Glossary

Accommodation: The adjustment of the eye for seeing near objects, accomplished by increasing the power of the crystalline lens by changing its shape through the action of the ciliary muscle.

Acquired: Contracted after birth.

Agnosia: Inability to recognize common objects despite an intact visual apparatus.

Albinism: A hereditary deficiency of melanin pigment in the retinal pigment epithelium, iris, and choroid.

Alternate cover test: Determination of the full extent of strabismus (heterotropia and heterophoria) by alternately covering one eye and then the other with an opaque object, thus eliminating fusion.

Amaurosis fugax: Transient loss of vision. Usually reserved for transient loss of vision due to retinal embolus.

Amblyopia: Reduced visual acuity in the absence of sufficient eye or visual pathway disease to explain the level of vision.

Ametropia: See Refractive error.

Amsler grid: A grid of vertical and horizontal lines to test the central 20° square of visual field.

Angiography: Imaging of the vascular system. The ocular circulation can be highlighted by intravenous injection of either fluorescein, which particularly demonstrates the retinal circulation, or indocyanine green, to demonstrate the choroidal circulation.

Aniridia: Congenital absence of the iris.

Aniseikonia: Image seen by one eye differs in size from that seen by the other.

Anisocoria: Unequal pupillary size.

Anisometropia: Difference in refractive power of the two eyes.

Anophthalmos: Absence of the globe.

Anterior chamber: Space bounded anteriorly by the cornea and posteriorly by

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the iris that is filled with aqueous.

Aphakia: Absence of the crystalline lens.

Aqueous: Clear, watery fluid that fills the anterior and posterior chambers.

Asthenopia: Eye fatigue from muscular, environmental, or psychological causes.

Astigmatism: Different power of refraction in various meridians.

Axis: The meridian specifying the orientation of a cylindrical lens.

Binocular vision: Ability of both eyes to focus on an object and fuse the two images into one.

Biomicroscope: See Slitlamp.

Blepharitis: Inflammation of the lids.

Blepharoptosis (ptosis): Drooping of the upper lid.

Blepharospasm: Involuntary spasm of the lids.

Blind spot: “Blank” area in the visual field corresponding to the position of the optic nerve.

Blindness: In the United States, the usual definition of blindness is corrected visual acuity of 20/200 or less in the better eye, or a visual field of no more than 20° diameter in the better eye.

Botulinum toxin: Neurotoxin A of the bacterium Clostridium botulinum injected into extraocular or facial muscles to produce temporary paralysis.

Buphthalmos: Enlarged globe in infantile glaucoma.

Canal of Schlemm: A circular modified venous structure in the anterior chamber angle that drains aqueous to the aqueous veins.

Canaliculus: Small tear drainage tube in inner aspect of upper and lower lids leading from the punctum to the common canaliculus and then to the tear sac.

Canthotomy: Usually implies lateral canthotomy—cutting of the lateral canthal tendon for the purpose of widening the palpebral aperture.

Canthus: The outer (lateral) or inner (medial) angle at either end of the lid aperture.

Cataract: Opacity of the crystalline lens.

Chalazion: Granulomatous inflammation of a meibomian gland.

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Chemosis: Conjunctival edema.

Choroid: The vascular middle coat between the retina and sclera.

Ciliary body: Portion of the uveal tract between the iris and the choroid. It consists of ciliary processes and the ciliary muscle.

Coloboma: Congenital cleft due to incomplete development of some portion of the eye or ocular adnexa.

Color blindness (deficiency): Diminished ability to perceive differences in color.

Concave lens: Lens having the power to diverge rays of light; also known as diverging, reducing, negative, or minus lens; denoted by the sign (–); and used to correct myopia.

Cones and rods: Two kinds of retinal photoreceptor cells. Cones are primarily involved in fine visual discrimination (optimal visual acuity) and color vision; rods in peripheral vision and vision in decreased illumination.

Congenital: Existing at or before birth but not necessarily inherited (hereditary).

Conjunctiva: Mucous membrane that lines the posterior aspect of the lids and covers the anterior sclera.

Contact lenses: Lenses that fit directly on the globe, usually on the cornea but sometimes on the sclera.

Convergence: The process of inward rotation of both eyes to direct their visual axes to a near point.

