Original article. Repeatability assessment of the New Numbers Contrast Sensitivity Chart

Abstract Background: The validity and agreement of the New Numbers Contrast Sensitivity Chart with the original Mars chart have been found to be good. The two charts can be used interchangeably; however, evidence of the repeatability of the new chart remains to be sought. This study was to assess the repeatability of the New Numbers Contrast Sensitivity Chart. Objectives: We assessed the repeatability of the Numbers Contrast Sensitivity Chart. Methods: Two hundred subjects from the ophthalmic clinic of the King Chulalongkorn Memorial Hospital, who were able to communicate and read Arabic numerals were recruited. The contrast sensitivity (CS) scores were collected by reading the same Numbers Contrast Sensitivity Chart in the same environment with each eye and both eyes ten minutes apart. The repeatability of the CS score was assessed by Bland-Altman plot analysis. Results: The visual acuity of subjects with variety in diagnoses ranged from 20/480 to 20/20. The mean differences were -0.006, -0.008, -0.002 log CS and the coefficients of repeatability were 0.155, 0.141, and 0.093 for the right eye, left eye, and both eyes, respectively. The plots showed a narrow range of 95% limit of agreement, which were (+0.146, -0.159) in the right eye, (+0.130, -0.147) in the left eye, and (+0.089, -0.093) in both eyes. Conclusions: The New Numbers Contrast Sensitivity Chart has good repeatability. With proven good validity and repeatability, this easy and convenient numbers chart is beneficial for practical use in a clinical setting where English is not used as the primary language.