Acanthamoeba:  A microscopic organism commonly found in soil, fresh water as well as chlorinated pools and jacuzzi’s.  This amoeba can cause serious infections of the eye, skin and central nervous system.  It can be introduced into the cornea via a contact lens, and cause acanthamoeba keratits, a potentially blinding infection.

Accomodation:  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).  A combination of ciliary muscle contraction and the zonular relaxation facilitates this change in shape.

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 lensesor spectacles, as well as with laser vision correction.  Almost all people have some degree of astigmatism.

Avascular:  Lack of blood vessels or blood supply.

Bandange 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.

Bifocal Contact Lens:  A soft contact lens that incorporates correction for both distance and near vision in the same lens.

Concave Contact Lens:  A lens that is thicker at the edges than in the center which causes light rays from an object to diverge.  This causes light rays in a myopic eye to focus on the retina which brings a blurry image in focus.  Nearsighted eyes focus their light rays in front of the retina.

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.

Contact Lens:  A small disc made of various silicone and or plastic materials usually containing an optical correction which is worn over the cornea as an alternative to spectacles , which can correct nearsightedness (myopia), farsightedness (hyperopia), astigmatism and presbyopia.

Contact Lens Technician:  An ophthalmic technician who performs the diagnostic measurements, under the supervision of an ophthalmologist, which help determine the contact lens parameters necessary for each individual patient.

Convex Contact Lens:   A contact lens that is thicker in the center than at the edges, which causes light rays from an object to converge.  This causes light rays in a hyperopic (farsighted) eye to focus on the retina which brings a blurry image in focus.  Farsighted eyes usually focus their light rays behind the retina.

Cornea:  The transparent window of the eye that covers the irispupil and anterior chamber and provides most of the eye’s optical power.  The cornea consists of 6 layers:  epitheliumBowman’s membranestromaDua’s LayerDescemet’s membrane and endothelium.

Corneal Abrasion:  An injury of the cornea in which the epithelium is scraped off.

Corneal Lubrication:  An essential component of safe contact lens wear, as it keeps the cornea moist and the contact lens hydrated and moving properly on the cornea.  This is particularly important because the cornea is mainly avascular and receives oxygen  from the tear film. Proper corneal lubrication may be aided with the use of over the counter natural tear drops (those approved for use with contact lenses).  In some cases, punctual plugs are also needed to increase the quantity of tears, or Restasis eye drops to increase the quality and quanity of the tear film.

Corneal Pannus:  Infiltration of the cornea by abnormal blood vessels in an otherwise avascular tissue.  This is typically the body’s defensive response to a lack of oxygen to the cornea which can be caused by an improper fitting contact lensand/or sleeping in contact lenses.

Corneal Ulcer:  A discontinuity or break in the epithelial tissue of the corneaassociated with inflammation in the cornea, that could be sterile or may be caused by bacterial, fungal or viral infection.  This is commonly seen in patients who over wear and/or sleep in their contact lenses and requires immediate treatment because it can be vision threatening, especially if it is located in the area of central vision.

Diopter:  The unit of measure used in ophthalmology to designate the refractivepower of a lens.

Epithelium:  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.

Eyeglasses:  See:  Spectacles

Eyestrain:  Discomfort or fatigue of the eyes usually after near vision tasks.

Farsightedness:  See:  Hyperopia

Giant Papillary Conjunctivitis (AKA:  GPC):  Inflammation of the conjunctiva on the undersurface of the upper eyelid often due to an allergy to contact lensmaterial.

GPC:  See:  Giant Papillary Conjunctivitis

Hard Contact Lens:  Contact lens made of a rigid plastic material that floats on the corneal tear film.

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 convex lenses in spectacles and contact lenses or with laser vision correction.  Younger patients may be able to compensate for this naturally.

Irregular Astigmatism:  A type of astigmatism producing distorted imagery in which the light rays are not oriented 90 degrees apart.  It may be due to contact lens wear, trauma, inflammation as well as developmental abnormalities.

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 becomes apparent in the 2nd decade of life.  This is typically corrected with a rigid gas permeable (RGP) contact lens.

Multifocal Contact Lens:  A soft contact lens that incorporates corrections for distance, middle and near vision in one lens.

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,concave lenses in spectacles and contact lenses or with laser vision correction.

Nearsightedness:  See:  Myopia

Ophthalmic Technician:  An allied health professional (both certified and non-certified) who performs preliminary diagnostic testing for, and under the supervision of, an ophthalmologist.

Ophthalmologist:  A surgeon (M.D.) who specializes in diagnosis and treatment ofrefractive, medical and surgical problems related to eye diseases and disorders, as well as vision conditions with spectacles and contact lenses.

Ophthalmology:  Medical specialty which deals with the eye, its function and diseases, including diagnosis and medical as well as surgical management of these diseases.

Optical:  Of or pertaining to optics.

Optical Power:  The degree to which a lens (contact or eyeglass), mirror, or other optical system converges or diverges light.

Optician:  A professional who makes and adjusts optical aids such as spectaclesand contact lenses from a prescription supplied by an ophthalmologist or anoptometrist.

Optics:  The branch of physics that deals with the properties of light and vision, for instance its refraction and reflection by lenses, prisms, mirrors and the eye.

Optometrist:  Doctor of Optometry. (O.D.) specializing in vision problems, treating vision conditions with spectacles, contact lenses and vision therapy and may also prescribe medications for certain eye diseases.

Pannus:  See:  Corneal Pannus

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 spectaclesand contact lenses.

Presbyopia:  Diminished power of accommodation due to loss of elasticity of the crystalline 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 abifocal or multifocal lens, in either spectacles or contact lenses, for near vision tasks.

Punctal Plugs: Small silicone (permanent) or collagen (absorbable) inserts that are placed inside the punctum (openings) of the eyelids to prevent normal tear drainage.  These plugs are used to treat dry eyes to keep natural tears on the eye longer to help the cornea and conjunctiva stay moist.

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 spectacles 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 spectacles, contact lenses and refractive surgery.

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.

RGP Contact Lens:  See:  Rigid Gas Permeable Contact Lens

Rigid Gas Permeable Contact Lens (RGP Lens):  Rigid plastic contact lens that rests on the cornea and is used for correcting a refractive error; smaller in diameter than a soft contact lens.

Soft Contact Lens:  A hydrophilic (water-absorbing) contact lens that rests on thecornea and is used for correcting a refractive error or protecting a damaged corneal surface.

Spectacles (Eyeglasses):   Optical aid which incorporates a combination of the appropriate lenses (concave, convex and toric) to correct various refractive errors.  There are many types of spectacles which include:  Bifocal, trifocal, single vision, progressive (multifocal), and transition lenses.

Tear Film:  Liquid that bathes the cornea and conjunctiva which consists of 3 layers, the outer oily layer secreted by the meibomian glands, the middle aqueous layer secreted by the lacrimal glands and the inner mucin layer produced by the conjunctival goblet cells.

Toric Contact Lens:  A contact lens that incorporates spherical and cylindrical components which is used for correcting astigmatism.

Visual Acuity:  Assessment of the eye’s ability to distinguish object details and shape, using the smallest object that can be seen at a specified distance, typically at 20 feet.