Optics

Question 0

Transverse magnification

Answer 0

The transverse magnification induced by a lens is given byM = U / V, where U is the incoming vergence, often from an object, and V is the output vergence of light leaving the lens. This might be remembered by the mnemonic MUV’in out M=U/V=i/o.

Question 1

Toric lenses

Answer 1

Toric soft contact lenses often have a centering mark in the approximately 6 o’clock position. A general rule of thumb is that if the mark has shifted to the LEFTthen youaddthe corresponding amount of cylinder axis. And if the mark has shifted to theRightthen yousubtractthe corresponding amount of cylinder axis. This can be remembered with the mnemonicLARS. One clock hour is about 30 degrees. In this patient, the mark has shifted to the right 2 clock hours or about 60 degrees. Therefore, you will order the contact lens in the 30 degree axis.

Question 2

Types of telescopes

Answer 2

Galilean telescope:
lowplus powerobjective
highnegative powerocular
lenses are separated by: 1/Pobjective- 1/Pocular(ignore positive or negative signs)
Mnemonic: Galileo was loved (+), but then he was reviled (-). But he was correct (upright). Look at objective over the daily (ocular)

Astronomical (Keplerian) telescope:
lowplus powerobjective
highplus powerocular
lenses are separated by: 1/Pobjective+ 1/Pocular

One way to remember this is that youAdd the focal lengths for anAstronomical telescope to determine how far the lenses are separated from each other.

An easy way to remember how to calculate angular magnification of telescopes is that they ALWAYS magnify an image. Thus, just divide the larger number by the smaller number.

Question 3

Fluorescein absorbs/emits which light

Answer 3

Fluorescein absorbs a photon of blue light and emits a photon of yellow/green light
B lue begins the FA
G reen Gets out of the eye

Question 4

Diverging (negative lens or mirror)

Answer 4

Always VERMIN
Virtual
Erect (upright)
MINified

Only works for NEGATIVE lenses/mirros

For positive lenses and positive mirrors, answer depends on where the object is in relation to the focal length of the lens/mirror

Question 5

For which class of laser will specular exposure to the eye cause injury in a time shorter than the blink reflex

Answer 5

Class 3B (or 3b in the older system).
Lowest class of laser for which direct exposure or specular reflection will damage the eye in less than one quarter of a second.

Question 6

To correct anisekonia after CL in aphakic eye:

Answer 6

1) place CL into phakic eye
2) place CL onto the phakic eye and also over-correct the aphakic eye to -3D and then wear glasses over that eye to reduce image size (empirically 3D works regardless of refractive error)

If patient can’t wear CL in phakic eye, can correct aphakic eye to -5 sphere and wear spectacles

Question 7

Duochrome

Answer 7

RAM-GAP

Red side better, refraction = too hyperopic (ADD MINUS)
Green side better, refraction = too myopic (ADD PLUS)

Question 8

convex mirror produces what type of image?

Answer 8

VErMin
Virtual
Erect
Minified