Optics Flashcards
Aphakic Lens
Astigmatism
Corneal Astigmatism
A convex lens of high plus dipper power used in the correction of vision in aphakia
A refractive error in which light rays entering the eye fail to come to a single focal point; caused by different degrees of refraction in various meridians of the cornea and/or lens, most often at right angles to each other
The astigmatism that is the result of the cornea not being spherical. It is determined by the K reading obtained from the cornea.
Residual Astigmatism
Irregular Astigmatism
Regular Astigmatism
The difference between the corneal astigmatism and the total astigmatism of the eye. The total astigmatism of the eye is the astigmatism present in the refraction. Thus the total astigmatism is composed of the corneal astigmatism and the residual astigmatism. The residual astigmatism is due to the tilt or other abnormality of the crystalline lens or other factors within the eye. It is also referred to as lenticular astigmatism.
Astigmatism where the two principal meridians of the eye are not at right angles to each other.
Condition in which light rays come to two focal image lines
Compound Regular
Mixed Regular
Simple Regular
The two focal lines of light rays are either in front of the retina, compound myopic astigmatism, or behind the retina, compound hyperopic astigmatism.
The light rays come to two focal lines-one in front of the retina and one behind the retina.
The light rays come to two focal lines-one on the retina and the other either in front of the retina (simple myopic astigmatism) or behind the retina (simple hyperopic astigmatism).
With-the-rule Astigmatism (WTR)
Against-the-rule Astigmatism (ATR)
Biconcave Lens
Most common type of astigmatism. The flattest meridian is in the horizontal plane and the steepest meridian is in the vertical plane; may be corrected with a horizontal minus cylinder or vertical plane; may be corrected with a horizontal minus cylinder or vertical plus cylinder, (e.g., -2.00 -2.00 x180 or -3.00 +2.00 x90).
The flattest meridians is in the vertical plane and the steepest meridians is in the horizontal plane; may be corrected with a vertical minus cylinder or horizontal plus cylinder, (e.g., -2.00 -2.00 x 90 or -4.00 +2.00 x180).
Refers to a lens where both surfaces are concave (minus) and sometimes referred to as a minus lens. This type of lens is used to correct for myopia, sometimes referred to as ‘shortsighted,” or “nearsighted.” Refer to lens.
Biconvex Lens
Compound Lens
Concave Lens
Refers to a lens where both surfaces are convex (plus) and sometimes referred to as a plus lens. It is used to correct for hyperopia, sometimes referred to as “farsightedness.” Refer to lens.
A spectacle lens which functions as a combination spherical lens and cylinder lens, and is used to correct astigmatism.
A lens having the power to diverge rays of light. Synonyms are diverging lens, reducing lens, negative lens, myopic lens or minus lens. A concave or minus lens is denoted by a minus sign (-).
Convergence
Convex Lens
Diopter
The directional property of a bundle of light rays turned or bent toward a real image point; to be distinguished from the divergence property of a bundle of rays emanating from a point source.
A lens on which one surface is plane and the other cylindrical, or a compound lens which has a spherical surface and the other surface toroidal, such that one meridian has zero power and a meridian 900 to it has maximum dioptric power.
A unit of measurement that is function of lens power. The number of diopters of power being equal to the reciprocal of the focal length in meters. Thus, a one diopter lens refracts light to a focal point of one meter. A two-diopter lens refracts light to a focal point of 0.5 meters, etc. Can also be used as a measurement of lens curvature, with the number of diopters of curvature being equal to the reciprocal of the medius of curvature of the lens in meters.
Dispersion
Divergence
Focal length
The act or state of being broken apart or separated. Chromatic dispersion is the breaking of white light into its component colors, as with a prism.
The directional property of a bundle of light rays emanating from a point source in all directions; to be distinguished from the convergence property of a bundle of rays bent towards a real image point.
The linear distance between a point of reference, usually a principal point, of an optical system and the corresponding primary or secondary focal point. Commonly refers to the linear distance from a lens to its focal point.
Focal point
Hyperopia (hypermetropia)
Image
The convergence or divergence of a pencil of light, typically through an optical system.
