Aberration: See: Spherical Aberration
Accommodation: Focusing within the eye to increase the optical power to maintain a clear image as an object is moved closer. This is accomplished by the natural lens of the eye changing its shape (both contracting to focus up close and then relaxing to focus on more distant objects).
Anisometropia: Unequal refractive errors in the two eyes. The difference is usually one diopter (unit of measurement in eyeglass prescriptions) or greater.
Anterior Chamber: The space within the eye between the innermost layer of thecornea (endothelium) and the iris (the part of the eye that gives the eye its color). This space is filled with a fluid known as aqueous humor. An open angle is necessary to drain the normal fluid within the eye. If the angle closes, it can lead to narrow angle glaucoma, which is an ophthalmic emergency when acute.
Applanation Tonometry: The measurement of intraocular pressure , given in millimeters of mercury, in which the amount of force required to flatten an area of the cornea, by contact, is documented. This is a routine screening test forglaucoma.
Astigmatism: A condition of the eye in which the curvature of the cornea focuses light rays at two different spots within the eye. This can create eyestrain and in some cases, blurry vision. This can be corrected with special, toric contact lenses or eyeglasses, as well as with laser vision correction. Almost all people have some degree of astigmatism.
Bandage Contact Lens: A soft contact lens that is used to cover and protect the epithelium of the cornea so that it is able to regenerate following trauma (eg: a corneal abrasion) or PRK refractive surgery.
Collagen: Connective tissue protein which is the structural backbone of the sclera,cornea, as well as other fibrous tissues of the body.
Collagen Crosslinking: A surgical procedure using UV light and a photosensitizer to strengthen the chemical bonds of corneal collagen. This technique is currently pending FDA approval and is indicated for the treatment of keratoconus, ectasia as well as other conditions that weaken corneal tissue.
Conjunctiva: The transparent mucous membrane that covers the outer surface of the eyeball (sclera), but excludes the cornea. It also lines the inner surface of the eyelids.
Cornea: The transparent window of the eye that covers the iris, pupil and anterior chamber and provides most of the eye’s optical power. The cornea consists of 6 layers: epithelium, Bowman’s membrane, stroma, Dua’s Layer, Descemet’s membrane and endothelium.
Corneal Flap: The portion of the cornea which is created with a microkeratome or the femtosecond IntraLase® laser and then folded back during the LASIK procedure so that the corneal bed underneath can be re-profiled with the excimer laser duringlaser vision correction.
Corneal Specialist: An ophthalmologist who has advanced training in microscopic surgery of the cornea.
Descemet’s Membrane: One of the 6 layers of the cornea, Descemet’s membrane is the thin layer deep within the cornea. The tissue of this membrane is just behind the endothelium and composed of collagen and elastic threadlike fibers.
Dilation (Pupillary): The widening of the pupil induced by eye drops to facilitate an examination of the fundus, the posterior portion of the eye, which includes: theretina, optic nerve and disc, macula and blood vessels.
Direct Ophthalmoscope: A handheld device used to visualize the fundus (retina) of the eye. It provides a magnified upright image of the retina.
Dua’s Layer: One of the 6 layers of the cornea. Previously undetected, the discovery of this layer was published by scientists at The University of Nottingham in 2013 after several years of research. This layer is situated between the stroma and Descemet’s membrane. Although this layer is thin, (only one hundredth the thickness of the entire cornea) it is a very strong layer.
Ectasia: In ophthalmology this term can mean a weakening of the cornea.
Endothelium: One of the 6 layers of the cornea, the endothelium is the innermost surface of the cornea, situated between Descemet’s membrane and the anterior chamber. It acts as a pump to keep excess water out of the stroma. The cornea needs to be more dehydrated than the rest of the body in order for it to be a clear window in the front of the eye.
Enhancement Procedure: Surgical fine-tuning of an earlier refractive procedure, usually within the first year.
Epithelium: One of the 6 layers of the cornea, the epithelium is the outermost layer of the cornea, situated between Bowman’s membrane and the tear film. This is the part of corneal tissue that is removed with the excimer laser during laser vision correction.
Excimer Laser: A cold ultraviolet (UV) laser used in refractive surgery procedures (PRK and LASIK) to reshape the cornea. The laser uses UV light to remove microscopic amounts of corneal tissue with minimal thermal damage. Its precision is at the level of a micron.
Farsightedness: See: Hyperopia
Fovea: The central point of the macula that produces the sharpest vision.
Hyperopia: A refractive error of the eye created by an underpowered eye that is too short for its optical power. Light rays from an object enter the eye and come to a focus beyond the retina, creating a blurry image. This condition can be corrected with plus powered lenses in eyeglasses and contact lenses or with laser vision correction. Younger patients may be able to compensate for this naturally.
iLASIK®: Trade name of the procedure which combines AMO WaveScan™ technology, the VISX® Star S4 excimer laser and the IntraLase® femtosecond laser for laser vision correction. This system is currently the only approved laser vision correction technique for use by NASA for its astronauts. Click here to learn more about iLASIK.
