Vocab Flashcards
Abberation
Deviation from a single focus of light rays emanating from one source
Accommodation
The ability of the eye to adjust focus for varying distances
Achromatic
Descriptive of a lens capable of refracting light without creating a rainbow effect
Acuity
Visual expression of sharpness of vision (20/20)
Addition
Difference in plus power between the reading and distance portions of a multifocal lens
Amblyopia
Loss of vision without any apparent disease of the eye
Ametropia
A refractive error in which the eye, when in a state of rest, does not focus the image of an object upon the retina (hyperopia, myopia, and astigmatism)
Anisekeikonia
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
Anisometropia
A condition in which the refraction error of one eye significantly differs from that of the other
Anterior Chamber
Front cavity or compartment of the eye, located between the cornea and the crystalline lens. Contains the aqueous humor
Apex
Thinnest edge of a prism
Aphakia
An absence of the crystalline lens of the eye
Pseudophakia
Having a false lens
Aspheric
Not spherical; a lens surface having a number of curves with different radii
Axis
The meridian of no cylinder power in a spherocylinder lens
Base
Thickest edge of a prism
Base curve
The curve used as a base of a series of powers; the degree of curvature of the front surface of a lens
Beam
A group of parallel rays of light
Binocular
Pertaining to vision with both eyes
Caliper
Instrument used to measure thickness, calibrated in fifths and tenths of a millimeter
Canthus
The angle at either end of the slit between the eyelids
Cataract
A condition when the crystalline lens of the eye becomes opaque
Choroid
Vascular (blood-rich) layer of the eye; its function is to nourish the other parts of the eye, primarily the retina
Chromatic Abberation
Distortion of an optical image produced by the dispersion of light passing through a lens and generally characterized by blurred, multicolored edges
Ciliary body
The thick rim of choroid to which the crystalline lens is attached
Compound hyperopic astigmatism
The refractive error that results in two points of focus falling in front of the retina
Cones
Light sensitive cells in the retina responsible for color vision, daytime vision, and the central portion of the visual field
Conjunctiva
The clear membrane that lines the eyelids and covers the exposed surface of the eyeball
Conjunctivitis
Inflammation of the conjunctiva (“pink eye”)
Cornea
The refractive, transparent, anterior wall of the eye, equal to 43 diopters
The Five Layers of the Cornea
Epithelium
Bowman’s Membrane
Stroma
Descemet’s Membrane
Endothelium
Crown Glass
Pure silicate glass of general excellence for the spectacle lens; index of refraction is 1.523
Crystalline Lens
A transparent, colorless body suspended in the front part of the eyeball, between the aqueous humor and the vitreous humor. It’s function is to bring light rays to a focus on the retina
Cycloplegia
Paralysis of the ciliary body; drops used for diagnostic purposes
Decentration
Distance between the optical center placement of a lens and its geometric center; expressed in mmD
Diffusion
The scattering of light
Diopter
Unit of measurement of the refractive power of a lens. A lens whose focal length is one meter has a power of one diopter. The higher the dioptric power, the shorter the focal length
Diplopia
The seeing of one object as two, due to uneven tracking of the eyes (double vision)
Distortion
Defect in the lens which causes a straight line to appear curved
Divergent
Two or more light rays proceeding outward from a point
Emmetropia
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
Esophora
A tendency for one eye to deviate off the visual axis toward the other eye
Esotropia
Actual deviation of one eye toward the vision axis of the other eye (cross eyed)
Exophoria
A tendency for one eye to deviate off the visual axis away from the other eye
Exotropia
Actual deviation of one eye away from the visual axis of the other eye (wall eyed)
Far point
Point in space which is sharply focused on the retina with the eye’s accommodation relaxed
Flint glass
A glass of high refractive index (1.65), containing lead
Focus
The point to which the rays of a pencil of light converge or where they appear to diverge. In plus lenses, the focus is a real focus; in minus lenses, it’s a virtual focus
Fusion
The power of coordination by which the images received by the two eyes become a single image
Geometric center
Point where the diagonals of a boxed lens meet
Glaucoma
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
Hyperopia
Farsightedness; a refractive error in which, because the eyeball in short or the refractive power of the lens in weak, the point of focus rays of light from distant objects falls behind the retina. Correction to increase refractive power (a plus lens) is necessary for distance vision as well as near vision