A refractive condition of the eye where the conjugate focus is behind the retina when accommodation is relaxed. Can simply be thought of as the state in which parallel rays of light entering the eye focus behind the retina in the absence of accommodation. Commonly referred to as “far sighted.” Traditionally, high hyperopia would refer to a correction of +5.00 diopters or greater, and low hyperopia would refer to a correction of +2.00 diopters or less. Often caused by an eye that is anatomically short.
In general, a likeness. The optical counterpart of an object produced by a lens, a mirror or other optical system. the subjective perception of a viewed object projected in visual space.
Index of refraction
Lens
Light
The ratio of the speed of light in a vacuum (or other medium of reference) relative to the speed of light in a given medium, obtained by Snell’s law and designated by the letter “n”. The higher the “n” of an optical medium, the greater the refraction ability (bending of light).
Any transparent substance (typically glass or plastic) existing or made into a shape that allows rays of light to converge or diverge. Also a shortened term for the crystalline lens.
Electromagnetic radiant energy in the 380 to 769 nanometer range that in humans gives rise to the sensation of vision upon stimulation of the retina.
Mirror
Myopia
Neutralization
Any smooth surface that forms images by reflection.
The condition of the eye when accommodation is relaxed, whereby parallel rays of light entering the eye focus in front of the retina. A minus-peered lens is required to correct this condition, which is commonly referred to as “near-sighted.” Typically, high myopia would refer to a correction of -6.00 diopters or greater, and low myopia would refer to a correction of -3.00 diopters or less.
Method of determining the power of the eye or of a lens. Commonly refer to using lensometer to determine the spherical power and cylinder power with axis (if present) power of a spectacle lens.
Plano
Plano Lens
Plano Concave
Without dioptric power; synonym is Afocal
A spectacle lens with zero power
Denotes a lens that is flat on one side and concave on the other
Plano convex
Prism
Reflection
Demotes a lens that is flat on one side and convex on the other.
Any transparent body bounded by two planes that are nor parallel; optical lens or system that deviates that path of light. A prism lens deviates incident light so that the emergent light is towards the prism base. Two prism lenses placed base to base produce a converging lens effect (plus lens) while two prism lenses placed apex to apex produce a diverging lens effect (minus lens).
The act of returning of light waves from a surface. Refer to mirror.
Refraction
Snell’s Law
Spectacles
The bending of a ray or wave, e.g., light, heat, sound, as it passes obliquely from one medium to another of different density, in which its speed is different, to through layers of different density in the same medium. In optics, this term refers to the ability (or measurement of this ability) of an eye to refract light entering it to form an image on the retina.
The ratio of the speed of light in a vacuum (or other medium of reference) to the speed of light in a given medium calculated as the sine of the angle of incidence to the sine to the angle of refraction. Also referred to as the law of Refraction.
A mechanical device that is placed in front of the eyes to correct refractive error. They consist of two ophthalmic lenses placed into a holding device called a frame. The frame is held in placebo having its front center sit on the bridge of the nose and its two rims fit over the tops of the ears. The term “spectacles” comes from the latin word “Specere” meaning “to look at”. Commonly referred to as eyeglasses or glasses.
Spherocylindrical Lens
Spherical Lens
Vergence
A lens that combines a spherical and cylindrical lens. The area between the two focal points of a spherocylindrical lens forms an elongated oval shape reared to as the “Conoid of Sturm” or “Sturm’s Conoid.” In the center area of the light bundles, the conoid forms a sphere and this is called the “Circle of Least Confusion.”
A lens where all refractive surfaces are spherical, resulting in the lens possessing a single dioptric value in all meridians (all light rays refractive equally); to be differentiated from a cylinder lens.
The reciprocal of the distance between the point of focus of a light bundle and any reference plane; measured in diopters.
Vergence Power
Vertex Power
Wave
The ability of an optical system to change the vergence of a pencil of rays, usually designated quantitatively by the reciprocal of the focal length of the system. A synonym is focal power.
The mergence power expressed with reference to tighter the posterior surface of an optical system at the optical axis, i.e., back vertex power, or anterior surface, i.e., front vertex power. The total power of a lens expressed in dioptric units.
A periodic undulation or modulation. The typical sine-wave paternities that light rays and other electromagnetic radiation propagates.
