test types used in optometry
DESCRIPTION
about different chart used to test visual acuityTRANSCRIPT
Visual acuity chart for infants
Optokinetic nystagmus drum Lea paddle.
Visual acuity chart for pre- school children
Landot ‘c’ Tumbling ‘E’ Sheridan Gardiner. Stycar visual acuity test . Lea symbol . Kay picture test. Cardiff chart . Allen card test .
Visual acuity chart for school going childrens /adults
Snellen chart LogMar chart
These chart are used only to test distance vision and not used for testing near vision .
For infants
Opto kinetic Nystagmus Drum[OKN]
It is a gross test and is based on preferential looking principle .
It consists of a drum which has alternate black and white strips .
The drum is passed through patient field of vision by rotating the drum and the eye movement of the patient is seen .
Optokinetic Nystagmus Drum
Optokinetic Nystagmus Drum It is done with both eye open . The child makes nystagmus
movements if the stripes are seen as the drum is rotated for these the patient should fixate the eye on the drum .
Black and white stripes are used because it gives contrast and suppose once the patient has fixated his eye on one black strip .
Optokinetic Nystagmus Drum Than immediately at a certain
standard distance he see second black strip and in these way constant eye movements are seen .
It is necessary to attach the childs attention towards the drum .
It is done at a close distance . The vision we get is only the
approximate value and we cant relay on it .
Lea paddle
Lea paddle
It is based on preferential looking and snellen principle .
The chart is placed at a distance of 1m from the patient .
It is usually used for the age group of 3 to 9 mths .
There are cards available of various thickness of lines .
At a time two cards are held infront of the patient .The blank infront and the one with lines ie, held behind it .
Then immediately the second card is flipped out and we keep on changing the positions.
The patient should appreciate the card with lines .
The test is done at same eye level and the eye movement of patient is seen .
It is necessary to fixate the patients attention .
The thickness of lines varies from 0.25 to 8 cpcm is the measuring unit .
Cpcm stands for cycle per centimeter .
It give only approximate value and so we can’t.
Landolt ‘c’ chart
For preschool children
Landolt ‘c’ chart It is usually used for age group of 3
to 6 yrs who cannot recognize letters .
The chart consist of broken circles with each broken ring subtending an angle of 5 min at nodal point .
The chart is shown to the patient at a distance of 6meter .
The patient has to identify the part from where the ring is broken by pointing the direction up ,down ,left,right by finger .
Landolt ‘c’-chart based on log MAR principle are also available .
They consist of 5 rings per line and the size goes on decreasing as we move a head .
Tumbling ‘E’ chart
Tumbling ‘E’ chart
It is similar to landolt ‘c’ except that it consist of letter ‘E’
The test is again done at a distance of 6 meter.
The child is given wooden or plastic letter E and is asked to point the direction of E as instructed by the examiner .
Or the patient is directly told to point the finger in the direction up down ,left, right as shown in the main chart .
SHERIDAN GARDINER TEST
SHERIDAN GARDINER TEST
It is used for the age group of 2-5yrs .
It is done at 6 meter and if child can’t read 6/60 we can do it at 3 meter .
The chart is available in the form of spiral booklet .
The main chart consists of letters HOTV of different size .
These letters are arranged may be in circular form to give proper orientation so that child can identify them properly .
The child is given a key card and is asked to match with the letter as shown in the main card.
The four letter ‘HOTV’ are only used as they are considered as standard letters for measuring visual acuity .
More over it is found that these letters are more child friendly .
STYCAR VISUAL ACUITY TEST
It is done at a distance of 10 to 20 foot distance .
The main chart consist of pictures of eating items or toys .
The child is given a key card and is asked to match with the pictures as shown in the main chart by the examiner .
LEA SYMBOL CHART
LEA SYMBOL CHART
LEA SYMBOL CHART
It is done at a distance of 3meter. The chart is available in simple as
well as spiral booklet form . The main card consist of 5 symbols
with one symbols in centre and the rest 4 are located in circular form around the central symbol .
These arrangement is done in particular to develop both crowding and confusing phenomenon for the child difficulty .
The examiner shows normally centre symbol but at the same time he can ask for other symbols too.
The patient is given a key card to point out the symbol .
These symbols are fixed and are kept a standard like apple ,house ,circle ,square etc ..
The size of pictures goes on decreasing from 3/9.5 to 3/2.4 and there are four cards for each size .
KAY PICTURE TEST
KAY PICTURE TEST
It is used for children of 2-3 yrs . The test is done at distance of 6 meter . It is based on snellen principle . The chart is in the form of spiral booklets . Each page has a single picture . The size goes on decreasing from 6/60 to
6/6 with each size having 3 cards. Again the patient is given a key card and
is asked to match with the picture as shown in the main chart .
The picture are set up as standard like house ,train ,shoe etc
CARDIFF TEST CHART
CARDIFF TEST CHART
It is done at a distance of 1 meter and if patient can’t appreciate than the chart workup can be done at 1/2meter also.
The chart consist of a single picture object .
The patient is shown the first object and than the second card having the same object but at different position is shown or the same first card is rotated and shown to the patient .
The test is done at same eye level and the patients eye movement is seen .
It is a gross test and based on preferential looking .
It is the most common chart used for screening , visual acuity for pediatric patient .
The charts are changed fast so that patients eye movement can be seen.
The pictures are of fish, house ,boat ,duck etc…
Another advantage of these chart is that the conversions in foot ,metre, decimal and logMAR for 1meter and ½ meter are given itself behind the card so that vision can be recorded accurately.
ALLEN CARD TEST/ALLEN PRESCHOOL VISION TEST It is done at a distance of 3 meter . It consist of a set of seven card with each
card containing a single picture . It is usually used for 2 yrs old child and older
. The child is first shown cards at close range
with both eyes open and is asked to name each picture .
Then one eye of patient is occluded the examiner shuffles the cards and presents them individually over greater distances.
The picture are of familiar objects so that the child can name them properly .
FOR SCHOOL GOING CHILDREN/ADULTS
SNELLEN CHART It was introduced in 1862 by snellen . The chart consist of seven row namely
6/60,6/36,6/24,6/18,6/12,6/9,6/6. and sometimes 6/5 ,6/4 also will be there.
These is the most common chart used to measure the vision.
The patient is told to occlude one eye and is asked to read the chart from top until the last line or letter that he can read and the vision is recored as vn OD ,OS .,
It consist of letters of varying size . It is done at 6 meter and we can take
it as 3meter also.
DISADVANTAGE
It has 100% contrast level same all over the chart .
If the patients visual acuity is in between 6/60 and 6/36 or 6/36 and 6/24 than it cannot be measured by these chart .
It cannot be used for low vision patients.
LOGMAR CHART
LOGMAR CHART
It was given by Bailey and lovie in 1916 and so it also called as Bailey lovie chart.
The production was done by light house .
The measurements are based on logarithm principle .
Bailey Lovie also gave another logMAR chart which had decreasing contrast as we move a head to measure the contrast level.
Advantage of logMAR chart over snellen’s chart It is used to find minimum visual
acuity . It can be used for low vision patients. The rate of progression is slow .Each
line consists of 5 letters . If the patient cant read the side
letters ,this will give the motivation level to the patient .
It is measured at a distance of 3 meter the chart work up can also be done at a distance 1/2 meter .
The spacing between two lines is equal to the width of the letter presented in earlier line and the spacing between two letter symbol present in the same line ,it gives accurate readings.
Disadvantages
It is very costly. Care should be taken .
Thanks to all