Eye Dictionary

Eye Dictionary - L

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lacrimal system: Orbital structures of the eye responsible for tear production and drainage. Tears are produced in the lacrimal gland above the outer corner of the eye. They flow across the eye surface and drain into the upper and lower puncta, which are openings at inner eyelid margins. They then go through the upper and lower canaliculi to the common canaliculus, into the tear sac. From there, tears flow through the nasolacrimal duct, down into the nose.
laser: Acronym for Light Amplification by Simulated Emission of Radiation. A very narrow, hi-intensity light, which can vaporize tissue and/or join structures. Eye care practitioners use several types of lasers for treating various eye conditions.
laser: Excimer: A high-energy, cold laser that is used in the Photorefractive Keratectomy (PRK) and Laser In-Situ Keratomileusis (LASIK) procedures to sculpt the central zone of the cornea to correct nearsightedness, farsightedness or astigmatism. Guided by a computer under the direction of an ophthalmologist, the laser emits a pulsating beam of ultraviolet light that ablates, or vaporizes, the corneal tissue to the precise depth and area required for refractive vision correction.
See Laser In-situ Keratomielusis, Photoreactive Keratectomy, Refractive Surgery in Eye Care Encyclopedia.
laser: CO2: High-energy laser which can be used for making surgical incisions and for skin resurfacing. Emits short, intense bursts of energy that vaporize the outer layer of skin without damage to the underlying skin.
laser: Erbium: Laser developed as a refinement to the CO2 laser used in skin resurfacing for acne scarring and wrinkle removal for shallow wrinkles. Erbium laser shows promise in a new procedure to emulsify the lens nucleus during cataract surgery.
laser: Holmium: Infrared (thermal) laser developed in the late 1980s. The laser’s beam is cool and can remove small areas of tissue without affecting surrounding tissue. In a refractive surgery procedure called Laser Thermal Keratoplasy (LTK), the Holmium laser is used to shrink the peripheral area of the cornea. This makes the shape of the cornea steeper and corrects mild to moderate cases of farsightedness. The laser works when moisture in the cornea absorbs energy from the laser pulses, causing corneal tissue to heat up and shrink.
See Refractive Surgery in Eye Care Encyclopedia.
Laser In-Situ Keratomileusis (LASIK): Currently the most widely used refractive eye surgery procedure. Combines the minimal post-operative discomfort of Automated Lamellar Keratoplasty (ALK) with the computer-controlled precision of Photorefractive Keratectomy (PRK). As in ALK, a flap of corneal tissue is lifted to expose underlying tissue, which is then sculpted by the Excimer laser as in PRK.
See Laser In-situ Keratomielusis, Photoreactive Keratectomy, Refractive Surgery in Eye Care Encyclopedia.
See Free Eye Tests.
laser pointers: Pointing devices that use a laser beam. Light energy that some laser pointers can deliver into the eye may be more damaging than staring directly into the sun. Even momentary exposure can cause discomfort and temporary vision impairment.
laser: Summit: One of two primary manufacturers of the Excimer laser used in refractive eye surgery.
Laser Vision Correction: Any of several surgical vision correction techniques that use a computer-controlled laser to gently sculpt the corneal tissue to correct vision error caused by corneas that are too steep (nearsighted), too flat (farsighted) or uneven (astigmatic).
See Refractive Surgery in Eye Care Encyclopedia.
Laser Vision Correction Evaluation
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laser: Visx: One of two primary manufacturers of the Excimer laser used in refractive eye surgery.
laser: Yag: Short pulsed, high-energy light beam that can be precisely focused by computer to optically cut, perforate, or fragment tissue.
LASIK: Acronym for Laser In-Situ Keratomileusis. Currently the most widely used refractive eye surgery procedure. Combines the minimal post-operative discomfort of Automated Lamellar Keratoplasty (ALK) with the computer-controlled precision of Photorefractive Keratectomy (PRK). A flap of corneal tissue is lifted to expose underlying tissue, which is then sculpted by the Excimer laser as in PRK.
