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PPO > Refraction > Flashcards

Refraction Flashcards

1
Q

anomaly of the refractive state of the eye in which, with accommodation relaxed, the image of objects at infinity is not formed on the retina and is therefore blurred

A

ametropia

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2
Q

image focuses in front of the retina

A

myopia

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3
Q

image focuses behind the retina (when accommodation is relaxed)

A

hyperopia

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4
Q

the point is focused as 2 lines resulting in a blurred and distored image; line foci may be in front of, behind or on the retina in part

A

astigmatism

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5
Q

normal decrease in amp of accommodation that occurs with age restulting in the need for plus over the distance RX to see clearly at near

A

presbyopia

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6
Q

a difference in has and needs, the eye has….

A

ametropia

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7
Q

the ___ eye has an axial length and refractive power that focuses parallel light onto the retina when the pt is NOT accommodating (and looking at dist)

A

emmetropic eye

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8
Q

the axial length of the eye is too long or too short for the power of the eye resulting in a refractive error, known as….

A

ametropia or discrepancy

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9
Q

if has > needs, the discrepancy is …… and the rx needed is …..
person is …..

A

person is myope

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10
Q

if the has < needs, the discrepancy is ____ and the rx is _______
person is ….

A

-
+
person is hyperope

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11
Q

how are the rx and discrepancy related

A

equal and opposite in power

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12
Q

where is the focus in a myope

A

in front of the retina

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13
Q

where is the focus in a hyperope

A

behind the retina

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14
Q

ametropia is also called… (2 things)

A

refractive error

discrepancy

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15
Q

the perfect eye model only takes into consideration the ________ and not the _____ and ______

A

difference or discrepancy

  • axial lengh
  • refractive power
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16
Q

the discrepancy lens is ______ NOT _____ or _______

A

CONCEPTUAL

NOT BIOLOGICAL OR PHYSICAL!!!!!!!!!!!

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17
Q

what is on the retina coming from a point source of light

A

blur circle

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18
Q

the distance between the retina and the actual point of focus

A

dioptric blur

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19
Q

quantitatively, the amount of diopters necessary to reduce to zero the dioptric distance btwn the retina and point of focus

A

dioptric blur

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20
Q

reduces the size of the blur circle w/o changing the dioptric blur

A

pin-hole

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21
Q

pinhole reduces the ______ of the blur circle w/o changing the ________

A

diameter

dioptric blur

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22
Q

in a good refraction, you make the blur circle smaller by reducing the ______

A

dioptric blur

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23
Q

in myopia, has _____ needs

  • too much ___ power
  • discrepency is _____ and corrected with a _____
A

greater
+
+, -

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24
Q

what does a minus powered lens do to a ray of light

A

diverges rays of light

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25
Q

what does a plus discrepency do to light on the myopic eye

A

converge light

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26
Q

why can the myopic eye see near objects clearly

A

accommodation

27
Q

what are responsible for accommodation

A

ciliary body and crystalline lens

28
Q

accommodation only provides ______ never ____

A

plus

minus

29
Q

the maximum power of accommodation

A

amplitude of accommodation

30
Q

why does accommodation only provide plus?

A

because it allows the organism to neutralize rays coming from near objects which are always minus in sign, NEVER PLUS

31
Q

all real objects nearer than optical infinity have ______ rays and therefore a power of ______

A

diverging

minus

32
Q

ampliitude peaks at age ____ and declines _____ w/ age after that

A

14

steadily

33
Q

what is hofstetter’s formula for amplitude

A

amp = 15 - 1/4age

34
Q

insufficient amplitude of accommadation due to healthy aging

A

presbyopia

35
Q

summation principle
blur: plus = _____ , minus = _______ retina

lens/rx: minus for ____, plus for _____, plus for __

objects: real objects are ____, objects at infinity are _____, virtual objects are ______
accomodation: ALWAYS ___ or _____

discrepancy/refractive error: ___ for myope, ____ for hyperope

A

blur: plus = in front of retinal, minus = behind retina
lens: minus for myope, plus for hyperope, plus for adds
ojects: real objects are minus, objects at infinity are 0, virtual objects are plus
accomodatoin: plus or 0
discrepancy: plus for myope, minus for hyperope

36
Q

what is the summation principle

A

B = L + O + A + D

37
Q

D = 100/ cm, D = 40/ in

A

cm= 100/D, inches = 40/D

38
Q

too much plus on purpose is…

A

fog

39
Q

why do we fog an eye?

A

to get the pt to relax his accommodation. pt can see best when accommodation is 0

40
Q

perfect eye with a minus discrepancy and needs an rx of plus power is…

A

hyperope

41
Q

parallel light focuses behind the retina when the pt doesnt accommodate is…

A

hyperope

42
Q

what is “myope’s revenge”

A
  1. discomfort during near activies (asthenopia)
  2. earlier presbyopia
  3. complete dependence on correction later in life
43
Q

what is discomfort during near activities

A

asthenopia

44
Q

the most distnat point the eye can see in focus.

-a point in space conjugate to the retina where accommodation is relaxed

A

the far point (punctum remotum)

45
Q

the area of defintion from the lower to the upper limits of a particular scale

A

range

46
Q

what is the range of clear vision. what can it be determined by..

A 
from the (near point) punctum proximum to the punctum remotum (far point) 
cc, sc, or thorugh an add
47
Q

the closest point the eye can see clearly using maximum accommodation

A

near point

48
Q

what do you enter for accommodation if you are searching for the far point? what about the near point?

A 
far = 0
near = amp
49
Q

if the meridians are of the maximum and minimum power, they are known as the

A

principal meridians

50
Q

what does axis of cylinder correspond to

A

principal meridian containing plano power

51
Q

what are the 2 lenses stuck together in a sphero cylindrical lens

A

simple sphere and plano cylinder

52
Q

the rx has a direct relationship to the _____ optical cross

A

component

53
Q

what does a plus sphere do to rays

A

focuses parallel rays to a point

54
Q

what does a minus sphere do to rays

A

diverges rays so they behave as if they came from the same point

55
Q

the lines and the blurry ellipses together form a solid “image” which is called….

A

conoid of sturm

56
Q

any lens containing cyl brings light from a point soure to a __________ rahter than to a _____

A

focal conoid of sturm

focal point

57
Q

if both arms of the optical cross have plus power and the incidnet rays are coming from infinity, the conoid will be a ….

A

real image in real space

58
Q

if both arms of the optical cross are minus in power and the incident rays are parallel, then all of the conoid will be a ….

A

virtual image

59
Q

the dioptric midpoint of the 2 line foci

A

circle of least confusion

60
Q

points that coincides with the circle of least confusion

A

sphero equivalent

61
Q

an eye with uncorrected ______ cant focus a point source of light to a point focus

A

astigmatism

62
Q

for an eye with astigmatism, its discrepancy lens is a ______ rather than a spherical lens

A

spero cyl lens

63
Q

a meridian forms an image of the line perpendicular to itself

A

rule of perpendiculars

PPO (14 decks)

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