Optics 1

Question 1

Minimum deviation position

Answer 1

Equal bending at each face of a prism produces the minimal amount of light bending through a prism.

Question 2

Does light bend towards the apex or the base of a prism?

Answer 2

Towards the base

Question 3

Prentice position

Answer 3

Position to place a glass lens in front of patient. Back surface must be perpendicular to the visual axis of the eye

Question 4

Frontal plane position

Answer 4

Position to place a plastic lens in front of a patient. Back surface must be perpendicular to the direction of the distant fixating object. These prisms have minimum deviation accounted for in their powers.

Question 5

What is the definition of a prism diopter?

Answer 5

Amount of displacement in centimeters of a light ray passing through a prism

Question 6

Which direction (towards the base or apex) is the virtual image displaced? (e.g., when looking through a prism as the patient)

Answer 6

Towards the apex

Question 7

Which direction is a real image displaced when looking through a prism as a patient?

Answer 7

Towards the base (though the virtual image is what is perceived). This means the that image (real) of the retina moves towards the base and the eye will in turn move towards the base.

Question 8

Does a minus lens add to a strabismic deviation or decrease? Plus lens?

Answer 8

Minus measures more (so adds) and plus measures less.

Question 9

What are ways you can compensate or correct induced prisms in anisometorpia spectacles?

Answer 9

1. Move the vertex distance closer (CL’s)2. Lower both optical centers so vertical imbalance at distance and near (hopefully the patient can compensate for)3. Prescribe dissimilar segments4. “Slab” off the more minus (or less plus) lens or more common today “reverse slab” on the more plus lens (basically adding base down to the more positive lens)

Question 10

What is image jump?

Answer 10

Produced by sudden introduction of prismatic power at the top of the bifocal segment

Question 11

What is image displacement?

Answer 11

Produced by the TOTAL prismatic power acting in the reading position (lens + the bifocal segment)

Question 12

Is image jump or image displacement generally better tolerated?

Answer 12

Image jump

Question 13

What are the 3 common types of bifocal segments and which produced NO image jump b/c the optical center is at the top?

Answer 13

Round Top–max image jumpFlat top–minimal image jumpExecutive (Franklin)–no image jump

Question 14

What type of bifocal segment would be preferred glasses with plus distance rx?

Answer 14

round top–the optical center is at the bottom and the base down effect of the bifocal segment is also base down so minimizing the transition zone is best.

Question 15

What type of bifocal segment would be preferred in glasses with minus rx?

Answer 15

flat top

Question 16

How much dioptric difference is there in lights at the opposite ends of the visible light in the normal human eye? Chromatic aberration question.

Answer 16

3.0 D

Question 17

How much dioptric difference is there between red and green lights in duochrome testing? How well do you need to see to do duochrome testing?

Answer 17

0.5D; 20/30 at least

Question 18

In retinoscopy, “with” movement implies what type of vergence? Against movement?

Answer 18

NAME?

Question 19

What are glasses normally made out of?

Answer 19

Plastic called CR39

Question 20

Are longer or shorter waves diffracted more through an aperture?

Answer 20

longer wave lengths (this is not the same princple as scattering in which shorter wave lengths are scattered more)

Question 21

Will a thick lens reduce or increase the dioptric power of the total lens?

Answer 21

Reduce

Question 22

What affect does tilting plus lenes have? Tilting minus lenes?

Answer 22

Tilting plus lenses adds positive cylinder in the axis of rotationTilting minus lenes adds minus cylinder in the axis of rotation

Question 23

Knapps law states says that if refractive error is do to just axial length you can place a spectacle at what distance in front of the eye and not get any anisekonia?

Answer 23

15.7mm which is equal to the anterior focal length of the eye.

Question 24

About how much anisekonia can the brain handle?

Answer 24

8%

Question 25

For piggy back lenses, how much do you need to correct for myopic and for hyperopic errors?

Answer 25

Myopic: 1 X refractive error (e.g. -2 error, correct with -2 IOL)Hyperopic: 1.5 X refractive error (e.g. +2.00, correct with +3 IOL)

Question 26

How much accomodation do you have at the age of 40? At the age of 48? How much do you loose every 4 years from 20-40? From 48 on?

Answer 26

6 at the age of 40, 3 at the age of 60;Loose 1 every 4 years from 20-40 then 0.5 every 4 years from 48 on;

Question 27

Does light bend towards or way from the normal when it goes from medium with n=2.2 to n=1.3?

Answer 27

It goes away from the normal

Question 28

In order for the critical angle to be reached light must pass from high to low or low to high index of refraction?

Answer 28

high to low

Question 29

Does light bend toward the normal or away from the normal when it goes from low index of refraction to high?

Answer 29

Toward

Question 30

What does Kestanbaum’s rule state?

Answer 30

estimation of strength of plus lens necesasary to read ordinary newspaper. Can be estimated by taking the inverse of the snellen acuity (e.g. 20/100 requires +5.00 D)