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124 Cards in this Set
- Front
- Back
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Relative Size Mag
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take an obj of a specific physical size and reproduce it in a larger physical size ie: large print newspaper
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Relative Size Mag
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take an obj of a specific physical size and reproduce it in a larger physical size ie: large print newspaper
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What is the Snellen VA of large print books? M size?
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20/100
2M |
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What is the Snellen VA of large print books? M size?
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20/100
2M |
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Relative Distance Mag formula:
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original distance/new distance
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Relative Distance Mag formula:
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original distance/new distance
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What is the RDM (relative distance mag) for CCTV viewed at 40 cm?
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1x
If viewed closer than 40cm, total mag = RDM x RSM |
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What is the RDM (relative distance mag) for CCTV viewed at 40 cm?
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1x
If viewed closer than 40cm, total mag = RDM x RSM |
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Explain LDDV
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Least distance of distinct vision = how close you need to hold something to make it look clear
standard was 25cm |
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Explain LDDV
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Least distance of distinct vision = how close you need to hold something to make it look clear
standard was 25cm |
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What power does a standard presbyopic and emmetropic patient need to see object at LDDV?
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Since that is at 25cm, need +4.00D
Therefore a +4.00D lens has a mag of 1x |
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What power does a standard presbyopic and emmetropic patient need to see object at LDDV?
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Since that is at 25cm, need +4.00D
Therefore a +4.00D lens has a mag of 1x |
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Effective Mag Formula
Conventional Mag Formula |
F/4
F/4 + 1 (takes into account acc by patient) |
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Effective Mag Formula
Conventional Mag Formula |
F/4
F/4 + 1 (takes into account acc by patient) |
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Where must object be held to use effective mag formula?
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obj held at focal length of magnifier
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Where must object be held to use effective mag formula?
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obj held at focal length of magnifier
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What creates the enlargement of an image in ANGULAR mag?
What devices is it used for? |
created only by optics of the device
Hand magnifiers and telescopes |
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What creates the enlargement of an image in ANGULAR mag?
What devices is it used for? |
created only by optics of the device
Hand magnifiers and telescopes |
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Formula for Ang mag:
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1 + hF
h = distance of mag from spec plane in meters |
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Formula for Ang mag:
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1 + hF
h = distance of mag from spec plane in meters |
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What devices is Equivalent power used for?
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1. microscopes
2. hand mag 3. stand mag |
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Equivalent Power formula:
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Feq = F1 + F2 - c(F1)(F2)
Feq = total diopters needed by pt F1 = power of LV device F2 = add/pt's acc c = seperation of LV device from spec (meters) |
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When does Feq = F1?
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When object is at focal point of F1.
F1 at spec plane or outside spec plane |
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When does Feq = F1 + F2?
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when object is inside f1 and F1 at spec plane.
Since obj is inside f1, divergent light leaves F1 and either acc or an add (F2) is required for image to be resolved. |
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When does Feq = F1+F2 - c(F1)(F2)
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when obj is inside f1 and F1 is outside spec plane (stand or hand mag)
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2 ways to predict Add power:
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1. Kestenbaum (inverted distance VA). Ie: VA 20/100, add = 5D
2. Lighthouse |
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Explain Lighthouse method:
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1. Place +2.50D add on distance Rx
2. hold near card at 40cm, illum, take VA 3. use RSD to determine add ie: at 40cm, with +2.50D pt can read 2M, so to read 1M chart must be moved to 20cm...5D needed |
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Acuity reserve method, what is the power needed for acuity reserve?
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power needed is 2x the predicted add
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If 1M needed 5D, then to read 0.5M what power is needed using acuity reserve method?
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2x the initial power....10D...means a working distance of 10cm
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What LV device provides the widest field of view
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Microscopes/ Specs
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What is the power limit available for microscopes as a LV device?
