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Part 1 > Ophthalmic Optics > Flashcards

Ophthalmic Optics Flashcards

1
Q

How to correct for seg being too high?

A
  1. INC panto tilt
  2. DEC vertex distance
  3. Spread the pads
  4. Move pads up
  5. Stretch the bridge
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2
Q

How to correct for seg being too low?

A
  1. DEC panto tilt
  2. INC vertex distance

Basically bring away from face

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3
Q

Center Thickness equation?

A

CT = (S1 + ET) - S2

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4
Q

Thickness, warp, BC, impact tolerance for glasses?

A

Thickness: +/- 0.3mm

Warp: +/- 1.00D

BC: +/- 0.75D

Impact: 5/8 inch steel ball fr 50” drop

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5
Q

Minimum Blank Size (MBS) equation?

A

MBS = ED + d + 2mm

ED: effective diameter
d: decentration = Frame PD - Pt PD
Frame PD=A+DBL

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6
Q

Lens clock power equation?

A

F lens = F lens clock [ (n lens - 1)/(n lens clock - 1)]

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7
Q

Frame adjustment if the frame “Falls down nose”?

A
  1. Pull in temples
  2. Bend down temple tips
  3. Pull in nose pads
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8
Q

Frame adjustment if “one lens closer to face”?

A
  1. Straighten temple

2. Pull in temple on same side

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9
Q

Frame adjustment if “touching cheek”?

A
  1. Reduce panto tilt
  2. Narrow bridge or pads to raise frame
  3. Narrow bright or pads to INC vertex distance
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10
Q

Frame adjustment if “too close to face”?

A
  1. Narrow pads
  2. Shrink bridge
  3. DEC face form to move lenses away from face
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11
Q

Frame adjustment if “too low on face”?

A
  1. Narrow bridge
  2. Add pads
  3. Lower the vertical portion of the pads to move frames up
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12
Q

Frame adjustment if “too high on one side”?

A

Pull up the temple

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13
Q

Index of crown glass?

A

n=1.532

Abbe=58.9 (high)

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14
Q

Index of Cr-39?

A

n=1.498

Abbe=58 (high, light, impact resistant)

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15
Q

Index of Polycarb?

A

n=1.586

Abbe=30 (low, great impact resistant, high chromatic aberrations)

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16
Q

Index of Trivex?

A

n=1.53

Abbe=43 - 45

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17
Q

How do you reduced Radial Astigmatism?

A

Picking the CORRECT Base Curves *

NOTE: radial astigmatism is oblique or marginal astig due to rays hitting lens or interface obliquely –> power altered by the tilt of the lens

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18
Q

What is the upper and lower limits of aspheric correction?

A

< -23.00D

> +7.00D

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19
Q

Which two aberrations contribute to warping along 2 axises?

A
  1. Radial Astigmatism (RA)
  2. Curvature of Field (COF)

NOTE: COF is when a Plane Object =/= Plane Image

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20
Q

An image surface created by a system w/ no radial astigmatism yet still warped by COF is considered what kind of surface?

A

Petzval Surface

NOTE: COF will be present in any ophthalmic lens system ANY time the Petzval Surface does NOT correspond to the FAR POINT sphere of the eye –> warpage

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21
Q

What is the point of a point focal lens?

A

These lenses correct completely for radial astigmatism NOT COF

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22
Q

What is the point of a Percival Form Lens?

A

These lenses correct for COF NOT Radial Astigmatism

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23
Q

Pincushion is caused by plus or minus lenses?

A

PLUS

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24
Q

Barrel distortion is caused by plus or minus lenses?

A

MINUS

25
Q

What type of qualitative aberration is inversely related to abbe value and results in a series of pt images along the axis?

A

Longitudinal Chromatic Aberrations (LCA)

26
Q

Which qualitative aberration produces diff size images , is related to prismatic effect, creates more harm as prismatic effect inreases, and underlies the R/G spherical test in clinic?

A

Lateral (transverse) Chromatic aberration

27
Q

What is the equation for chromatic aberration?

A

CA = d*F/v

d –> distance to optical center of lens
F –> lens power
v –> Abbe number
Therefore, lower abbe = MORE CA

28
Q

Describe the purpose of an achromatic doublet.

A

Combines (+) lens of one material w (-) lens of another to eliminate CA (CA total = 0)

F total = F1 + F2 –> CA total = CA1 + CA2
0 = F1/v1 + F2/v2

29
Q

What are the aberrations of most concern to least in lens materials w low abbe values?

A
  1. Oblique astigmatism
  2. Curvature of Field
  3. Distortion

NOTE: use a SHORTER vertex distance, Monocular PDs, use sufficient PANTO tilt (less than 10 degrees for HIGH powered lenses)

30
Q

Prism Power & Thickness equation?

A

prism power = [100*g (n-1)]/L

g –> difference in thickness btwn apex & base
L –> apex to base length

31
Q

Equation for Lensometer?