Indirect Ophthalmoscope: Instrument consisting of a bright light source and a handheld magnifying lens used to visualize the posterior portion of the eye (thefundus). It creates an inverted image of the fundus projected in the front of the eye. This instrument has a wider field of view than the direct ophthalmoscope and the binocular model allows stereoscopic depth perception of the retina.
Intacs®: Trade name for plastic rings which are implanted into the peripheral corneal stroma. This is a type of refractive surgery. The rings are used to flatten the cornea to reduce myopia (nearsightedness). This procedure is sometimes reversible, but may leave scarring.
IntraLase®: The laser method o creating a corneal flap used in laser vision correction. This blade less, all-laser method creates a very precise depth and diameter. Click here to learn more about IntraLase.
Intraocular: Inside the eye.
Iris: The pigmented tissue behind the cornea which gives color to the eye and controls the amount of light entering the eye by changing the size of the pupillaryopening. This function of the iris is similar to the aperture of a camera lens.
Kerato- (prefix): Pertaining to the cornea.
Keratoconus: A degenerative corneal disease which may affect vision and is characterized by thinning and cone-shaped protrusion of the central cornea. This disease typically affects both eyes, although not symmetrically, and usually comes apparent in the 2nd decade of life.
Keratomileusis: Refers to a corneal refractive surgery procedure that is involved with creating a laser flap.
LASIK (Laser In-Situ Keratomileusis): LASIK is a laser vision correctionprocedure that combines a corneal flap created by a microkeratome or an intralase laser, along with an excimer laser to correct visual refractive abnormalities. It combined two previously used surgical procedures (listed below) and has been performed millions of times worldwide:
1. The creation of a corneal flap by a procedure known as keratomileusis.
2. The use of an excimer laser to precisely reshape the corneal tissue beneath the flap. This enables light rays to be more accurately focused on the retina at the back of the eye, thereby improving vision. The flap is then returned to its original position.
Click here to watch a live LASIK surgery performed by Dr. Mandel.
Microkeratome: An oscillating blade used for dissecting a precise thickness of tissue from the cornea to create a corneal flap in LASIK. This method has now been replaced with a more advanced blade less, all-laser method of flap creation known as the IntraLase femtosecond laser.
Mitomycin: An anti-cancer drug that is used as a standard of care for many PRKrefractive surgery patients to control inflammation and scarring.
Monovision: An alternate method of correcting presbyopia. One eye (the dominant eye) is corrected for distance vision and the other eye (non-dominant eye) is corrected for near. This can be accomplished with contact lenses orrefractive surgery, but usually does not work with eyeglasses.
Myopia: (AKA: Nearsightedness): A refractive error of the eye created by an overpowered eye which has too much optical power for its length. Light rays coming from a distant object are brought to a focus before they reach the retina, creating a blurry image. Nearsighted people can read clearly without glasses, but distance vision is blurry. This condition can be corrected with minus powered lenses in eyeglasses and contact lenses or with laser vision correction.
Narrow Angle Glaucoma: A form of glaucoma which is categorized by a rise inintraocular pressure in patients with narrow anterior chamber angles. This condition can be acute with accompanying pain and loss of vision if not treated promptly.
Nearsightedness: See: Myopia
Occluder: An ophthalmic instrument used for covering one eye at a time during vision testing or treatment.
Open Angle Glaucoma: The most common type of glaucoma in which the anterior chamber is open. It is characterized by an increase in intraocular pressure which causes damage to the optic nerve as well as visual field (peripheral vision) loss. There are types of open angle glaucoma called low tension, or low pressure, glaucoma that do not have an increased level of pressure but do damage to the eye. Open angle glaucoma is painless and that is why regular eye exams are so important. Vision may not be affected until it is too late to treat.
Ophthalmic Technician: An allied health professional (both certified and non-certified) who performs preliminary diagnostic testing for an ophthalmologist.
Ophthalmologist: A surgeon (MD) who specializes in diagnosis and treatment ofrefractive, medical and surgical problems related to eye diseases and disorders.
Ophthalmoscope: An illuminated instrument for visualizing the interior of the eye, particularly the fundus at the back of the eye. There are two types of ophthalmoscopes, the direct ophthalmoscope and the indirect ophthalmoscope.
Optic Nerve: The second cranial nerve and the largest sensory nerve of the eye. The optic nerve carries impulses for sight from the retina to the brain’s visual cortex.
Pachymetry: A diagnostic tool used for measuring corneal thickness usingultrasound. (sound waves). This is a very important tool for laser vision correctioncandidates. Corneal thickness can also be measured using a pentacam diagnostic tool.
Pentacam: An advanced analysis system utilizing a slit illumination system and a Scheimpflug camera which rotates around the eye. This produces a set of three-dimensional measurement data which gives a precise geometric description of the anterior eye segment. This data in turn can be used to generate data on elevation, curvature, thickness and depth of the anterior chamber. Click here to learn more about Pentacam technology.
Phoropter: Refraction device which incorporates a series of spherical and cylindrical lenses and also includes prisms, occluders and pinholes. This device is used to determine an eye’s refractive error as well as a prescription for eyeglasses and contact lenses.
