SV Flashcards
Measurement of visual acuity is a component of the evaluation that allows one to quantify
the degree of high-contrast vision loss and clearly identifies the patient’s visual impairment
as it relates to the chief complaint
Visual Acuity Measurement
- Helps determine the best corrected visual acuity
- Monitor the effect of stability and progression of the treatment of a disease
- Assess eccentric viewing postures and skills, patient motivation, scanning ability
(for patients with restricted fields) - Teach basic concepts and skills (i.e., to eccentrically view) relevant to the
rehabilitation process.
Visual Acuity Measurement
Comes in the form of loose-leaf cards containing numbers ranging from 700 to 20
feet in size (designating 20/700 to 20/20 acuity if used at a distance of 20 feet) as
well as cards containing letters ranging from 600 to 60 feet in size (for 20/600 to
20/60 acuity at 20 feet). If they are used at a 10-foot testing distance, the range of
acuities available is from 10/700 (20/1400)
Feinbloom number and letter charts
Designed so there is a constant size
progression ratio through the chart, each
row having the same number of symbols
and a constant spacing being used
between rows and between letters.
Ferris-Bailey Chart or ETDRS
It is designed on a logarithmic basis and
visual acuity is designated in terms of the
logarithm of the minimum angle of
resolution or logMAR
Ferris-Bailey Chart or ETDRS
first to incorporate a log scale which has stepwise changes
- Calculation of required magnification easy
- Five letters per line. There is constant size progression ratio of 5/4 and each line is 1.25X
bigger/smaller than previous.
Ian Bailey and Jan Lovie
Using a 1-meter viewing distance brings a practitioner in line with the metric system and
provides for much easier calculations that does the use of feet and inches.
- Since the metric system is used to measure the viewing distance, the letter size is also
expressed using the metric unit
SLOAN or M-units
introduced the ‘M-unit’ to prevent confusion with the symbol ‘D’ for diopters
Louise Sloan
used to assess the presence or absence of a refractive error
improvement in vision through indicates that the person may benefit from refractive
correctio
Pinhole Acuity Assessment
In this step the patient identifies or reads certain typeset of a smaller size from a nearer
distance. The distance is accurately recorded. The typeset size is denoted in M units.
- Reading acuity is the patient’s ability to read a more congested and complex typeset prints
from a measured distance.
- In low vision, near vision testing is recorded as the size of the print that can be read fluently
and easily.
Near Acuity Assessment
Perform near testing at two distances:
Assess the current reading ability
Assess the functional reading ability
Introduced by Snellen in 1866 as a means of
recording near visual acuity
- Chart was designed so that a 20/20 letter
would subtend a 5-minute angle at a given
distance (typically 40cm). The recording of the
acuity would be 20/20 with a 40cm working
distance understood. As in the standard
Snellen distance chart, the levels of acuity are
limited.
Reduced Snellen’s Chart
An 8-point opto type (N8) subtends 5 minutes of an arc at 1M viewing distance.
- N notation may be converted to M notations by dividing 8. For example, 4point
(N4) is the equivalent of 0.5M point (4/8)
Point N System
Consists of continuous test cards that can be
used to evaluate reading speed as well as near
acuity. This helps to determine a “critical print
size” which is the minimum size of print that
allows the maximum reading speed.
MN Read Test (Minnesota Low Vision Reading Test)
Sensitivity to contrast is the ability of the eye to perceive the smallest difference in
luminance and thus to appreciate the niceties of shading and slightest nuances of
brightness which are decisive for the forms and shapes
Contrast Sensitivity Assessment
