ABO numbers, math, formulas (ACCURATE!!)
Prentice's Rule -answer- P = f x c
P = amount of prism correction
f = lens power (in diopters)
c = decentration (the distance between the pupil centre and the lens's optical centre, in
millimeters)
Cornea IOR -answer- 1.37
Tear Film, Vitreous IOR -answer- 1.33
Crystalline lens IOR -answer- 1.42
Optical Standard index of refraction -answer- 1.53
Crown Glass index of refraction -answer- 1.523
High index IOR -answer- 1.74
CR-39 IOR -answer- 1.49 - 1.50
Poly index of refraction -answer- 1.586
Air IOR -answer- 1.00
How fast does light travel through air -answer- 186,000 mi/sec
Minimum Blank Size (MBS) formula -answer- (GCD - PD) + ED
A + DBL + ED - PD
Frame PD - PD + ED
Dec. + ED
GCD = geometric center distance or A + DBL
PD = Pt. PD
ED = effective diameter
Dec. = Decentration
Focal length formula, diopters known -answer- 1/Dioptic Power
Dioptic Power formula, foci known -answer- 1/Focal Length (m)
Anisometropia -answer- Difference of 2 diopters between OD & OS
, What is the Radius of a 1 diopter curve? -answer- 530mm
Radius formula -answer- 530/Power = R
Power formula -answer- 530/Radius = Diop.
Vertical Decentration formula -answer- Seg.ht. - B/2
OC height - (B measurement / 2)
How much HORIZONTAL prism tolerance is allowed? -answer- 2/3 of a diopter
-or-
0.667
How much VERTICAL prism tolerance is allowed? -answer- 1/3 of a diopter
-or-
0.333
Base Curve tolerance -answer- +/-0.75
Sphere Tolerance up to 6.50 -answer- +/- 0.13
Sphere Tolerance above 6.50 -answer- +/- 2%
Cylinder Axis Tolerance >1.50 -answer- +/-2°
Cylinder Axis Tolerance >0.50 / less than or equal to 1.50 -answer- +/-3°
Cylinder Axis Tolerance >0.25 / less than or equal to 0.50 -answer- +/-7°
Cylinder Axis Tolerance >0.00 / less than or equal to 0.25 -answer- +/-14°
Drop ball test for Safety lenses -answer- 5/8ths in. diameter, weighing 0.56 oz.
dropped 50ft
Frame PD -answer- A box + DBL
Total decentration -answer- Frame PD - Patient PD
A + DBL - PD (divide by 2 to get decentration per lens)
Base IN (MINUS) -answer- If lens PD is GREATER than pt. PD
Base OUT (MINUS) -answer- If lens PD is LESS than pt. PD
Thindex glass IOR -answer- 1.8
Prentice's Rule -answer- P = f x c
P = amount of prism correction
f = lens power (in diopters)
c = decentration (the distance between the pupil centre and the lens's optical centre, in
millimeters)
Cornea IOR -answer- 1.37
Tear Film, Vitreous IOR -answer- 1.33
Crystalline lens IOR -answer- 1.42
Optical Standard index of refraction -answer- 1.53
Crown Glass index of refraction -answer- 1.523
High index IOR -answer- 1.74
CR-39 IOR -answer- 1.49 - 1.50
Poly index of refraction -answer- 1.586
Air IOR -answer- 1.00
How fast does light travel through air -answer- 186,000 mi/sec
Minimum Blank Size (MBS) formula -answer- (GCD - PD) + ED
A + DBL + ED - PD
Frame PD - PD + ED
Dec. + ED
GCD = geometric center distance or A + DBL
PD = Pt. PD
ED = effective diameter
Dec. = Decentration
Focal length formula, diopters known -answer- 1/Dioptic Power
Dioptic Power formula, foci known -answer- 1/Focal Length (m)
Anisometropia -answer- Difference of 2 diopters between OD & OS
, What is the Radius of a 1 diopter curve? -answer- 530mm
Radius formula -answer- 530/Power = R
Power formula -answer- 530/Radius = Diop.
Vertical Decentration formula -answer- Seg.ht. - B/2
OC height - (B measurement / 2)
How much HORIZONTAL prism tolerance is allowed? -answer- 2/3 of a diopter
-or-
0.667
How much VERTICAL prism tolerance is allowed? -answer- 1/3 of a diopter
-or-
0.333
Base Curve tolerance -answer- +/-0.75
Sphere Tolerance up to 6.50 -answer- +/- 0.13
Sphere Tolerance above 6.50 -answer- +/- 2%
Cylinder Axis Tolerance >1.50 -answer- +/-2°
Cylinder Axis Tolerance >0.50 / less than or equal to 1.50 -answer- +/-3°
Cylinder Axis Tolerance >0.25 / less than or equal to 0.50 -answer- +/-7°
Cylinder Axis Tolerance >0.00 / less than or equal to 0.25 -answer- +/-14°
Drop ball test for Safety lenses -answer- 5/8ths in. diameter, weighing 0.56 oz.
dropped 50ft
Frame PD -answer- A box + DBL
Total decentration -answer- Frame PD - Patient PD
A + DBL - PD (divide by 2 to get decentration per lens)
Base IN (MINUS) -answer- If lens PD is GREATER than pt. PD
Base OUT (MINUS) -answer- If lens PD is LESS than pt. PD
Thindex glass IOR -answer- 1.8
