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Amblyopia Decreased visual acuity without any apparent disease of the eye
Aphakia Absence of the crystalline lens of the eye, normally as a result of cataract surgery.
Astigmatism Distortions in the cornea, or sometimes in the lens, that focus light rays at different lengths, making it difficult to focus well at any distance
Axis An axis is a line dividing a regular figure symmetrically.  As used in optometry, two axes define the direction of the longest and shortest radii of an oval (astigmatic) lens system of the eye.  Common usage refers to the longer axis of a lens, the direction of least power, as the cylinder axis.
Bifocal A lens with two optical zones, one for near vision and one for distance vision.
Bilateral Relating to or affecting both right and left eye.
Blepharitis Inflammation of the eyelids, usually with redness, swelling and itching
Blindness Having central visual acuity of 20/200 or less in the better eye after correction; or having visual acuity of better than 20/200, but having a field of vision of no greater than 20 degrees (legal definition).
Cataract Opacity or clouding of the natural crystalline lens, causing foggy vision.  Symptoms may include necessity of more light to read, more difficulty driving at night due to glare from headlights, or loss of contrast sensitivity.
Corneal Topography (CT) Measurement to map exact areas and degree of corneal astigmatism.
Corneal Ulcer Area of epithelial tissue of loss from the corneal surface; associated with inflammatory cells in the cornea and anterior chamber.  Usually caused by bacterial, fungal, or viral infection.
Conjunctiva Thin, translucent layers of mucous membrane, which lines the eyelids and covers the front part of the eyeball, excluding the cornea.
Conjunctivitis Inflammation of the conjunctiva (See Above).  Characterized by discharge, grittiness, redness and swelling.  Contagious; usually viral in origin.
Contact Lens A lens constructed to fit directly on the eyeball.
Cornea 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.  The outer layer (the epithelium) is the eye’s protective layer.  This layer is made up of highly regenerative cells that have the ability to grow back within three days.  You generate a completely new epithelial layer every five days.  This allows for fast healing of superficial injuries to the cornea.  Most of the inner layers provide strength to the eye.
Crystalline Lens A transparent lens suspended inside the eye immediately behind the iris, which brings rays of light to a focus on the retina.
Diabetic Retinopathy Spectrum of retinal changes accompanying long-standing diabetes mellitus. Background retinopathy (non-proliferative) is the early stage; may advance to proliferative retinopathy, which consists of growth of  abnormal new blood vessels (neovascularization) and accompanying fibrous tissue.
Dilate To spread wide. Enlarge or extend.  In eye care, dilation describes the degree of opening of the pupil.  The pupil can be further dilated by the installation of cycloplegic drops.
Diopter A unit of measurement of strength or refractive power of lenses.  Can also refer to the relative curvature of a lens surface.
Dry Eye Syndrome Corneal and conjunctival dryness due to deficient tear production, predominantly in menopausal and post-menopausal women.  Can cause foreign body sensation, burning eyes, filamentary keratitis and erosion of conjunctival and corneal epithelium.
Emmetropia The focal condition of the normal eye in which there is no refractive error.
Floaters Particles that float in vitreous and cast shadows on the retina; seen by patient as spots, cobwebs, spiders, etc.  Occurs normally with aging or with vitreous detachments, retinal tears or inflammation.
Fundus The back of the eye, which can be seen with an ophthalmoscope.
Glaucoma A progressive disease of the eye, which is characterized by pressure inside the eye being too high and causing the nerve fibers running through the optic nerve to slowly deteriorate.  There is no cure for glaucoma.  It is managed with various treatments including drops, laser treatment and traditional surgery.  A patient with glaucoma is not a candidate for laser vision correction.
Halo A hazy rung around bright light, seen by patients with a refractive error.
Haze A clouding of vision sometimes reported following Laser-PRK.  The condition usually corrects itself, after a period ranging from weeks to months.
Hyperopia Farsightedness.  The length of the eye is too short and the light rays are focusing too far behind the retina.  Farsighted patients had trouble with near tasks and close up vision can be non-existent or difficult.  Distance vision may also be affected but it is usually clearer than the near vision when comparing the two.
Intraocular Lens (IOL) An artificial lens put in the eye to replace the natural crystalline lens.
Intraocular Pressure (IOP) The pressure of the contents of the eyeball.  Increased IOP can be an indicator of an unwanted steroid response which could lead to secondary glaucoma.
Iris The colored portion of the eye.  This muscle actually contains a contracting and expanding muscle within it.  It regulates the amount of light that enters the eye and controls the size of the pupil with it’s movements.
Keratoconus A deformity in which the corneal curvature gets progressively steeper, making the cornea somewhat cone shaped.
