VISUAL ACUITY
TESTING
Prelims-4
S. A. Samillan, OD.
VISUAL ACUITY
LogMAR (Bailey-Lovie Chart)
• Founded by Bailey and Lovie
• Logarithm of Minimum Angle of Resolution
• The character size change is a logarithmic
progression of letter sizes
• Inverted triangle shape
• Used when precision is required in the
examination of VA as compared to other
acuity charts (e.g. Snellen chart)
• Usually used in research studies
• Each line comprises the same number of
letters (5)
Bailey and Lovie designed their logMAR- British letters
ETDRS used Sloan Letters
Sloan- C D H K N O R S V Z (5x5)
British- D E F H N P R U V Z (5x4)
Ferris and colleagues made a chart for the Early Treatment of Diabetic Retinopathy Study (ETDRS)
using Sloan letters rather than the British letters that were used in the original version of the BaileyLevie chart.
However, the EDTRS charts with the Sloan optotypes have been so commonly used in research
studies around the world that this chart and its optotypes have effectively become the "gold standard"
to which alternatives should be compared.
LogMAR (Bailey-Lovie Chart)
• Each letter has a score of 0.02
log units
• The progression of optotype
heights is geometric,
decreasing in 0.1 log unit
increments.
• Each line contains 5 optotypes
• Total score of each line is 0.10
log units (0.02 x 5= 0.10)
LogMAR Recording
Method 1
If patient A reads the 3rd line
completely and 2 letters of the next line
LogMAR score of 4th line is 0.7
LogMAR score:
Completely read line - (# of letter read
on the next line x 0.02)
=0.8 - (2 x 0.02)
=0.8 - (0.04)
=0.76 logMAR
LogMAR Recording
Method 2
If patient A reads the 3rd line
completely and 2 letters of the next line
LogMAR score of 4th line is 0.7
LogMAR score:
LogMAR of partially read line + (# of
letter not read x 0.02)
=0.7 + (3 x 0.02)
=0.7 + (0.06)
=0.76 logMAR
• UNAIDED/ NAKED VA: Measured without any spectacles or contact lenses (i.e., with “lenses
off”). This becomes a benchmark against which the benefits of using a refractive correction may
be referred.
• HABITUAL VA: Measured under the refractive conditions that the patient habitually uses when
performing distance vision tasks of daily life. It is not uncommon for patients to be wearing
optical corrections that are distinctly inappropriate (old correction prescribed many years ago or
spectacles obtained at a flea market, from a relative, or OTC)
• PINHOLE VA: Measured using pinhole apertures (1.0-1.5mm) placed before the patient’s eye to
determine whether a reduced VA is a result of optical defects. The pinhole increases the depth
of focus so that the blur created by optical irregularities or refractive error becomes reduced;
consequently, VA improves. However, no significant impact on conditions such as amblyopia or
some retinal disorders
Visual Acuity Procedure
Equipment:
-Distance Visual acuity chart
-Near Visual acuity chart (ex. N series, reduced Snellen
chart)
-Occluder
-Lamp
Visual Acuity Procedure
Set-up:
-Acuity should be measured without correction first, then
habitual
-The patient holds the occluder
-Room illumination should maximize contrast on the visual
acuity chart used. (Higher illumination is needed or printed
charts and dimmer illumination is needed or projected or
computerized charts.)
Step-by-step Procedure:
1. Always observe the patient, not the chart. The examiner should
memorize the letters on the chart so he is able to observe the patient
throughout the procedure.
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 smaller line,
even if he has to guess. Stop the patient when more than half the letters
on a line have been missed.
5. Have the patient cover the right eye and repeat steps 2, 3, and 4.
Subnormal VA
6. Sometimes the patient will be unable to read even the largest letter
on the chart. Have the patient walk toward the chart until he can just
make out the largest letter (usually a 20/400 E). Note the distance at
which this occurs (MODIFIED DISTANCE)
Subnormal VA
7. If the patient cannot see the letters at any distance, initiate the following testing, stopping at the level
at which the patient can accurately respond.
a. Counting fingers (CF): At a distance o approximately 1 ft, expose a selected number of fingers.
Ask the patient to tell you how many fingers you are holding up. Increase the distance from the
patient until his responses are no longer accurate. Move back toward the patient until he can
reliably report the number of fingers presented. Counting fingers at 2 ft is equivalent to Snellen
acuity of 20/2000.
b. Hand motion (HM): Using your moving hand as the target, ask the patient if he can see the hand
moving. Begin at approximately 1 ft and increase the distance until the patient reports he no longer
detects the motion. Then move back toward the patient until he detects the motion once again.
c. Light projection (LProj): Holding a penlight or transilluminator at a distance of approximately 20
inches rom the patient, position the light in different areas o the patient’s visual eld. Each time ask the
patient to point at the light and note the areas of the field in which the patient has vision.
d. Light perception(LP): Direct a penlight or transilluminator at the patient and ask if he can see the
light.
NEAR VISUAL ACUITY TESTING
8. Now test near visual acuity. Repeat steps 1 through 5 at
near using the following setup:
a. Provide high illumination on the near point card. The
light source should be either above or slightly behind the
patient. Care should be taken that the light is not directed at
the patient’s eyes.
b. Instruct the patient to hold the card at the appropriate
distance or which the card is calibrated, 16 in (40 cm) or a
reduced Snellen Acuity Card.