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45 Cards in this Set
- Front
- Back
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MN Read chart
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used to test reading rate, Critical Print Size, Threshold Print Size
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Equivalent viewing distance
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Working Distance
distance at which original object would subtend same angular size as the angular size of image formed by plus lens |
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4 types of Mag
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Non Optical
Lateral Mag Angular Mag Effective Mag |
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RSM
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making it bigger
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RDM
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bringing it closer
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MN Read chart
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used to test reading rate, Critical Print Size, Threshold Print Size
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Equivalent viewing distance
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Working Distance
distance at which original object would subtend same angular size as the angular size of image formed by plus lens |
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4 types of Mag
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Non Optical
Lateral Mag Angular Mag Effective Mag |
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RSM
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making it bigger
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RDM
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bringing it closer
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Lateral Mag
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Linear Mag
Transverse Mage Ratio of L/L' object NOT at infinity |
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Conventional Mag
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using up close w/Bifocal @ 25cm
= 1 + F/4 |
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Refractive error at Near & mag
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Uncorrected Myopia --> more Mag
Uncorrected Hyperop --> less Mag |
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Hand held Mag & RDM
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Mag remains if Object is at Magnifiers focal length
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FOV & Hand held Mag
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FOV increases as lens is brought to eye
FOV = (diam of lens) (f/eye to lens distance) |
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Eq Power (Fe) of HH-Mag & GLS-Add
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Fe= Fm +Fa - (z * Fm * Fa)
z < fm, get full Mag (even if not looking through Add) z > fm, not getting full Mag (must look through distance) |
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Stand Mag
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getting closer increases Mag, need more Acc
WD = GLS to image |
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Stand Mag calculation
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Multacc Factor (Mt) = Transverse Mag = Enlargment factor
Mt = (L'-F)/L' Fe = Fa * Mt |
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Eq Power of Stand Magnifier
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Fe = Fa * Mt
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Low vision Microscope: Basic
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Mag is angular mag
Active Acc increases resulting mag |
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Types of Low Vision Microscopes
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Prism 1/2 eye
Full Field Microscope Bifocal Loupe High + CLS |
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full field microscope types
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Microscopic Doublet
Aspheric lens/lenticular Diffraction grating system (noves) |
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Microscopic Doublet
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full field microscope
2 + lens separated by air to min Aberrations good for > + 20D |
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Aspheric Lenticular
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minimize aberations
aspheric on plano base: fried egg +10 to +48D |
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Diffractive grating system
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light/thinner
+12 to +20D |
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Rx'ing High add in binocular form
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1 prism /Diopter add + 2
up to +12 prism half eye > 12 aspheric or Doublet |
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Single Vision lens design guidlens
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< 10D standard lenses
10 - 16D use aspherics > 16 use microscopic Doublet |
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Spec Mounted Microscope
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wide FOV
Broad range of power Rx Bad: Close WD, weight hard to get lighting expensive |
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Hand Held Mag
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flex WD (eye to lens can vary)
Limited FOV (dependent on eye to lens) |
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Galilean
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+ objective, - Eye
Image erect Small FOV Shorter up to 4X Mag Myopes borrowing have less Effective Power & Mag |
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Keplerian
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+ / + lenses
External Exit Pupil => larger FOV Better image up to 10X Mag Myopes borrowing have more Effective Power & Mag |
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TS tube length change & Rx error
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increases for Hyperopes
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Vergence Amplification
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If vergence enters TS it will be Mag
L ~ Msquared * L1 |
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Label TS
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Mag * Objective in mm
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Verifying TS
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Direct Comparision Method
Exit Pupil Measurement (K only) Lateral Magnification (lensometer) |
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Exit pupil movement
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Against = Galilean
With = Keplerian |
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CLS Telescopes
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Galilean
aphakia, high hyperopia, only have to hold + lens (objective) |
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How to modify TS for near
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Add + btw eyepeice & eye (Vergence Amp)
Alter tube (lengthen, increases Mag) Reading Cap + lens = WD |
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TS w/reading cap Fe formula
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Fe = M * Fcap
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VF loss has functional difficulties
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bilateral
monocular |
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Field expansion for Constricted VF
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Reverse TS
Channel (Prism wedge) |
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Field Expansion helps (most to least)
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HH
Quadrant Bilateral Altitudinal/monocular inferior loss |
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Peli/EP horizontal
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brings missing VF into "seeing"
improve navigation expands 20 degrees 40D base out on same side as VF loss Needs Binocularity |
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Sector/Gottlieb VFAS
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less shift needed to see periphery on defective side
20D on both eyes Scan to prism, turn head; learn to avoid blind spots |
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Low vision Yolked prism
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Postural Restriction
Visuospatial Neglect Visual Midlen Shift Syndrome |
