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113 Cards in this Set
- Front
- Back
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Aberration
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Deviation from a single focus of light rays emanating from one source.
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Accommodation
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The ability of the eye to adjust focus for varying distances.
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Achromatic
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Descriptive of a lens capable of refracting light without creating a rainbow effect
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Acuity
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Visual expression of sharpness of vision (20/20 distance, J.1 near).
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Addition
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Difference in plus power between the reading and distance portions of a multifocal lens.
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Amblyopia
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Loss of vision without any apparent disease of the eye.
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Ametropia
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A refractive error in which the eye, when in a state of rest, does not focus the image of an object upon the retina; includes hyperopia, myopia, and astigmatism.
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Aniseikonia
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A condition in which the image of an object as seen by one eye differs so much in size or shape from that seen by the other eye that the two images cannot be fused into a single impression.
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Anisometropia
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A condition in which the refractive error of one eye significantly differs from that of the other.
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Anterior Chamber
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Front cavity or compartment of the eye, located between the cornea and crystalline lens. Contains the aqueous humor.
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Apex
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Thinnest edge of a prism.
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Aphakia
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An absence of the crystalline lens of the eye(pseudophakia: having a false lens).
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Aspheric
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Not spherical; a lens having a number of curves with different radii.
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Astigmatism
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A defect of the eye, of a lens or of an image formed by either. the curvature of the refracting surface or surfaces being different in different planes. This results in the focal lengths also being different in different planes (the curvature of the cornea in the case of the eye).
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Axis
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The meridian of cylinder power in a spherocylinder lens.
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Base
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Thickest edge of a prism.
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Base Curve
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The curve used as a base of a series of powers; the degree of curvature of the front surface of a lens.
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Beam
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A group of parallel rays of light.
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Binocular
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Pertaining to vision with both eyes.
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Caliper
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Instrument used to measure thickness, calibrated in fifths and tenths of a millimeter.
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Canthus
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The angle at either end of the slit between the eyelids.
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Cataract
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A condition when the crystalline lens of the eye becomes opaque.
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Congenital cataract
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One, which originates at birth.
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Hyper-mature Cataract
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The lens has become either solid and shrunken or soft and liquid.
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Incipient Cataract
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Any cataract in its early stages.
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Mature Cataract
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The lens is completely opaque.
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Senile Cataract
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A hard opacity of the lens occurring in the aged.
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Traumatic Cataract
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Cataract following an injury.
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Choroid
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Vascular (blood-rich) layer of the eye; its function is to nourish the other parts of the eye, primarily the retina.
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Chromatic Aberration
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Distortion of an optical image produced by the dispersion of light passing through a lens and generally characterized by blurred, multicolored edges.
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Ciliary Body
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The thick rim of the choroid to which the crystalline lens is attached.
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Compound Hyperopic Astigmatism
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The refractive error which results in two points of focus falling behind the retina. Example:
+1.00+2.00x090 |
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Compound Myopic Astigmatism
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The refractive error which results in two points of focus falling in front of the retina. Example:
-1.00-2.00x090 |
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Cones
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Light sensitive cells in the retina responsible for color vision, daytime vision, and the central portion of the visual field. (6 million)
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Conjunctiva
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The clear membrane that lines the eyelids and covers exposed surface of the eyeball.
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Conjunctivitis
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Inflammation of conjunctiva; commonly referred to as "pink eye".
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Cornea
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The refractive, transparent, anterior wall of the eye, equal to 43 diopters in power. This is the fastest healing part of the body. The five layers of the cornea in order are:
Epithelium Bowman's Membrane Stroma Descemet's Membrane Endothelium |
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Crown Glass
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Pure silicate glass of general excellence for the spectacle lens; index of refraction is 1.523.
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Crystalline Lens
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A transparent, colorless body suspended in the front part of the eyeball, between the aqueous humor and vitreous humor. Its function is to bring light rays to a focus on the retina.