What direction prism can be added to decrease convergence demand? |
+14.00D
use BI |
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How to calc binoc converg demand:
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pupillary distance (cm) / reading distance (m)
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To decrease convergence demand, what are usual amounts of prism used for:
+4, +6 and +10? |
+4 = 6 BI each eye
+6 = 8 BI each eye +10 = 12 BI each eye |
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To use a hand mag, the object should be held where?
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ant focal point of mag
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if an object is held at the ant focal point of the mag, then what is the Mag?
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Mag= F/4
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When using a hand mag, when should you look thru the Add and when should you look thru distance?
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Feq = F1 + F2 use ADD
Feq > F1 use ADD Feq = F1 used Add or dist Feq < F1 use dist |
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When a patient uses a +10 HH mag for reading and hold the print at focal point, what is the equivalent power?
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+10.00D
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If your IOL pt with +2 readers puts a 10HH mag up to his eye and holds print closer than the focal point of the mag, what is Feq?
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+12
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Spec mag is the result of what type of mag?
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Distance! Specs magnify things so that you can bring things closer
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What type of tasks are hand magnifiers useful for?
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brief spotting tasks, such as reading price tags, labels...
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As the power of hand magnifier increases, what happens to the useable field of view?
As the distance of the hand mag from the spec plane increases, field of view...? |
Decreases
Decreases! |
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Formula for determining linear field of view in hand magnifiers?
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W = (d) (f/h)
W = linear width of visible field d = lens diameter h = distance of lens from eye |
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If the magnifier is held 1 focal length from the eye, what does the field of view equal?
What if it is held 2 mag focal lengths from the eye? What if it is held 1/2 focal length from the eye? |
equal to the diameter of the lens
equal to 1/2 diameter of the lens equal to 2 diamters of the lens |
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3 parameters of fixed focus stand magnifier:
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1. Image distance
2. Eq power 3. ADD/Acc |
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Enlargement Ratio
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= (U - Fm)/ U
U = image vergence Fm = eq power of plus lens Eq power = mag X Add....review in notes!!! |
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Explain what MNREAD does:
how many letters/words per sentence? |
measures reading acuity and speed (important in deciding final mag to use in LV pt)
10 words, 60 letters range from 8M to 0.13M |
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Reading Speed =
If read 4M print size in 6 sec, what is the WPM? |
reading speed = 60 sec x 10words/time in sec = WPM
600/6sec = 100WPM |
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How many WPM needed for reading comprehension?
Critical print size or reading acuity? |
>85 wpm
4M |
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What Rx should the patient use when performing MNREAD?
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+2.50 ADD over distance Rx, test at 40cm
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Your patient reads 2M at 40cm. What would be your working distance to read 1M?
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20cm
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Acuity reserve: ratio of what?
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target acuity/patient's threshold acuity.
If threshold is 1M, may not be able to read fluently at 1M, need reserve such as 1.5M to read fluently. |
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4 impediments to low vision reading:
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1. inadequate acuity reserve
2. inadequate contrast reserve 3. inadequate field of view 4. central scotoma |
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What CSF values indicate that patient should have Level 1 LV or Level 2 LV help?
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>1.4 Level 1
<1.05 Level 2 |
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Acuity reserve: ratio of what?
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target acuity/patient's threshold acuity.
If threshold is 1M, may not be able to read fluently at 1M, need reserve such as 1.5M to read fluently. |
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4 impediments to low vision reading:
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1. inadequate acuity reserve
2. inadequate contrast reserve 3. inadequate field of view 4. central scotoma |
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What is normal log CSF for patient older than 60yrs?
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1.5
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With stand magnifiers, Feq is usually NOT the same as mag power. When do you need to acc or have an add additional to the mag? (where is the material held)
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Need to acc/add when material is held closer than focal point of lens, because divergent rays.
Image is erect, virtual |
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What CSF values indicate that patient should have Level 1 LV or Level 2 LV help?
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>1.4 Level 1
<1.05 Level 2 |
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Acuity reserve: ratio of what?
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target acuity/patient's threshold acuity.
