Optics - REFRACTION

Question 1

What are the 2 ways Pinhole acuity works?

Answer 1

1. It reduces the size of the blur circle

2. Increases depth of focus of eye

Question 2

How many diopters can pinhole correct for?

Answer 2

3D

Question 3

What does a Pinhole of <1.2mm do?

Answer 3

1. Increase diffraction

2. Decrease amount of light entering the eye.

Question 4

Legal blindness is defined as what?

Answer 4

1. BCVA in better ye is 20/200 or worse

2. VF in better eye is 20 degrees or less in diameter.

Question 5

Where is the far point for hyperopia and is it real or virtual?

Answer 5

Behind the eye and virtual.

Question 6

What is the difference between far point and focal point?

Answer 6

Far point can extend all the way to infinity.

Focal point never more than few mm away from retina.

Question 7

Total internal reflection occurs only from what to what type of index?

Answer 7

From Higher to Lower index.

Question 8

What is an example of Chromatic aberration ?

Answer 8

Duochrome Test

Question 9

In the duochrome test where is the green light focused?

Answer 9

In front of the eye. When Green is brighter, more plus is needed to move the green light to the focus closer to the retina.

Question 10

What is the duochrome test pneumonic?

Answer 10

RAM - GAP

Question 11

Up to what vision can the duochrome test be used?

Answer 11

20/30. Remember only 0.5D seperates red and green on visual axis spectrum.

Question 12

What is COMA? What produces COMA?

Answer 12

Coma is an off axis spherical aberration. Peripheral rays produce coma. The image is a series of circles that form a comet shape. This is a primary problem for large aperture optical systems an can be ignored in spectacles b/c of limited affect of the pupil.
When the aperture is closer to the lens, great coma occurs.

Question 13

What is the REFRACTIVE power of the Cornea?

Answer 13

45D

Question 14

On the ETDRS chart a 3 line gain or loss indicate what of the visual angle?

Answer 14

Doubling or halving

Question 15

What is stenopeic slit?

Answer 15

An elongated pinhole that may be useful as a guide to determine subjective astigmatic refractive error.

Question 16

Vertex distance is measured from where to where?

Answer 16

From the back of the spectacle lens to the surface of the CLOSED eyelid.

Question 17

Calculating the vertex distance for a myopic lens do you add or subtract the vertex distance to calculate the new lens power?

Answer 17

SUBTRACT

Question 18

What does pantoscopic tilt do?

Answer 18

Changes BOTH sphere and cylinder of the same sign of the original lens.

Question 19

How does Radial Keratotomy work?

Answer 19

Radial incisions that steepen the periphery (with compensatory flattening in the center)

Question 20

When does Krypton have an advantage over Argon?

Answer 20

When there is VH or mature len b/c it is poorly absorbed by heme and xanthophyll.

Question 21

Why does Diode laser work through sclera?

Answer 21

Minimal diode laser is absorbed by the sclera and is SOLELY absorbed by MELANIN in RPE layer with thermal damage to surrounding tissues.

Question 22

What is the order of cycloplegics from most to least?

Answer 22

Atropine, scolpolamine, homatropine, cyclopentolate, tropicamide

Question 23

Submerging a persons head in water without googles does what to their refraction and why?

Answer 23

Refractive hyperopia. An increase in the index of refraction of water induces a decrease in power of the cornea.

Question 24

What is 2 examples of spherical aberration?

Answer 24

1. Night myopia (low light causes a larger pupil allowing more peripheral rays to enter the eye and the focus shifts anteriorly)
2. Fluctuating vision following keratorefractive surgery

Question 25

The bifocal segment is usually how far down from the optical axis?

Answer 25

2mm

Question 26

When people read how far down and in do they look?

Answer 26

8mm, 2mm

Question 27

According to Knapp’s law, the anterior focal point is how anterior to the cornea?

Answer 27

15.7mm (people like to work at 12mm and this causes 2% change in magnification or minification of the image)

Question 28

During duochrome test if the patient see red better what does that mean?

Answer 28

too hyperopic - add minus (RAM)

Question 29

During duochrome testing if the patient sees green better what does that mean?

Answer 29

too myopic - add plus (GAP)

Question 30

Thick lenses with multiple nodal points does what to the dioptric power of a lens?

Answer 30

REDUCES!!

Question 31

In retinoscopy the orientation of the streak equals?

Answer 31

AXIS (horizontal or vertical)

Question 32

In retinoscopy the direction of movement equals?

Answer 32

Meridian of POWER (up or down, left or right)