Convex lens: Lens having power to converge rays of light and to bring them to a focus; also known as converging, magnifying, or plus lens; denoted by the sign (+); and used to correct hyperopia and presbyopia.

Cornea: Transparent portion of the outer coat of the globe forming the anterior wall of the anterior chamber.

Corneal graft (keratoplasty): Replacement of a portion of the cornea, either involving the full thickness (penetrating keratoplasty), only a superficial layer (lamellar keratoplasty), or only the endothelium (endothelial keratoplasty), with donor cornea from the same human (autograft), or another human (homograft).

Cover test: Determination of the presence and degree of manifest strabismus (heterotropia) by covering one eye with an opaque object and examining for any movement of the uncovered eye to fixate a target.

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Cross cylinder: A specialized spherocylindrical lens to measure astigmatism.

Crystalline lens: Transparent biconvex structure suspended behind the iris between the aqueous and the vitreous. Its function is to focus the visual image on the retina. Accommodation is achieved by changing its shape to increase its power. (Usually called simply the lens.)

Cyclodestructive procedures: Destruction of portions of the ciliary body to reduce aqueous production in the treatment of intractable glaucoma, using cryotherapy (cyclocryotherapy), laser (cyclophotocoagulation), or diathermy.

Cycloplegic: Drug that relaxes the ciliary muscle, paralyzing accommodation.

Cylindrical lens: Segment of a cylinder, the refractive power of which varies in different meridians, used to correct astigmatism.

Dacryocystitis: Infection of the lacrimal sac.

Dacryocystorhinostomy: Formation of an opening between the nasolacrimal duct and the nasal cavity to relieve an obstruction in the nasolacrimal duct, or sac.

Dark adaptation: The ability to adjust vision to decreased illumination.

Diopter: Unit of measurement of refractive power of lenses.

Diplopia (double vision): Seeing one object as two. It is usually binocular, being overcome by covering one eye, due to misalignment of the eyes. Monocular diplopia is usually due to focusing abnormality.

“E” test: A system of testing visual acuity in illiterates, particularly preschool children.

Ectropion: Turning out of the lid.

Emmetropia: Absence of refractive error.

Endolaser: Application of laser from a probe inserted into the globe.

Endophthalmitis: Extensive intraocular infection.

Enophthalmos: Abnormal retrodisplacement of the eyeball.

Entropion: Turning inward of the lid.

Enucleation: Complete removal of the globe.

Epicanthus: Congenital skin fold that overlies the inner canthus.

Epi-LASIK: Corneal excimer laser ablation under an epithelial flap created by a

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mechanical keratome to treat refractive error.

Epiphora: Excessive tearing.

Esophoria: Tendency of the eyes to converge (latent convergent strabismus).

Esotropia: Manifest inward deviation of one eye (manifest convergent strabismus).

Evisceration: Removal of the contents of the globe.

Exenteration: Removal of the contents of the orbit, including the globe and part or all of the lids.

Exophoria: Tendency of the eyes to diverge.

Exophthalmos: Abnormal protrusion of the globe.

Exotropia: Manifest outward deviation of one eye.

Familial: Pertaining to traits, either hereditary or acquired, occurring in families.

Far point: The point at which the eye is focused when accommodation is completely relaxed.

Farsightedness: See Hyperopia.

Field of vision: The entire area that can be seen without shifting gaze.

Floaters: Moving images in the visual field due to vitreous opacities.

Focus: A point to which rays of light are brought together to form an image; focal distance is the distance between a lens and its focal point.

Fornix: Junction of the palpebral and bulbar conjunctiva.

Fovea: 1.5-mm-diameter zone of the central retina, characterized histologically by thinning of the outer nuclear layer.

Foveola: 0.3-mm-diameter thinnest (0.25 mm) area of the central retina, clinically apparent as a depression, in which there are only cone photoreceptors and which provides optimal visual acuity. It corresponds to the retinal avascular zone on fluorescein angiography.

Fundus: The posterior portion of the eye visible through the pupil.

Fusion: Combining the images received by the two eyes into one image.

Glaucoma: Disease characterized by optic disk cupping and reduction of visual field, usually associated with raised intraocular pressure.

