Visual Assessment 5% Flashcards
Visual Acuity opto types
The normal human eye can distinguish 2 points separated by an angle of 1 arc minute
Each section of the letter E subtends 1 minute of arc
The whole letter E subtends 5 minutes of arc
All of the symbols we use to check visual acuity are term optotypes thi sis the snellen eye chart the tumble E’s, ellen picture chart and landolt broken ring test all of those are opto types, and all have in common each opto type subtends 5 arc minutes and each section subtends 1 arc minutes an arc minutes is a way to measure space it has to do with the angle the eye is viewing the opto type from theres different way to measure space in degrees in angle or in minutes of arc.
Recording VA in US measurements
20/20 -
numerator = distance in feet pt is from chart
Denominator = Distance in feet that someone with normal vision could correctly read the letters
The larger the number, the worse the vision
To report visual acuity in US measurements we use 20 foot as the numerator this is the distance in feet that the pt is from the chart, the denominator thats the bottom number is the distance in feet that someone with normal vision can stand and read the letters correctly, the larger the number the worst the vision. The snellen eye chart measures the ability to see small high contrast images.
Recording VA in metric converting feet to meters
20/15 = 20/20= 20/25= 20/30 = 20/40 = 20/50 = 20/60 = 20/80 = 20/100 = 20/200 = 20/400 =
Divide the denominator by 3 to get approx meters
1 meter = 3.28 feet
20/15 = 6/5 20/20= 6/6 20/25= 6/ 7.5 20/30 =6/9 20/40 = 6/12 20/50 = 6/15 20/60 = 6/18 20/80 = 6/24 20/100 = 6/30 20/200 = 6/60 20/400 = 6/120
To convert feet to meters
Theres approximately 3 feet per meter and the actual meter is 3.28 feet per meter. but if you can remember the 3 and 1 ratio you should be able to figure out the right answer on multiple choice test lets look at 20/15 20 is the numerator and becomes 6 in metrics 6 meter = 20 feet our denominator in US measurements us the 15 if we divide 15 by 3 we get 5 therefore 20/15 in US measurements is equivalent 6/5 because there 3.28 feet per meter and not 3 feet the 3 and 1 ratio is less accurate the higher that you go in numbers, lets look at 20/400 the 20 becomes 6 meters and you divide 400 divide by 3 you will get 133.3, and 120 is equivalent which is approximately 133.3 if your just learning using metric equivalent for a test multiple choice JCAHPO test need to remembered 3 and 1 ration if you know the approximate of 3 and 1 ration you can figure out the right answer on test look at 20/20 , 20/20 is the same as 6/6
20/40 40 is twice 20 whats twice 6 is 12 so 20/40 is equivalent to 6/12 for 20/200 , 200 is 10x 20 whats 10 x 6 is 60 therefore 20/200 is equivalent to 6/60 therefore, you can also look at ratio between the denominator and numerator to figured out what the metric equivalent as long as you remembered that your first number in metric will always be 6 meters
Low vision
If patient cant see 20/400 E have the patient move towards the chart until he can read the 20/400 E 4/400 (patient 4’ away from screen read 400 line)
if my patient has low vision and cannot see 20/400 E have the pt move towards the chart until he/she can read the 20/400 E if the patient can read from 4 feet away their vision will be 4/400 because the first number is always in distance in feet that the pt is away from the screen.
If the patient cannot distinguished the 20/400 E even from a close distance
Hold your one or two fingers up in from a distance of 5
Move 1 - 2 closer until the patient can accurately count your fingers
record as CF ( Counting fingers @ _____ )
If the patient cannot distinguished the 20/400 E even from a close distance then your going to go to the end if the room and hold fingers up 1 or 2 fingers distance about 5 feet you going to mover closer and closer to the patient about a foot or two until they can actually count your fingers you would record their vision at CF @ 5 feet if they can see your fingers at 5 feet away if you have to move closer and closer to them you would measure as count fingers at 1 foot of 2 foot if they cant count fingers at a close distance the need t check for hand motion.
If patient cannot count fingers
Move your hand side to side or up and down in front of the eye.
Am I moving my hand up and down or side to side
If he/she can accurately perceive you hand motion record as HM @ 1 feet- hand motion @ 1 feet
to determined hand motion visual acuity go to the end of the room about 5 feet from the patient move you hand up and down or side to side ask the pt i the can tell you which way your hand is moving, then your going to record the distance which you were away from the pt when they identify which way your hand was moving so record as HM(hand motion @ 2 feet) if thy cant see you hand motion at 5 feet move closer until they can see it if they detect your hand moving even from a very close distance then your going to check for light perception.
