2. ◉ Visual acuity is measurement of the ability to
discriminate and recognize the smallest
differences between tow objects . This may
be thought of as the ability of the eye to see
fine detail.
◉ The ability to identify minimal separation
between tow targets
3. Visual acuity should be done on all patients
as the first procedure following the case
history.
indications
4. purpose
◉ To measure the clarity of vision or the ability
of the visual system to resolve detail. A
patient ,s visual acuity depends on the
accuracy of the retinal focus , the integrity of
the eye's neural elements ,and the
interpretive faculty of the brain
5. To assess the adequacy of spectacle
correction and as a key indicator to the ocular
health .
To assess person's fitness to drive or enter to
the some professions such as police.
what are objectives of
measuring visual acuities?
9. Projector with visual acuity slide or wall
mounted acuity chart
Occluder
lamp
Equipment
10. Set- up
◉ The patient wear his hapitual correction for
the distance being tested. When the examiner
wants to measure the patient,s VA both with
(cc) and without (sc) correction, the acuity
should be measure wihout correction first .
◉ The patient hold the occluder
◉ An acuity chart , with lines from 6/60 to 6/5
exposed, is shown
11.
12.
13.
14.
15. Step –by- step procedure
1. always observe the patient , not the chart.
2. Instruct the patient to cover his left eye and
not to squint.
3. Instruct the patient to read the smallest line
of letters he can.
4. Encourage the patient to read the letters on
the next smallest line ,even he has to guess.
stop the patient when more than half have
been missed.
16.
17. 5. Have the patient cover the right eye and
repeat the above steps.
6. Sometimes the patient will be unable to read
even the largest letter on chart in this event
the patient walk towards the chart until he
can read the largest letter .
7. If the patient cannot see the letter at any
distance ,initiate the following:
18. a. counting fingers
b. Hand motion (HM)
c. Light projection(L Proj)
d. Light perception (LP)
19. ◉ Testing distance / distance at
which optotype would subtend 5
min of arc at retina
Snellen fraction