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Gonioscopy: Examination of the anterior chamber angle that requires a special corneal contact lens.

Hemianopia: Reduction of one side of the field of vision of one or both eyes.

Heterophoria (phoria): See Strabismus.

Heterotropia (tropia): See Strabismus.

Hippus: Exaggerated spontaneous rhythmic movements of the iris.

Hordeolum, external (sty): Infection of gland of Moll or Zeis.

Hordeolum, internal: Infection of meibomian gland.

Hyperopia, hypermetropia (farsightedness): Refractive error in which light rays from a distant object are focused behind the retina.

Hyperphoria: Latent vertical strabismus.

Hypertropia: Manifest vertical strabismus.

Hyphema: Blood in the anterior chamber.

Hypopyon: Pus in the anterior chamber.

Hypotony: Abnormally low intraocular pressure (5 mm Hg or less).

Inherited (hereditary): Transmitted from parents to offspring.

Injection: Congestion of blood vessels.

Iridectomy: Excision of a sector of iris to form a direct communication between the anterior and posterior chambers.

Iridoplasty, peripheral (laser) iridoplasty: Procedure to contract the iris stroma by application of usually argon laser burns to the peripheral iris.

Iridotomy, peripheral (laser): Formation of a hole in the iris to form a direct communication between the anterior and posterior chambers, usually performed with the neodymium:YAG laser.

Iris: Colored, annular membrane, suspended behind the cornea and immediately in front of the lens.

Ishihara color plates: Test for color vision using pseudoisochromatic multicolored charts.

Isopter: Boundary of the visual field to a particular target. Isopters to targets of different colors and sizes allow differentiation of relative from absolute visual field defects.

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Jaeger test: Near vision test using various sizes of type.

Keratic precipitate (KP): Accumulation of inflammatory cells on the posterior cornea in uveitis.

Keratitis: Inflammation of the cornea.

Keratoconus: Cone-shaped deformity of the cornea.

Keratomalacia: Corneal softening, usually due to vitamin A deficiency.

Keratometer: Instrument to measure the curvature of the cornea, used to diagnose and monitor corneal disease, fit contact lenses, and determine intraocular lens power prior to cataract surgery.

Keratopathy, bullous: Edema of the cornea with painful epithelial blisters (bullae).

Keratoplasty: See Corneal graft.

Keratoprosthesis: Implant surgically placed in an opaque cornea to achieve optical clarity.

Kerato-refractive surgery (refractive keratoplasty): Corneal surgery to correct refractive error.

Keratotomy: Incision in the cornea. In arcuate keratotomy, circumferential incisions are made to correct astigmatism.

Koeppe nodule: Accumulation of inflammatory cells on the iris in uveitis.

Lacrimal sac: Dilated area at the junction of the nasolacrimal duct and canaliculi.

Laser epithelial keratomileusis (LASEK): Corneal excimer laser ablation under an epithelial flap to treat refractive error.

Laser in situ keratomileusis (LASIK): Corneal excimer laser ablation under a stromal flap to treat refractive error.

Lens: A refractive medium having one or both surfaces curved. (See also Crystalline lens.)

Lensometer: Instrument for measuring the power of optical lenses.

Limbus: Junction of the cornea and sclera.

Macula: 5.5- to 6-mm-diameter area of central retina bounded by the temporal retinal vascular arcades. It is known to anatomists as the area centralis, to

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differentiate it from the macula lutea, and is defined as the part of the retina in which the ganglion cell layer is more than one cell thick.

Macula lutea: 3-mm-diameter area of the central retina defined anatomically by the presence of yellow xanthophyll pigment.

Maddox rod: Lens composed of parallel strong cylinders through which a point of light is seen as a line—used to quantify heterophoria.

Magnification: Ratio of the size of an image to the size of its object.

Megalocornea: Abnormally large cornea (> 13 mm diameter).

Metamorphopsia: Wavy distortion of vision.

Microphthalmos: Abnormally small globe with abnormal function (see Nanophthalmos).

Miotic: Drug causing pupillary constriction.

Mydriatic: Drug causing pupillary dilation.

Myopia (nearsightedness): Refractive error in which light rays from a distant object are focused anterior to the retina.

