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PPO > Lensometry > Flashcards

Lensometry Flashcards

1
Q

the purpose of the lensometer is to….

A

to measure the vertex power of the lens

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2
Q

we measure the vertex power of a lens to… (3 things)

A
  1. measure pts habitual correction
  2. verfiy the rx of new glasses receiced from the lab (power, axis, bifocal add, PD, prism)
  3. verfiy dioptric power of CL
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3
Q

the lensometer measures the vertex power of the len’s ______

A

surface

NOT FOCAL LENGTH

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4
Q

Reciprocal of the distance btwn a surface of the lens and its secondary focal point

A

vertex power

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5
Q

the common term for measure of power of a lens using a lensometer is…

A

neurtralize

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6
Q

vertex power is not true….

A

focal lenght

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7
Q

the back vertex power is…..

A

measured from the back surface (faces eye)

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8
Q

the front vertex power is….

A

meausred from the surface that faces light

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9
Q

which is most commonly used vertex power in opthalmic optics

A

back vertex power

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10
Q

where the optical axis of a lens intersects the front and back surfaces

A

optical center of a lens

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11
Q

distance btwn the visual axes of the pts eye

A

PD

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12
Q

distance btwn optical centers of the 2 ophthalmic lenses

A

spectacle PD

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13
Q

what are the measurments of PD, spectacle PD, and optical center of a lens given in

A

mm

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14
Q

for spectacle pd, you typically want to match the _______ of the pts lenses to the _______ of the 2 eyes

A

optical center

visual axes

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15
Q

a compact holder (transparent plexiglass) used for inspection and neutralization of soft CL

A

wet cell

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16
Q

the eyecup is a rubber ring that protects the outer-most lens and your eyeglasses lens from damage. it also helps block peripheral light. the focus ring allows focusing the instrument to your indiv. eye

A

eyepiece

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17
Q

the metal ring rotates the ______

A

reticle

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18
Q

rotates target and indicates direction of principle meridians of the lens

A

axis wheel

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19
Q

indicate power in diopters of the lensometer

A

power wheel/drum

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20
Q

platform where the glasses are placed w/ a brace to hold the glasses in place

A

lens stage

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21
Q

the handle of this allows to lock the lenses in place

A

lens holder

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22
Q

what the back surface of the lens rest in

A

lens-stop

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23
Q

how do you change vergence of rays in the lensometer (2)

A
  1. moving the target (mires)

2. moving the light source

24
Q

brings the target (light) to infinity when the instrument is set to zero (plano) and there is no unknown lens placed to be measured

A

standard or badal lens (or collimator lens)

25
Q

these are the cross-hatched series of lines (2 names)

A

target

mires

26
Q

moved to effect a chnage in divergence and thus measure the power of the unknown

A

light source

ALWAYS KEEP A SPARE!

27
Q

some lensometers (topocon) have a prism measuring device called _____ mounted at the end of the objective

A

Risley prism

make sure its set to 0 and 90 b4 starting

28
Q

the telescope contains these 3 things in order of the lensometer

A

eyepiece
reticle
objective

29
Q

the badal system is the

A

standard lens
target
light source

30
Q

with zero setting and NO glasses, target’s image (mire) is seen at ______

A

infinity

31
Q

when an unknown lens is introduced, the image is blurry bc….

A

the telescope is no longer collimated (parallel rayss) and the image of the target (mire) is blurry

32
Q

what do you need to do to bring the image to focus

A

move the target (mires) by an amount equal to distance it takes to make the rays parallel again ( in focuse)

33
Q

what happens to the light and the mires when a + lens is introduced

A

light is converged and mires are out of focus

34
Q

how do you clear the image of the + lens

A

target is moved closer, generating more divergent rays

35
Q

what happens to the light when a - lens is introduced

A

light is diverged

36
Q

how do you clear the image of a - lens

A

target needs to be moved further away to generate more converging rays

37
Q

every ____mm of movement equals 1D of power

A

2.5

38
Q

what are the steps to measuring a SV lens

  2. focus the _____
  3. determine _______
  4. calibrate ______
  5. position _______
  6. center the ______
  7. check the ______
  8. chck the ______ and ______
  9. mark the ______
  10. repeat ______ for the _____ lens
  11. turn _____
  12. _____results
A
  1. Turns lensometer on
  2. focus the black reticle
  3. determine which is sphere and cyl lines (thinner lines is sphere)
  4. calibrate the mires (focus w/ drum)w
  5. the glasses ( right lens first) on the stage
  6. lens
  7. sphere power
  8. cyl power and axis
  9. optical center
  10. repeat 5-9 for OS
  11. turn off
  12. record
39
Q

when you focus the reticle, first turn the eyepice all the way ______ and then slowly _____ until the reticle is shart and clear

A

counter-clockwise

clockwise

40
Q

it your pts optical axis (center of pupil) is not aligned w/ the opitcal center of the lens (pt PD and spec PD dont match) there will be an …

A

induced prismatic effect

41
Q

the prismatic effect depends on the….

A

power of the lens

and how far away the pupil is from the lens’ opticla center

42
Q

how do you measure induced prism

A

calculate (prentice rule)

measred w/ lensometer

43
Q

what is prentice’s rule

A

prism power = F x d / 10
F=power of the lens
d=decentration in mm

44
Q

what does the direction of the prism base depend on

A
  1. the location of the pt’s line of sight

2. whether the lens is minus or plus

45
Q

2 prisms are placed base to base

A

plus lens

46
Q

2 prisms are placed apex to apex

A

minus lens

47
Q

to meausre prism power….

  1. dot each lens using pts _____
  2. place glasses in ______
  3. determine location of the ____ o fmires on the ring
  4. use concentric rings of ____ to calculate amount of prism
  5. determin base _____
A
  1. PD
  2. lensomter
  3. center
  4. reticle
  5. direction of prism
48
Q

w/ a risley prism, center ___ on reticle then ___prism amnt from the scale

A

mires

record

49
Q

what do you do when the prism is too large that it is outside your view

A

use hand held prism to bring the image in

50
Q

in a line bifocal, the carrier lens is the _______

the segment is the…..

A

distance vision rx

near add

51
Q

which vertex is used to determine the bifocal add

A

front vertex power

52
Q

in trifocals: the in btwn distance and near (power usually 50% of near add power)

A

intermediate add

53
Q

the greatest plus power, near (reading) portion

A

near add

54
Q

btwn 4D and 8D there is a ____ difference in the add

A

0.25D

55
Q

markings indicate ad power in …

A

progressive lenses

56
Q

the lens stage and holder contains 2 things:

A 
marking device (3 ink dots) 
and lens stop
57
Q

what is the distance portion of the lens called

A

carrier- holds near and intermiediate power lenses

PPO (14 decks)

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