ABO Practical Comprehensive
Questions (Frequently Tested) with
Verified Answers Graded A+
Single Vision - Answer: corrects for one distance
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)
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 - Answer: PD
Vertical Centration - Answer: OC
Horizontal & Vertical Centration Formula - Answer: Given PD/OC - Human PD/OC= mm moved
Questions (Frequently Tested) with
Verified Answers Graded A+
Single Vision - Answer: corrects for one distance
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)
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 - Answer: PD
Vertical Centration - Answer: OC
Horizontal & Vertical Centration Formula - Answer: Given PD/OC - Human PD/OC= mm moved
