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Optics > Ophthalmic Equations > Flashcards

Ophthalmic Equations Flashcards

1
Q

Newton’s formula

A

x=f^2 *Fv

x- distance target moved
f= focal length standard lens
Fv=BVP

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2
Q

Magnification

A

m= I/O

m=o/i

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3
Q

Converting K to power

A

F=(1.3375-1)/r=0.3375/r

F=337.5/r (where r in mm)

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4
Q

Lens clock

A

F lens= (n lens-1)/(n lensclock-1)*F lens clock

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5
Q

Fresnel law

A

R= |(n2-n1)/(n2+n1)|^2

Reflection of light boundary of two indices

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6
Q

Transmittance

A

Ts=1-R

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7
Q

CL BVP

A

Fv=F2+ F1/{1-(t/n)*F1}

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8
Q

CL power from spec RX

A

Fc=Fs/(1-dFs)

Fs=refraction at vertex distance
d=vertex distance
Fc=refraction measured at the cornea

d=0 corresponds to K

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9
Q

Total power req at K

A

Rc= Fcl+Ftl

Rc=power req at K
Fcl= power at K
Ftl= power tear lake

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10
Q

_____ is the distance btwn the peripheral edge of the GP CL and the K. Adjusted by changing the peripheral radii in ___mm steps.

A

Edge lift; 1.0mm

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11
Q

Excessive edge lift is characterized by ___ peripheral pooling of fluorescein. desiccation, increased awareness, decreased CL centrationand 3&9 o’clock pooling

A

excessive

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12
Q

In adequate edge lift characterized by minimal pooling of fluorescein in the ____ results in debris trapped underneath CL

A

periphery

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13
Q

The more ______ center of gravity the better contraption of CL

A

posterior

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14
Q

_____ fit- negative TL; center of the CL will have K bearing with broad ring of mid-periphery and periphery of CL

A

Flatter than K

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15
Q

_______ fit fluorescein with pool in the center of the CL due to due to apical clearance with K bearing (minimal fluorescein) in mid periphery and periphery of CL

A

Steeper than K fit

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16
Q

Spherical fit over ____ astigmatism- fluorescein will pool across vertical (steepest) meridian with a horizontal dumbbell shaped pattern (dumbbell where touching)

A

WTR

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17
Q

Spherical fit over ____ astigmatism- fluorescein will pool across horizontal (steepest) meridian with a vertical dumbbell shaped pattern (dumbbell where touching)

A

ATR

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18
Q

Bitoric GP lens - ______ K astig and ______ Residual astig. Back surface is ___ astig and remaining astig is on the front. (>/= 2.50D K astig)

A

increase; increase; K

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19
Q

Bitoric GP-
_____ fit is equal alignment in both principal meridians btwn CL and K.
_______unequal alignment btwn principal meridians- fit on K -0.25 flatter than K for flat K meridian

A

Saddle fit; low topic simulation

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20
Q

_______ toric lens- indicted in >/= 2.50 D K astigmatism AND the magnitude of spec astig is = 1.5xK astig; (need more ref astig than K bc Back surface toric d

A

Back surface Toric GP

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21
Q

_______ toric lens- spherical back surface and topic front surface- K astig <2.50D unacceptable mag of residual astg

A

Front surface Toric GP

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22
Q

______ incorporates BD prism in order to minimize CL rotation during blink

A

Prism ballasting

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23
Q

_______ CL progressively flatten toward periphery of CL similar to peripheral flattening- improved alignment, decreased magnitude

A

Aspheric GP CL

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24
Q

Back surface aspheric CL indicated for ppl _____ astig, irregular K astig

A

ATR

25
Q

Front surface aspheric CL indicated for ppl with excessive ____ astig for ppl hypercritical

A

excessive

26
Q

Primary disadvantage of fitting a aspheric GP is _____ tear exchange due to decrease in CL movement

A

decreased

27
Q

Multifocal RGP
______ design- D&N located pupil at same time (centration critical)
______design-CL segmented different focal zones for different viewing distances;

A

simultaneous; translating

28
Q

Center thickness ____ lenses have more flexure

A

thinner

29
Q

Magnitude of K astig K astig cause for increase flexure with >/= ____D K astig

A

1.50D

30
Q

Flexure only measures on ____; measure w keratometer

A

the eye

31
Q

OZD increases the sag depth of the CL which ____ flexure

A

increases

32
Q

CL material ___Dk materials tend to have more flexure

A

higher

33
Q

Base curve ____ BC often results in more flexure

A

steeper

34
Q

Plus GP K lenses tend to maintain their shape as do minus- with center thickness greater than ____mm

A

0.13mm

35
Q

Flexure ____ the amt of residual astig bc LL provides less astig correction compared to magnitude of the K astig

A

increases

36
Q

Soft CL have ____ flexure bc it completely conforms to the shape of the K resulting in a plano lacrimal lens power

A

total

37
Q

Warped GP lens has a ____ BC

A

toric

38
Q

GP CL flexing will have ____ BC

A

spherical

39
Q

If K astig is = ____D; fit 0.50 D flatter than K

A

0.75D

40
Q

For every ____D increase in K astig, steepen the BC by ___D until bitoric GP lens is necessary

A

0.50D; 0.25D

41
Q

Every 0.4 mm increase (decrease) in OZD/OAD flattens(steepens) the BC by ____D in order to achieve same fit

A

0.25D

42
Q

Increase thickness, _____ oxygen

A

decreases

43
Q

Gas permeability

A

P = Dk

44
Q

Myopes ____ Dk (25-50) for daily wear; ____ Dk (51-99) for extended wear

A

low; high

45
Q

Hyperopes and aphakes _____Dk for daily wear and _____Dk (>100) for extended wear

A

high; hyper

46
Q

Toric lens- every clock hour movement ____ degrees axis change; ____

A

30 degrees; LARS

47
Q

Silicone hydrogel decrease in water content, ______ oxygen

A

decrease

48
Q

BC selection-

BC that is ___D flatter than K

A

4.00D

49
Q

SCL- Average K value- fit median BC or the ___ BC

A

flatter

50
Q

SCL- For steeper K value (>45) , fit ____ BC

A

steeper

51
Q

SCL-For flatter K value (<45), fit _____ BC

A

flatter

52
Q 
FDA soft CL
Group 1- \_\_\_ water content; \_\_?\_\_\_ ionic
Group 2-\_\_\_\_water content;\_\_?\_\_\_ ionic
Group 3-\_\_\_\_\_water content; \_\_?\_\_ionic
Group 4-\_\_\_\_\_\_water content; \_\_\_?\_\_ionic
Group 5-
A

Grp 1- low; non-ionic
Grp 2-high; ionic
Grp 3- low; non-ionic
Grp 4-high; ionic

53
Q

High water content, ____ silicone content;_____ permeability

A

high; low; low

54
Q

Deposits are more likely in ___lenses with a ____ water content

A

ionic; high

55
Q

Hyperopes accom ____ with CLs compared to specs

A

less

56
Q

Myopes accom ___ with CLs compared to specs

A

more

57
Q

Hyperopes have ___ retinal image size with CL compared to specs due to ___ spec mag

A

smaller; less

58
Q

Myopes have____ retinal image size with Cl compared to specs due to ___spec mag

A

larger; less

59
Q

RGP- apical touch ____ BC

A

steepen

Optics (1 decks)

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