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Pelli Robson Test
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Supplemental: Multiple Sclerosis (MS) and Parkinson's Disease (PD)
Short Description of Instrument
Construct measured: Contrast sensitivity.
Generic vs. disease-specific: Generic.
Means of administration: Observation.
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
Background: The Pelli-Robson test measures contrast sensitivity using a single large letter size (20/60 optotype), with contrast varying across groups of letters. Specifically, the chart uses letters (6 per line), arranged in groups whose contrast varies from high to low.
Scoring and Psychometric Properties
Scoring: The subject is assigned a score based on the contrast of the last group in which two or three letters were correctly read. The score, a single number, is a measure of the subject's log contrast sensitivity. Thus, a score of 2 means that the subject was able to read at least two of the three letters with a contrast of 1% (contrast sensitivity = 100 % or log 2). A Pelli-Robson score of 2.0 indicates normal contrast sensitivity of 100 %. Scores less than 2.0 signify poorer contrast sensitivity. Pelli-Robson contrast sensitivity score of less than 1.5 is consistent with visual impairment and a score of less than 1.0 represents in visual disability. This score (1.0) represents an approximately 10-fold loss of contrast sensitivity. That is, a person with contrast sensitivity of 1.0 requires 10 times as much contrast to see as compared with a person with normal vision.
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.
Strengths: May be useful for predicting the threshold visibility, such as of large trucks in the fog.
Weaknesses: Not useful for determining the presence of small objects such as the child on the street.
Administration: Patients read the letters, starting with the highest contrast, until they are unable to read two or three letters in a single group. Each group has three letters of the same contrast level, so there are three trials per contrast level.
Key Reference:
Pelli DG, Robson JG, Wilkins AJ. The design of a new letter chart for measuring contrast sensitivity. Clinical Vision Sciences. 1988;2(3):87-199.
Additional Reference:
Stenc Bradvica I, Bradvica M, Matic S, Reisz-Majic P. Visual dysfunction in patients with Parkinson's disease and essential tremor. Neurol Sci. 2015 Feb;36(2):257-62.
Document last updated August 2022