If Patient cannot accurately detect Hand Motion
Darken room
Project transilluminator from 15’’
(be sure to keep fellow eye covered)
check all 4 quadrants for LP
if patient cannot see trnsilluminator use indirect ophthalmoscope and try again
Record as LP with projection or Light perception with projection
If Patient cannot accurately detect the position of the light but can perceive the light record as LP or Light perception.
Dark in the room cover the fellow eye project transilluminator from 15’’ from all 4 quadrants thats supra nasal, infra nasal, supratemporal and intertemporal ask the patient if they can tell when theres a light and if they can tell you which quadrant the light is coming from, if they can tell you where the light is coming from and when the light appears that will be recorded as Light perception with projection, if they can only tell you there’s a light, but cant tell you where’s coming from that will be recorded as just light perception you must check all 4 quadrants because they might be light perception inly in 1 quadrant and NLP in the other quads, if the pt cant see the transilluminator get the indirect ophthalmolscope and try again you do not call them NLP unless until they cannot see the indirect ophthalmoscope light
If the patient is unable to perceive the light
Record Absent light perception
No light perception or NLP
If the pt cannot perceive the light of indirect ophthalmoscope your going to record as Absent light perception or No light perception or NLP
Checking VA of pre-verbal patients
3 months- 2 years old
Observe patients gaze
Cover each eye separately and see if patient focuses on a light ( fixate and follow)
Fixate centrally = Grossly NL
Eccentric fixation but steady=Probably < NL
Unsteady and eccentric fixation = VA probably extremely poor and eye defective.
Children should be able to follow light by age 3 months and reach for toy by 4 to 6 months.
Preverbal patients should be able to follow the light by about 3 months and reach a toy by 4 to 6 months if there3 months to 2 years old of age observe the patients gaze cover each eye separately and see if the pt follows the light as you move it if they do you record that as fixate and follow ( F& F) if they have unsteady or central fixation their vision is probably very poor and their eye maybe defective F & F is consider grossly normal VA for a child or 3 month to 2 years of age.
Checking Vision of Infants
Teller acuity cards
Infants and pre verbal
use verticle black and white stripes
Teller acuity cards are used for infants and preverbal children its a preferential vision test meaning that baby likely to look at high contrast images so its uses verticle black and white stripes on a poster board in the middle of poster board us a pin hole that the examiner can monitor the patients (grid, brid?) your going to cover each eye separately and present the large stripe down to smaller and smaller ones as the patient is observed if the examiner presents the stripes than you can assume that they saw them if they see the stripes you move to smaller and smaller , harder and harder to see the stripes until the pt no longer looks at the stripes when presented and thats how you determine visual acuity.
Evaluation of fixation in Infants
CSM= Central, steady, Maintained CSUM= Central Steady, UnMaintained CUSUM= Central Unsteady, Unmaintained UCUSUM= Uncentral, Unsteady, Unmaintained
One way to determine in infant approximately visual acuity by evaluating the patients fixation this is performed with best correction in place using a
non- accomodative target held at 40 cm this
not accomodative target is moved and the patient fixation is observed if the pt can maintained steady central fixation you would record CSM on the chart if the fixation is central and steady but cannot maintained you would record as CSUM on the chart if the fixation is central but is not steady and they are not able to maintained you would record CUSUM, if the fixation is not central, not steady and not maintained you would record UCUSUM on the chart.
Checking vision of children and illiterate patient
Allen picture chart
Preschool children age 2+ and mentally challange older children or illiterate adults
Used in school screenings
30’ denominator
Show pictures at close range with OV open the occlude one eye, present pictures while backing away
Greatest distance at which 3 picture are accurately identified in each eye is recorded
15 feet vision = 15/30
10 feet vision =10/30
Difference between eyes VA of 75 = referral to doctor for evaluation
The allen picture chart is used for preschool children mentally challenged older children illiterate adults, the pt does not have to know the alphabet we use this a lot in school screening we can use a 15 foot, 10 foot, or 30 foot denominator you show the pt pictures at a very close range with both eyes open then you occlude one eye and present the pictures then backing away the greatest distance at which 3 pictures are accurately identify in each eye is recorded if theres a difference between the two eyes visual acuity more than 5 feet thats called for a referral to doctor for evaluation for possible AMBLYOPIA
Tumbling E
Pre school children at age 2+ and illiterate adults
Point their finger or a plastic E in the direction of the E on the chart
Let patient practice so she knows how to performed test before you begin
The tumbling E is good for preschool children and illiterate adults usually point their finger in the orientation of the E that they see let the patient practice so that they know how to perform the test before you actually begin
Landolt’s Broken ring test
Illiterate and pre school children
Patient identifies where the break is
Landolts broken ring test is good for illiterate and preschool children the patient identifies where in the ring the break is, The sheridan Gardiner is a matching test this is good for young mentally challenged or adults
