Formulas Flashcards
Minimum amplitude of accommodation
Minimum = 15 - (1/4) age
* fail if 2.00 D or more below
Normal NRA
+2.00 (+/- 0.50D)
* negative relative accommodation
* uses plus lenses
Accommodative convergence/ accommodation
AC/A ratio = PD + near (near phoria - far phoria)
PD= pupillary distance (centimeters)
Near= near distance (meters)
(-) exo
(+) eso
What is the dioptric equivalent of a lens that has a base curve of 8.3mm?
Convert BC from mm to diopters
337.5/8.3 =40.663 40.66 D
What is the formula to calculate Seg inset for bifocals?
(Distance PD - near PD)
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2
How to calculate vergence demand
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
JND for trial frame refraction
- Snellen denominator/ 100
- 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
Javal’s rule
Refractive astigmatism = (1.25 x diff K) +/- 0.5
WTR: subtract 0.50
ATR: add 0.50
Oblique: 0.50 dropped from equation
Sheards criterion
S = 2/3D - 1/3R
D: phoria
R: compensating fusional vergence
EXO: BO blur
ESO: BI blur
Sheard’s criterion
In order for pt to remain asymptomatic the amount of reserve fusional vergence (reports blur) must be _____ that of the phoria
TWICE
* look at blur point
For XP look at PFV blur
For EP look at NFV blur
MBS
MBS = ED + TLD
TLD for minimum blank size
TLD = |( A + DBL) - PD|
*absolute value
Calculate A1c—-> FBS
(A1c x 28.7) -46.8
Example:
A1c = 6.7
FBS = ?
(6.7 x 28.7) - 46.8 =145.49
What does the red lens test evaluate?
The binocular system
* suppression
* shallow suppression vs deep suppression
Suppression:
*with red over right eye = pt sees white light = suppressing right eye
*with red over right eye = pt sees pink light = fusion
* with red over right eye = pt sees red light = suppressing left eye
Shallow vs deep:
Shallow = suppression in mid lighting but fusion in dark lighting
Deep = suppression in both mid and dark lighting
What should the patient report seeing when the red lens is held over the preferred eye?
A pinkish or red/white shimmering circle
This indicates a composite image of the two eyes.
What does it indicate if a patient observes a white light during the red lens test?
The patient is suppressing the eye behind the red lens.
What does it indicate if a patient reports seeing a red circle during the red lens test?
The patient is suppressing the eye without the red lens.
At what distance should the red lens test be repeated using a penlight or transilluminator?
40 cm
What type of suppression is classified when it occurs at 40 cm?
Peripheral suppression
This occurs due to the large image size covering a greater retinal area.
What type of suppression is classified when it occurs at 6 m but not at 40 cm?
Central suppression
Less of the retina is involved due to a smaller image size.
What characterizes shallow suppression?
Suppression occurs in moderate but not dim illumination.
What characterizes deep suppression?
Suppression is present under both moderate and dim illumination.
