Optics

Question 1

why do we see blurry when underwater?

Answer 1

most of refractive power of the eye comes from the air cornea interface. if the interface were water-water, the refractive power would be less and you would only rely on the curvature of the cornea for refraction. Hence, you would be far sighted (not enough plus so acts like hyperope)

Question 2

why do we see underwater physics principle

Answer 2

refracting power of a spherical surface formula n’-n/r tells us that in air the refracting power of the K is 52.9, but in water it is only 5.7D

Question 3

what’s the spherical equivalent of -1.00+2.00x45?

Answer 3

sphere + 1/2 cyl= -1.00+1.00= 0 PLANO Threfore this is a jackson cross

Question 4

Transpose +2.00-3.00x90 to plus cyl

Answer 4

1)add old sph and old cyl 2) change sign of the sphere 3) add 90 to axis -1.00+3.00x180

Question 5

Loupes are an example of what type of telescope and what 2 types of lenses are used in that case?

Answer 5

Galiean telescope, causes upright image objective is (+) and eyepiece is (-) lens

Question 6

What is the magnification of a direct ophthalmoscope?

Answer 6

15x uses principle of simple magnifier (Mag= D./4) The D of the ophthalmoscope is 60 Therefore 60/4= 15.

Question 7

How do + and - lenses act like prisms?

Answer 7

+ lenses act like base down prisms - lenses act like base up prisms

Question 8

Why do myopic lenses make faces seem narrower?

Answer 8

B/c the prismatic effect of the (-) lenses w BO (like a bowtie) will displace the virtual image of the face toward the apex

Question 9

How do you compensate for small vertical deviations caused by anisometropic glasses? 3 things

Answer 9

1) Try contacts
2) lower both optical centers - to compromise vertical imbalance between distance and near
3) give slab off prisms

Question 10

What are slab off prisms?

Answer 10

Used in cases of anisomeropic glasses

you measure the deviation in PD caused by the glasses, and put that prism amount on the more minus lens

Question 11

what do all the dials represent?

R

O

OC

+0.50

10♦in

PH

+0.12

GL

WMHWMV

P

Answer 11

R- retinoscopy (puts up a +1.50D lens)

O- open

OC- occlude

+0.50- fused cross cylindar to meaure add

10♦in- 10 PD base in

PH- pinhole

+0.12- for very picky pts

GL- green lens

WMH- white maddox rod horizontal

WMV- white maddox rod vertical

P- polarized - for fly test

Question 12

what does this represent?

Answer 12

6 PD base up OD and 9PD base out OS

where the arrow points is where the base is

Question 13

In trial frames in which slot should you place the following lenses?

1) high power sphere
2) cylinder
3) low power lenses

Answer 13

1) high power sphere- rear cell
2) cylinder- middle cell
3) low power sphere- front cell

Question 14

what is the basecurve of a lens in glasses and how can you check if it’s off?

Answer 14

the basecurve of a lens is different on the front and back. ex a minus lens actually has a plus front and a stronger power munis in the back. you can measure this w a geneva lens clock. sometimes a pt may not tolerate a change in the BC

Question 15

what is this dial used for on a lensmeter?

Answer 15

if you are assessing prism in glasses and you need more prism (more than 3)

Question 16

what is this and what is it used for?

Answer 16

placido disc-

doctors view on left, pts view on right

has a battery and rings that light up can assess k curvature grossly to assess for irrigular astigmatism

Question 17

how does goldmann applinator work?

Answer 17

split prism 3.06mm diameter circle. when you press on the k just the right amount the circle becomes 3.06mm. why 3.06mm? its the force in dynes x10 = IOP when the circle is 3.06

Question 18

whats the red line on the goldmann applinator for?

Answer 18

measuring iop in pts w astigmatism, you can line up the applinator with their axis of their negative cyl

Question 19

whats the name of the fundus lens attached to the slit lamp and why did dr glaser like to use it?

Answer 19

Hruby lens. Its a 55 D lens and its best to look at ON

Question 20

which is the best lens to look at the fovea?

Answer 20

goldmann contact lens- gives you an upright image

Question 21

what are the 3 componants needed in an operating microscope?

Answer 21

1) binoculars
2) magnification changer (works by galiliean telescope)
3) objective lens

Question 22

whats the magnification when you look at the retina using a 30D lens?

Answer 22

transverse mag= power of eye/power of lens

60/30=2x

what the tansverse mag of that? 2^2= 4x

Question 23

what does laser stand for?

Answer 23

light amplification by stimulated emission of radiation

Question 24

by what principle does argon laser work?

Answer 24

photocoagulation (local rise is tissue temperture) energy is absorbed by the tissue

Question 25

by what principle does the yag laser work?

Answer 25

photodisruption- target is ionized and a shock wave is released

Question 26

by what mechanism does an eximer laser work?

Answer 26

photoablation- disruption of covalent bonds-

high power ultraviolet radiation, no heat, it is a “cold “laser

Question 27

whats the principle of femtosecond laser?

Answer 27

photoablation??

Question 28

what are the 3 things you need to make a laser?

