

Epithelium: The cornea's outer layer of cells.

Excimer laser: An ultraviolet laser used in refractive surgery to remove corneal tissue.



Farsightedness: Also known as hyperopia. Farsighted people are able to see objects far away in focus but objects near are blurry.

Femtosecond laser: Device that creates bursts of laser energy at an extremely fast rate. These pulses break apart tissue at a molecular level, without damaging adjacent areas. It is routinely used to create the flap in LASIK procedures often replacing the microkeratome mechanical blade.

Fovea: Part of the retina which provides acute eyesight.



Ghosts: Complication of Laser Eye Surgery which causes patients to see distorted images.

Glare: Complication of Laser Eye Surgery which causes patients to see luster around lights.

Glaucoma: Disease which may occur when the natural fluids of the eye don't drain properly. This creates intraocular pressure causing optic nerve damage and subsequent peripheral vision loss. Glaucoma is the leading cause of blindness and is not limited to the elderly.



Haloes: Complication of Laser Eye Surgery which causes patients to see rings around lights.

Read more about potential risks and complications of LASIK.

Haze: Clouding of the cornea that causes the sensation of looking through smoke or fog.

Higher-order aberration: Refractive errors, other than nearsightedness, farsightedness, and astigmatism that cannot be corrected with glasses or contact lenses.

Please see WaveFront Custom LASIK to learn more about higher-order aberrations and how they can be solved

Hyperopia: Also called farsightedness. Farsighted people are able to see objects far away in focus but objects near are blurry.



Inflammation: The body's reaction to trauma, infection or a foreign substance, often associated with pain, heat, redness, swelling and/or loss of function.

Informed Consent Form: A document disclosing the risks, benefits and alternatives to a procedure. As to LASIK surgery, it must be signed by the patient before the procedure will take place.

Intraocular lens: (IOL) Artificial lens that a surgeon places in a patient's eye after removing the eye's natural lens. Like a contact lens, it has a built-in refractive power tailored specifically to the patient's visual condition.

Intraocular pressure: The pressure exerted on the eye by the aqueous humor.

Iris: The pigmented membrane that lies between the cornea and the lens. It controls the amount of light that enters the eye.



Keratectomy: Surgical removal of part of the cornea.

Keratotomy: an incision of the cornea.

Keratitis: Inflammation of the cornea.

Keratoconus: A disorder, which may be genetic in nature, characterized by an irregular corneal surface resulting in blurred and distorted images.

Keratoplasty: A term referring to many types of corneal surgery, such as shrinking of collagen to decrease farsightedness and a cornea transplant to treat Keratoconus



Laser: A laser is a device that emits a powerful beam of light, used in Laser Eye Surgery to ablate tissue.

LASEK: Procedure that is similar to LASIK used mostly for people with thin corneas who are poor candidates for LASIK.

For more on LASEK

LASIK: Surgical procedure in which a tiny flap is created and the corneal tissue is ablated with an excimer laser.

For more on LASIK

Lens: Part of the eye which provides focusing power. The lens is able to change shape allowing the eye to focus at different distances.

LTK (Laser Thermal Keratoplasty) Also called Laser Thermokeratoplasty. Surgery to correct mild farsightedness in people over 40 a holmium laser is used to heat the cornea and shrink its collagen.



Microkeratome: Small instrument, either mechanical or laser, that surgeons use to cut the corneal flap during many Laser Surgeries.

Monovision: Vision correction method, either with contacts or refractive surgery for people with presbyopia.

For more on Monovision

Myopia: Also known as nearsightedness, myopia is a condition resulting in blurred distance vision.



Nearsightedness: Also known as myopia. Condition resulting in blurred distance vision.



Ophthalmologist: A medical doctor specializing in the diagnosis and medical or surgical treatment of visual disorders and eye disease. They may also write prescriptions for eyeglasses or contact lenses.

Optician: An expert in the making and fitting of glasses made to a certain prescription.

Optic nerve: The part of the eye that carries stimuli from the rods and cones to the brain.

Optometrist: A primary eye care provider who diagnoses, manages, and treats disorders of the visual system and eye diseases. They must complete four years of post-graduate optometry school for their doctorate.

Orbit: Eye socket.

Overcorrection: A complication of refractive surgery where the achieved amount of correction is more than desired.

For more on Risks and Complications



Posterior chamber: Part of the eye behind the iris and in front of the lens.

Presbyopia: A condition, beginning around age 40, where people are unable to focus at all distances, often noticed when fine print begins to blur.

PRK: A procedure using a computer-controlled excimer laser to reshape the stroma, which is less invasive than LASIK.

For more on PRK

Punctal cautery: A procedure using heat or laser energy to permanently close channels from which tears drain to help dry eye.

Punctal plugs: Tiny inserts often placed in channels or ducts of the eye where moisture drainage occurs to help dry eye.

Pupil: A hole in the center of the iris that changes size in response to changes in lighting.



Refractive error: Imperfections in the focusing power of the eye, for example, hyperopia, myopia, and astigmatism.

Refractive surgery: Surgery that improves visual acuity, with the objective of reducing or eliminating the need for glasses and contacts.

Retina: A layer of tissue that lines the inside wall of the eye. The retina transforms the images into electrical signals, and sends the signals to the brain.

Rod: A photosensitive receptor in the retina that helps you to see in low light.



Sclera: The outer coat of the eyeball that forms the visible white of the eye and surrounds the optic nerve at the back of the eyeball.

Snellen chart: Standard eyechart, developed by Herman Snellen, which measures visual acuity with letters, numbers, or symbols printed in rows of decreasing size.

Stroma: The middle layer of the cornea.



20/20 vision: A measurement that indicates normal vision. 20/20 is considered the average visual acuity for human beings.



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

For more on Risks and Complications

Uvea: This layer of the eye consists of the iris, ciliary body and choroid.



Visual acuity: Sharpness of vision, as measured with the use of a Snellen Chart.

Vitreous body: Part of the eye between the lens and the retina, containing a clear jelly called the vitreous humor.



Wavefront: This is the technology used to map the eye.

For more on WaveFront Custom LASIK

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