Low Vision Techniques Flashcards
what is the set of guidelines called that outline the respectful way to interact with a patient who is visually impaired or blind
sighted guide
what are the first 2 steps in sighted guide
ask patient if they need assistance and then make contact with their arm
what is your arm position in sighted guide
relaxed by your side- bend elbow for patients who are unstable or frail
what is your body position in sighted guide
the patient is a half-step behind you- they follow the movements of your body
what are you telling the patient in sighted guide
providing verbal cues about environment, location, direction traveling, inform what is in rooms and if there are people in the room
what do you do in sighted guide while going through a door, narrow space or crowd
move your arm behind back and position yourself to open the door with your free hand
what is the sighted guide procedure for stairs
alert the patient when you approach stairs, say up or down, inform them where the hand rail is and tell them when the last step is coming
what are the steps to taking a distance VA
reduce test distance, hand motion (record distance), light projection and light perception *Do not do count fingers!
which chart method is in meters
ETDRS
what chart method is in feet
Feinbloom
what chart is the gold standard in low vision
ETDRS (also used in research)
what are some advantages of an ETDRS chart
improves standardization and accuracy in measuring VA, same number of optotypes per row, equal spacing and uses log scale, variable test distance, equal optotype difficulty, and high contrast optotypes
what are some benefits of the Feinbloom chart
portable, test at any distance, high contrast numbers, large optotypes, can measure less than 20/800
what are 2 disadvantages of the Feinbloom chart
variable number of optotypes per page and variable spacing between optotypes
what is M notation used for
metric system for measuring VA in vision rehabilitation distance and near testing
what is the starting distance for ETDRS
2m (can move to 1m if needed) - easy conversion to 20 feet
what is the starting distance for Feinbloom
10 feet (move closer if needed 5, 4, 2, 1 feet)- multiple of 20 for easy conversion
which chart is useful for eccentric viewing testing
Feinbloom
when can you not use reduced snellen near VA
if test distance is different than 40cm
what is the equation to convert to snellen equivalent
VA= test distance / letter size and cross multiply and divide by acuity (2/16=20/x –> x=160)
how can you do the snellen conversion in your head
when testing at 2 meters- multiply both numerator and denominator by 10 (if 1 meter multiply by 20)
what is point notation
based on typography (computers)- measures the size of typeface or the height of the letter
what is the conversion triangle for snellen - point - meters
Snellen –(Divide by 6)→ Point –(divide by 8)→ Meters –(multiply by 50)→ Snellen
what is JND
just noticeable difference - minimum lens change that a patient can appreciate during a trial lens refraction
what does JND equal
the denominator of equivalent snellen VA (move decimal place to 1/100 position) units are diopters
what loose lens do you choose for a trial frame refraction
+/- JND/2
You have the ETDRS chart at 1 meter and the patient reads the 8 M line. How do you record the visual acuity?
1M/8 (20/160)
Kathy read all of the letters on the 15M line when you placed the chart at 2 meters away from her.
How do you properly record her visual acuity?
2M/15 (20/150)
You use the Feinbloom chart at 10 feet and the patient reads the 150 foot line. How do you record the visual acuity?
10ft/150 (20/300)
how do you record near VA in low vision
record exact test distance and actual letter size - measure near VA at patient’s preferred working distance (record in METERS)
how would you record if a patient read 1.6M letter size at 20cm
0.20/1.6M
Karen is wearing her glasses. The chart is held at 20 cm, The patient reads to 1.25 M with both eyes open. how would you record near VA
OU cc 0.20/1.25M (20/125)
Stacey needs to read 6 point type bank statements while working at a financial institution. What is the M-Unit?
0.75M
During the vision rehabilitation examination, Josh was able to read the 1.25M letter size on the Lighthouse near acuity chart. What is the equivalent point type that he’ll need to use on his computer in order to see it?
10 point
OD 2M/16 (20/160)
OS 2M/25 (20/250)
What is the OD JND?
1.60D
OD 2M/16 (20/160)
OS 2M/25 (20/250)
What are the loose lenses you will select to produce JND for OD?
1.00D
OD 5ft/120 (20/480)
OS 5ft/240 (20/960)
What is the JND for OD?
4.80D
how do you determine the distance magnification needed
denominator of actual VA/ denominator of goal VA
what is distance magnification specified in terms as
angular magnification with unit “x”
what is the purpose of predicting magnification
determine the starring power of optical devices
what is the formula we will use for predicting near magnification
Equivalent viewing distance
what is angular magnification
using an optical system to increase the angular subtense of the image compared to the angular subtense of the object itself
OD 2M/25 (20/250) OS 2M/8 (20/80) and goal VA 2M/4 (20/40) for driving- what is distance magnification for OD and OS
25/4 = 6.25x 8/4 = 2x
what is the equivalent viewing distance (EVD) formula
(actual near VA denominator/goal near VA) x (accommodative demand or reference add power)
OD 0.20M/2.5, OS 0.20M/3.2, reference add used +5 D
Goal VA for reading large print fiction books 1.6M
what is the near magnification needed
OD: 2.5M/1.6M x +5D = +7.8D
OS: 3.2M/1.6M x +5D = +10D
if a patient need +12D near magnification, what is the working distance going to be?
8cm –> focal distance of 12D lens = 1/12
what are 5 categories of optical devices
near, intermediate, distance, adaptive/assistive technologies and non-optical
what are some examples of near optical devices
specs: high +, microscopic lenses, base-in prisms, doublet lenses, hand or stand magnifiers, and reading telescopes
what are 2 examples of intermediate optical devices
loupes and telescopes
what are some distance optical devices
monocular telescopes, spec mounted telescopes, and binocular telescopes
what are some adaptive/assistive technologies for optical devices
desktop CCTV, computer software programs, OCR technology, GPS navigation systems
what are some non-optical devices
absorptive filters (sunglasses), fitover sunglasses, typoscope, liquid level indicator, lamps, felt tip pens, talking watch/clock, dots
what is the california central visual field test
several laser brightness intensities to allow for more sensitivity in plotting clinically significant scotomas