Answer 28

1) pulsed power to supply energy
2) active medium (photon emitter) to make light monochromatic
3) chamber w miror at opposite ends

the mirrors reflect the photons multiple time and makes the light unidirectional, the laser cavity acts like an optical resonator and 2% of the photons get transmitted through the laser

Question 29

if a person sees 20/20 but still complains of poor vision what else can you test?

Answer 29

contrast sensitivity

Question 30

how can you assess amblyopia in non-verbal child?

Answer 30

occlusion test

Question 31

how do you check if baby has at least 20/200 vision?

Answer 31

okn drum-

if it induces nystagmus then baby can see at least 20/200

Question 32

7 ways you can test va in pre-literate child

Answer 32

1) HOTV
2) Allen figures (house tree etc)
3) OKN
4) Teller cards
5) tumbling E
6) blink to light
7) vep

Question 33

what is the 4 bars surrounding 1 letter for?

Answer 33

amblyopic kids- due to crowding phenomenon amblyopic kids can see one letter at a time better than a whole line

Question 34

what is the etdrs acuity chart

Answer 34

1) letters of equal viewing difficulty
2) each line has 5 letters
3) spacing between the letters = letter size on that line
4) optotypes change in 0.1 log unit increments
5) 3 line change= a doubling of the visual angle

Question 35

what is the equivalent of 5/30 in 20 languange (ie they can see 30 line at 5 feet?)

Answer 35

multiply it by 4

30x4= 120

therefore 5/30= 20/120

Question 36

what are the steps in assessing for scl?

Answer 36

1) obtain accurate manifest refraction
2) slit lamp exm
3) keratometry
4) discuss rigid v scl
5) perform power calulations
6) fit lenses

Question 37

what do you have to look for on sle when fitting scl?

Answer 37

L/L- anomilies, flip lids

Tears- asess tear film

Pupil- look for essentricty

K- contour, staining, neo

Question 38

explain the bc of a scl?

Answer 38

shorter radius of the cl = steeper curve

therefore steep K will get like an 8mm

flat k will get like a 9mm

Question 39

how do you determine the power of scl for a pt?

Answer 39

1) manifest refraction
2) if sph less than 1 then just use sph equiv otherwise needto give a toric
3) calculate the real power given vertex distance
4) if pts power is >4 then take off 0.25D for every 1D over 4 (eg if im a -6 glasses- thats 2 D over 4 so take off 0.5D off the cl)
4) check Ks- if between 42.5-44.0 then use bc 8.7

if between 44.5-46.0 then use bc 8.3

Question 40

what are the 5 steps in calculating rigid lens power?

Answer 40

1) chose a BC +0.50 steeper than low K value
2) convert rx to minus cyl form
3) drop the cyl
4) convert to zero vertex distance
5) subtract +0.50 from final value

Question 41

how do you solve vertex distance questions?

Answer 41

1) understand that the glasses rx is not the refactive error of the eye!
2) find FP from the glasses and add the vertex dist- that’s the true fp of the eye
3) find reciprocal of that dist to find real D error of eye

OR USE THE BACK OF THE TYLERS QUARTLY PARAMETER GUIDE IT HAS ALL THE VERTEX CORRECTIONS

Question 42

what phenomenon causes the sky to be blue?

Answer 42

scattering (blue is scattered, the rest of the wavelengths are diffracted)

scattering means that when light hits an irregularity in its path, it scatters. Shorter wavelengths tend to scatter, and longer wavelengths (like red) tend to diffract (has ability to bend around corners)

Question 43

how do you make a CL fit tighter (2 options)

Answer 43

1) decr BC
2) incr diameter

Question 44

What do flourescein staining patterns look like if the RGP is

1) good fit
2) steep
3) flat

Answer 44

1) diffuse flourescein pattern
2) steep=pooling centrally
3) flat= peripheral pooling

Question 45

how do you assess fit of a toric lens?

Answer 45

the scribe mark (ie lines) on the scl should sit at 6 oclock

if they dont use LARS acronym- (left add minus cyl, right subtract minus cyl)

Question 46

how do you assess fit of a scl?

Answer 46

look for movement

poor movement- too tight= bc too steep

excessive movement- too flat

Question 47

you prescribe a pt scl with very high minus- but the edges of the lens get causght under the lid what can you do?

Answer 47

bevel edges - they create a flange in the scl so it sits better

Question 48

can a person w scl use solution from hard contact?

Answer 48

nope bc hard cl solution contains bak

Question 49

person w scl sees halo at end of day what is the issue?

Answer 49

k edema- can cause halos and also an increase in myopia and astigmatism

Question 50

scl user comes to you with chronic mucous and red itchy eye, what is the problem?

Answer 50

gpc

d/c the contacts use cromlyn and possibly low dose steroids

Question 51

whats the srk formula?

Answer 51

A-2.5L-0.9K

Question 52

What formula do you use for very short or long eyes?

Answer 52

srk2

it has a differnt a constant

the original srk formula is goog only for avg length eyes (22-24.5mm eyes)

Question 53

which type of iol gives the least chromatic abberation?

Answer 53

one that is flat in the front and curved in the back