ABO Practical Exam Questions and Correct
Answers| Updated
Single Vision
corrects for one distance
Multifocal
Corrects with two or more prescriptions (or 'powers')
Bifocal
lens having two focus strengths
Trifocal
pertaining to having three focus strengths
Calculating Prismatic Effects
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
BI & BI
BO & BO
,BU & BD
Cancelling Prism
BI & BO
BD & BD
BU & BU
Prentice's Rule
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
The difference in vertical prism power at the reading level in a pair of lenses.
OC Height's by lens
SV = 1/2 of B
Progressive = Fitting cross
FT = 5mm above segment
, Vertex Compensation
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
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
PD
Vertical Centration
OC
Horizontal & Vertical Centration Formula
Given PD/OC - Human PD/OC= mm moved
Frame PD is found by adding A+DBL
Answers| Updated
Single Vision
corrects for one distance
Multifocal
Corrects with two or more prescriptions (or 'powers')
Bifocal
lens having two focus strengths
Trifocal
pertaining to having three focus strengths
Calculating Prismatic Effects
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
BI & BI
BO & BO
,BU & BD
Cancelling Prism
BI & BO
BD & BD
BU & BU
Prentice's Rule
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
The difference in vertical prism power at the reading level in a pair of lenses.
OC Height's by lens
SV = 1/2 of B
Progressive = Fitting cross
FT = 5mm above segment
, Vertex Compensation
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
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
PD
Vertical Centration
OC
Horizontal & Vertical Centration Formula
Given PD/OC - Human PD/OC= mm moved
Frame PD is found by adding A+DBL
