| Glossary |
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Accommodation: Ability of the eye to change its focus between distant objects and near objects. Acuity: Sharpness or clarity of vision. Amblyopia: Blurring of the vision since childhood despite an essentially normal eye exam and therefore not correctable with glasses or surgery. Sometimes called a lazy eye, wherein one eye becomes dependent on the other eye to focus. Due to improper development of the visual centres in the brain during childhood. Often associated with strabismus. Aqueous humor: Clear fluid produced inside the eye that maintains eye pressure. ARMD: Age related macular degeneration: Destruction and loss of the photoreceptors in the macula (central) region of the retina resulting in decreased central vision. In advanced cases may cause blindness. Astigmatism: Condition of the eye usually due to the cornea being more curved in one direction than another causing light from an object to be focused to different points instead of a single point. An astigmatic cornea is not perfectly rounded like a basketball but has an irregular shape more like the side of a football. Astigmatism is most often combined with myopia or hyperopia. Best corrected visual acuity (BCVA): Best possible vision a person can achieve with corrective lenses, measured in terms of Snellen lines on an Eye Chart. Bifocals: Lenses containing two focal lengths, usually arranged with the focus for distance above and near focus below. Binocular vision: Simultaneous use of the two eyes. Normal binocular vision yields a stereoscopic image and depth perception. Blepharitis: Inflammation of the eyelids. Capsular haze: A thin film of scar tissue that occasionally forms on the posterior capsule behind the intraocular lens implant following cataract surgery and removed with a YAG laser. Sometimes called a “secondary cataract” Cataract: Gradual clouding of the crystalline lens resulting in reduced vision or eventual blindness, correctable by cataract surgery. Cataract surgery: Removal of a cataract, replacing it with an intraocular lens implant. Ciliary muscle: Muscle attached to the crystaliline lens responsible for focus. Clear Lens Extraction (CLE): Procedure in which the eye’s natural clear crystalline lens is removed and replaced with an intraocular lens implant, using the same technique as cataract surgery. Also called refractive lens exchange (RLE). Conjunctiva: Mucous membrane lining the inner surface of the eyelids and covering the front part of the sclera (white part of eye), responsible for keeping the eye moist. Conjunctivitis: Inflammation or irritation of the conjunctiva. Symptoms can be present in just one eye, or it can affect both eyes and include redness of the eyes or the edges of the eyelids, swelling of the eyelids or itching. Contact lens: Small, thin removable plastic lens worn directly on the front of the eyeballs, usually used instead of ordinary eyeglasses for correction or protection of vision. Cornea: Transparent tissue that forms the front part of the eyeball, covering the iris and pupil. The cornea is the first part of the eye that bends the light and provides most of the focusing power. Corneal curvature: Shape of the front of the eye. Corneal mapping, topography: A tool used to see the refractive problems that might be present in the cornea. Corneal transplant (penetrating keratoplasty): Surgical operation of grafting a replacement cornea onto an eye. Crystalline lens: Transparent part of the eye, located behind the iris and in front of the vitreous body. Works in conjunction with the cornea to focus incoming rays of light onto the retina. Cylinder: Refers to the degree of astigmatism (uneven roundness) present in the cornea. Depth perception: Ability of the vision system to perceive the relative positions of objects in the visual field. Detached retina: A retinal detachment occurs when the retina is pulled away from its normal position in the back of the eye. Diabetic retinopathy: Deterioration of retinal blood vessels in diabetic patients, possibly leading to vision loss. Dilated, dilation: Enlargement of the pupil. Diplopia: Condition in which a single object is perceived as two. Also known as double vision. Double vision: Same as diplopia. Eyelid: Moveable, protective, fold of flesh that covers and uncovers the front of the eyeball. Flashes & floaters: Light spots or streaks and dark moving specks due to the vitreous traction on the retinal (light flashes) and solid vitreous material or blood (floaters). Fluorescein angiography: Diagnostic test by which the veins deep inside the eye are examined. Dye is injected into a vein in the arm and circulated by the blood to the back of the eye, allowing for visual examination. Fundus: Furthest point at the back of the eye, consisting of the retina, choroid membrane , sclera, optic disc and blood vessels, seen by means of the ophthalmoscope. Glare: Scatter from bright light that decreases vision. Glaucoma: Painless disease of the eye characterized by increased pressure within; left untreated it leads to a gradual impairment of sight often resulting in blindness. Halos: Rings around lights due to optical imperfections in, or in front of, the eye. Hyperopia: Also called farsightedness, hyperopia is the inability to see near objects as clearly as distant objects, and the need for accommodation to see distant objects clearly. Inflammation: Body's reaction to trauma, infection, or a foreign substance, often associated with pain, heat, redness, swelling, and/or loss of function. Intraocular lens implant (IOL): Permanent, artificial lens surgically inserted inside the eye to replace the crystalline lens following cataract surgery or clear lens extraction. Intraocular pressure (IOP): Fluid pressure within the eye created by the continual production and drainage of aqueous fluid in the anterior chamber. Iris: Colored part of the eye. Elastic, pigmented, muscular tissue in front of the crystalline lens that regulates the amount of light that enters the eye by adjusting the size of the pupil in the center. Ischemia: Restriction or blockage of blood flow through a blood vessel. Ischemia is a causative agent of certain heart attacks and strokes and is involved in various types of visual field losses. Keratitis: Inflammation of the cornea. Keratoconous: Rare, serious, degenerative corneal disease, in which the cornea thins and assumes the shape of a cone. Laser: Device that generates an intense and highly concentrated beam of light. Acronym for: Light Amplification by Simulated Emission of Radiation LASIK: (Laser Assisted In-Situ Keratomilieusis) After creating a corneal flap a laser is used to reshape the corneal surface to change the prescription of the eye. Lazy eye: Amblyopia, an eye condition noted by reduced vision not correctable by glasses or contact lenses and is not due to any eye disease. Legally blind: 20/200 vision and over is the qualification of legal blindness in Canada. Lens: Same as the crystalline lens. Clear part of the eye, behind the iris and in front of the vitreous humor. Serves to focus the various rays of light so as to form an image on the retina. Limbal relaxing incisions (LRI): Small incisions placed on the far peripheral aspect of the cornea resulting in a cornea that is more round, for correcting astigmatism. Limbus: Thin area that connects the cornea and the sclera. Low vision: Condition occurring when ordinary eyeglasses or contact lenses are unable to bring a patient's sight up to normal sharpness. Macula: Central part of the retina responsible for seeing fine detail. Macular edema: Collection of fluid in and under the macular portion of the retina. Macular degeneration: Disease of the macula, which results in the loss of central vision. Monovision: Purposeful adjustment of one eye for near vision and the other eye for distance vision. Myopia: Also called nearsightedness or shortsightedness, the inability to see distant objects as clearly as near objects. Nearsighted: Common term for myopia. Neovascularization: Often associated with diabetes, involves the formation of new blood vessels, often fragile and inappropriate for the location. Normal vision: Occurs when light is focused directly on the retina rather than in front or behind it. Ocular hypertension: Elevated fluid pressure. Ophthalmologist: An ophthalmologist is either a medical doctor (M.D.) who is qualified and especially trained to diagnose and treat all eye and visual system problems, both medically and surgically, as well as diagnose general diseases of the body. Optic disc: The head of the optic nerve that is formed by the meeting of all retinal nerve fibers. Optic nerve: Bundle of nerve fibers that connect the retina with the brain. The optic nerve carries signals of light to the area of the brain called the visual cortex, which assembles the signals into images called vision. Optician: Expert who designs, verifies and dispenses lenses, frames and other fabricated optical devices upon the prescription of an ophthalmologist or an optometrist. Optometrist: Eye care professional, graduate of optometry school, provides non-surgical visual care. Specifically educated and trained to examine the eyes, and determine visual acuity as well as other vision problems and ocular abnormalities. An optometrist prescribes glasses and contact lenses to improve visual acuity. Orbit: Boney socket containing the eyeball, fat, extraocular muscles, nerves and blood vessels. Orthoptics: Exercises