Unit 2 Flashcards
What is the standard prism tolerance in eyeglasses?
1/2 prism
If two images of an object fall on identical points on the retina, the object is seen as ______.
One
If 2 vertical prisms are in the same direction, do we add them or do they cancel each other out?
Cancel
We split a prism between the eyes when it is ___ or more diopters.
2
Two horizontal prisms going in the same direction - do we add them together or do they cancel each other out?
add
Two horizontal prisms going in opposite directions - do we add them together or do they cancel each other out?
cancel
Comparing the eye to a camera, the retina would be the _____.
film
Comparing the eye to a camera, the cornea is the ____ of the eye.
lens
How tall are the Snellen letters at the 20/20 line?
8.87 mm
Glasses are prescribed for which 3 reasons?
- refractive errors
- comfort
- safety
Define asthenopia.
uncomfortable vision
Define orthophoria.
the eyes are aligned straight
At age 10, our eyes can accommodate ____ diopters.
14
A plus lens decentered down produces prism base ____.
down
What is the Prentice’s Rule for calculating prism?
prism = Dd/10
How do we calculate decentration?
decentration = 1/2( frame PD - patient’s PD)
How do we calculate monocular decentration?
mono. dec. = 1/2(frame PD) - patient’s mono PD
Prisms deviate light towards the _____.
base
Prisms displace images toward the _____.
apex
Prisms are prescribed for phorias and _____.
tropias
A tendency of the eye to turn in or out.
phoria
The eye is permanently turned in or out.
tropia
How do we calculate the amount of decentration needed to produce a prescribed prism?
decentration = A10/D
A=prism
For plus lenses, the direction of decentration is in the _______ direction.
same
For minus lenses, the direction of decentration is in the _______ direction.
opposite
A minus lens decentered down produces prism base _____.
up
How tall are the Snellen letters at 20/40?
17.74 mm
Presbyopia is a refractive error.
False - it is a condition, not an error.
A hyperopic child tends to ____ - converge and ____ accommodate.
over, over
A hyperopic child’s eyes may lead to _______ if not corrected.
esophoria (tendency to turn in)
A myope tends to ______ converge and ____ accommodate.
under, under
An uncorrected myopic child’s eyes may have the tendency to turn ______.
out (exophoria)
At age 40, we have the ability, on average, to accommodate ____ diopters.
4.5