If threshold is 1M, may not be able to read fluently at 1M, need reserve such as 1.5M to read fluently. |
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What power do the stand magnifiers start at?
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7D (2.8x)
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What is normal log CSF for patient older than 60yrs?
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1.5
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If transverse mag = 2x and Add = 3.25, what is the total power of the system?
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(3.25)(2) = 6.5
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With stand magnifiers, Feq is usually NOT the same as mag power. When do you need to acc or have an add additional to the mag? (where is the material held)
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Need to acc/add when material is held closer than focal point of lens, because divergent rays.
Image is erect, virtual |
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4 impediments to low vision reading:
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1. inadequate acuity reserve
2. inadequate contrast reserve 3. inadequate field of view 4. central scotoma |
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What 3 factors can affect reading but are NOT part of the decision tree?
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1. Age
2. training 3. Psychosocial issues |
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What CSF values indicate that patient should have Level 1 LV or Level 2 LV help?
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>1.4 Level 1
<1.05 Level 2 |
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What is normal log CSF for patient older than 60yrs?
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1.5
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Patient with CSF = 1.05 and norm Amsler, do they need acuity reserve for spot reading?
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NO, can spot read with predicted add
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What power do the stand magnifiers start at?
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7D (2.8x)
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If transverse mag = 2x and Add = 3.25, what is the total power of the system?
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(3.25)(2) = 6.5
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With stand magnifiers, Feq is usually NOT the same as mag power. When do you need to acc or have an add additional to the mag? (where is the material held)
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Need to acc/add when material is held closer than focal point of lens, because divergent rays.
Image is erect, virtual |
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Which patients will need acuity reserve?
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any patient with decreased in CSP and Amsler defects...even if VA is good!!! At least double the prediced add for fluency.
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What 3 factors can affect reading but are NOT part of the decision tree?
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1. Age
2. training 3. Psychosocial issues |
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What power do the stand magnifiers start at?
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7D (2.8x)
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If transverse mag = 2x and Add = 3.25, what is the total power of the system?
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(3.25)(2) = 6.5
have to look up transverse mag in chart using model number of device |
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Patient with CSF = 1.05 and norm Amsler, do they need acuity reserve for spot reading?
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NO, can spot read with predicted add
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What 3 factors can affect reading but are NOT part of the decision tree?
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1. Age
2. training 3. Psychosocial issues |
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Patient with CSF = 1.05 and norm Amsler, do they need acuity reserve for spot reading?
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NO, can spot read with predicted add
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Which patients will need acuity reserve?
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any patient with decreased in CSP and Amsler defects...even if VA is good!!! At least double the prediced add for fluency.
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Which patients will need acuity reserve?
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any patient with decreased in CSP and Amsler defects...even if VA is good!!! At least double the prediced add for fluency.
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Snellen VA for mandatory reporting of legal blindness?
ETDRS VA? Field? |
20/200 Snellen
anything worse than 20/100, ie:20/160 but always report with Snellen VA Field less than a diameter of 20 (using 6mm test object) |
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Min VA for driving (night/day)?
Min Field? Min VA for driving with telescope? |
Driving anytime: 20/40 distance VA and not less than 120 field
DAYTIME: 20/50-20/70 and not less than 120 field Telescope: 20/40 and at least 20/100 in each eye and not less than 120 horiz field |
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Is a person legally blind if they can only read 1 letter on the ETDRS?
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NO!!!
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If you want to help register someone as legally blind, should you use Humphrey or Goldman VF? (which is harder)
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Humphrey, will give worse VF
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Are prisms allowed to be used to help a patient increase their VF while driving?
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NO
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Which affects driving ability more:
VF, CSF, color vision? |
VF....color vision has NO impact on dirving
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What 3 variables does driving on the streets depend on?
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1. Obj vision - detecting obj
2. Visual Clutter 3. Speed - decrease speed to decrease visual clutter |
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Fienbloom is tested at what distance?
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10ft
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what is the size of a 1M letter?
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1.45mm at 1 meter
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Advantages of ETDRS chart?
