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38 Cards in this Set
- Front
- Back
In the conoid of Sturn, where is the location of the circle of least confusion?
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halfway (dioptrically) from each of the two lines
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What is the equation that relates the lens power in air and in fluid?
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D(air) = N(iol) - N(air)
------- -------------------- D(fluid) N(iol) - N(fluid) |
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A Rodenstock lens gives you what kind of image
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Inverted and reversed
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Use two lines to identify an image
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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. |
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Describe the power cross
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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).
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Convert a power cross to negative cyl Rx
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(most positive #) - (difference) x (Axis of most positive meridian)
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in a concave/convex mirror system, what is the relation of the radius and focal point
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Radius = 2 x focal point
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Equation for transverse magnification
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M = U = image height = image distance
-- ------------------ -------------------- V object height obj distance |
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Equation for angular magnification
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M = D/4 D = lens power
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Equation for magnification of a telescope
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M = D eyepiece/D objective
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IOL power calculation
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D = A -2.5(AL) - 0.9(avg K)
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Equation for the reflecting power of a spherical mirror
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D = 100/f =200/r
f & r in cm |
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Gradient method for AC/A
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PDsc -PDcc
------------------ | Dsc - Dcc | |
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using a + cyl to correct for astigmatism of the cornea. Where would the axis be placed
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at the steeper meridian
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Define Kestenbaum's rule
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power of lens needed to read newsprint = reciprocal of VA
e.g. 160/20 = +8 magnifier |
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When light enters a medium of higher index what happens to speed, wavelength and frequency
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Frequency remains the same, and speed and wavelength slow down.
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As wavelength increases what happens to
1. refraction 2. defraction |
1. decreases
2. increases |
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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 |
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Position of prisms:
1. glass 2. plastic |
1. prentice position: one surface perpendicular to the light
2. angle of min deviation |
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What is the equation for refracting power of a surface?
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D = (n' - n)/r
r is in meters D is +/- based on rectangle, with high n being colored in |
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Aspects of a thick lens
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two nodal points/planes. If n is different from one side to the other, nodal points move to the higher n
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Basic scematic of the eye
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+60D
nodal point 17mm from retina & 5.5 from cornea |
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Describe relation between degrees, seconds, minutes and Snellen acuity
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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) |
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When using free lenses and a retinoscope, describe the results in an axis cross.
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axis is the same as the light of the intercept. lens power would be the lens used minus the working distance (~1.5)
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Describe the different telescopes
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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 |
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What is the amount of mag/min induced by glasses?
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2% per diopter
- lens minifies + lens magnifies 6% image difference is tolerable |
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describe ray tracing with mirrors
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central ray goes through radius, not the focal point
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Describe how cromatic light is bent at a prism
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Blue base
red top |
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When using free lenses and a retinoscope, describe the results in an axis cross.
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axis is the same as the light of the intercept. lens power would be the lens used minus the working distance (~1.5)
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Describe the different telescopes
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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 |
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What is the amount of mag/min induced by glasses?
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2% per diopter
- lens minifies + lens magnifies 6% image difference is tolerable |
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describe ray tracing with mirrors
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central ray goes through radius, not the focal point
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Describe how cromatic light is bent at a prism
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Blue base
red top |
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Go through the steps involved with converting glasses to RGP contacts.
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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) |
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RK does what to the focal power of the cornea?
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It makes it more minus (flattens the center)
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When measuring strabismus in glasses, what is the correction?
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minus measures more
2.5 x D = x% subtract that percentage from the observed value in a minus lens |
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What is the reflecting power of a mirror
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1/f (in meters)
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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 |