Low vision examination
- Comprehensive case history
- Determination of the patient’s visual enhancement needs
- The examination/refraction sequence
- Visual function tests
- Health assessment
- Determine applicability of selected low vision devices
- Determine needed magnification for devices
- Report preparation
Areas of comprehensive case history
General information
Financial status
Ocular history and current status
General health or systemic history and current status
Educational history
Functional task analysis
Devices used in the past
Measuring VA allows the practitioner to:
- 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.
Comes in the form of loose-leaf cards
Feinbloom number and letter charts
A chart designed so there is a constant size progression ration through the chart, each row having the same number of symbols and a constant spacing being used between rows and between letters.
Bailey-Lovie chart or ETDRS
ETDRS means
Early treatment diabetic retinopathy study
Who incorporated a log scale first
Ian bailey and Jan Lovie
Advantages of LogMAR chart
- Equal number of optotypes per line and allows the use of single-letter scoring which reduces test–retest variability
- Equal logarithmic interval between lines
- Equal average legibility for each line. It ensures that letter size is the sole determinant of difficulty on a given line
- Consistent spacing between letters and lines i.e. Proportional inter-letter and inter-line spacing.
- Geometric progression of letter sizes and allows testing distance to be variable. Vision recording is done at 4m to 2m to 1m. Correction factor of 0.3 should be added to the Log score when the distance is halved.
Who introduced the “M-unit”
Louise Sloan
Used to assess the presence or absence of a refractive error improvement in vision
Pinhole acuity test
Perform near testing at two distances:
Assess the current reading ability
Assess the functional reading ability
Calibrated in meter equivalent and simplify calculation of magnification
M-series charts
Near Acuity charts
Reduced snellen’s chart
Point n system
Mn read test (Minnesota low vision reading test)
Introduced by snellen in 1866 as a means of recording near visual acuity
Reduced snellen’s chart
Chart was designed so that a 20/20 letter would subtend a 5-minute angle at a given distance (typically 40cm)
Reduced snellen’s chart
An 8-point opto type (N8) subtends 5 minutes of an arc at 1M viewing distance.
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
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
Contrast sensitvity tests
Lea’s contrast test
Pelli Robson chart
Contrast sensitivity testing is important to find:
- Need for magnification
- Ability to use optical devices
- Lighting (functional adaptive device)
- Dominant eye
- Over-all function – contrast enhancing techniques
reduction of visual function cause by scattering of incoming light.
Glare
Color vision tests
Ishihara PIPs
D-15 panel
Gross colors
Most acquired color vision defects in low vision
Blue-yellow defects
3 ocular health examinations that should be performed in the same manner as the normally sighted px
Biomicroscopy, ophthalmoscopy, tonometry
