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KMK Physiological Optics > Physiological Optics 1 > Flashcards

Physiological Optics 1 Flashcards

1
Q

BIO compared to direct

A

BIO has a

  • Larger FOV
  • Less magnification
  • inverted real image
  • Larger depth of focus
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2
Q

How BIO works

A

Retina is the object –> Light leaves and focuses into an image between the patient and doctor. The new image becomes the object for the doctor’s eye, which is focused on the doctor’s retina.

Condensing lens forms an intermediate, inverted, real image.

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3
Q

The lensometer measures what

A

The back vertex power of the lens.

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4
Q

Formula for lensometer

A

x = (focal length of the standard lens)^2 (back vertex power of lens)

x= meters that you move the dial. Away from you = negative, myopia
Towards you = positive, hyperopia

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5
Q

Hand neutralization

A

Minus lens –> With motion

Plus lens –> Against motion

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6
Q

What 2 images do you see in the radiuscope

A

The first image is from the surface of the lens. Now set it at zero.

The second image is the center of curvature for the GP lens.

Take the difference between the 2 positions of focus to find the radius of curvature.

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7
Q

What does the keratometer measure

The cornea acts as a

A

Measures the radius of curvature of the CENTER of the cornea along certain axes

Convex mirror (minus lens)

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8
Q

How does a keratometer work

A

Keratometer projects an image onto the K. We see the reflection back. Then measure the size of the reflection by turning vertical and horizontal dials so the +’s cross.

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9
Q

Keratometer assumes n of the cornea is

A

1.3375 and treats the K like a single spherical refracting interface (SSRI)

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10
Q

Formula for power of kertatometry

A

F= 3375.5/radius in meters

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11
Q

Lens clock measures what

A

The sag of the lens

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12
Q

Formula to correct for different n when using the lens clock

A

F of pt lens = (n of lens - 1) / (n of lens clock - 1) x F of lens clock

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13
Q

How to calculate mag factor based on lens used (90D vs 78D)

A 
Mag = - (F eye) / (F lens)
Mag = -(F ocular) / (F objective)

F of the eye is 60D

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14
Q

The drop ball test is apart of which ANSI standards

A

Z87.1

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15
Q

ASNI Z87.1

A

Drop ball test/High mass impact: pointed projectile, 500g, dropped from 50 inches

High VELOCITY impact: Steel ball, 0.25 aches in diameter, fired at 150 feet per second

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16
Q

Equiconvex and equiconcave

A

Half of the total power is due to the front surface and half is due to the back surface

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17
Q

What formula connects sag to radius

A

Sag = h^2/ 2r

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18
Q

Decentration per lens

A

Frame pd - pt pd/ 2

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19
Q

Minimum blank size equation

A

= ED + 2(decentration) + 2mm

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20
Q

Major reference pt

A

Point on the lens through which the line of sight (visual axis) passes.

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21
Q

How many mm is the distance from the seg to near OC

  1. FT28
  2. Executive/Franklin
  3. Round
A
  1. 5mm
  2. 0mm
  3. Half of the radius. radius = 22mm? Distance is 11mm
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22
Q

Hard and soft progressive designs

A

Hard- small corridor, high add

Soft- large corridor, low add

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23
Q

Inset

A

Geometrical center(frame PD) to the pt’s distance pd

GC- pt pd/ 2

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24
Q

Seg inset

A

Pt’s distance pd to their near pd

Distance pd - Near pd / 2

25
Q

Total inset per lens

A

Distance from geometrical center(frame pd) to near pd

GC- near PD / 2

26
Q

How to measure the add power of a bifocal lens using lensometer

A

Measure distance front vertex and near front vertex. Subtract

27
Q

N and abbe of:

  1. Glass
  2. CR9
  3. Poly
  4. Trivex
A
  1. 1.523, 58
  2. 1.499, 58
  3. 1.586,30
  4. 1.53,44
28
Q

Coma monochromatic aberrations only occurs for what sources

A

Off axis

Results in asymmetric comet patch

29
Q

How are longitudinal spherical aberrations formed

A

Marginal rays bend more than paraxial rays

30
Q

The tschernig ellipse allows us to find the best base curve to reduce what types of aberrations ?

A

Radial/oblique/marginal
Curvature of field

*Based on the Ostwald curve, which is flatter.

31
Q

How dose refractive index depend on wavelength?

A

ROYGBIV
Red is long, violet is short. Shorter wavelengths bend more!

Green will bend quicker than red.

32
Q

Equations connecting chromatic aberrations and abbe

A

CA = F/Abbe

CA= dF/Abbe

33
Q

What eliminates chromatic aberrations?