Index of refraction
The ratio of the speed of light in air to the speed of light in a given media
Infinity
Distance great enough that the rays of light appear to be parallel; 20 ft or beyond
Inset
Amount of decentration from the distance optical enter to the optical center of the bifocal segment, usually 1.5mm per eye
Iris
The colored, circular membrane suspended behind the cornea and immediately in front of the lens. The iris regulated the amount of light entering the eye by changing the size of the pupil
Irregular Astigmatism
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
Iseikonic lenses
Spectacle lenses specially designed to manipulate image size when dissimilar sizes make it difficult to impossible for fusion to occur
Lacrimal
Pertaining to tears; secretion or conduction of tears
Limbus
The border between the iris and the sclera. Often used as a point of reference when manually measuring pupillary distance
Macula
Oval area in the center of the retina devoid of blood vessels; most responsible for color vision and central vision
Mechanical Center
Point on the lens surface around which a lens is edged
Meniscus
Crescent-shaped lens with a curved, convex front surface and a curved, concave back surface (bent lens)
Mixed Astigmatism
The refractive condition in which light comes to two points of focus where one point is in front of the retina, and the other is behind
Monocular
Pertaining to vision in one eye; the distance from the center of the bridge of the nose to the center of the pupil of one eye
Mydriasis
Prolonged or excessive dilation of the pupil of the eye, drops cause dilation
Myopia
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. (a minus lens)
Neutralization
The determination of dioptric power of an optical lens with a lens of the opposite power to cancel the original or return to plano; lensometry
Nystagmus
Rapid, involuntary oscillation of the eyeballs, usually the result of brain or ear disease
Oblique
Having a direction which makes an angle less or greater that a right angle with a surface of reference; neither parallel or perpendicuar
Optic nerve
The special nerve of the sense of sight that carries impulses from the retina to the brain
Optical Center
A point in a lens through which light passes with no deviation
Orbit
The cavity in the skull that contains the eyeball
Orthoptics
Technique of eye exercise designed to correct the visual axes of eyes not properly coordinated for binocular vision
Phoria
Tendency for the eye to deviate from its visual axis or the normal
Plano
no refractive power
Presbyopia
Gradual lessening of the power of accommodation due to a physiologic change that becomes noticeable about the age of 35
Prism
A device used to disperse light or change its direction; consisting of a transparent solid with two nonparallel plane faces
Prism Diopter
A unit of measurement of the deviation of light by a prism
Ptosis
Paralytic drooping of the upper lid
Pupil
The central opening of the iris through which light is permitted to enter the eye
Refraction
The determination of “refractive errors” of the eye. The change in direction as light passes obliquely from one medium to another of a different density
Regular Astigmatism
A refractive condition in which rays of light come to two focal points, and can be corrected by cylinders
Retina
The membrane which forms the inner lining of the back wall of the eye, constituted of two kinds of cells which respond to stimulus of light and send nervous impulses to the brain through the optic nerve
Rods
Specialized visual cell in the retina responsible for peripheral and night vision
Sclera
The “white” part of the eye; a tough covering which, with the cornea, forms the external, protective layer of the eye
Simple hyperopic astigmatism
the refractive condition where one point of the focus falls on the retina and the other point of focus falls behind the retina
Simple Myopic Astigmatism
The refractive condition where one point of the focus falls on the retina and the other point of focus falls in front of the retina
Sphere
A lens with the same power and curvature in every direction
Strabismus
Failure of the two eyes to simultaneously direct their gaze at the same object because of muscle imbalance
Transposition
Changing the cylinder from a plus or minus to the opposite without changing its refractive power
Tropia
An obvious deviation from normal of the axis of the eyes
Vertex
The point at which the optical axis of a lens intersects the ocular surfaces
Vertex Power
The refractive power of a lens measured from its vertex to its principal focus; significant in determining power of a corrective lens
Vitreous humor
The transparent, colorless mass of soft, gelatinous material filling the eyeball behind the lens; keeps retina intact
Zonule of Zinn
The suspensory apparatus of the lens; very thin, durable material that resembles fishing line