Nanophthalmos: Abnormally small globe with normal function (see Microphthalmos).

Near point: The point at which the eye is focused when accommodation is fully active.

Nearsightedness: See Myopia.

Nystagmus: Involuntary rhythmic oscillation of the globe that may be horizontal, vertical, torsional, or mixed.

Ophthalmia neonatorum: Conjunctivitis in the newborn.

Ophthalmoscope: Instrument with special illumination system for viewing the inner eye, particularly the retina and associated structures.

Optic atrophy: Optic nerve degeneration, manifesting clinically as pallor of the optic disk.

Optic disk: Ophthalmoscopically visible portion of the optic nerve.

Optic nerve: The nerve that carries visual impulses from the retina to the brain.

Orbital cellulitis: Inflammation of the orbital tissues surrounding the globe.

Orthoptics: Study and treatment of defects of binocular visual function or of the

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muscles controlling movement of the eyes.

Oscillopsia: Subjective illusion of movement of objects caused by ocular instability such as nystagmus.

Palpebral: Pertaining to the lid.

Pannus: Infiltration of the cornea with blood vessels.

Panophthalmitis: Inflammation of the globe and orbital tissues.

Papilledema: Swelling of the optic disk due to raised intracranial pressure.

Papillitis: Inflammatory swelling of the optic nerve head.

Partially seeing child: For educational purposes, a partially seeing child is one who has a corrected visual acuity of 20/70 or less in the better eye.

Perimeter: Instrument for quantifying the field of vision.

Peripheral vision: Ability to perceive the presence and movement of objects outside the direct line of vision.

Phacoemulsification and phacofragmentation: Techniques of extracapsular cataract surgery in which the nucleus of the lens is disrupted into small fragments by ultrasound, thus allowing its aspiration through a small wound.

Phakomatoses: Group of hereditary diseases characterized by the presence of spots, cysts, and tumors in various parts of the body—for example, neurofibromatosis, Von Hippel-Lindau disease, and tuberous sclerosis.

Phlyctenule: Localized lymphocytic infiltration of the conjunctiva.

Phoria: See Strabismus.

Photochemical damage: Tissue damage due to creation of oxygen free radicals by excessive exposure to visible or near ultraviolet light that can be used for corneal disease (crosslinking) or retinal disease (photodynamic therapy).

Photodecomposition: Tissue damage by direct separation of chemical bonds by absorption of very-short-wavelength ultraviolet light (eg, from excimer lasers).

Photodynamic therapy (PDT): Retinal laser augmented by intravenous injection of a dye (verteporfin).

Photomechanical damage (photodisruption/plasma-mediated ablation):

Tissue damage produced by the breakdown of “plasma,” which is a state of ionization created by spot focusing a high-energy laser source (eg, neodymium:YAG).

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Photophobia: Abnormal sensitivity to light.

Photopsia: Visual sparks or flashes due to abnormal retinal stimulation.

Photorefractive keratectomy (PRK): Surface corneal excimer laser ablation to treat refractive error.

Phototherapeutic keratectomy (PTK): Surface corneal excimer ablation to treat anterior corneal disorders such as recurrent corneal erosion.

Photothermal damage: Thermal damage to tissues due to absorption of high levels of light (including laser) energy, resulting in small rise (10–20°C) in temperature (photocoagulation) or large rise in temperature (reaching 100°C) (photovaporization).

Phthisis bulbi: Atrophy of the globe with blindness and decreased intraocular pressure, due to end-stage intraocular disease.

Placido disk: Disk with concentric rings used to determine the regularity of the cornea by observing the ring's reflection on the corneal surface.

Poliosis: Depigmentation of the eyelashes.

Posterior chamber: Space filled with aqueous anterior to the lens and posterior to the iris.

Presbyopia (“old sight”): Physiologically blurred near vision, commonly evident soon after age 40, due to reduction of power of accommodation.

Prism: Wedge of transparent material that deviates light rays without changing their focus.

Prism cover test: Extension of the alternate cover test using different strength prisms to quantify the total magnitude of strabismus.

Prism diopter: Unit of prism power.

Pseudoisochromatic charts: Charts with colored dots of various hues and shades forming numbers, letters, or patterns, used for testing color discrimination (see Ishihara color plates).

