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The Mars Letter Contrast Sensitivity Test (MLCST) is a simple portable set of contrast-calibrated letter charts for testing contrast sensitivity that was developed by The Mars Perceptrix Corporation. Its design is similar to, but improves upon that of the well-known Pelli-Robson chart. The Mars test follows many of the same design principles; it uses the identical Sloan letter forms used in that test, and presents these letters declining in contrast from across and down the chart. However, the Mars test uses much smaller contrast decrements (0.04 log unit) than the Pelli-Robson, which uses 0.15 log unit decrement between triplets of letters. Studies performed in the Lighthouse Vision Laboratory show that it yields results that are entirely comparable to those of the Pelli-Robson; in fact, using both analytic and Monte Carlo simulations and a model of visual performance identical to that used in the design of the Pelli-Robson the test yields scores almost identical to the Pelli-Robson, yet has 28% better accuracy (i.e. 28% smaller score standard deviations; Arditi, 2005).

The only substantial differences between the proximal stimuli of the two tests (at the retina) are the particular sequence of Sloan letters chosen, and the finer gradations of contrast. Because of the high degree of similarity between the stimuli of the MLCST with those of the Pelli-Robson chart and the equivalence of its scores, all of the normative data that applies to the P-R chart can be applied to the MLCST (Arditi, 2005). The reduced size and format of the test makes it far easier to illuminate evenly, and more convenient to administer than the P-R test. In addition to testing of the MLCST in a clinical setting (Arditi & Faye, 2004), reliability and validity have also been favorably assessed by independent studies at Ohio State University (Dougherty et al., 2005), Dalhousie University's Medical School (Haymes et al., 2006), and Moorfield's Eye Hospital in London (Thayaparan et al., in press).

Further Reading

Arditi, A. (2005). Improving the design of the letter contrast sensitivity test. Investigative Ophthalmology and Visual Science, 46(6), 2225-2229.

Arditi, A. (2006). Lapses in the verbal letter reporting task. Vision Research. 46(8-9) 1327-1330.

Arditi, A. and Faye, E. (2004). Monocular and binocular letter contrast sensitivity and letter acuity in a diverse ophthalmologic practice. Supplement to Optometry and Vision Science, 81 (12S), 287.

Dougherty, B. E., Flom, R. E., & Bullimore, M. A. (2005). An evaluation of the Mars Letter Contrast Sensitivity Test. Optometry & Vision Science, 82(11), 970-975.

Haymes, S. A., Roberts, K. F., Cruess, A. F., Nicolela, M. T., LeBlanc, R. P., Ramsey, M. S., et al. (2006). The Letter Contrast Sensitivity Test: Clinical Evaluation of a New Design. Investigative Ophthalmology and Visual Science, 47(6), 2739-2745.

Thayaparan, K., Crossland, M. D., & Rubin, G. S. (2007). Clinical Assessment of Two Novel Contrast Sensitivity Tests: A Comparison With the Pelli-Robson Chart. British Journal of Ophthalmology, 91, 749-752.

 

 

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