visual acuity. PPT Ramji pandey consultant optometrist

PPT

1. Visual acuity assessment
Ramji pandey

2. VISUAL ACUITY
It is the power of the eye by which objects are distinguished
from the other.
It is also a measure of the smallest retinal image which can be
appreciated regarding it’s shape and size.
Two distinct points can be visible as separate, when the minimal
angle subtended by them at the nodal point of the eye is 1
minute.

3. IMPORTANCE OF VISUAL ACUITY
•IT GIVES AN IDEA ABOUT THE INTEGRITY OF THE VISUAL
SYSTEM
•HELP IN DIGNOSIS AND MONITORING OF EYE DISEASES
•VISUAL ACUITY CRITERIA IS USED BY SOME LICENSING
AUTHORITIES AND EMPLOYERS AS ELIGIVILITY CRITERIA
FOR CERTAIN OCCUPATIONS(AIRLINE,PILOTE,POLICE,

4. VISUAL ACUTY & VARIATION
CHARTS
pinhole
IMPROVING NOT IMPROVING

5. IMPROVING
REFRECTIVE
ERROR

6. NOT IMPROVING
AMLYOPIA MELINGRING
PATHALOGICAL
DISEASE

7. TYPES OF VISUAL
ACUITY
RECOGNITION
ACUITY
( Ex-lea symbols,
Tumbling E,
landolt C,
Allen symbols )
RESOLUTION
ACUITY
( Teller acuity
Cards, Optokinetic
Nystagmus,
visual evoked
Potential )
DECTECTION
ACUITY
( Light perception,
Light projection
Testing )

8. INTERPRETATION OF SNELLENS FRACTION
•Numerator /denomenator
•Numerator is the distance at which
chart is kept from the patient
•Denomenator is the distance at
which letter can be read by a
person having normal V.A.

9. CALCULATION OF LETTER SIZES IN
SNELLEN’S CHART
•Tan 0 = X/6 = height of letter/6
•x=6(tano)
•X=6(0.00291)
•X=0.001746 meters
•X=1.746 mm
•Height of the letter should be 5 times the gap
• =1.746x5=8.73 mm
•The width of the letter should be 4 times of gap
•=1.746x4=6.984 mm

10. Snellens chart is used at 6 mts only
because:
Distance less than 6 mts stimulate accommodation.
Distance beyond 6 mts make resolution,legibility
of the text difficult.
Advantages of Snellens chart:
The chart is familiar
Inexpensive
Quick
Easy to use and interpret

11. Disadvantages of Snellen chart
Snellen chart have one 6/60 letter and an increasing number of letters
as We go down the lines.This is mainly done to keep the size of the
chart to the smallest size possible.
Patients with poor acuity are required to read LESS no. of letters than
those with good V.A.
The letters on the lower lines are more crowded than those on the top
of the chart.
Due to small number of large letters, this chart is not very useful in
assessing V.A. in low vision patient.

12. Visual angle
•Visual angle is the angle subtended at the nodle point of the
eye by the physical dimention of an object in the visual field.

13. DIAGRAM OF VISUAL ANGLE

14. VARIOUS TYPES OF VISUAL ACUTY
CHART
Tumbling E-test:it consists of different sizes of E in one of the four
positions.
Isolated hand-figure test: Sjogren has replaced the E with the
isolated figure of a hand.
Sheridan-Gardiner HOTV test- This is an initiative test,used to
test vision in the age group of 2-5 years
Pictorial vision charts: Allen preschool chart.
Broken wheel test: A pair of cars in progressively smaller size,
one of which has a wheel cut across, like Landolt C (broken wheel)
is shown to the child and he is asked to indentify the one with the
broken wheel

15. Boek candy bead test: The child is asked to
match beads at 40 cm. snellen’s visual acuity
equivalent of 20/200 is estimated by this method.
Light home picture cards: A chart containing
an apple, house and umbrella, arranged in
snellen’s equivalent of 20/200 to 20/10 is used
and the child is asked to indentify the pictures
along the lines. The test is carried out at 10 feet.

16. VISION TESTS IN 2- 3 YEARS
Dot visual acuity test: child is shown an illuminated
box with dots of different sizes printed on it. The
smallest dot identified denotes the visual acuity
of the child.
Coin test: In this test the child is asked to indentify
the two face of coins of different sizes held at
different distances

17. Measurment of V.A. in
infants(Age<2 Yrs)
•T.A.C.-(Teller acuity cards) are large photographic plates with
line gratings printed at one end.
•The examiner looks through a central pinhole to
determine the baby’s direction og gaze.

19. OPTOKINETIC NYSTAGMUS DRUM
•Used any regularly striped object.
•Stripes are passed slowly and steadily in front of the baby
while the examiner
•observes the movement of the baby’s eyes.
•Horizontal OKN should be present before 3 months of age.
•Vertical OKN is used older than 6 months of age.

20. O.K.N. DRUM

21. Near Acuity Test
•The test is usually performed at 14 inches with a printed ,
handheld card.
•Each eye should be tested separately
•J notation(jaeger’s notation)
•20/20 =J1
•N notation
•20/20=N5

23. Variables in Acuity
Measurements
•Decreased distance acuity in the presence of good near aacuity indicates
,patient is probably myopic.
•Near acuity is poorer than distance acuity include the following:
•Presbyopia
•High hyperopia
•Overcorrected myopia
•Small,centrally located cataracts
•Accommodative effort
•Convergence insufficiency

24. VISUAL LY EVOKED RESPONSE
•FLASH VER-
•PATTERN VER
•INDIRECT ASSESSMENT OF VISUAL ACUTY in infants
can be made by observing the various milestones in
the dovelopment of vision as follows:

25. •Blink reflex in response to sound is present since birth
•Menace reflex i.e reflex closure of the eyes on the
approach of an object usually present after the age of 5
months if vision is normal
•Test based on fixation reflex are useful in making a rough
estimate of vision in infants.

26. •These include:
•Fixation behavior test
•Binocular fixation pattern
•CSM method of rating monocular fixation