Final Exam Part 2 Flashcards
US and Canda Definition of blindness
20/200 or worse or 20/125 or worse on logMar. Greatest VF less than 20 degrees with goldman III4e.
US and Canada Definition of VI
20/70 or worse.
Visual Impairment
A functional limitation of the eye
Visual Disability
A limitation of the abilities of the individual
Visual Handicap
A limitation of personal and socioeconomic independence
Main cause of blindness
ARMD (in developed) Cataracts (in undeveloped) Glaucoma, DR.
_____ of kids with VI are multiply handicaped
75%
Central Vision loss causes
Hereditary macular dystrophies, ARMD, foveal hypoplasia (Aniridia, Albinism)
Peripheral Vision Loss
RP like dystrophies, glaucoma, CVA, TBI.
Central and peripheral vision loss
ON conditions, late stage dystrophies, DR, ROP
Conditions with photosensitivity
aniridia, albinism, achromtopsia, Retinal dystrophies, corneal scar/dystrohies, congenital glaucoma.
Conditions with color vision changes
achromtopisa, cone dystrophies, ON disease.
Conditions with contrast changes
cataracts, glaucoma, retinal dystrophies, corneal dystrophies/scarring.
Conditions with Nystagmus
Any early onset diseases affecting the foveal pathway
VA when don’t need LV but maybe an add
20/100 or better (kid) or 20/50 (adult)
LV when need magnification 2-5X
20/100-20/250 (kid) or 20/60-20/100 (adult)
Need LV devices
20/300-20/800 (kid) or 20/100-20/400 (adult)
Brail use
20/1000 (kid) or 20/400 adult.
What does VI impact in a child’s development
Gross and fine motor skills, cognitive develop, socialization and communication.
Walking age for VI child
18-24 months (normal is 9 months)
Fine motor development in VI
Vision leads tactile exploration and vice versa so it is delayed.
Language acquisition in VI
Have the same rate of language development but their development of descriptive language lags.
Those with _____ VI complain of decreased hearing ability
acquired.
Conceptual issues with VI
colors, entire object in 3D, figure ground, size and shape.
Who with VI is most likely to suffer from literacy
Moderate (20/100-20/400)
Bioptic Driving laws
20/70-20/200. Daylight driving.
Why would adults need higher magnification than predicted based on VA
Hard for them to find a new preferred foveal locus.
VA that leads to good prognosis with LV device
20/800 or better
Do you trial frame with a phoropter
NO! use a trial frame. Allows for vertex distance and eccentric viewing.
Which axis should you scope?
Patient’s axis of fixation
JND equation
(denominator)/100
Prescribing for near
Need 2x magnification above threshold for comfortable viewing.
How to use an add for pre-oresbyope?
Use RDM. They get closer. Plus lens will barely do anything. Will just make them more comfortable. No WOW factor.
Contrast threshold
The lowest threshold the patient can recognize optoptypes
Contrast reserve
The ratio of contrast of object to contrast threshold.
Most people CT
1-3% of the acuity demands of reading material so contrast reserve 20/1 or 30/1
What contrast reserve will the patient have difficulty
below 10/1
Bailey Lovie charts
10% contrast and 90% contrast with change in optotype size. Normal difference is 2 lines. Drop of 4 lines is significant.
Peli-robinson
Perform at 2x threshold. Functional defficeins with CT is 5% or greater.
Which CT is better
Bailey Lovie better for early dystrophies and things like cataracts. Peli can be used on LV patient.
How to help BV in young children
Add with BI prism
Stereo test to use on LV
Local test. Very rarely get global.
Testing VF in LV
Can use goldman or 24-2 or 30-2.
Confrontation VF
Finger wiggling works the best.
Tangent Screen and Campimeter
Test with 9mm whit stimulus at 1 m. Next test 18 mm target at 2 m. The field should expand to twice the original size. Failure to expand is nonphysiolgoical.
Testing bulls eye lesion with macular lesion
tell them to center their blindspot over the target.
Lesion in relation to PRL
If to the right make it hard to saccade when reading. If to the left make it hard to saccade to beginning of line.
VA is technically a measure of ____ but is described in ____ terms
angular, linear
Types of VA in increasing difficulty
detection, resolution, recognition, hyperaciuity.
Levels of VA documentation
NLP (or total blindness), LP w/o projection, LP with projection, VA.
Do you take into account EF when measuring?
NO! Look at their central vision.
VF determination for LV
Widest diameter VF is 20 degrees or less or -22 DB of worse mean deviation on automated
VF determination for VI
Visual field loss in the periphery (such as glaucoma or RP) or in a sector.
