How many mm is the distance from the seg to near OC 1. FT28 2. Executive/Franklin 3. Round

1. 5mm 2. 0mm 3. Half of the radius. radius = 22mm? Distance is 11mm

Physiological Optics 1 Flashcards by Emme Gilchrist

BIO compared to direct

BIO has a

Larger FOV
Less magnification
inverted real image
Larger depth of focus

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How BIO works

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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The lensometer measures what

The back vertex power of the lens.

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Formula for lensometer

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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Hand neutralization

Minus lens –> With motion

Plus lens –> Against motion

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What 2 images do you see in the radiuscope

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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What does the keratometer measure

The cornea acts as a

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

Convex mirror (minus lens)

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How does a keratometer work

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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Keratometer assumes n of the cornea is

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

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Formula for power of kertatometry

F= 3375.5/radius in meters

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Lens clock measures what

The sag of the lens

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Formula to correct for different n when using the lens clock

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

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

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

F of the eye is 60D

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The drop ball test is apart of which ANSI standards

Z87.1

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ASNI Z87.1

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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Equiconvex and equiconcave

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

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What formula connects sag to radius

Sag = h^2/ 2r

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Decentration per lens

Frame pd - pt pd/ 2

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Minimum blank size equation

= ED + 2(decentration) + 2mm

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Major reference pt

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

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

FT28
Executive/Franklin
Round

5mm
0mm
Half of the radius. radius = 22mm? Distance is 11mm

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Hard and soft progressive designs

Hard- small corridor, high add

Soft- large corridor, low add

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Inset

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

GC- pt pd/ 2

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Seg inset

Pt’s distance pd to their near pd

Distance pd - Near pd / 2

Total inset per lens

Distance from geometrical center(frame pd) to near pd GC- near PD / 2

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

Measure distance front vertex and near front vertex. Subtract

N and abbe of: 1. Glass 2. CR9 3. Poly 4. Trivex

1. 1.523, 58 2. 1.499, 58 3. 1.586,30 4. 1.53,44

Coma monochromatic aberrations only occurs for what sources

Off axis | Results in asymmetric comet patch

How are longitudinal spherical aberrations formed

Marginal rays bend more than paraxial rays

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

Radial/oblique/marginal Curvature of field *Based on the Ostwald curve, which is flatter.

How dose refractive index depend on wavelength?

ROYGBIV Red is long, violet is short. Shorter wavelengths bend more! Green will bend quicker than red.

Equations connecting chromatic aberrations and abbe

CA = F/Abbe CA= dF/Abbe

What eliminates chromatic aberrations?

Achromaic doublet

Deviation power of prism

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

Apex angle

DAN-1 equation Deviation= apex angle (n-1)

1 degree of angle deviation in prism is how many pd

1.75 pd

Prentice's rule

= dF distance from OC measured in cm

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

= square root (horiz squared + vertical squared)

Difference between image jump and total prismatic effect

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.

Spectacle mag compares what? What is the equation

Compares the retinal image sizes of an uncorrected vs corrected eye. Spec mag= corrected/uncorrected

Spec mag for thick lenses general equation

SM = shape factor x power factor

Shape factor equation

Shape factor= 1 ____ 1-(t/n)F1 *Always order same thickness and BC for aniso patients to keep shape factor the same.

Power factor equation

Power factor = 1 ____ 1-h(Fv) h= vertex power + 3mm

How does SM change for a plus lens if you: 1. Increase vertex distance 2. increase thickness 3. increase BC 4. Increase n

1. Increase --> more plus 2. Increase 3. Increase (BC = F1) 4. decrease

How does SM change for a minus lens if you: 1. Increase vertex distance 2. increase thickness 3. increase BC 4. Increase n

1. Decrease --> more minus 2. Increase 3. Increase. 4. Decrease

Relative spectacle magnification - Compres what - Equation

Compares retinal images of corrected eye vs standard emmetropic eye RSM= Corrected ametrope retinal image size /emmetrope retinal image size

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

Specs, Knapps law

Refractive ametropes are best corrected with ___

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

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

Myopes have largest retinal imag

How does retinal image change with corrected refractive ametropes?

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

Types of aniseikonia: 1. Anatomical 2. Induced 3. Meridional

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,

How to prescribe lenses for: 1. Small differences RSM 2. Large differences in RSM

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.

For 1.00D of power difference, what % of aniso will there be? What D difference usually becomes a problem?

1% 3.00D/3% usually becomes a problem

Define: Anisokonia Anisometropia

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

Who is more likely to develop amblyopia? | Hyperopic anisometrope or myopic anisometrope?

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.

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

Reflected by the front or back surfaces | Absorption by the material

Formula for reflectance

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

How to calculate total transmission through a lens

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)

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

Power of lens in direct = patient Rx + Doctor Rx