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Cyclopegia
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Paralysis of the ciliary body
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Decentration
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Distance between the optical center placement of a lens and its geometric center; usually expressed in millimeters.
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Diffusion
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The scattering of light.
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Diopter
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Unit of measurement of the refractive power of a lens.
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Diplopia
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The seeing of one object as two, due to uneven tracking of the eyes. Commonly known as double vision.
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Distortion
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Defect in a lens which causes a straight line to appear curved.
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Divergent
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Two or more light rays proceeding outward from a point.
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Emmetropia
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The refractive condition of a normal eye. When the eye is at rest, the image of distant objects is brought to a focus on the retina.
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Esophopia
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A tendency for one eye to deviate of the visual axis toward to other eye.
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Esotropia
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Actual deviation of one eye toward the visual axis of the other eye (cross eyed).
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Exophoria
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A tendency for one eye to deviate off the visual axis away from the other eye.
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Exotropia
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Actual deviation of one eye away from the visual axis of the other eye (wall eyed).
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Far Point
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Point in space which is sharply focused on the retina with the eye's accommodation relaxed.
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Flint Glass
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a glass of high refractive index(1.65), containing lead.
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Focus
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The point to which the rays of a pencil of light converge or where they appear to diverge. In pluss lenses, the focus is a real focus; in minus lenses, it is a virtual focus.
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Fovea
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A small depression in the retina, at the back of the eye. It is part of the macula adapted for the clearest vision.
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Fusion
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The power of coordination by which the images received by the two eyes become a single image.
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Geometric center
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Point where the diagonals of a boxed lens meet.
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Glaucoma
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An ocular disease having as its primary characteristic a sustained increase in intraocular pressure that the eye cannot withstand without damage to its structure or impairment of its function. Primary symptom is a loss of peripheral vision.
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Hyperopia
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Also known as farsightedness. A refractive error in which, because the eyeball is short or the refractive power of the lens is weak, the point of focus for rays of light from a distant objects falls behind the retina. Correction to increase refractive power (a plus lens) is necessary for distance vision as well as near vision.
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Index of Refraction
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The ratio of the speed of light in air to the speed of light in a given medium.
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Infinity (Optical Infinity)
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Distance great enough that the rays of light appear to be parallel; 20 feet or beyond, since accommodation is in effect for anything within 20 feet.
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Inset
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Amount of decentration from the distance from optical center to the optical center of the bifocal segment, usually 1.5mm per eye.
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Iris
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The colored, circular membrane suspended behind the cornea and immediately in front of the lens. It regulates the amount of light entering the eye by changing size of the pupil.
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Irregular Astigmatism
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A refractive condition caused by a cornea which is damaged and irregular, so that rays of light come to many focal points on the retina. Cannot be corrected by cylinders.
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Iseikonic Lenses
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Spectacle lenses specially designed to manipulate image size when dissimilar sizes make it difficult or impossible for fusion to occur, such as in aniseikonia.
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Lacrimal
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Pertaining to tears; secretion or conduction of tears.
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Limbus
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The border between the iris and sclera. Often used as a point of reference when manually measuring pupillary distance.
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Macula
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Oval area in the retina devoid of blood vessels; most responsible for color vision and central vision.
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Mechanical Center
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Point on the lens surface around which the lens is edged.
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Meniscus
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Crescent-shaped lens with a curved, convex front surface and a curved, concave back surface. Also known as a bent lens.
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Mixed Astigmatism
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The refractive condition in which light comes to two points of focus where one point is in the front of the retina, and the other is behind the retina. Example:
+1.00-2.00x180 |
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Monocular
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Pertaining to vision in one eye. Monocular pupillary distance from the center of the bridge of the nose to the center of the pupil of one eye.
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Mydriasis
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Prolonged or excessive dialation of the pupil of the eye.
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Myopia
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Also known as nearsightedness. A refractive error in which the eyeball is too long in relation to its focusing power, thus the point of focus for rays of light from distant objects is in front of the retina. Correction to decrease refractive power (a minus lens) is necessary for distance vision as well as near vision.
