ABO Practical Exam Latest

ABO Practical Single Vision - corrects for one distance Multifocal - Corrects with two or more prescriptions (or 'powers') Bifocal - lens having two focus strengths Trifocal - pertaining to having three focus strengths Calculating Prismatic Effects - obtained at the center of an optical lens by producing a difference in edge thickness, either by grinding the back surface at an angle to the front surface during lens surfacing or, if the lens has sufficient power, de-centering the optical center of the lens Compounding Prism - BI & BI BO & BO BU & BD Cancelling Prism - BI & BO BD & BD BU & BU Prentice's Rule - P=hcm x D P=amount of prism created h= number of cm OC moved cm= centimeters (convert to mm, divide by 10) D= power in meridian with error Vertical Imbalance - The difference in vertical prism power at the reading level in a pair of lenses. OC Height's by lens - SV = 1/2 of B Progressive = Fitting cross FT = 5mm above segment Vertex Compensation - A plus lens when moved farther from the eye gains in plus power Distance is 0 with CL because they are on the eye Vertex compensation Formula - De= Dl/(1 + d xDl) De= diopter effective value of error created D/= lens power (given power) d= amount in METERS lens moved from refracted position to position lens is worn Keep sign for what it is (+/-) - to d means moves away Horizontal Centration - PD Vertical Centration - OC Horizontal & Vertical Centration Formula - Given PD/OC - Human PD/OC= mm moved Frame PD is found by adding A+DBL Power in Oblique Meridians - Dt= (sina)²x Dc +Ds Dt= Total Power we need (sina)²= degree we have degree we need Dc= cylinder power Ds= sphere power Lensmeter - is an ophthalmic instrument. It is mainly used by optometrists and opticians to verify the correct prescription in a pair of eyeglasses, to properly orient and mark uncut lenses, and to confirm the correct mounting of lenses in spectacle frames. (also known as a focimeter or vertometer) Lens Measurement Devices - lens clock, calipers, millimeter ruler, circumference gauge Lens Clock - is used to measure the surface powers base curve of a lens Lens Calipers - Measures thickness of lenses in mm Millimeter ruler - measures interpupillary distance, or seg heights, or OC heights