MT 1 Flashcards
What is LV
Reduced BCVA Or field loss and the need of lighting or a device
Standards for LV
20/200 snellen in best eye. 20/100 loggmar with 20/126 0r 20/160 line. OR less than 20 degrees usable VF.
Standard for VI
20/70 or worse
VI most common causes in adults
Cataracts, ARMD, glaucoma, DR.
Cause of VI in kids
Cortical impairment, OA, hereditary retinal dz, etc
20/100 in kids or better and 20/50 in Adults
No devices needed. Consider an Add
20/1,000 in kids and 20/400 in adults
Brail.
Photosensitivity caused by…
aniridia, glaucoma, albinism, achormatopsia, retinal dystrophy, conceal dystrophies
Color vision caused by…
chromatopsia, cone dystrophies, optic nerve disease
Contrast caused by
cataracts, glaucoma, retinal dystrophies, corneal dystrophies
Nystagmus
Caused by all early onset conditions affecting foveal pathway
What does VI in infants impact
fine and gross motor skills, cognitive development, socialization and communication
Walking in VI kids
18-24 months. Normal child? 9 and 12 months.
VI kids and language
Develop language at the same rate but their description is lacking.
Hearing and VI
Some VI kids will have reduced auditory acuity as they do not have visual cues for partly auditory communication. However, those that have VI early will increase hearing and motor skills.
Feelings and VI
VI cannot see nonverbal communication which shows feelings.
Transparecny
VI may not be aware of their facial expressions.
Cognitive development
Severe VI can make it difficult to grab conceptual concepts such as colors, 3D, figure ground relationships, size and shape characteristics.
Literacy and VI
Children with VI are at risk for becoming low achieving in reading. Braille and auditory users generally have higher literacy than children who are print readers
What VI groups is at greatest risk for literacy problems
Moderate (20/100-20/400)
Brightfield Magnifiers
Great for kids with 20/250 or better
Bioptic Driving Law
VI (20/70-20/200) can have a restricted drivers license with bioptic device.
Aging and LV
Very slow exam pace.
LV Case Hx
- Educate/clarify purpose of exam 2. Review underlying condition 3. Evaluate all areas of patient function that may impact adaption to vision loss 4. clearly outline goals/expectations
ADL
Need to understand patients life to understand vision needs.
What qualities indicate good prognosis with low vision adi
independently motivate, good cognition, previous success with low vision aid. 20/800 or better vision, positive self image, long standing stable condition
How different should near and far be?
one line
Refraction of LV patient
trial frame and retinoscopy best!
JND from BCVA
20 ft. snellen denometer/100.
Prescribing for near
Need 2x mag above acuity threshold to read comfortably.
Near add for pre-presbyopes
Use relative distance magnification
Adds for kids
No WOW factor. Increase comfort in long term.
Contrast threshold
The lowest contrast a patient can recognize optotypes. Normally a precent.
Contrast reserve
Ratio of contrast of an object to contrast threshold of the patient.
When contrast reserve falls below what will the patient have reduced functional deficits?
10/1
Bailey Lovie Chart
Measure VA at 10% contrast. Normal patient will drop 2 lines. Have optotype change.
Pelt-Robison chart
One size optotype with changing contrast. Test at twice the acuity threshold of the patient. VA deficits with 5% CT or greater.
Which Contrast test is better?
Bailey love for showing contrast drop off with early stage disease/cataracts.
Improving contrast sensitivity
increase magnification, increase lighting, etc.
Why test BV on low vision patients?
May need to teach them to suppress bad eye or if nearly equal acuity need to teach them binocular summation.
Binocular challenges with working close
Have mergence and accommodation needs when working at close working distance. Can use lenses and BI prism.
Testing stereopsis in LV
Use a local test (global is rare in LV population)
VF testing
Binocular fields are more relevant in a low vision exam. Testing is challenging due to poor fixation. Need a big fixation target. Need for legal blindness, mobility, driving, central vision tasks.
How to test VF in LV by standards
Goldmann II4e target. 30-2 or 24-3 used.
How to test VF if goldman not available?
Can do confrontation but use FW. Must present in more fields.
Tangent screen and campimeter
Test patient at 1m and then move patient back to 2m. Should expand twice the original size.
Macular Testing
White on black gives better testability for LV patients. Can also use penlight against the back to create a kinetic mapping stimulus.
Macular testing condition
May fixate with pseudo fovea.
Scotoma and reading
scotoma to the right of fixation make it difficult to read. Scotia to the left make it hard to saccade to next line.
Definition of VA
The threshold to discriminate a small object or detail of high contrast
Va is an _____ measure expressed in _____ terms
Angular, linear. Typically based on viewing distance and the distance the target subtends 5 arc min.
Types of VA
- Minimum detectable 2. Minimal resolution 3. Recognition 4. hyperacuity
Hyperacuity boundaries
Can get down to 3-8 arc seconds. Up to 10x finer than resolution.
Levels of VA
NLP, LP, L perception with projection, HM, quantified va.
Legal blindness
snellen is 20/200. 20/125 or worse with logmar. VF of 20 degrees or less
VF blindness when no goldman
Can use mean deviation of -22 db or worse.
Patients with 20/40-20/70
Not designated as VI but have driver restrictions.
Hyperacidity measure in LV
A measure where hyperacidity result is better than VA suggests that the patient has some macular function.
H54.8
The code you should always code first with a LV patient.
Snellen acuity
biased for a normal visual acuity as number of letters decrease and there are only three lines between 20/100 and 20/400.
LogMar demand change
Going up or down the chart by 3 lines changes the demand by a factor of 2.
Demand from one line to another on LogMar chart
0.1
VA on logera with +/-
Each character is 0.02. If you get extra it decrease. If you get less it adds.
Fein bloom chart
Calibrated in feet. Can measure acuity for much higher demands. Up to 20/14,000.
How close can test distance be in feinbloom
1 foot. Typically only have one character for the low demand lines.
Freiburg visual acuity test (FrACT)
A computer based system based on the orientation of the C’s. Has low demands such as feinbloom.
Berkeley Rudimentary Vision Test (BRVT)
Paddles with tumbling E’s on one card, gratings, and squares. Show at 100 or 25 cm. Document which one they can see and at what distance.
Chart options
Printed on a screen, printed on paper or cardboard, displayed on a device, projected directly on the retina.
Reverse contrast charts
Can convert black letter on a white background to white on black
Color contrast
Such as yellow on blue or blue on yellow.
What does improved VA on reversed contrast indicate
Need for tinted spectacles or goggles for use at far and magnifying devices for use at near.
Grating
Must identify the orientation
Landolt C
Can be 20-25% better as resolution and not recognition.
Lighthouse Flash Cards
Outdated pictures and do not blur equally.
Lighthouse Game card
Ask the patient to read. Increases the cognitive load.
Snellen denominater
The distance that the optotype subtends five arc minutes.
Half of JND
Power of individual plus and minus sphere bracketing lenses. Also power of cylinder test lenses and JCC lens.
Full JND
Power of individual plus and minus cylinder bracketing lenses
Going from 100-20 feet what is the change in MAR
It will be 5x greater.
Spatial Frequency
Square wave or line is one dark and one bright. An E has 2.5 cycles tall.
Threshold measure of spatial frequency
One cycle is twice the MAR. In cpd.
Preferred method for recording near VA for low vision patients
M notion.
Afocal telescope
Will increase the angular subtense without changing vergence
RIM
RDM X RSMx LIM
LIM for afocal
1/1-tFobj. Will always be greater than one.
Magnification issue in LV
Size of object patient can see/size of object patient needs to see.
