Clinical Optics

Question 1

Orthokeratology using RGP lenses can help reduce what problem?

Answer 1

low amounts of myopia up to -6.00 D and low amounts of astigmatism (1.75D)

Question 2

Light property used by scanning laser polarimeter to measure nerve fiber layer thickness

Answer 2

polarization

Question 3

Lensmaker’s equation

Answer 3

P = (n2-n1)/r

N1 and n2 are refractive indices of the regions to the left and right of the refracting interface

u is the distance from the source object point to the refracting interface

v is the signed distance from the refracting interface to the inmage of the source object point and r is the signed radius of curvature fo the refracting interface

Question 4

Increasing the dioptric power of a convex lens has what effect on focal length

Answer 4

reduction

Question 5

SAM-FAP rule

Answer 5

steeper CL add minus - Flatter Add Plus

Question 6

4 year old with 20/25 each eye has hyperopia of +1.75 sphere OU. Treatment at this time?

Answer 6

No treatment. Unless esodeviation, anisometropia or evidence of reduced vision, not necessary to correct low hyperopia.

Question 7

What does Dk/t describe in a contact lens?

Answer 7

oxygen transmissibility/permeability of the lens - depends on the lens material and the central thickness (L)

DK - oxygen permeability of lens material where D is diffusion coefficient for oxygen movement in the material. K is the solubility constant of oxygen in the material

Question 8

Wetting angle

Answer 8

refers to the wettability of a lens surface. A low wetting angle means water will spread over the surface, increasing surface wettability. A high Dk/t and low wetting angle are desirable.

Question 9

Optical advantage of a Galilean telescope is used by surgical loupes?

Answer 9

the image orientation, which is upright

high-powered negative ocular lens (eyepiece) and low-powered positive objective lens separated by the difference between their focal lengths.

Question 10

Post-operative topography shows irregular astigmatism. Treatment

Answer 10

gas-permeable contact lens or other rigid contact lenses neutralize irregular astigmatism because tear fluid fills irregular space between lens and cornea

Question 11

Property illustrated by the ability of a light wave from a laser to form stable interference fringes with another wave from the same beam, separated in time.

Answer 11

temporal coherence

Question 12

physical extent of the light source and presence or absence of a fixed phase relationship between different parts of a light source

Answer 12

spatial coherence

Question 13

variation of refractive index with frequency and is unrelated to interference

Answer 13

Dispersion

Question 14

brightness of a source

Answer 14

intensity

Question 15

Excimer laser removes corneal tissue by what light-tissue interaction and at what wavelength of light?

Answer 15

Photoablation; 193 nm

Question 16

Rhodopsin absorbs this light best

Answer 16

green - 510 nm

Question 17

light-tissue interaction and wavelength of Nd:YAG laser

Answer 17

photodisruption 1064 nm

Question 18

Entrance pupil varies from the actual pupil by what amount?

Answer 18

13-15%

cornea has high plus power, image of the pupil is not the same size as the actual pupil (image seen is ‘entrance pupil’)

Question 19

How does smaller radius of a base curve affect steepness of lens

Answer 19

smaller the radius of base curve, the steeper the lens

Question 20

Type of fit if base curve of RGP lens is smaller than base curve of cornea

Answer 20

apical clearance

Question 21

cornea and RGP have the same base curve

Answer 21

apcial alignment

Question 22

base curve of a lens is larger than the cornea, producing a flatter RGP in comparison to the cornea

Answer 22

Apical bearing

Question 23

manifesting a 92 year old with BCVA 20/100. Technique

Answer 23

refine refraction using larger-step changes in shpere and cylinder. +/- 0.75 or 1.00 D in sphere and 0.75 to 1.00 change in jackson cross cylinder

Question 24

What adjustment should be made to IOL power selection in an eye containing silicone oil?

Answer 24

Increase IOL power by 3-5 D if the silicone oil will remain in the eye.

creates negative lens power if biconvex IOL (standard in US)

Question 25

Presbyopia-correcting lens is more effective at higher lens power

Answer 25

crystalens IOL

Question 26

What logMAR value is equivalent to a Snellens VA of 20/20?

Answer 26

0.00

Question 27

What is logMAR

Answer 27

base-10 logarithm of the minimum angle of resolution

Question 28

What lens design would lead to a higher rate of capsular opacification?

Answer 28

lens with a round edge

Question 29

Option for least image magnification in an aphakic patient

Answer 29

posterior chamber IOL (PCIOL)

Aphakic spectacles 20-35% magnification

CL 7-12% magnification

ACIOL - 5%

Question 30

Retinal image size in the Gullstrand model is based on this primciple

Answer 30

geometric principle of similar triangles

Question 31

Information needed to prescribe the most accurate add?

Answer 31

Amplitude of accomodation and reading distance

Select a lens that keeps half the amount of accomodation in reserve

Question 32

One focal line falls on the retina while the other focal line lies posterior to the retina

Answer 32

simple hyperopic astigmatism

Question 33

One focal line falls on the retina, other focal line lies anterior to the retina

Answer 33

simple myopic astigmatism

Question 34

Both focal lines lie posterior to the retina

Answer 34

Compound hyperopic astigmatism

Question 35

Both focal lines lie anterior to the retina

Answer 35

compound myopic astigmatism

Question 36

energy causes active medium’s electrons to rise to a higher energy state

Answer 36

population inversion

Question 37

When does stimulated emission occur?

Answer 37

When some high-energy electrons undergo spontaneous emmsion generating photons and if these photons encounter other high energy electrons, stimulated emission occurs

Question 38

How much does a 15D prism bend light in degrees?

Answer 38

8.53 degrees

for small angles, prism diopters produces a little more than half a degree of deviation