Formulas

Question 1

Minimum amplitude of accommodation

Answer 1

Minimum = 15 - (1/4) age
* fail if 2.00 D or more below

Question 2

Normal NRA

Answer 2

+2.00 (+/- 0.50D)
* negative relative accommodation
* uses plus lenses

Question 3

Accommodative convergence/ accommodation

Answer 3

AC/A ratio = PD + near (near phoria - far phoria)

PD= pupillary distance (centimeters)
Near= near distance (meters)

(-) exo
(+) eso

Question 4

What is the dioptric equivalent of a lens that has a base curve of 8.3mm?

Answer 4

Convert BC from mm to diopters

337.5/8.3 =40.663 40.66 D

Question 5

What is the formula to calculate Seg inset for bifocals?

Answer 5

(Distance PD - near PD)
———————————
2

Question 6

How to calculate vergence demand

Answer 6

Demand = target separation/ training distance

Target separation in cm
Training distance in meters

Example: variable tranaglyphs when separation is 4cm at a distance of 80cm
Demand = 4cm/ 0.80 m =5 PD

Question 7

JND for trial frame refraction

Answer 7

1. Snellen denominator/ 100
2. JND/2 (these are the lenses you show)

Example: VA 20/500
JND = 500/100 =5
5/2 =2.50
Therefore you show +2.50 and -2.50

Question 8

Javal’s rule

Answer 8

Refractive astigmatism = (1.25 x diff K) +/- 0.5

WTR: subtract 0.50
ATR: add 0.50
Oblique: 0.50 dropped from equation

Question 9

Sheards criterion

Answer 9

S = 2/3D - 1/3R

D: phoria
R: compensating fusional vergence

EXO: BO blur
ESO: BI blur

Question 10

Sheard’s criterion
In order for pt to remain asymptomatic the amount of reserve fusional vergence (reports blur) must be _____ that of the phoria

Answer 10

TWICE
* look at blur point
For XP look at PFV blur
For EP look at NFV blur

Question 11

MBS

Answer 11

MBS = ED + TLD

Question 12

TLD for minimum blank size

Answer 12

TLD = |( A + DBL) - PD|

*absolute value