Pseudophakia: Presence of artificial intraocular lens implant following cataract extraction.

Pterygium: Triangular growth of tissue that extends from the conjunctiva over the cornea.

Ptosis: Drooping of the upper lid.

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Puncta: External orifices of the upper and lower canaliculi.

Pupil: Round hole in the center of the iris that corresponds to the aperture of a camera.

Refraction: (1) Deviation in the course of rays of light in passing from one transparent medium into another of different density. (2) Determination of refractive error of the eye and its correction by lenses.

Refractive error (ametropia): Optical defect that prevents light rays from being brought to a single focus on the retina.

Refractive index: Ratio of the speed of light in a vacuum to the speed of light in a given material.

Refractive media: The transparent parts of the eye having refractive power, of which the cornea is most powerful but the (crystalline) lens is under voluntary control (see Accommodation).

Retina: Innermost coat of the eye, consisting of the sensory retina, which is composed of light-sensitive neural elements connecting to other neural cells, and the retinal pigment epithelium.

Retinal detachment: Separation of the neurosensory retina from the retinal pigment epithelium and choroid.

Retinitis pigmentosa: Hereditary degeneration of the retina.

Retinoscope: Instrument for objective determination of refractive error.

Rods: See Cones and rods.

Sclera: The white part of the eye—a tough covering that, with the cornea, forms the external protective coat of the eye.

Scleral spur: Normal protrusion of sclera into the anterior chamber angle.

Scotoma: Blind or partially blind area of the visual field.

Slitlamp biomicroscope: A combination light and microscope for examination of the eye, particularly allowing stereoscopic imaging.

Small incision lenticule extraction (SMILE): Excision of a portion of corneal stroma with a femtosecond laser to treat refractive error.

Snellen chart: Test of visual acuity consisting of lines of letters or numbers, graded in size according to the distance at which they can be discriminated by a normal eye.

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Sphincterotomy: Incision of the iris sphincter muscle.

Staphyloma: Thinned part of the wall of the globe, resulting in protrusion of intraocular structures.

Strabismus: Misalignment of the eyes (ocular deviation) that may be present under binocular viewing conditions (manifest strabismus, manifest ocular deviation, heterotropia) or only when binocular vision has been interrupted by occlusion of one eye (latent strabismus, latent ocular deviation, heterophoria).

Sty: See Hordeolum, external.

Symblepharon: Adhesions between bulbar and palpebral conjunctiva.

Sympathetic ophthalmia: Intraocular inflammation (uveitis) in both eyes following trauma.

Synechia: Adhesion of the iris to the cornea (anterior synechia) or lens (posterior synechia).

Syneresis: Degenerative process within a gel; specifically applied to the vitreous.

Tarsorrhaphy: Surgical procedure to join the upper and lower lid margins such as to protect the cornea.

Tonometer: Instrument to measure intraocular pressure.

Trabeculectomy: Surgical procedure to create an additional aqueous drainage channel in the treatment of glaucoma.

Trabeculoplasty: Laser photocoagulation of the trabecular meshwork in the treatment of open-angle glaucoma.

Transpupillary thermotherapy: Diffuse treatment of fundal lesions with lowenergy diode laser.

Trichiasis: Rubbing of the eyelashes against the globe.

Tropia: See Strabismus.

Uncover test: Extension of the cover test to determine the presence of heterophoria by detection of corrective movement of the covered eye as it is uncovered.

Uvea (uveal tract): Iris, ciliary body, and choroid.

Uveitis: Inflammation of one or all portions of the uveal tract.

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Visual acuity: Measure of the spatial resolution of the eye.

Visual axis: Imaginary line connecting a point in space (point of fixation) with the foveola.

Vitiligo: Localized patchy decrease or absence of skin pigment.

Vitrectomy: Surgical removal of the vitreous to clear vitreous hemorrhage, allow treatment of retinal detachment or retinal vascular disease, or treat intraocular infection or inflammation.

Vitreous: Transparent, colorless, gel filling the globe behind the crystalline lens.

Xerosis: Drying of tissues of surface of the globe.

Zonule: One of numerous fibrils that arise from the surface of the ciliary body and insert into the equator of the crystalline lens to hold the crystalline lens in place.

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