The Low Vision Exam - Part 1

What are the purposes of VA testing? (4)

1. Gives the practitioner information needed determination of low vision device powers
2. Offers patient an opportunity to appreciate functional vision is present.
3. Provides a quantification to follow rehabilitation progress
4. Used to verify eligibility for driver's license, legal blindness, disability, etc.

VA testing does not tell us about an individual's _________ of vision

Quality

Why is counting fingers not recommended for distance VA?

If the patient can see CF, they likely have measurable acuity on a LV chart. The average finger is roughly the size of a 200 foot letter

What is the difference between light projection and light perception?

Light projection = identifying light in a certain quadrant

Light perception = seeing light but can't tell where the source is coming from

What test distance should you start testing for a Feinbloom chart?

10 ft

How many ft are in 3 meters?

Roughly 10 ft

What are the test distances used for EDTRS charts as you move them closer to the patient?

4m, 2m, 1m

(for 4m calibrated chart)

What are the test distances used for Feinbloom charts as you move them closer to the patient?

10ft, 5ft, 3ft, 2ft, 1ft

What 4 things should you include when recording visual acuities?

1. Distance from chart/distance at which the height of optotype subtends 5 min of arc (found on chart)
2. Name of chart used
3. Eccentric viewing and direction of EV (recorded as clock hour from the patient's view)
4. Quality of illumination (average, reduced, or bright illumination)

True or false: projection distance VA charts are acceptable for vision impaired pts

FALSE!

What is the best distance VA chart for pts with very poor acuity or pts with eccentric viewing?

Feinbloom distance chart

List the advantages of the Feinbloom distance VA chart (8)

1. Flip chart is inexpensive and portable
2. 10 ft acuity range (10/10 to 10/700)
3. Can vary test distance and record accurately
4. More sensitive at lower levels of vision
5. Provides psychological advantage - many low vision patients can identify some numbers before reaching their visual limit
6. Limits contour interaction effects
7. Allows for evaluation of eccentric viewing, scanning abilities, and motivation
8. Pediatric version with symbols instead of numbers is available

Feinbloom distance VA charts limit ____________ effects, which are increased when more symbols are used per line at smaller acuity levels

Contour interaction

How do you test someone's vision using the Feinbloom distance VA chart?

1. Present the largest letter at 10 ft
2. Encourage head/eye movement which might facilitate Eccentric Viewing (except if testing for legal blindness, disability, or license vision requirements)
3. If the patient identified the largest symbol, turn the pages to the smaller numbers until the patient can no longer respond
4. If the patient cannot identify the largest symbol at 10 ft, then move to 5 ft (then 3 ft, then 2 ft, then 1 ft) until the largest symbol is identified

The distance (in feet) at which the smallest symbol is identified is the numerator for your acuity recording. The smallest letter size identified is the denominator. This value is on the bottom of the chart and is measured in feet.

_________ is the LogMAR chart used most often in LV

EDTRS

What are the advantages of LogMAR?

1. Logarithmic/proportional change in letter size and spacing
2. Optotypes of equal legibility/difficulty
3. Contour interaction effects equal throughout

Each letter of the logMAR chart is equal to ______ log units

0.02

Each line of the logMAR chart is separated by _____ log units

0.1

The visual angle ______ every 3 lines of the logMAR chart

Doubles (or halves depending on which direction you go)

A pt reads 20/200 on the logMAR chart and then moves half-way closer (to 10 ft) from the chart. What is their visual acuity now?

20/100

Pt reads 10/100 line uncorrected and 3 lines better corrected, acuity will be _______

10/50 (halved)

What is MAR?

Indicates angular size of critical detail with just-resolvable optotype (inverse of acuity)

General rule of thumb: distance VA should be recorded in _______ (regardless of chart used) and near acuity should be recorded in __________

Feet; metric notation

List the features of a Bailey-Lovie chart

1. 5 letters per line
2. Non-serifed, uppercase font
3. Separation between letters is equal to the letter size
4. High and low contrast options

List the features of a EDTRS chart

1. 5 letters per line
2. Space between letters is equal to letter size on that line
3. Back-illuminated for equal contrast and luminance (so consider the glare for some patients)
4. Calibrated for 4m, 2m, 1m, but for easy conversion can use 3M chart and test at 10ft (snellen equivalent listed on chart)

What is the conversion of EDTRS to snellen when tested at 4m, 2m, and 1m

4m = multiply top/bottom by 5x
2m = multiply top/bottom by 10x
1m = multiply top/bottom by 20x

How do you test near acuity using ETDRS chart?

