| Optotype set used | Comes with either letters or numerals types. Letter version uses the full set of 10 standard Sloan letters (letter version), Numeral version uses 10 numerals following Sloan's original design principles. | Only Sloan version uses the original 10-letter Sloan set. PV-Numbers and Patti-Pics each use only 5 optotypes | 10-letter Sloan set | Using 10 letters or numerals) for all Mars test charts and variations keeps guessing probability constant at 1/10, allowing easy comparison of letter- and numeral- version CS scores; tests with fewer than 10 symbols are easier to guess, less accurate and more difficult to compare with CS norms. |
| Accuracy | Score standard deviation: 0.08 log unit | Score standard deviation: 0.11 log unit for Sloan version. Unknown but likely worse for Patti-Pics and Number variations due to smaller optotype sets | Score standard deviation: 0.11 log unit | Mars is substantially more accurate (28% smaller score standard deviation) |
| Number of different contrasts in each chart | 48 (successive letters decline by 0.04 log unit in contrast) | 16 (successive triplets of letters decline by 0.05 log unit in contrast) | 16 (successive triplets of letters decline by 0.05 log unit in contrast) | The Mars has finer gradations in contrast than any other test |
| Dimensions | Each chart is 9.5 x 14 in/24.1 x 35.6 cm) | Each chart is 11.5 x 9 in/29.2 x 22.8 cm | 23.6 x 33.4 in/60 x 85 cm | Original Pelli-Robson must be wall- or easel-mounted, and thus vulnerable to bumps, dust, constant effects of sun and room light exposure. Handheld charts like the Mars and Near Pelli-Robson, are substantially easier to illuminate evenly. |
| Weight | 7.3 oz per chart (3 charts included in full set) | 2.9 oz per chart (3 charts included in full set) | 10.6 oz per chart (2 charts included in full set) | The handheld Mars has a more solid sturdy feel than other near CS tests |
| Mounting substrate | non-warping non-denting plastic | foam board | cardboard | The Mars will not warp or dent. |
| Finishing | finished, rounded corners | reverse beveled edges, square corners | square corners | Mars has no sharp corners to dent |
| Scoring and stopping rule. | Simple letter-by-letter scoring system. Test stops when two successive letters (or numerals) are incorrectly identified. Score is log contrast of the last correctly identified letter minus 0.04 times the number of previous errors. | Manufacturer instructions: log CS is determined by triplet at which 2/3 or 3/3 of the letters are correctly identified). In practice, most user and virtually all research studies use one of a variety of stopping rules and letter-by-letter scoring that all provide better accuracy than the manufacturer-provided instructions. | For 10-letter (and numeral) tests The Mars's single stopping/scoring rule has higher accuracy than any of the many stopping/scoring rules combinations provided by the manufacturer or available in the scientific literature for the Pelli-Robson. For tests with smaller optotype sets, accuracy will be even worse. |
| Standards | All three tests follow the luminance, font, and letter spacing recommendations of the Committee on Vision of the National Academy of Sciences and National Research Council (Adv. Ophthal 41, 103-148, 1980). | |
| Price (US dollars) | $395.00 | $349.00 | $540.00 | Mars isn't the cheapest contrast sensitivity test but combines high accuracy, quality and convenience with low cost. |
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