A

x = f^2(F vertex)

32
Q

Where is the segment line relative to the GC for:

a. FT 28 mm (or less)
b. FT 35 mm
c. FT >35 mm
d. Curve/Panoptic
e. Executive/Franklin
f. Round Segs

A

a. FT 28 mm –> 5 mm below
b. FT 35 mm –> 4.5 mm below
c. FT >35 mm –> 0 mm below
d. Curve/Panoptic –> 4.5 mm below
e. Executive/Franklin –> 0 mm below
f. Round segs –> Seg radius (r)

33
Q

What type of magnification compares the retinal image size in an UNCORRECTED eye w the retinal image size in a CORRECTED eye?

A

Spectacle Magnification

SM=(I glasses)/(I w/o glasses)

SM smaller for myopes & bigger for hyperopes

34
Q

What is the spectacle magnification formula when taking shape and power factor into account?

A

SM = (Shape Factor)*(Power Factor)

35
Q

Equation for Shape Factor?

A

Shape Factor=Ms=1/[(1-(t/n)*(F1’)]

36
Q

Equation for Power Factor?

A

Power Factor=Mp=1/(1-h*Fv’)

h –> distance btwn BACK surface of the lens & entrance pupil of the eye

37
Q

How does increasing vertex distance affect SM in (+) vs (-) lenses?

A

(+) –> INCREASES SM

(-) –> DECREASES SM

Just use the Power factor equation

38
Q

What kind of magnification compares retinal image of corrected eye vs retinal image from a STANDARD eye?

A

Relative Spectacle Magnification

39
Q

Which law is a rule for RSM in axial ametrope where RSM=1 if a thin lens is placed at the primary focal point of the eye?

A

Knapp’s Law

Knapp’s Rule states that lenses placed at the anterior focal point of the eye, generally 15 mm in front of the eye, will create similarly sized images on the retina, whenever the disparity between the two eyes is due to a difference in axial length of the eyes.

Axial ametrope primary focal point is about 15-17 mm in front of cornea

Provide intution as to why spectacles work better for axial ametropes

40
Q

Where is the primary focal point in an axial ametrope?

A

15 to 17 mm in front of the cornea

41
Q

What are refractive ametropes best corrected with?

A

Best corrected with CONTACT LENSES (no effect on magnification)

NOTE: uncorrected refractive myopes, hyperopes, emmetrope all have the same image size formed on the retina; we would want magnification to remain constant after correction –> make SM small by choosing CL

42
Q

Compare the retinal image sizes for an uncorrected AXIAL ametrope:
Myope, Hyperope, Emmetrope

A

Myope > Emmetrope > Hyperope

NOTE: when corrected, RSM = ~1 thus its still M>E>H

43
Q

Compare the retinal image sizes for an uncorrected REFRACTIVE ametrope:
Myope, Hyperope, Emmetrope

A

M=H=E

NOTE: when corrected w CL’s RSM=~1; spectacles result in LARGER image for Hyperopes & Smaller for Myopes

44
Q

Spherical equivalent equation?

A

Fse=Fc/2 + Fs

45
Q

Describe Meridional Aniseikonia.

A

Due to differences in CYL power btwn OD and OS

The effect is prominent in ONE meridian –> vertical image may appear to be tilted to pt w MERIDIONAL anisekonia

46
Q

When is aniseikonia a problem?

A

When it is >3%

47
Q

If there is a SMALL difference in Relative Spectacle Magnification, how would you prescribe?

A

Rx equal BC

Rx equal thickness

48
Q

If there is a LARGE difference in Relative Spectacle Magnification, how would you prescribe?

A

Rx thin, flat lenses for eye with the HIGHEST RSM

Rx thicker, steeper lens for the eye w LOWEST RSM

49
Q

If there is aniso >4.00D, how would you prescribe?

A

Rx spectacles to minimize aniseikonia; likely axial

50
Q

If there is a small amount, how would you prescribe?

A

CL minimize aniseikonia bc likely refractive

51
Q

If there is aniesikonia bc large astigmatism, how would you prescribe?

A

CL bc large amounts of astigmatism usually from the cornea

NOTE: every 1.00D power difference, there will be approx 1% aniseikonia

52
Q

For every 1.00D of power difference btwn the eyes, there will be approx how much aniseikonia?

A

1%

53
Q

Seg Width?

A

Longest horizontal dimension of the seg

54
Q

Seg Depth?

A

Longest vertical dimension of the seg

55
Q

Seg Height?

A

Dist from lowest pt on lens to top of seg

56
Q

Seg Drop?

A

Vertical distance btwn the MRP and top of seg

57
Q

Inset?

A

Distance from GC to the MRP

58
Q

What is Seg Inset?

A

Accounting for near PD

Distance from GC to the MRP

59
Q

Total Inset?

A

Distance from GC to Center Seg

I total = I seg + I

Part 1 (31 decks)

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