ABO PRACTICAL EXAM ADVANCED QUESTIONS AND ANSWERS

ABO PRACTICAL EXAM ADVANCED QUESTIONS AND ANSWERS Single Vision - CORRECT ANSWER-corrects for one distance Multifocal - CORRECT ANSWER-Corrects with two or more prescriptions (or 'powers') Bifocal - CORRECT ANSWER-lens having two focus strengths Trifocal - CORRECT ANSWER-pertaining to having three focus strengths Calculating Prismatic Effects - CORRECT ANSWER-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 - CORRECT ANSWER-BI & BI BO & BO BU & BD Cancelling Prism - CORRECT ANSWER-BI & BO BD & BD BU & BU Prentice's Rule - CORRECT ANSWER-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 - CORRECT ANSWER-The difference in vertical prism power at the reading level in a pair of lenses. OC Height's by lens - CORRECT ANSWER-SV = 1/2 of B Progressive = Fitting cross FT = 5mm above segment Vertex Compensation - CORRECT ANSWER-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 - CORRECT ANSWER-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 - CORRECT ANSWER-PD Vertical Centration - CORRECT ANSWER-OC Horizontal & Vertical Centration Formula - CORRECT ANSWER-Given PD/OC - Human PD/OC= mm moved Frame PD is found by adding A+DBL Power in Oblique Meridians - CORRECT ANSWER-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 - CORRECT ANSWER-is an ophthalmic instrument. It is mainly used