ABO Practical exam questions &
answers
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
Frame PD is found by adding A+DBL
Power in Oblique Meridians - 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
answers
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
Frame PD is found by adding A+DBL
Power in Oblique Meridians - 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