LASIK LASIK, or Laser In-Situ Keratomileusis, is a surgical procedure to reduce refractive errors that cause nearsightedness, farsightedness and astigmatism; conditions that are historically corrected by spectacles or contact lenses.  First, the inner layers of the cornea are gently separated from the outer layers with a micro-surgical instrument.  Next, a cool ultraviolet laser applies pulses of energy on those inner layers of the cornea to slightly reshape and thin it.  Because the cornea accounts for approximately 70% of the eye’s total light bending ability, slight changes can dramatically reduce an individual’s continued dependence on corrective lenses.
Lens The lens is the clear structure located behind the pupil.  Its primary function is to provide fine tuning for focusing and reading.  The lens performs this function by altering it’s shape.  At about the age of 40 or 50, the lens becomes less flexible and Presbyopia begins.  At about the age of 60 to 70, the lens becomes cloudy and hard which prevents light from entering as well.  This condition is called a cataract.
Macula The small area of the central retina that surrounds the fovea, which contains yellow pigment.  This regions provides the most distinct vision in the retina.
Macular Degeneration One of the most common causes of decreased vision after the age of 60.  Usually evident as a loss of pigment from pigment epithelium and deposits of yellowish material in the sub-pigment epithelial layer in the central retinal zone.  Abnormal new blood vessels may grow under the retina and leak fluid and blood.  Similar changes can occur in younger patients as part of a hereditary disease.
Manifest Refraction A subjective refraction without the use of cycloplegic drops.
Myopia Nearsightedness.  The eye is too long and the light rays are focusing too far in front of the retina.  Nearsighted patients have very little trouble seeing up close but distance vision is blurry.
Nearsightedness A refractive error in which, because the eyeball is too long in relation to its focusing power, the point of focus or rays of light from distant objects is in front of the retina.
Ocular Dexter (OD) Right Eye
Ocular Sinister (OS) Left Eye
Oculi Uniter (OU) Both eyes
Ophthalmologist An MD who specializes in diagnosis and treatment of defects and diseases of the eye, performing surgery when necessary and/or prescribing other types of treatment.
Optic Disc Head of the optic nerve in the eyeball.  There is a complete absence of rods and cones here, thus it is insensitive to light and referred to as the blind spot.
Optic Nerve The optic nerve serves to carry the nerve fibers of the retina to the brain.  If the optic nerves are damaged from trauma or disease, then permanent loss of vision can occur.
Optician One who grinds lenses, fits them into frames and adjusts the frames to the wearer.
Optometrist A specialist in diagnosing and treating visual and optical disorders of the eye, prescribing lenses, vision training and other treatment.  The primary eye and vision care practitioner.
Orbit The bony cavity in the skull that houses the globe, the extraocular muscles, the blood vessels and the nerves.
Pachymetry Ultrasound measurement of the corneal thickness.
Phakic Lens The natural lens.
Photorefractive Keratectomy (PRK) A procedure to correct refractive error by ablating the surface of the central area of the cornea using an excimer laser.  The laser beam ablation pattern is shaped to create the necessary corrective refraction.
Phototherapeutic Keratectomy (PTK) A procedure to treat pathologic conditions of the surface of the cornea using an excimer laser.  The laser beam ablation pattern is flat to create a smoothing of the corneal surface
Pink Eye Inflammation of the conjunctiva (mucous membrane that covers white of eye and inner surfaces of eyelids).  Characterized by discharge, grittiness, redness and swelling.  Contagious; usually viral in origin.
Presbyopia The age-related inability of the crystalline lens to change or accommodate to focus on near objects (normally occurs in individuals over age 40).  Patients require a prescription to see tasks clearly and up close.
Pseudophakic Lens A surgically implanted lens.
Pupil The pupil is the black circle that you see in the center of a person’s eye.  The primary function of the pupil is to control the amount of light entering the eye.  When you are in a bright environment the pupil becomes smaller to let less light through.  When it is dark, the pupil expands to allow more light to reach the back of the eye.
Refraction In optics, the bending of light rays as they travel from one medium to another.  Also, a test to determine the refractive error of an eye and the best corrective lenses to be prescribed.
Retina Inner-black surface of the eye.  The retina contains light sensitive cells that convert light to electric impulses that are carried to the brain.
Retinal Detachment A separation of the retina from the choroid.
Sclera White tissue (the white part of the eye) that forms the main structural component of the globe (eyeball).  The sclera tissue is continuous from the cornea on the front of the eye to the optic nerve sheath in the back of the eye.
Strabismus Sometimes called squint, a failure of the two eyes simultaneously to direct their gaze at the same object because of muscle imbalance.
Stye Acute inflammation of a sebaceous gland in the margin of the eyelid, due to infection and usually resulting in the formation of pus.
Vision Sight; the faculty of seeing
Vitreous The gelatinous, transparent, colorless substance filling the space in the eyeball between the crystalline lens and the retina.
YAG Peripheral Iridotomy Use of a laser to put holes in the iris to help relieve pressure by allowing aqueous outflow.
YAG Posterior Capsulotomty Use of a laser to put holes in the posterior chamber that has become opaque.