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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