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1. constant # letters per line
2. seperation between letters = letter size 3. log progression, 0.1log between each line 3 line step in either direction either doubles or halves the symbol size |
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Convert metric VA to Snellen:
4M 2M 1M |
4M, multiply by 5
2M, multiply by 10 1M, multiply by 20 |
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Snellen equivalent of 1M?
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20/50
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Distance of chart to measure Peli Robson contrast?
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1 meter, use distance Rx and +0.75 if needed
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Difference between Peli-Robson and Mars test?
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Both measure contrast, but Peli is done in triplets, in Mars each letter is a diff contrast, so more efficient
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Normal contrast for adult >65yrs
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1.52-1.76
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What VA qualifies a patient for Level 1 vision care?
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Level 1: 20/40-20/100
NO dense scotoma! |
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Disease and assoc VF defect:
AMD, Cat, Glauc, Diabetic Ret. |
AMD- central scotoma
Cat - no VF defect (overall blur) Glauc - peri DR- all of the above |
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Amsler grid: test distance? ADD? Monoc/binoc?
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33cm
+3.00 ADD (over distance Rx) Binoc > monoc |
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What is JND of 10/100?
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convert: 10/100 > 20/200
divide by 2: 200/2 = 1 JND= +/- 1.00 |
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What JCC to use in trial frame Refraction?
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up to 20/50: +/- 0.25
up to 20/100 +/- 0.50 up to 10/160 +/- 0.75 20/200 or worse +/- 1.00 |
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Size of 20/20 Snellen letter?
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8.7 mm
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Size of 1M letter? Snellen equivalent of 1M?
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1.45 mm
20/50 |
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If 20/400 letter measures 10mm, what is the M print size?
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10/1.45 = 7M
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Normal size of newspaper print?
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1M
8 point 20/50 |
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Main reason the trial frame refraction is recommended for LV patient?
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TF offers larger jumps in power for JND
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If patient's eccentric viewing is 10 degrees or more off the fovea, what is estimate of best VA?
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20/100
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If patient has no ret reflex, what can you do?
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Use very large brackets...+/-10 etc
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What test has a min lighting requirement that the doctor will need to measure before using the test?
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Peli-Robson Contrast Sensistivity
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Task oriented lighting for older adult should be:
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400-500 lux
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Best corrected VA decreased the fasted for which group in the Beaver Dam study?
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over age 75
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Convert metric VA to Snellen:
4M 2M 1M |
4M, multiply by 5
2M, multiply by 10 1M, multiply by 20 |
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Distance of chart to measure Peli-Robson?
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1 meter, using distance Rx and +0.75 if needed
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Difference between Peli-Robson and Mars?
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Mars is more efficient, every letter has different contrast value, instead of having triplets
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Normal contrast for >65yrs
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1.52-1.76
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What Va qualifies a patient for Level 1 vision care?
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20/40-20/100
NO dense scotoma! |
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Amsler grid test distance? ADD? binoc/monoc?
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33cm
+3.00 ADD (over distance Rx) Binoc, then monoc |
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What is JND of 10/100?
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convert to Snellen: 20/200
divide by 2: 200/2 = +-1.00 |
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What JCC to use in trial frame refraction?
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up to 20/50 +/- 0.25
up to 20/100 +/- 0.50 up to 20/160 +/- 0.75 20/200 or worse +/-1.00 |
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Main reason why low vision charts were developed to track the progression of disease, instead of using Snellen was?
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bc Snellen did not have optotypes between 20/100 and 20/200
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Snellen fraction for printed text which counts 20 letters and spaces in one inch?
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20/50
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WHich devices would be best for long duration reading?
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Stand magnifier and CCTV
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Most common functional problem in person with stroke?
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will run into things on one side
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During low vision refraction, what are Jannelli clips used for?
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Over Refraction
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Patient has 20/20 OU, with 5 degree VF. What would you recommend?
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REVERSE telescope
Orientation and Mobility training |
