Glossary of Terms Related to Eye Care



AccommodationFunction. The eyes ability to increase optical power in order to maintain a clear image (focus) as objects are moved in closer.

ADD or ADHDCondition. Attention deficit/hyperactivity disorder. A chronic condition, usually in children, including inattention, hyperactivity and impulsiveness.

AmblyopiaFunctional defect. Decreased vision in one or both eyes

AstigmatismRefractive Error. Inability of an eye to focus sharply (at any distance), due to the optical surfaces of the eye curved more in one direction than another. Light rays entering the eye are bent unequally, which prevents formation of sharp focus. Corrected with eyeglasses or contact lenses.



BifocalsOptical device. Eyeglasses that incorporate two different powers in each lens, usually for distance and near corrections. Can be “Lined” or “No-Line”.

BlepharitisCondition. Inflammation of the eyelids, usually with redness, swelling and itching. Can be due to many causes including infection and allergy.

Blue Blocking Lenses Optical Device. Eyeglass lenses designed to block high intensity blue light from smartphones, computer screens and tablets.



CataractCondition. Age related opacity or cloudiness of the eyes crystalline lens, which may prevent a clear image from forming on the retina. Surgical removal of the lens may be necessary if visual loss becomes significant. Replaced by an intraocular lens.

Color blindnessCongenital defect. Reduced ability to discriminate between colors, especially shades of red and green. Hereditary.

ConjunctivaAnatomy. Transparent mucous membrane covering outer surface of the eyeball, and the inner surface of the eyelids

ConjunctivitisCondition. “Pink Eye”. Inflammation of the conjunctiva. Characterized by discharge, grittiness, redness and swelling.

Contact LensOptical device. Small plastic disc containing optical correction, worn on the eye to correct vision.

Convergence InsufficiencyFunctional Defect. Eye muscle condition in which the eyes cannot be pulled sufficiently inward (toward each other) to maintain single vision while looking at an object up close. Characterized by eye fatigue and double vision.

CorneaAnatomy. Transparent front part of the eye that covers the iris and pupil. Provides most of the eyes optical power.

Cover TestDiagnostic test. Used to detect eye misalignment



Diabetic RetinopathyCondition. Series of progressive retinal changes accompanying diabetes mellitus. Yearly dilated eye exam is recommended in all diabetic patients.

DilateFunction. To widen an opening, such as the pupil. Allows the doctor to better view the health of the eye. Recommended yearly.

DiplopiaSymptom/Functional Defect. “Double Vision”. Perception of seeing two images, from one object.

Dominant eyeFunction. Preferred eye for various tasks.

DrusenAnatomic Defect. Tiny, white hyaline deposits in the retina. Common after the age of 60; sometimes an early sign of macular degeneration.

Dry Eye SyndromeCondition. A chronic, multifactorial condition of the eye causing decrease in tear production and/or tear quality. Can cause foreign body sensation, itching, scratching, burning, grittiness, excessive tearing, redness, and pain, intermittent blurry vision.



EsotropiaFunctional Defect. Eye misalignment in which one eye deviates inward (towards the nose) while the other eye stays straight ahead.

ExotropiaFunctional Defect. Eye misalignment in which one eye deviates outward (away from the nose) while the other eye stays straight ahead.

Eye Examination – Evaluation of vision for distance and near, intraocular pressure, pupil function, checks for eye infections, disease or defects, inspection of the lens and retina through a dilated pupil. Recommended yearly in order to maintain eye health.



Glare – Undesirable sensation produced by brightness that is much greater than what the eyes are adapted to. Causes annoyance, discomfort, or loss in visual performance.

GlaucomaCondition. A group of diseases characterized by increased intraocular pressure resulting in damage to the optic nerve. Can result in loss of vision and blindness.



HemorrhageClinical Sign/Pathologic Condition. Bleeding

HyperopiaRefractive Error. Focusing defect. “farsightedness”. Farsighted people can see clearly in the distance but only if they use more focusing effort (accommodation) than those who have normally powered eyes; close-up vision may be blurred because it requires even more focusing effort. Corrected with plus lenses.



InflammationPathologic Condition. Body’s localized protective response to injury, infection or irritation. Characterized by heat, pain, redness and swelling.

Intraocular Pressure (IOP) – Function. Fluid pressure inside the eye.

IOL (intraocular lens)Optical Device. Plastic lens that is surgically implanted during cataract surgery to replace the eyes natural lens.

IrisAnatomy. Pigmented tissue lying behind the cornea that gives color to the eye and controls the amount of light entering the eye by varying the size of the pupillary opening.



