ABO Study Guide Questions with
complete solutions
Aberration - ANSWER-Deviation from a single focus of light rays emanating from one source.
Accommodation - ANSWER-The ability of the eye to adjust focus for varying distances.
Achromatic - ANSWER-Descriptive of a lens capable of refracting light without creating a rainbow effect.
Acuity - ANSWER-Visual expression of sharpness of vision. (20/20 distance, J.1 near)
Addition - ANSWER-Difference in plus power between the reading and distance portions of a multifocal
lens.
Amblyopia - ANSWER-Loss of vision without any apparent disease of the eye.
Ametropia - ANSWER-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.
Aniseikonia - ANSWER-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 - ANSWER-A condition in which the refractive error of one eye significantly differs from
that of the other.
Anterior Chamber - ANSWER-Front cavity or compartment of the eye, located between the cornea and
crystalline lens. Contains aqueous humor.
,Apex - ANSWER-Thinnest edge of a prism.
Aphakia - ANSWER-An absence of the crystalline lens of the eye. (Pseudophakia: having a false lens)
Aspheric - ANSWER-Not spherical; a lens surface having a number of curves with different radii.
Astigmatism - ANSWER-A defect of the eye, of a lens or of an image formed by either, the curvature of
the refracting surface or the 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)
Axis - ANSWER-The meridian of no cylinder power in a spherocylinder lens.
Base - ANSWER-Thickest edge of a prism.
Base Curve - ANSWER-The curve used as a base of a series of powers; the degree of curvature of the
front surface of a lens.
Beam - ANSWER-A group of parallel rays of light.
Binocular - ANSWER-Pertaining to vision with both eyes.
Caliper - ANSWER-Instrument used to measure thickness, calibrated in fifths and tenths of a millimeter.
Canthus - ANSWER-The angle at either end of the slit between the eyelids.
Cataract - ANSWER-A condition when the crystalline lens of the eye becomes opaque.
Congenital Cataract - ANSWER-One, which originates at birth.
Hyper-mature Cataract - ANSWER-The lens has become either solid and shrunken or soft and liquid.
,Incipient Cataract - ANSWER-Any cataract in its early stages.
Mature Cataract - ANSWER-The lens is completely opaque.
Senile Cataract - ANSWER-A hard opacity of the lens occurring in the aged.
Traumatic Cataract - ANSWER-Cataract following an injury.
Choroid - ANSWER-Vascular (blood-rich) layer of the eye; its function is to nourish the other parts of the
eye, primarily the retina.
Chromatic Aberration - ANSWER-Distortion of an optical image produced by the dispersion of light
passing through a lens and generally characterized by blurred, multicolored edges.
Ciliary Body - ANSWER-The thick rim of choroid to which the crystalline lens is attached.
Compound Hyperopic Astigmatism - ANSWER-The refractive error which results in two points of focus
falling behind the retina.
Ex: +1.00 / +2.00 x 090
Compound Myopic Astigmatism - ANSWER-The refractive error which results in two points of focus
falling in front of the retina.
Ex: -1.00 / -2.00 x 090
Cones - ANSWER-Light sensitive cells in the retina responsible for color vision, daytime vision, and the
central portion of the visual field.
Conjunctiva - ANSWER-The clear membrane that lines the eyelids and covers the exposed surface of the
eyeball.
, Conjunctivitis - ANSWER-The inflammation of the conjunctiva; commonly referred to as "pink eye".
Cornea - ANSWER-The refractive, transparent, anterior wall of the eye, equal to 43 diopters power. It is
the fastest healing part of the body.
Crown Glass - ANSWER-Pure silicate glass of general excellence for the spectacle lens; index of refraction
is 1.523.
Crystalline Lens - ANSWER-A transparent colorless body suspended in the front part of the eyeball,
between the aqueous and the vitreous, the function of which is to bring the rays of light to a focus on
the retina.
Cycloplegia - ANSWER-Paralysis of the ciliary body; drops are used for diagnostic purposes.
Decentration - ANSWER-Distance between the optical center placement of a lens and its geometric
center; usually expressed in millimeters.
Diffusion - ANSWER-The scattering of light.
Diopter - ANSWER-Unit of measurement of the refractive power of a lens. A lens whose focal length is
one meter has a power of one. The higher the power, the shorter the focal length.
Diplopia - ANSWER-The seeing of one object as two, due to uneven tracking of the eyes. Commonly
known as double vision.
Distortion - ANSWER-Defect in a lens which causes a straight line to appear curved.
Divergent - ANSWER-Two or more light rays proceeding outward from a point.
Emmetropia - ANSWER-The refractive condition of the normal eye. When the eye is at rest, the image of
distant objects is brought to a focus on the retina.
complete solutions
Aberration - ANSWER-Deviation from a single focus of light rays emanating from one source.