designed to help the eye muscles work together to improve visual perception. Peripheral vision: Ability to perceive the presence, motion, or color of objects outside the direct line of vision. Phacoemulsification cataract surgery: Cataract removal procedure which involves making a tiny incision, about 1/8" long. A pen-like instrument, inserted through the opening, is used to emulsify and aspirate the clouded lens material, using gentle sound waves. Then an intraocular lens is inserted into place. Phakic Intraocular Lenses (IOLs): Placed inside the eye without removing the natural lens, and performs much like an internal contact lens. Photophobia: Sensitivity to light. Pink eye: Type of conjunctivitis, commonly seen in children. Posterior capsule: The thin membrane in the eye that holds the crystalline lens in place. Posterior Vitreous Detachment (PVD): Separation of the vitreous body from its attachment from the retinal surface due to shrinkage from degenerative or inflammatory conditions or trauma. An age-related condition. Presbyopia: Inability to maintain a clear image (focus) as objects are moved closer. Presbyopia is due to reduced elasticity of the lens with increasing age. PRK: Photo-Refractive Keratectomy. A procedure which reshapes the corneal surface to change the prescription of the eye. Progressive lenses: Bifocal or trifocal lenses which appear to be single vision with no distinct lines between the various focal lengths. Pupil: Black circular opening in the center of iris through which light passes into the crystalline lens It changes size in response to how much light is being received by the eye, larger in dim lighting conditions and smaller in brighter lighting conditions. Refraction: Test to determine the refractive power of the eye; also, the bending of light as it passes from one medium into another. Refractive errors: The degree of visual distortion or limitation caused by inadequate bending of light rays, includes hyperopia, myopia, and astigmatism. Refractive Lens Exchange: Procedure in which the eye's natural clear crystalline lens is removed and replaced with an intraocular lens implant, using the same technique as cataract surgery. Refractive surgery: Type of surgery (such as clear lens exchange that affects the refraction of vision. Retina: Layer of fine sensory tissue that lines the inside wall of the eye, composed of light sensitive cells known as rods and cones. Acts like the film in a camera to capture images, transforms the images into electrical signals, and sends the signals to the brain by way of the optic nerve. Retinal Detachment: Condition wherein retina breaks away from the choroid membrane, causing it to lose nourishment and resulting in loss of vision unless successfully surgically repaired. Sclera: White part of the eye. Tough covering that (with the cornea) forms the external, protective coat of the eye. Stereopsis: Ability to perceive three-dimensional depth. Strabismus: Condition occurs when the muscles of the eye do not aligned properly and binocular vision is not present. Patients with a history of strabismus may develop double vision after refractive eye surgery. Tonometry: Procedure for the measurement of intraocular pressure. Topography: A tool used to see the refractive problems that might be present in the cornea. Toric: Lens (eyeglasses, intraocular lens, or contact lens) that is the warped (astigmatic) opposite to that of the eye, thereby canceling out the error. Trifocals: Lenses containing three focal lengths, usually arranged with the focus for distance above, intermediate distance in the middle, and near vision below. Twenty-twenty, 20/20 vision: To have 20/20 vision means that when you stand 20 feet away from the Snellen eye chart you can see what the majority of people can see at that same distance. Uncorrected visual acuity (UCVA): Best possible vision a person can achieve without corrective lenses measured in terms of Snellen lines on an eye chart. Visual acuity: Clearness of vision; the ability to distinguish details and shapes, which depends upon the sharpness of the retinal image. Visual field: Area or extent of space visible to an eye in a given position of gaze. There is a central visual field - the area directly in front of us, and a peripheral visual field - our "side vision". The fields of each eye partly overlap. We do not perceive the blind spots from each eye because the area that is missing in one eye is present in the other. Vitreous humor, fluid, or body: Jelly-like, colorless, transparent substance occupying the greater part of the cavity of the eye, and all the space between the crystalline lens and the retina. Vitrectomy: Surgical removal of vitreous humor that is diseased or has lost its transparency. |