ABO PRACTICAL
REVIEWED QUESTIONS
AND CORRECT ANSWERS
GRADED A+ 2025-2026
Single Vision - ANS-corrects for one distance
Multifocal - ANS-Corrects with two or more prescriptions (or 'powers')
Bifocal - ANS-lens having two focus strengths
Trifocal - ANS-pertaining to having three focus strengths
Calculating Prismatic Effects - ANS-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 - ANS-BI & BI
BO & BO
BU & BD
Cancelling Prism - ANS-BI & BO
BD & BD
BU & BU
, Prentice's Rule - ANS-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 - ANS-The difference in vertical prism power at the reading level in
a pair of lenses.
OC Height's by lens - ANS-SV = 1/2 of B
Progressive = Fitting cross
FT = 5mm above segment
Vertex Compensation - ANS-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 - ANS-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 - ANS-PD
Vertical Centration - ANS-OC
Horizontal & Vertical Centration Formula - ANS-Given PD/OC - Human PD/OC= mm
moved
REVIEWED QUESTIONS
AND CORRECT ANSWERS
GRADED A+ 2025-2026
Single Vision - ANS-corrects for one distance
Multifocal - ANS-Corrects with two or more prescriptions (or 'powers')
Bifocal - ANS-lens having two focus strengths
Trifocal - ANS-pertaining to having three focus strengths
Calculating Prismatic Effects - ANS-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 - ANS-BI & BI
BO & BO
BU & BD
Cancelling Prism - ANS-BI & BO
BD & BD
BU & BU
, Prentice's Rule - ANS-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 - ANS-The difference in vertical prism power at the reading level in
a pair of lenses.
OC Height's by lens - ANS-SV = 1/2 of B
Progressive = Fitting cross
FT = 5mm above segment
Vertex Compensation - ANS-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 - ANS-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 - ANS-PD
Vertical Centration - ANS-OC
Horizontal & Vertical Centration Formula - ANS-Given PD/OC - Human PD/OC= mm
moved