Hyperacidity typical threshold
3-8 arc seconds
Resolution typical threshold
1 arc minute
What does a better hyperacidity than a resolution in LV indciate
There is some macular function left.
Coding with LV
Code for medical or pathological conditions, Code for legal blindness, and then anything after
Code for legal blindness
H54. 8
logMar Distance
Either 4m or 6m. Most often 4m though.
Variation of LogMar based on lines and letter
Each line varies by 0.1 and each letter by 0.02.
Fein bloom chart
Calibrated for feet. Can get as close at 2-3 feet.
FrACT
A computer based test where you have to indicate the position of landolt C’s. Can get as low as Feinbloom chart.
BRVT
Goes from tumbling E’s to grating to b and white pair.
Standards for contrast
Background luminance by 80-320 and characters be no more than 15% of the background luminance.
What does increased VA with color contrast indicate
The need for tinted spectacles.
Landolt C’s can by ____ better than other optotypes
20-25% as it is resolution and not recognition.
What does snellen fraction mean
The denometer is the distance that the target subtends 5 arc min.
1/2 JND
Sphere bracketing lens, cya test lens, crossed cylinder lens
full JND
Cylinder bracketing lens
Angular subtense of MAR
5 times the MAR
Preferred method for recording VA
M notation
Point
1 point is 0.353 mm
Point to snellen
Multiple pt by 6.25
Recommendations for testing vA
Binocular and then better eye.
Spectacle plane
12-15 mm from cornea
Keplerian
Two positive lenses with focal spots corresponding.
Galilean
Objective is positive and eyepiece is negative.
LIM
w image/w object or 1-du/1-dv
RDM
uref/uaided
RSM
y2/y1
Telescope LIM
1/1-tFobj.
How to predict Near VA
From Far VA
Near viewing with high or irregular astigmatism
Can be increased VA at near due to increased DOF
Predicting Near VA in M notation
(MAR)uref or (VA)RDM
Predicted add to read 1 M print
1/far VA
Predicted add for any demand
1/far va (1/actual demand)
RIM
Measured VA/Demand
Magnification value on telescopes
NOT RIM
Equivalent dioptric value
the value that allows the comparison of different magnification devices
Principal plane of plano convex lens
Vertex of the convex surface
Principal plane of biconvex
midpoint of front and back lens
Gaussian Equation
Feq=F1+F2-t/n(F1F2)
Calculating power from lens clock
FT=FC(Nt-1/NC-1) NC=1.53 or 1.56
Finding Feq by measuring image formed
1/distance
Finding Feq by measuring image sizes
y2(u/y1). u must be greater than v and greater than 4 times y1.
Systems that do incorporate Ametropia, accommodation, or add
Feq=F1+F2-DF1F2.
Myopic RE is
+
Hyperopic RE is
-
If a device is held in the spectacle plane what does the LIM equal
- Only helps with the working distance. so RIM=RDM
RIM of a LV device when V=0
RIM=FeqX-uref
RDM
Ref/uaided or Feq X -uref
When is RIM constant?
When V=0
Maximum equivalent power of an add
When d=0
When d=fdevice
then the add will not contribute to Feq.
When d>Fdevice
Then Feq will be less than Fdevice
ER
Feq=ERX F add
EVD
Where we would have to place an object to subtend the same angle as the virtual image. ER=d-v/ER
Predicted VA
EVD X Initial VAm/initial viewing distance
FOV
A/d(EVD) or A/D(feq)
FOV when working distance equals focal lenghth
FOV equals the aperture size regardless of the image distance.
When does FOV incresase
when working distance is greater than focal length and image mergence is non zero
Effective magnifiaction
F/4
Conventional magnification
F/4+1
Largest value that binocular vision can occur
+10D
Advantages of high plus spectcles
Largest FOV as close to spectacle plane.
Disadvantages of high plus spectacles
Fixed lens position poor for patients who use eccentric viewing. Writing is difficult if add greater than 10.
When should you do single vision reading prescription
If add more than 3.50D
Hand magnifiers advantages
Greater working distance, good for eccentric viewing,
Hand magnifiers disadvantages
Reduced FOV, Must use correct working distance
Guidelines to prescribe hand magnifers
Should minimize working distance and view through distance correction,
Freestanding devices advantages
Normal reading distance, good for short tasks,
Distanvatges to freestanding devices
smallest FOV, Aberrations is viewed at an angle. Patient must accommodate.
