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
Contrast Sensitivity Assessment charts provides a good way to measure contrast
Lea’s contrast test, Pelli Robson chart
reduction of visual function cause by scattering of incoming light.
- Clear ocular media is required for clear image on the retina.
Glare Testing
Aid in the diagnosis of visual loss or determining the underlying etiology
2. Assessment to advise patients how to cope up with activities that require color
discrimination.
Color Vision Testing
color vision tests include
Ishihara PIPs, D-15 panel, Gross colors
performed in the same manner
as the normally sighted patients
Ocular Health Examination
- Biomicroscopy, ophthalmoscopy, and tonometry
for the normally sighted person is done to detect any disease
condition affecting the visual fields.
Visual Field Examination
Visual Field Examination tests
Perimetry, Confrontation Test, Amsler grid, perimetry
extent of peripheral visual field
Perimetry
30 degrees central / total: 60 degrees
Tangent Screen
20 degrees total central
- visual fields of 5 degrees or less may limit the amount of magnification
Amsler Grid
findings are included in the patient’s previous record, the refractive
examination should begin with keratometry.
- Since many low vision patients has opaque media (making retinoscopy difficult),
information concerning astigmatism obtained by keratometry can be of great importance.
Keratometry
should be done with a trial frame and trial lenses.
- With trial lenses, it will be possible for the examiner to watch the patient’s eyes and
determine whether central or eccentric fixation is used.
Keratometry
the examiner moves into whatever distance is necessary to
obtain a retinoscopic reflex and subtracts the appropriate working distance lens power
from the finding.
Radical Retinoscopy
Chart should be placed at 10-foot distance or 3 meters if visual acuity was found to be
adequate at that distance. Otherwise, a closer distance may have to be used. This gives
the patient a feeling of accomplishment; starting the acuity test at 20 feet will discourage
the patient if few letters can be seen
Subjective Refraction
Bailey suggested subjective testing should begin with +6.00D,
plano, -6.00D to bracket the patient’s refractive endpoint
Bracketing Technique
helps in determining the interval between two
lenses that are being compared and is based on the patient’s best visual acuity at 10 feet.
Just Noticeable Difference (JND)
