Ophthalmic Equations

Question 1

Newton’s formula

Answer 1

x=f^2 *Fv

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

Question 2

Magnification

Answer 2

m= I/O

m=o/i

Question 3

Converting K to power

Answer 3

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

F=337.5/r (where r in mm)

Question 4

Lens clock

Answer 4

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

Question 5

Fresnel law

Answer 5

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

Reflection of light boundary of two indices

Question 6

Transmittance

Answer 6

Ts=1-R

Question 7

CL BVP

Answer 7

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

Question 8

CL power from spec RX

Answer 8

Fc=Fs/(1-dFs)

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

d=0 corresponds to K

Question 9

Total power req at K

Answer 9

Rc= Fcl+Ftl

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

Question 10

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

Answer 10

Edge lift; 1.0mm

Question 11

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

Answer 11

excessive

Question 12

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

Answer 12

periphery

Question 13

The more ______ center of gravity the better contraption of CL

Answer 13

posterior

Question 14

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

Answer 14

Flatter than K

Question 15

_______ 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

Answer 15

Steeper than K fit

Question 16

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

Answer 16

WTR

Question 17

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

Answer 17

ATR

Question 18

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

Answer 18

increase; increase; K

Question 19

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

Answer 19

Saddle fit; low topic simulation

Question 20

_______ 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

Answer 20

Back surface Toric GP

Question 21

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

Answer 21

Front surface Toric GP

Question 22

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

Answer 22

Prism ballasting

Question 23

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

Answer 23

Aspheric GP CL

Question 24

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

Answer 24

ATR

Question 25

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

Answer 25

excessive

Question 26

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

Answer 26

decreased

Question 27

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

Answer 27

simultaneous; translating

Question 28

Center thickness ____ lenses have more flexure

Answer 28

thinner

Question 29

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

Answer 29

1.50D

Question 30

Flexure only measures on ____; measure w keratometer

Answer 30

the eye

Question 31

OZD increases the sag depth of the CL which ____ flexure

Answer 31

increases

Question 32

CL material ___Dk materials tend to have more flexure

Answer 32

higher

Question 33

Base curve ____ BC often results in more flexure

Answer 33

steeper

Question 34

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

Answer 34

0.13mm

Question 35

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

Answer 35

increases

Question 36

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

Answer 36

total

Question 37

Warped GP lens has a ____ BC

Answer 37

toric

Question 38

GP CL flexing will have ____ BC

Answer 38

spherical

Question 39

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

Answer 39

0.75D

Question 40

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

Answer 40

0.50D; 0.25D

Question 41

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

Answer 41

0.25D

Question 42

Increase thickness, _____ oxygen

Answer 42

decreases

Question 43

Gas permeability

Answer 43

P = Dk

Question 44

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

Answer 44

low; high

Question 45

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

Answer 45

high; hyper

Question 46

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

Answer 46

30 degrees; LARS

Question 47

Silicone hydrogel decrease in water content, ______ oxygen

Answer 47

decrease

Question 48

BC selection- | BC that is ___D flatter than K

Answer 48

4.00D

Question 49

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

Answer 49

flatter

Question 50

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

Answer 50

steeper

Question 51

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

Answer 51

flatter

Question 52

``` 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- ```

Answer 52

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

Question 53

High water content, ____ silicone content;_____ permeability

Answer 53

high; low; low

Question 54

Deposits are more likely in ___lenses with a ____ water content

Answer 54

ionic; high

Question 55

Hyperopes accom ____ with CLs compared to specs

Answer 55

less

Question 56

Myopes accom ___ with CLs compared to specs

Answer 56

more

Question 57

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

Answer 57

smaller; less

Question 58

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

Answer 58

larger; less

Question 59

RGP- apical touch ____ BC

Answer 59

steepen