Lecture 7 and 8 specialized visual acuity

for a snellen chart, where do we start reading?

at the top or the lowest line the patient can see

limitations of snellen VA methods (6)

too few optotypes for worse snellen VA, poor geometric proportions, different spacing between letters, letters not equally legible, projectors, high (poor) test/re-test variability

why is poor geometric proportions a limitaition in the snellen VA chart?

Validity of test changes with VA level

why is different spacing between letters a limitaition in the snellen VA chart?

because letters have varied crowding

why do we use the snellen chart? (5)

convenient, efficient, inexpensive, consistent (widely used), logMAR not practical

what is the distance when reading near card for snellen VA?

40 cm

with infants and toddlers, what acuity testing method should you use?

preferential looking or fix follow maintain

with toddlers, pre-k and kindergarten children, what acuity testing method should you use?

number, pictures, or symbols optotypes, or matching

with older child, what acuity testing method should you use?

snellen acuity method

what cards do we use for preferential looking with infants and toddlers?

Teller acuity cards (TAC) and Cardiff test

how does the Teller acuity cards work?

it relies on natural tendency of infants to look at patterned details with increasing spatial frequency over plane surfaces

how does the Cardiff test work?

it relies on natural tendency of infants to look at detailed picture over a blank space

what standardized charts are use for young child (toddlers, kindergarten)? (5)

LEA symbols, Broken Wheel, Patti Pics, Kay, Allen Figures

for vision screenings, which charts should we use?

Lea symbols or HOTV

why is there a rectangle around the symbols in Lea symbols chart?

to induce spatial crowding so that resolution is impaired by neighbouring objects

what is the standardized chart to use for toddlers and young children in MA?

Massachusetts Visual Acuity Test (MassVAT) with Lea Symbols

what is the standardized chart to use for older child in MA?

HOTV/Sloan letters

what are the special properties of the MassVAT card? (4)

equal blur of optotypes, LogMAR progression, 5 symbols per line, and crowing bar

why is the crowding bar important in the MassVAT card with infants or toddlers?

to detect for amblyopia

What should be the distance from the child if using a Lea symbol chart?

10 feet

What is the critical line when testing toddlers or infants?

the only line that we need to test based on a toddler or infant’s age

for children 3 years or younger, which line are expected to read with the Lea symbols chart? in both 20 feet (snellen) and 10 feet

20/50 (10/25 line)

for children that are 4 years old, which line are expected to read with the Lea symbols chart? in both 20 feet (snellen) and 10 feet

20/40 (10/20 line)

for children that are 5 years old, which line are expected to read with the Lea symbols chart? in both 20 feet (snellen) and 10 feet

20/32 (10/16 line)

what should be done first with a child age 3-5 before conducting a VA test with the Lea symbols?

identify each picture binocularly at 2-3 feet

what is the purpose of identify each picture binocularly at 2-3 feet with the Lea symbols chart for young children?

to know what the child chooses to call and go with it

what is the passing requirement with the Lea symbols chart for children 3-5 years old?

4 out of 5 shapes identified correctly on critical line with each eye

what charts are used for low vision patients? (2)

Feinbloom chart or ETDRS (Early Treatment of Diabetic Retinopathy Study) charts

what are the main advantages for Feinbloom and ETDRS charts? (3)

movable, patients allowed to move head to find best viewing, positions and conditions made optimal for patients

the Feinbloom chart is calibrated at how many feet?

10 feet

what units should you use to record for Feinbloom chart?

feet or M units (mostly feet)

what is the range for the Feinbloom chart and what is the snellen equivalent?

10/700 to 10/10, Snellen equivalent: 20/1400 to 20/20

what is the optotype for Feinbloom chart?

numbers

what is the disadvantages for Feinbloom? (3)

not log scale, different number of optotypes at each acuity level

If a patient cannot see the Feinbloom chart at 10 ft, how close up can they get?

1 foot

When do we stop with a Feinbloom chart?

whem more than half of the line is wrong

what is the unit used to record with the ETDRS chart for low vision patients?

M units (M notation)

how far should the chart be set for ETDRS chart when recording with M units? (3 possible distances)

4m, 2m, 1m

for research, what distance and what method of recording are used with the ETDRS chart?

4m, logMAR testing method and recording

why is M units used for low vision patients? (2)

easy to convert to snellen notation, practical

why do low vision patients use near reading cards?

cards with isolated letters measure VA and reading cards are better judge of visual function in the real world

what optotype is used for the ETDRS chart?

sloan optotypes

for the ETDRS chart, the space between letters is proportional to what

to the size of the letter

how much is each letter worth in the ETDRS chart?

0.02 log units

how much does each line differ from the previous line in the ETDRS chart?

0.10 log units

when should we stop recording for the ETDRS chart?