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Neutralization
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The determination of dioptric power of an optical lens with a lens of the opposite power cancel the original or return to plano (shake method); reading of focal length (lensometry).
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Nystagmus
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Rapid, involuntary oscillation of the eyeballs, usually the result of brain or ear disease.
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Oblique
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Having a direction which makes an angle less or greater than a right angle with a surface of reference. Neither parallel nor perpendicular.
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Opaque
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Not transparent; impervious to light.
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Optic Nerve
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The special nerve of the sense of sight that carries impulses from the retina to the brain.
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Optical Center
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A point in a lens through which light passes with no deviation.
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Orbit
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The cavity in the skull which contains the eyeball.
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Orthoptics
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Technique of eye exercises designed to correct the visual axes of the eyes not properly coordinated for binocular vision.
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Palpebral
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Pertaining to the eyelid.
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Pencil
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A group of parallel light rays emanating from a far point.
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Phoria
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Tendency for the eye to deviate from its visual axis or the normal.
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Photophobia
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Abnormal sensitivity to light; light discomfort.
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Plano
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No refractive power.
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Presbyopia
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Gradual lessening of the power of accommodation due to physiologic change that becomes noticeable about the age of 35.
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Prism
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A device used to disperse light or change direction, consisting of a transparent solid with two nonparallel plane faces.
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Prism Diopter
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A unit of measurement of the deviation of light by a prism. Can deviate the light 1 centimeter at the distance of 1 meter.
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Ptosis
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Paralytic drooping of the upper eyelid.
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Ptosis Crutch
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A small, spring wire attached nasally to a spectacle frame to lift a drooping eyelid.
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Pupil
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The central opening of the iris through which light is permitted to enter the eye.
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Pupillary Distance (PD)
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The distance between the centers of the pupils when in distance or near positions. Generally expressed in millimeters.
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Ray
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The path of a single corpuscle of light from a single point on a light source. A group would make a pencil, and a group of pencils would make a beam.
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Refraction
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The determination of "refractive errors" of the eye. The change in direction of light as it passes obliquely from one medium to another of different density.
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Regular Astigmatism
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A refractive condition in which rays of light come to two focal points, and can be corrected by cylinders.
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Retina
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The membrane which forms the inner lining of the back wall of the eye, constituted of two kinds of cell which respond to the stimulus of light (rods and cones) and send nervous impulses to the brain through the optic nerve.
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Retinoscope
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An instrument for measuring refractive error of the eye.
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Rods
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Specialized visual cell in the retina responsible for peripheral and night vision. (120 million)
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Sclera
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The "white" part of the eye. A tough covering which, with the cornea, forms the external, protective layer of the eye.
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Scotoma
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A blind area of reduced vision in the visual field.
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Simple Hyperopic Astigmatism
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The refractive condition where one point of focus falls on the retina and the other point of focus falls behind the retina. Example:
Plano+1.50x180 |
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Simple Myopic Astigmatism
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The refractive condition where one point of focus falls on the retina and the other point of focus falls in front of the retina. Example:
plano-2.00x180 |
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Sphere
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A lens with the same power and curvature in every direction.
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Strabismus
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Failure of the two eyes to simultaneously direct their gaze at the same object because and support the lens in place.
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Suspensory Ligaments
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Numerous fine tissue strands that stretch from the ciliary processes to be lens equator and support the lens in place.
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Transposition
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Changing the cylinder from + or - to the opposite without changing its refractive power.
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Tropia
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An obvious deviation from normal of the axis of the eyes.
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Vertex
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The point at which the optical axis of a lens intersects the ocular surfaces.
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Vertex Power
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The refractive power of a lens is measured from its vertex to its principle focus. It is a significant factor in determining the power of a corrective lens.
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Vitreous Humor
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The transparent, colorless mass of soft, gelatinous material filling the eyeball behind the lens. Helps to keep the retina intact.
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Zonule of Zinn
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The suspensory apparatus of the lens; very thin, durable material that resembles monofilament line.
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