Measurement of vision and visual acuity

Question 1

what is vision?

Answer 1

.the eyes ability to discriminate or resolve spatially organised detail.
.measure of smallest angle can be resolved

Question 2

what are the two types of vision?

Answer 2

peripheral and central

Question 3

what is the standard observation of vision?

Answer 3

6/6

Question 4

why do we measure vision?

Answer 4

.allows us to quantify what people can see and cant
.early detection and diagnosis of disease
.assess benefits of optical devices
.set base line to monitor changes

Question 5

what are the reasons for reduced vision/visual acuity?

Answer 5

.un corrected refractive error

.eye disease

Question 6

what is the difference between vision/visual acuity?

Answer 6

vision- is what we see without our spectacles or contact lens
visual acuity- ability to distinguish between two different points with spectacles or contact lens

Question 7

what commonly used charts do we use to measure vision/visual acuity?

Answer 7

.snellen chart

.LOGMAR chart

Question 8

what are the snellen numbers?

Answer 8

numbers relate to the distance that this letter would create an angle of 5 at the eye

Question 9

what does 6/12 mean in the snellen chart?

Answer 9

6- is how many m away the chart is

12- refers to the line read on snellen chart

Question 10

what is MAR?

Answer 10

minimum angle of resolution

which is the angle created by a limb of a letter that can be seen

Question 11

how do you write down MAR?

Answer 11

6/12

MAR is 2

Question 12

what are the advantages of snellen chart?

Answer 12

.cheap and readily available

.can be used to obtain baseline visual acuity measurement

Question 13

what are the disadvantages of snellen chart?

Answer 13

.insufficient acuity levels for accurately testing low vision patients
.non-uniformity in letter size progression
.inability to easily score letter by letter acuity

Question 14

how to measure vision/visual acuity for child under 5?

Answer 14

1. place snellen chart at 6m
2. room lighting ON
3. for VA : ask patient to wear their distance spectacle
4. occlude left eye
5. ask what is the smallest line that you can read
6. repeat for left eye by covering right eye

Question 15

how many letters are there in log MAR chart?

Answer 15

there are five letter per line
we can score 0.02 logMAR per letter
acuity levels on this chart progress in step of 0.1

Question 16

how to record vision/visual acuity in logMAR chart?

Answer 16

.for each error that is made add 0.02 to the vision score
e.g. if a patient reads all of line 0.30 except one letter their score is 0.32
.for each letter that is correct subtract 0.02 to vision score
e.g. if patient reads 0.00 line and 2 letters of next line their score is -0.04
e.g. if patient reads the 0.30 line and 2 letters on next score is 0.26

Question 17

what are the advantages of logMAR chart?

Answer 17

.equal number of letters in every line

.more popular in research setting

Question 18

what are the disadvantages of logMAR chart?

Answer 18

.large size

.cost

Question 19

when is it important to use pinhole?

Answer 19

if visual acuity is less than 6/9 or logMAR 0.20

assess through pinhole

Question 20

how does pinhole work?

Answer 20

pinhole helps your eyes focus by shielding your vision from indirect rays of light

Question 21

what to do if vision is less than 6/60?

Answer 21

.test at 2m then 1m
.if patient cant see at 1m ask how many fingers your holding
.if patient still cant see try hand movement then check if they can determine light

Question 22

how to measure near vision?

Answer 22

.use specifically designed reading card
.each size is numbered
.test each eye separately make sure the lighting is good
.record smallest print read
e.g. R.N8 at 25cm

Question 23

what does the N notation mean?

Answer 23

indicates measurement is near

N is the point size of the print

Question 24

what other test can be used?

Answer 24

illiterate E - where the E is facing

landolt c

Question 25

what is contrast sensitivity?

Answer 25

.ability to distinguish object from background

.smallest difference in luminance observer can detect

Question 26

how is contract sensitivity measured?

Answer 26

measured with sine gratings

expressed as %

Question 27

what is the pelli-robson letter chart?

Answer 27

pelli-robson score of 2 indicates contrast sensitivity is 100%
less than 1.5 visual impairment
less than 1.0 visual disability

Question 28

why do we measure contrast sensitivity?

Answer 28

• maybe used to indicate everyday tasks patient has trouble with
• evaluation of function particularly for patients with LOW VISION
• correlates better than VA with the performance on daily living tasks such as reading and mobility

Question 29

What is the sphere?

Answer 29

+VE for hypermetropia

-VE for myopia

Question 30

What is the cyl and axis?

Answer 30

amount and direction of astigmatism