A

Achromaic doublet

34
Q

Deviation power of prism

A

Light deviation in cm / how far away the screen is in m

35
Q

Apex angle

A

DAN-1 equation

Deviation= apex angle (n-1)

36
Q

1 degree of angle deviation in prism is how many pd

A

1.75 pd

37
Q

Prentice’s rule

A

= dF

distance from OC measured in cm

38
Q

How to combine prisms (Horizontal and vertical) using vector addition

A

= square root (horiz squared + vertical squared)

39
Q

Difference between image jump and total prismatic effect

A

Image jump- just multiply the add x distance from seg to near OC in cm.

Total prismatic effect- Sum of the prism induced from looking away from the distance and seg OC. 1 eye.
First determine prism induced when looking away from the distance OC.

Then determine prism induced when looking away from seg OC.

40
Q

Spectacle mag compares what? What is the equation

A

Compares the retinal image sizes of an uncorrected vs corrected eye.

Spec mag= corrected/uncorrected

41
Q

Spec mag for thick lenses general equation

A

SM = shape factor x power factor

42
Q

Shape factor equation

A

Shape factor=
1
____
1-(t/n)F1

*Always order same thickness and BC for aniso patients to keep shape factor the same.

43
Q

Power factor equation

A

Power factor =
1
____
1-h(Fv)

h= vertex power + 3mm

44
Q

How does SM change for a plus lens if you:

  1. Increase vertex distance
  2. increase thickness
  3. increase BC
  4. Increase n
A
  1. Increase –> more plus
  2. Increase
  3. Increase (BC = F1)
  4. decrease
45
Q

How does SM change for a minus lens if you:

  1. Increase vertex distance
  2. increase thickness
  3. increase BC
  4. Increase n
A
  1. Decrease –> more minus
  2. Increase
  3. Increase.
  4. Decrease
46
Q

Relative spectacle magnification

  • Compres what
  • Equation
A

Compares retinal images of corrected eye vs standard emmetropic eye

RSM= Corrected ametrope retinal image size /emmetrope retinal image size

47
Q

Axial ametropes are best corrected with __ according to ___’s law

A

Specs, Knapps law

48
Q

Refractive ametropes are best corrected with ___

A

CLs

*refractive ametropes all have the same size image formed on the retina. Keep mag constant with CLs.

49
Q

Uncorrected axial ametropes. Do myopes or hyperopes have larger retinal images?

A

Myopes have largest retinal imag

50
Q

How does retinal image change with corrected refractive ametropes?

A

Retinal image will be largest for hyperope due to increased mag.

51
Q

Types of aniseikonia:

  1. Anatomical
  2. Induced
  3. Meridional
A
  1. Some anatomical asymmetry such as a discrepancy in the density of photoreceptors.
  2. Due to the optics of the corrected eye, due to a difference in spec mag.
  3. Due to difference in cyl power between left and right eyes. A vertical object might appear tilted,
52
Q

How to prescribe lenses for:

  1. Small differences RSM
  2. Large differences in RSM
A
  1. Small differences RSM: Equal BC and equal thickness.
  2. Large differences in RSM: Thin, flat lens for the eye with high RSM. Prescribe thicker, steeper lens for the eye with lowest RSM.
53
Q

For 1.00D of power difference, what % of aniso will there be?

What D difference usually becomes a problem?

A

1%

3.00D/3% usually becomes a problem

54
Q

Define:
Anisokonia
Anisometropia

A

Anisokonia- Difference in size or shape of the images seen by the left and right eyes.
Anisometropia- Refractive state of the left eye differs from the right eye, usually by 1.00D

55
Q

Who is more likely to develop amblyopia?

Hyperopic anisometrope or myopic anisometrope?

A

Hyperopic anisometrope because accommodation occurs equally in both eyes. Pt will be using the least hyperopic eye all the time at distance and near.

A myopic anisometrope could use the less myopic eye at distance and the more myopic eye at near.

56
Q

When light falls upon a lens, how can it be lost?

A

Reflected by the front or back surfaces

Absorption by the material

57
Q

Formula for reflectance

A

Reflectance = ( (n2-n1) / (n2+n1) ) ^2

This tells you how much light was reflected off the front surface. Can assume it was the same for the back surface as long as both sides are surrounded by air.

To determine transmittance, subtract this value from 1

T= 1-Reflectance

58
Q

How to calculate total transmission through a lens

A

Multiple Transmission of the front surface x back surface x T through medium

(They would have to give you the amount absorbed by the material. 1-absorption= transmission through material)

59
Q

Formula to calculate Power of the lens needed in the direct ophthalmoscope based on patient rx and Dr Rx

A

Power of lens in direct = patient Rx + Doctor Rx

KMK Physiological Optics (2 decks)

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