Presbyopia: Diminished power of accommodation due to loss of elasticity of thecrystalline lens of the eye which changes shape to change focus between distant and near objects. Patients with presbyopia are unable to see up close and need a bifocal, trifocal or progressive lens for near vision tasks. This condition can also be corrected with monovision laser vision correction.
PRK (Photorefractive keratectomy): Refractive surgery performed with anexcimer laser on the corneal surface after the epithelium is removed with the use of a gentle epithelial brush. The difference between this procedure and LASIK is that there is no flap created in PRK. Click here to watch a live PRK procedure performed by Dr. Mandel.
Pupil: Black circular opening in the center of the iris that changes size to regulate the amount of light entering the eye.
Pupillometer: An ophthalmic instrument used to measure the size (diameter) of the pupil.
Radial Keratotomy ( R.K.): An early refractive surgery procedure (for myopiaand astigmatism) in which the cornea was flattened using a blade to create spoke-like (radial) incisions in the cornea. PRK and LASIK are advanced technologies that were born from this original technique.
Refract: To bend. In ophthalmology, light rays are refracted when they pass through different types of lenses.
Refraction: A subjective determination of an eye’s refractive error as well as the best prescription for glasses and contact lenses to correct it. This test involves a series of lenses in graded powers which are presented to the patient to determine which lens, or combination of lenses, provides the sharpest visual acuity.
Refractive Error: Optical defect in which parallel light rays are not brought to a sharp focus precisely on the retina producing a blurred retinal image. Types of refractive errors include myopia, hyperopia, astigmatism and presbyopia which can be corrected with eyeglasses, contact lenses and refractive surgery.
Refractive Surgery: Any surgical procedure to change the eye’s refractive error.
Retina: Light sensitive nerve tissue in the eye, composed of rods and cones, that converts images from the eye’s optical system into electrical impulses that are sent along the optic nerve to the brain to be interpreted as vision.
Retinoscope: A hand held instrument which is used to determine an eye’srefractive error objectively (with no response required from the patient). Light from the retinoscope is projected into the eye and the movements of the light reflection are neutralized (eliminated) with corrective lenses.
Sclera: Opaque, fibrous, protective outer layer of the eye. The sclera is seen as the ‘white’ part of the eye surrounding the ‘colored’ part of the eye and is covered by the conjunctiva. The sclera is continuous with the cornea in front and the sheath covering the optic nerve in the back of the eye.
Slit Lamp Biomicroscope: A table-top microscope that is used to examine the anterior portion (front portion) of the eye. This instrument cross-sections the eye so that the structures of the eye can be viewed in layer-by-layer detail. With the aid of a special handheld lens, it can also be used to examine the posterior portion (back portion, or fundus) of the eye.
Snellen Chart: A test chart for assessing visual acuity. The chart contains rows of letters, numbers or symbols in standardized sizes with a designated distance at which each row should be legible to the normal eye. The standard testing distance is typically 20 feet.
Spherical Aberration: Type of visual aberration caused by light rays from an object hitting the periphery of the eye (cornea and crystalline lens) instead of the center of vision. This can cause the light rays to be over-refracted (bent too much) which causes blurred vision (positive spherical aberration.)
Stroma: One of the 6 layers of the cornea, the stroma is the middle layer tissue that forms 90% of the cornea. It is situated beneath Bowman’s membrane and above Descemet’s membrane and is composed of layered collagen fibers and cells. It is this layer of the cornea that is mainly reshaped during laser vision correction.
Tonometry: See Applanation Tonometry
Topography: A measurement of the curvature of the cornea. A color map is created from a picture of the cornea that details the variations in the front surface curvature of the cornea.
Transilluminator (AKA: Pupil light): A hand held instrument with an intense light beam used to evaluate pupillary reaction for the neurological aspect of the ophthalmic exam.
Ultrasound: A method of diagnostic testing in which high frequency sound waves are transmitted into the eye from a hand-held probe. The sound waves are reflected by the ocular tissues. This method is used in pachymetry to measure the thickness of the cornea, in Ascan biometry to measure the length of the eye and in Bscan biometry to aid in the diagnosis of eye and orbital problems.
Undercorrection (after laser vision correction): After refractive surgery, a change in refractive error that does not correct the desired amount of correction. This can typically be remedied with an enhancement procedure.
VISX Star S4 Laser: The VISX® system provides a whole new dimension in technology, accuracy, and safety in laser eye surgery. It combines the safety of 3-D active eye tracking, computerized centration, the precision and personalized treatment of variable sized beams and variable repetition rate for speed and smoothness. This system helps minimize glare and halo effects. Click here to learn more about the VISX Star S4 laser.
Wavefront: Wavefront technology creates a unique fingerprint of the visual aberrations of your eye. Wavefront sensors measure light rays reflected from the inside of your eye to detect refractive changes that previously were not capable of being diagnosed. It is used both as a diagnostic and therapeutic tool to enhance our abilities to measure your eyes with an accuracy that was previously unattainable. Click here to learn more about Wavefront Technology.