ABO PRACTICAL MARKING SCHEME
EXAM DRILL Q&A COMPLETE QUESTIONS
AND ANSWERS 2026 PERFECT GRADE
RECORD.
⫸ Multifocal. Answer: Corrects with two or more prescriptions (or
'powers')
⫸ Bifocal. Answer: lens having two focus strengths
⫸ Trifocal. Answer: pertaining to having three focus strengths
⫸ Calculating Prismatic Effects. 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. Answer: BI & BI
BO & BO
BU & BD
⫸ Cancelling Prism. Answer: BI & BO
, BD & BD
BU & BU
⫸ Prentice's Rule. 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. Answer: The difference in vertical prism power
at the reading level in a pair of lenses.
⫸ OC Height's by lens. Answer: SV = 1/2 of B
Progressive = Fitting cross
FT = 5mm above segment
⫸ Vertex Compensation. 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. Answer: De= Dl/(1 + d xDl)
De= diopter effective value of error created
D/= lens power (given power)
EXAM DRILL Q&A COMPLETE QUESTIONS
AND ANSWERS 2026 PERFECT GRADE
RECORD.
⫸ Multifocal. Answer: Corrects with two or more prescriptions (or
'powers')
⫸ Bifocal. Answer: lens having two focus strengths
⫸ Trifocal. Answer: pertaining to having three focus strengths
⫸ Calculating Prismatic Effects. 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. Answer: BI & BI
BO & BO
BU & BD
⫸ Cancelling Prism. Answer: BI & BO
, BD & BD
BU & BU
⫸ Prentice's Rule. 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. Answer: The difference in vertical prism power
at the reading level in a pair of lenses.
⫸ OC Height's by lens. Answer: SV = 1/2 of B
Progressive = Fitting cross
FT = 5mm above segment
⫸ Vertex Compensation. 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. Answer: De= Dl/(1 + d xDl)
De= diopter effective value of error created
D/= lens power (given power)