Keratitis – Pathologic Condition. Inflammation of the front surface of the eye, the cornea. Can cause a “pink eye” appearance.



LASIK (Laser in Situ Keratomileusis)Refractive Surgery. Method of reshaping the front surface of the eye to change its optical power using a laser.

LensOptics. Any piece of glass or other transparent material that can bend light predictably.

Lids, eyelidsAnatomy. Structures covering the front of the eye. Their function is to protect the eye, limit amount of light entering the eye, and distribute tears over the eye.



Macula – Anatomy. Small central area of the retina. Used for reading, discriminating fine detail, and color.

Macular DegenerationPathologic Condition. Condition causing deterioration of the macula, resulting in loss of sharp central vision. Two types: “Dry”, characterized by macular pigment and deposits; and “Wet”, characterized by abnormal blood vessel growth, bleeding and leaking fluid. Most common cause of decreased vision in individuals over the age of 50.

Monovision Function. Method of correcting Presbyopia. One eye is corrected for distance and one eye is corrected for near with contact lenses.

Multifocal LensesOptical Device. Eyeglasses or contact lenses that incorporate more than one power in order for the eyes to allow focusing at different distances.

MyopiaRefractive Error. Focusing defect. “nearsightedness”. Nearsighted people see close-up objects clearly, but their distance vision is blurry. Corrected with a minus lens.



NeovascularizationPathologic Condition. Formation of new abnormal blood vessels.

NystagmusFunctional defect. Involuntary, side-to side or up and down movement of the eyes. Movement is faster in one direction than the other.



OCT (Optical Coherence Tomography)Test. Computerized instrument that scans the eye. Used for evaluating the retina, optic nerve, cornea, and macula.

Optic Disc Anatomy. End of the optic nerve. Evaluated when glaucoma is suspected.

Optic NerveAnatomy. Largest sensory nerve in the eye, carries the light signal detected by the eye’s retina, to the brain in order to see.



Peripheral VisionFunction. Side Vision.

PhotoreceptorsAnatomy. Rods and cones. Retinal cells that detect light and convert it into electrical signals to be sent to the brain.

PresbyopiaRefractive Error. Diminished power of accommodation that occurs with age, usually becomes significant after age 45.

PrismOptical device. Wedge-shaped transparent lens that bends light. Used in glasses to correct double vision.

Progressive Addition LensOptical Device. “No Line bifocal”. Eyeglasses that provide correction for distance, intermediate and near vision, with no bifocal demarcation line.

PterygiumPathologic Condition. Wedge shaped growth on the surface of the eye. May advance onto the cornea and require surgical removal. Related to sun and wind exposure.

PtosisFunctional Defect. Drooping or sagging of the upper lid.

PupilAnatomy. The black circular opening in the center of the iris. Regulates the amount of light that enters the eye.



RefractionTest. Determination of an eye’s best glasses prescription.

Refractive AmblyopiaFunctional Defect. Decreased vision in one or both eyes associated with large refractive error (glasses prescription) without damage to the retina or visual pathway. Vision may improve after several months of eyeglass or contact lens correction.

Refractive ErrorFunctional Defect. Optical defect. Light is not brought into sharp focus on the retina, producing a blurry image. Can be corrected by eyeglasses, contact lenses, or refractive surgery.

RetinaAnatomy. Light sensitive nerve tissue in the back of the eye that converts images from the eyes optical system into vision.

Retinoscope Instrument. Hand-held device used for measuring an eye’s glasses prescription with no response required from the patient.

Retinoscopy Test. Measuring an eye’s glasses prescription using a retinoscope



ScleraAnatomy. White protective layer of the eye.

Slit LampInstrument. Table-top microscope used for examination of the eye.

SpectaclesOptical device. Eyeglasses.

StrabismusFunctional defect. Eye misalignment “lazy eye”



Tear FilmAnatomy. Liquid that covers the front of the eye. Contains 3 layers: a mucous layer closest to the surface of the eye, a middle aqueous (watery) layer and a top oily layer. If any of these layers are not sufficient, dry eye results.

TopographyTest. A tool used to map and describe the shape of the front surface of the eye.

TrifocalOptical Device. Eyeglass lenses that combine three lenses of different powers.



Visual FieldFunction. Full extent of the area an eye can see.

VitreousAnatomy. Gelatinous mass that fills the inside of the eye.

Vitreous FloatersPathologic Condition. Particles that float in the vitreous and cast shadows on the retina.