Accommodation - ANSWER-The ability of the eye to adjust focus for varying distances.
Achromatic - ANSWER-Descriptive of a lens capable of refracting light without creating a rainbow effect.
Acuity - ANSWER-Visual expression of sharpness of vision. (20/20 distance, J.1 near)
Addition - ANSWER-Difference in plus power between the reading and distance portions of a multifocal
lens.
Amblyopia - ANSWER-Loss of vision without any apparent disease of the eye.
Ametropia - ANSWER-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.
Aniseikonia - ANSWER-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 - ANSWER-A condition in which the refractive error of one eye significantly differs from
that of the other.
Anterior Chamber - ANSWER-Front cavity or compartment of the eye, located between the cornea and
crystalline lens. Contains aqueous humor.
,Apex - ANSWER-Thinnest edge of a prism.
Aphakia - ANSWER-An absence of the crystalline lens of the eye. (Pseudophakia: having a false lens)
Aspheric - ANSWER-Not spherical; a lens surface having a number of curves with different radii.
Astigmatism - ANSWER-A defect of the eye, of a lens or of an image formed by either, the curvature of
the refracting surface or the 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)
Axis - ANSWER-The meridian of no cylinder power in a spherocylinder lens.
Base - ANSWER-Thickest edge of a prism.
Base Curve - ANSWER-The curve used as a base of a series of powers; the degree of curvature of the
front surface of a lens.
Beam - ANSWER-A group of parallel rays of light.
Binocular - ANSWER-Pertaining to vision with both eyes.
Caliper - ANSWER-Instrument used to measure thickness, calibrated in fifths and tenths of a millimeter.
Canthus - ANSWER-The angle at either end of the slit between the eyelids.
Cataract - ANSWER-A condition when the crystalline lens of the eye becomes opaque.
Congenital Cataract - ANSWER-One, which originates at birth.
Hyper-mature Cataract - ANSWER-The lens has become either solid and shrunken or soft and liquid.
,Incipient Cataract - ANSWER-Any cataract in its early stages.
Mature Cataract - ANSWER-The lens is completely opaque.
Senile Cataract - ANSWER-A hard opacity of the lens occurring in the aged.
Traumatic Cataract - ANSWER-Cataract following an injury.
Choroid - ANSWER-Vascular (blood-rich) layer of the eye; its function is to nourish the other parts of the
eye, primarily the retina.
Chromatic Aberration - ANSWER-Distortion of an optical image produced by the dispersion of light
passing through a lens and generally characterized by blurred, multicolored edges.
Ciliary Body - ANSWER-The thick rim of choroid to which the crystalline lens is attached.
Compound Hyperopic Astigmatism - ANSWER-The refractive error which results in two points of focus
falling behind the retina.
Ex: +1.00 / +2.00 x 090
Compound Myopic Astigmatism - ANSWER-The refractive error which results in two points of focus
falling in front of the retina.
Ex: -1.00 / -2.00 x 090
Cones - ANSWER-Light sensitive cells in the retina responsible for color vision, daytime vision, and the
central portion of the visual field.
Conjunctiva - ANSWER-The clear membrane that lines the eyelids and covers the exposed surface of the
eyeball.
, Conjunctivitis - ANSWER-The inflammation of the conjunctiva; commonly referred to as "pink eye".
Cornea - ANSWER-The refractive, transparent, anterior wall of the eye, equal to 43 diopters power. It is
the fastest healing part of the body.
Crown Glass - ANSWER-Pure silicate glass of general excellence for the spectacle lens; index of refraction
is 1.523.
Crystalline Lens - ANSWER-A transparent colorless body suspended in the front part of the eyeball,
between the aqueous and the vitreous, the function of which is to bring the rays of light to a focus on
the retina.
Cycloplegia - ANSWER-Paralysis of the ciliary body; drops are used for diagnostic purposes.
Decentration - ANSWER-Distance between the optical center placement of a lens and its geometric
center; usually expressed in millimeters.
Diffusion - ANSWER-The scattering of light.
Diopter - ANSWER-Unit of measurement of the refractive power of a lens. A lens whose focal length is
one meter has a power of one. The higher the power, the shorter the focal length.
Diplopia - ANSWER-The seeing of one object as two, due to uneven tracking of the eyes. Commonly
known as double vision.
Distortion - ANSWER-Defect in a lens which causes a straight line to appear curved.
Divergent - ANSWER-Two or more light rays proceeding outward from a point.
Emmetropia - ANSWER-The refractive condition of the normal eye. When the eye is at rest, the image of
distant objects is brought to a focus on the retina.
