Ophthalmic Optics Exam 1

Front 1

what was the first correction of refractive errors with man made lenses

Back 1

correcting presbyopia with PLUS lenses

Front 2

what material has the best optical quality

Back 2

crown glass

Front 3

which material has the highest abbe value

Back 3

crown glass

Front 4

how do you make crown glass safer to wear

Back 4

1. tempered by heating or chemical processes
2. heating is faster
3. chemical is preferred method because more impact resistance

Front 5

what is a lost cost alternative to polycarbonate

Back 5

CR39

Front 6

what is the abbe value of CR39 in relation to other materials

Back 6

1. SECOND highest
2. HIGH ABBE VALUE (58)

Front 7

which material will give you the thickest lens

Back 7

CR39 (lowest index)

1. must be over 2.0mm to be safe
2. approx. half the weight of glass

Front 8

what material is the most impact resistance

Back 8

polycarbonate

Front 9

how does POLYCARBONATE compare physically to CR39

Back 9

1. polycarbonate is lighter and thinner than CR39
2. greater safety

Front 10

what market share does polycarbonate have?

Back 10

50%

C39: 40%

Front 11

what are some disadvantages of polycarbonate

Back 11

1. more easily scratched
2. low abbe value
3. more reflections
4. edging and beveling require special tools

Front 12

what does specific gravity correspond to?

Back 12

WEIGHT

lightest to heaviest
1. polycarbonate
2. CR39
3. Crown Glass

Front 13

when is polycarbonate indicated

Back 13

all children or anyone at risk should have polycarbonate glass

Front 14

what are the advantages of CR39

Back 14

1. impact resistant
2. chemical inertness
3. resistance to pitting and fogging
4. tintability
5. versatility of optical design

Front 15

when are ANSI standards require and voluntary

Back 15

1. voluntary for DRESS eyewear
2. REQUIRED (by OSHA) for safety eyewear

Z80.1 for Dress
Z87.1 for Safety

Front 16

what is Duty to Warn

Back 16

1. tell patient buying a pair of dress eyewear that most impact resistant material is polycarbonate
2. not required, but a good idea to DECREASE liability

Front 17

what entity requires safety eyewear in the workplace

Back 17

OSHA

Front 18

what entity requires impact resistance of spectacle lenses

Back 18

FDA

Front 19

what entity requires Rx release at the end of an exam

Back 19

FTC

Front 20

what is the equation for curvature

Back 20

Curvature=1/r

r=radius of curvature

Front 21

what is the formula for dioptric power

Back 21

F=(n'-n)/r

Front 22

what is the equation for sagittal depth

Back 22

S=(h^2)/(2r)

Front 23

what is the relationship between curvature and sagittal depth

Back 23

S=C(h^2)/2

1. directly proportional
2. important for lens thickness and CL fitting

Front 24

what is the relationship between sagittal depth and diameter

Back 24

1. steeper surface=greater sagittal depth

for a particular curvature:
increase diameter=increase sag depth

Front 25

what instrument takes a physical measurement of the sagittal depth

Back 25

LENS CLOCK

1. movement of center pin=sag depth
2. must be calibrate for the right index

Front 26

the lens clock gives us a way to measure...

Back 26

1. base curve
2. approximate power

Front 27

what formula do you use to measure a lens with different index than the lens clock

Back 27

(nt-1)/Ft=(nc-1)/Fc

Front 28

why use meniscus lens for spectacle corrections?

Back 28

LESS ABERRATIONS

Front 29

where is the BC for a minus cylinder form

Back 29

1. toric on back surface
2. BC is the front spherical curve

Front 30

what is base curve

Back 30

base curve usually refers to the surface power NOT the curvature

Front 31

why do we make lenses in minus cylinder (back toric)?

Back 31

1. looks better
2. it is place closer to the eye so the magnification between the two meridians will be reduced

Front 32

what is corrected curve lenses

Back 32

1. oblique astigmatism and curvature of image aberrations can be minimized by appropriate selection of base curve
2. also called best form

Front 33

how do you calculate where the optical center is

Back 33

distance from front pole to OC
A1O=(dF2)/(F1+F2)

Front 34

where is the optical center for a meniscus lens

Back 34

falls outside the lens

Front 35

1. what is the formula for spherical equivalent?
2. when is it most likely used?

Back 35

S.E.=sph+(cyl/2)

1. when fitting soft lens
2. cyl low relative to sphere
3. patient not use to wearing cyl.

Front 36

when do we encounter oblique cross cylinders in practice

Back 36

when doing an overrefraction

Front 37

what is approximate power (Fa)

Back 37

Fa=F1+F2

1. use to estimate BACK vertex power
2. not accurate for thick lenses
3. measure with lens clock

Front 38

what is back vertex power (Fv)

Back 38

1. standard for prescribing corrective lenses
2. takes into account the lens thickness
3. measured with lensometer

Front 39

what is front vertex power (Fn)

Back 39

1. neutralizing power
2. power of lens at front vertex (pole)
3. lensometer or hand neutralization

Front 40

what is equivalent power (Feq)

Back 40

1. used to specify low vision devices
2. power of single lens to replace a lens system

Front 41

what is the effective power

Back 41

the effect (on refraction at the eye) of moving a lens closer to or farther from the eye

for example:
+10.00DS from spectacle plane to corneal plane?

Feff= F/(1+dF)
Feff=+10/(1+(0.012x10)
Feff= +8.92

Front 42

what is compensating power

Back 42

the new lens power required when changing vertex distance to get the same effect as the original lens

Fcomp= F/(1-dF)

Front 43

what is the relationship between compensating power and effective power

Back 43

for example:

plus lenses INCREASE in effective dioptric power when you move it away from the eye. BUT the compensating power will be DECREASED

Front 44

what is the lensometer equation

Back 44

Xs=(fs^2)(Fv)

minus Xs= minus unknown lens
plus Xs= plus unknown lens

Front 45

what are the factors that influence lens thickness

Back 45

tc-te= (h^2 x F)/2(n-1)

1. power
2. index
3. diameter
4. base curve
5. minimum thickness

Front 46

that are the lens thickness formulas

Back 46

ET=CT-S1+S2

tc-te= (h^2 x F)/2(n-1)

Front 47

when neutralizing an unknown lens what happens to the lensometer

Back 47

1. target must be moved CLOSER for a PLUS LENS
2. target must be moved FARTHER for a MINUS LENS

position relative to the eye

Front 48

for compensating power when moving from spectacle to corneal plane...

Back 48

1. minus lens becomes less minus
2. plus lens become more plus

Front 49

for compensating power when moving from corneal plane to spectacle plane...

Back 49

1. minus lens becomes MORE minus
2. plus lens becomes LESS plus

Front 50

what is the benefit of pantoscopic tilt

Back 50

top away from face (6degs)

1. looks better
2. reduces reflections

Front 51

what happens when tilting a spherical lens

Back 51

induces power
1. tilting a lens causes incident light to enter the lens obliquely, resulting in both a change in spherical power and induces cyl power

Front 52

which one has a higher change in magnitude for pantoscopic tilt? (cyl or sphere)

Back 52

CYLINDER

(+) cyl induces more (+) cyl
(-) cyl induces more (-) cyl

Front 53

face form and pantoscopic tilt in relation to cyl induction

Back 53

face form:
1. when frames are rotated along the vertical axis
2. induces cyl on axis 90

pantoscopic tilt:
1. when frames are rotated along the horizontal axis
2. induces cyl on axis 180