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Sloan Low Contrast Letter Acuity
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Supplemental-Highly Recommended: Friedreich's ataxia (FA), Multiple Sclerosis (MS)
Sloan Low Contrast Acuity is a part of the MS Outcomes Assessments Consortium (MSOAC) Battery of tests, which is recommended as Supplemental – Highly Recommended for MS:
Timed 25 Foot Walk
9-Hole Peg Test
Sloan Low Contrast Letter Acuity
Symbol Digit Modalities Test
Each of the measures in the Consortium can be used individually as primary or secondary endpoints.
Short Description of Instrument
Construct measured: Low contrast letter acuity
Generic vs. disease specific: Generic
Means of administration: Assessment
Intended respondent: Patient
# of items: N/A
# of subscales and names of sub-scales: N/A
# of items per sub-scale: N/A
Comments/Special Instructions
Scoring: Charts are scored based on the number of letters identified correctly. This format provides continuous scoring and may allow Sloan charts to capture losses of losses of vision at low contrast. The size of the letters is used to quantitate the loss. The lowest suggested density is 2.5%.
Background: Low contrast acuity testing provides information on patient- reported aspects of vision. This testing is performed using low-contrast Sloan letter charts. Each chart corresponds to a different contrast level (shade of gray letters on white/retroilluminated background).
Strengths/Weaknesses: Sloan charts have a standardized format based on Early Treatment Diabetic Retinopathy Study visual acuity charts, which are the standard used for ophthalmology clinical trials. Weaknesses include deciding on the worst eye, best eye, both eyes and the impact on the question being addressed. Can also use too low contrast so that inability to complete gets to prevalent.
The 100% chart is equivalent to Snellen Visual Acuity. A density of 1.25% may be too low for many participants and therefore 2.5% may be the lowest density to be used.
Psychometric Properties: Inter-rater agreement was described with the intraclass correlation coefficient (ICC) and comparison of mean scores. Excellent inter-rater agreement (ICC=0.86-0.95) was demonstrated at each contrast level among MS patients (n=100) and visually-asymptomatic volunteers (n=33). Average letter scores at the lowest contrast level (0.6%) were highly variable in the MS group, even among patients with visual acuities of 20/20 or better, and among those who required no assistance for ambulation.
Administration: Patients are instructed to stand 1 m away from the Sloan letter charts and read the letters, starting with the highest contrast.
Balcer LJ, et al. Contrast letter acuity as a visual component for the Multiple Sclerosis Functional Composite. Neurol. 2003; 61:1367-1373.
Other References:
Balcer LJ, et al. New low-contrast vision charts: reliability and test characteristics in patients with multiple sclerosis. Mult Scler June 2000; 6(3):163-171.
Balcer LJ, et al. Validity of low-contrast letter acuity as a visual performance outcome measure for multiple sclerosis. Mult Scler. 2017;23(5):734-747.