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38 Cards in this Set
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In the conoid of Sturn, where is the location of the circle of least confusion?

halfway (dioptrically) from each of the two lines


What is the equation that relates the lens power in air and in fluid?

D(air) = N(iol)  N(air)
  D(fluid) N(iol)  N(fluid) 

A Rodenstock lens gives you what kind of image

Inverted and reversed


Use two lines to identify an image

1. line parallel to the axis will exit lens and travel through the focal point.
2. line through the optical center will not deviate. * The three line principal will use a third line that will pass through the focal point and leave the lens parallel to the axis. 

Describe the power cross

The power cross represents a lens system using meridians, which indicate what location the light is acted on which is 90* from the axis of a lens that causes that change (which can be represented with an axis cross).


Convert a power cross to negative cyl Rx

(most positive #)  (difference) x (Axis of most positive meridian)


in a concave/convex mirror system, what is the relation of the radius and focal point

Radius = 2 x focal point


Equation for transverse magnification

M = U = image height = image distance
   V object height obj distance 

Equation for angular magnification

M = D/4 D = lens power


Equation for magnification of a telescope

M = D eyepiece/D objective


IOL power calculation

D = A 2.5(AL)  0.9(avg K)


Equation for the reflecting power of a spherical mirror

D = 100/f =200/r
f & r in cm 

Gradient method for AC/A

PDsc PDcc
  Dsc  Dcc  

using a + cyl to correct for astigmatism of the cornea. Where would the axis be placed

at the steeper meridian


Define Kestenbaum's rule

power of lens needed to read newsprint = reciprocal of VA
e.g. 160/20 = +8 magnifier 

When light enters a medium of higher index what happens to speed, wavelength and frequency

Frequency remains the same, and speed and wavelength slow down.


As wavelength increases what happens to
1. refraction 2. defraction 
1. decreases
2. increases 

To increase power applied per delivery do what to:
1. energy 2. time 3. other things that increase power 
1. increse
2. decrease 3. q switch and mode lock 

Position of prisms:
1. glass 2. plastic 
1. prentice position: one surface perpendicular to the light
2. angle of min deviation 

What is the equation for refracting power of a surface?

D = (n'  n)/r
r is in meters D is +/ based on rectangle, with high n being colored in 

Aspects of a thick lens

two nodal points/planes. If n is different from one side to the other, nodal points move to the higher n


Basic scematic of the eye

+60D
nodal point 17mm from retina & 5.5 from cornea 

Describe relation between degrees, seconds, minutes and Snellen acuity

1 sec of arc = 1/60 of a minute of arc
1 minute of arc = 1/60 of a degree 20/20 means that you can distinguish at 1 arc minute (with a 5 minute E  which has five 1' lines and gaps) 

When using free lenses and a retinoscope, describe the results in an axis cross.

axis is the same as the light of the intercept. lens power would be the lens used minus the working distance (~1.5)


Describe the different telescopes

Astronomic: uses two + lenses, image is inverted, length of scope is the sum of the focal lengths
Galilean: uses one + and one  lens, upright image, Length = difference in focal lengths 

What is the amount of mag/min induced by glasses?

2% per diopter
 lens minifies + lens magnifies 6% image difference is tolerable 

describe ray tracing with mirrors

central ray goes through radius, not the focal point


Describe how cromatic light is bent at a prism

Blue base
red top 

When using free lenses and a retinoscope, describe the results in an axis cross.

axis is the same as the light of the intercept. lens power would be the lens used minus the working distance (~1.5)


Describe the different telescopes

Astronomic: uses two + lenses, image is inverted, length of scope is the sum of the focal lengths
Galilean: uses one + and one  lens, upright image, Length = difference in focal lengths 

What is the amount of mag/min induced by glasses?

2% per diopter
 lens minifies + lens magnifies 6% image difference is tolerable 

describe ray tracing with mirrors

central ray goes through radius, not the focal point


Describe how cromatic light is bent at a prism

Blue base
red top 

Go through the steps involved with converting glasses to RGP contacts.

1. set base curve +0.50 steeper than the flattest K
2. convert glasses to minus lens 3. drop the cylinder 4. correct vertex distance based on far point 5. subtract 0.50 (tear lens) 

RK does what to the focal power of the cornea?

It makes it more minus (flattens the center)


When measuring strabismus in glasses, what is the correction?

minus measures more
2.5 x D = x% subtract that percentage from the observed value in a minus lens 

What is the reflecting power of a mirror

1/f (in meters)


give the refractive indicies of:
1. Water 2. cornea 3. lens 4. PMMA 5. crown glass 6. polycarb 
1. 1.33
2. 1.37 3. 1.42 4. 1.49 5. 1.52 6. 1.59 