Use adjacent illumination source. Test OD, OS, OU. Begin with isolated high contrast letters or numbers. When smallest line is identified, retest with continuous text material. Observe the patient and listen for increase in speed and drop-off in speed

What things must be included when recording near visual acuity with ETDRS?

1. Record in METRIC notation
2. Name of chart used
3. Type of symbols identified
4. Contrast quality
5. Quality of illumination (increased, decreased, average)
6. Eccentric viewing
7. Facility

1M = ________ (snellen acuity) = ___________ (pt print) = __________ (Jaeger) = ________mm = Average _____ print

1M = 20/50 = 9 point print = J5 = 1.45mm = average newspaper print

Your patient reads 2M print size at a test distance of 20cm. How would you record this?

0.20/2M

Your patient reads 1.25M print size at a test distance of 40cm. How would you record this?

0.40/1.25M

In room light your patient holds the continuous text near card at 15cm and reads the 1M line without correction. How would you properly document this in your chart?

NVAsc: 0.15/1M high contrast continuous text, average illumination

How can you modify color vision tests for pts who are visually impaired?

Jumbo D15 or Ishihara plates at closer working distance

How can you modify testing for ocular alignment in visually impaired patients?

CT should be performed with a threshold target for the poorer eye if vision is good enough, or do kappa/Hirschberg test instead

How can you modify stereopsis testing for patients with visual impairments?

Test at a closer distance

What do the ishihara test plates test for specifically?

Detect congenital color vision defects and do not allow for screening of Tritan (blue-yellow defects)

VA usually must be _________ or better in each eye for binocularity to be present

20/100

When should pupil testing be done and why?

Should be done after all optical device testing is completed.

Some LV patients (ex. those with rod-cone dystrophy) can remain bleached for 30 min

What are the reasons for testing contrast sensitivity?

1. Important for functional assessment
2. Allows for explanation of functional impairment when acuity doesn't seem to correlate
3. Starting point for filter selection
4. Differences in monocular and binocular can give indication on binocular vision potential with LV devices

Acuity testing is ________ whereas contrast testing is ___________

Quantitative; qualitative

The Pelli-Robson CS chart is tested at a distance of _____m

1m

Which CS chart has letters grouped into triplets with 2 groups of letters per line?

Pelli-robson

How do you test using the Pelli-Robson chart?

Ask patient to start at top left and read letters. Strike each incorrectly read letter. Stop when the patient misses 2/3 of a triplet.

A score of ______ on the Pelli-Robson chart indicates normal CS, while a score below _____ suggests a sensitivity impairment

2.0; 1.5

How much does each triplet decrease in CS log units in Pelli-Robson chart?

0.15 log units

Which CS chart decreases in contrast by 0.04 log units each letter?

MARs chart

How do you measure MARs CS chart?

Stop when patient misses 2 consecutive letters. Record logCS value of final correct letter subtracting 0.04 for each error

How many degrees of the VF does the Amsler grid test?

Central 10 degrees of vision from fixation in all directions (20 degrees in diameter)

The Amsler grid is made up of 20 horizontal and vertical rows of ____mm white squares

5mm

When testing at 30cm each 5mm square of the Amsler grid subtends ____degrees on VF

1 degrees

What is mild metamorphopsia?

Metamorphopsia less than 6 degrees in diameter not affecting fixation

What is moderate metamorphopsia?

Larger than 6 degrees and/or involving fixation (defined clinically as central metamorphopsia)

What is a minimum scotoma?

Scotomas less than 6 degrees in diameter not affecting fixation

What is a significant scotoma?

Scotomas larger than 6 degrees or any scotoma involving fixation regardless of size

When/why should glare testing be done?

Should be done on every patient AFTER all other functional testing. This helps differentiate discomfort glare vs. disability glare

How do you test for glare (without the BAT)?

Begin with high contrast distance acuity chart above threshold acuity. Introduce source of glare (penlight) from an angle into the visual field close to line of fixation. Observe patient's physical reaction and letter identification speed. Repeat with continuous text at near. If decreased, introduce filters.

If using the BAT, if VA is reduced _______ or more lines, glare is interfering with visual function under bright light conditions suggesting the need for filters, typoscopes, hats, etc.

2 or more lines

Why is the BAT only used when necessary in the LV clinic?

Due to the longer recovery time

What is important to consider if fitting pt with filters?

Indoor and outdoor settings, may get 2 very different preferences