See Laser In-situ Keratomielusis, Photoreactive Keratectomy, Refractive Surgery in Eye Care Encyclopedia.
See Free Eye Tests.
lateral: In eye care terminology, denoting a position farther from the median plane or midline of the eye.
lateral geniculate nucleus: Structure in the thalmus, which is a major recipient of axons from the retina.
lazy eye: Condition of decreased vision in one or both eyes without detectable structural abnormalities or disease in the eye or visual pathways. Also known as amblyopia. Best-corrected vision is usually less than 20/20.
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lens: aspheric: Premium contact lens for borderline astigmatic patients and emerging presbyopes.
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lens: bifocal: Eyeglass lens made up of a main lens on top for distance vision and an additional lens on the bottom for near vision.
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lens: bitoric: Toric contact lens used to correct residual astigmatism.
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lens: crystalline: Natural lens of the eye that lies behind the iris and helps bring light rays to focus on the retina. Muscular elastic fibers contract or expand the lens so that it can focus on objects at varying distances. In this manner, the lens fine-tunes the focus of the light rays refracted by the cornea so that a sharp, clear and colorful image is focused on the retina. The lens of the eye is often compared to the lens of a camera.
lens: high index: Eyeglass lenses manufactured from higher refractive index material enabling the thickness and weight to be reduced while maintaining the same optical qualities.
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lens: meter: Device used for determining the refractive power of an eyeglass or contact lens.
lens: multifocal: Eyeglasses or contact lenses that enable the wearer to focus through two or more prescriptions for different distances on one lens. Bifocals have two points of focus, one for distance and the other for near, while trifocals have three points of focus — distance, intermediate and near. Progressive “no-line” eyeglass lenses offer a continuous range of focus from top to bottom.
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lens: progressive: “No-line” multi-focal eyeglass lenses with progressive powers that graduate from distance to reading power. Although progressive lenses often require a greater period of adjustment, these are the most versatile of all multi-focal designs because of the continuous range of focus.
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lens: prescription: Any lens, eyeglass or contact that has been fabricated to correct for nearsightedness, farsightedness or astigmatism.
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lens: spheric: Eyeglass or contact lens with a single continuous curve across the entire front surface.
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lens: toric: Contact lens that contains both a spherical and cylinder component to correct astigmatism. Thickness of lens may be modified from one meridian to another, thereby enabling the lens to maintain correct orientation on the eye.
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lens: trifocal: Eyeglass 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.
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lensectomy: Surgery to remove the natural crystalline lens of the eye. During most cataract surgery, the cloudy cataract lens is removed and replaced with a plastic prescription lens. In a procedure called “Clear Lens Extraction” or “Clear Lensectomy,” the eye’s natural lens is also removed and replaced with a plastic prescription lens in order to correct refractive disorders. The word “clear” denotes that the natural lens that is removed is clear, rather than a cloudy cataract lens.
See Cataracts in Eye Care Encyclopedia.
lenses: Pieces of glass or other transparent materials used for magnification or increased visual acuity.
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lensometer: Device used for determining the refractive power of an eyeglass or contact lens.
lenticular: Special noncataract lenses for patients who have cataracts.
lipid: A fat or fatty substance that collects on contact lenses, making them uncomfortable.
light adaptation: The automatic adjustment of the pupil or the retina to the amount of light that is present at any given time.
low vision: The condition that exists when ordinary eyeglasses, contact lenses, intraocular lens implants or refractive surgery do not provide clear vision. Should not be confused with blindness. People with low vision have useful vision that can be improved with vision devices. The terms “legally blind” or “partially sighted” are often used in association with low vision. A person is considered legally blind when the best-corrected vision in the better eye is no more than 20/200 and/or the field of view is less than 20 degrees. A person with best-corrected vision of no more than 20/70 in the better eye is considered partially sighted or visually impaired.
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luminance: The amount of light coming off a surface.
lutein: Yellow carotenoid pigment found in body fats, egg yolks and green plants that promotes healthy eyes. One of two primary pigments found in the central part of the retina which helps filter out damaging light.
lysozyme: A basic protein that is present in egg white, saliva, and tears.