4 out of 5 letters incorrect in a line

when should we keep going for the ETDRS chart?

if get 2 correct in a line

when should patients start reading for the ETDRS chart?

every letter from the top line down

how many total lines are there in the ETDRS chart?

14

how many total letters are there in the ETDRS chart?

70

what is the logMAR for 20/20 snellen VA?

0.00

if logMAR is positive, is vision better or worse than normal?

worse

if logMAR is negative, is vision better or worse than normal?

better

for the ETDRS chart/logMAR system, how much difference (number or letters) between the eye is considered significant?

0.16, 8 letters

for the ETDRS chart/logMAR system, a difference or reduction of how much (numbers and letters) from one exam to anpther is considered significant?

0.10, 5 letters, 1 line

what is the Landolt C chart?

chart with ring with 1 minarc gap

for dynamic visual acuity with VOR, a loss of how many lines is significant for possible vestibular dysfunction?

3 lines or more

what is the optokinetic drum used for?

to induce nystagmus

what is an electrorectinogram (ERG)?

it measures electrical response of rods and cones (retinal cells)

what is an electrooculography (EOG)?

it measures corneal-retinal standing potential (function of epithelium)

what is the Visual Evoked Potential (VEP) or Visual Evoked Response (VER)?

measurement of electrical signal at the scalp with probes over occipital cortex

what does the Visual Evoked Potential (VEP) measure?

responses to light stimulus

why is Visual Evoked Potential (VEP) used?

it is an objective measurement of acuity or vision

who do we use Visual Evoked Potential (VEP) on?

amblyopia patients or patients with cortical or psychological loss

name all the methods used to measure VA (6)

Snellen fraction, Snellen decimal, Minutes of Arc, logMAR, M units, cycles per degree

what does cycles per degree measure?

spatial frequency

if patient cannot see the large E on a Snellen chart, what other methods should you use? (5)

count fingers, hand motion, light projection, light perception, no light perception

if patients can count fingers, which chart should they use

Feinbloom chart

is counting fingers tested monocularly or binocularly?

monocularly

how far should you stand away from the patients for the counting fingers method?

1 foot

when should you record the distance with the counting fingers method?

when patients can no longer reliably name number of fingers present, move forward again until response is reliable

is hand motion tested monocularly or binocularly?

monocularly

how should you test with the hand motion method?

wave hand in front of patient at 1 foot and ask if they can see, then move backwards

when should you stop testing with the hand motion method?

when patients can no longer detect moving hand, move forwards again until motion is re-detected

is the light projection (LProj) method tested monocularly or binocularly?

monocularly

what equipment and how far should you be standing from the patient with the light projection method?

hold transilluminator or penlight about 20 inches from patient

where should you shine the light on patient for the light projection method?

on four quadrants in the visual field

what are the four quadrants of the visual field with the Light Projection method?

Superior-temporal, inferior-temporal, superior-nasal, inferior-nasal

is the light perception (LP) method tested monocularly or binocularly?

monocularly

what equipment and how far should you be standing from the patient with the light perception method?

hold transilluminator or penlight about 1 to 2 feet from patient

what are possible explanations for reduced VA? (3)

due to provider, test/equipment or patient

what are possible reasons that VA is reduced due to patients?

optical or visual, pathological, psychological or psychosocial reasons

what are possible reasons that VA is reduced due to the provider? (6)

knowledge of what test to used, whether same test was used previously, appropriate instructions given, language barrier, patients peeking out, patients memorizing letters

what are possible reasons that VA is reduced due to the test/equipment? (3)

limitations of the device, test set up such as calibration, design of the chart (if correct optotype or chart was used)

what is Differential diagnosis (DDx)?

distinguishing between a disease or condition that presents with similar signs and/or symptoms

what are possible optical or visual reasons for reduced VA due to patients? (4)

Refractive error (retinal defocus), amblyopia, slow light/dark adaptation, pupil size

what is emmetropia?

absence of refractive error

what is myopia?

nearsightedness

what is hyperopia?

farsightedness

what is ametropia?

presence of refractive error (retinal defocus)

for emmetropia, where are images of distant objects formed?

at the retina

for ametropia, where happens to images of distant objects?

they are not focused on the retina

for myopia, where are images of distant objects formed / where are the light ray focused?

in front of the retina

for myopia, what lens do we need to correct it?

minus lenses

for hyperopia, where are images of distant objects formed / where are the light ray focused?

behind the retina

for hyperopia, what lens do we need to correct it?

plus lenses

what is astigmatism?

different powers between two main major meridians of the eye resulting in two retinal foci

what do we need to correct astigmatism?

cylinder (toric) lenses

what is presbyopia?

ability to focus (accommodate) due to crystalline lens decreasing with age

how should we correct presbyopia?

corrected with plus (+) lenses over (or in addition to) the distance correction