Which contrast sensitivity chart is organized in triplets of varying contrast?

Which contrast sensitivity chart is organized in triplets of varying contrast?

• A. Pelli-Robson
• B. Vistech Contrast Test System
• C. Bailey-Lovie Chart
• D. ETDRS

Answer: (A)

Contrast sensitivity testing looks at how well you can recognize letters as their contrast changes, not just how small or clear they appear. The Pelli-Robson chart is unique in that it groups letters into triplets, with each row using the same level of contrast. As you move down the chart, the contrast drops, so you’re challenged to identify letters at progressively lower contrasts. The key idea is that you determine your threshold by whether you can correctly identify at least two of the three letters in a given triplet, which defines your ability to distinguish objects that differ in contrast. This design is different from other charts. Acuity charts like Bailey-Lovie or ETDRS vary the size of the letters to measure sharpness of vision, not contrast sensitivity. The Vistech system uses patches or gratings across different spatial frequencies and contrasts, rather than triplets at a single contrast level. So the triplet-at-each-contrast arrangement is the hallmark feature of the Pelli-Robson chart.

Contrast sensitivity testing looks at how well you can recognize letters as their contrast changes, not just how small or clear they appear. The Pelli-Robson chart is unique in that it groups letters into triplets, with each row using the same level of contrast. As you move down the chart, the contrast drops, so you’re challenged to identify letters at progressively lower contrasts. The key idea is that you determine your threshold by whether you can correctly identify at least two of the three letters in a given triplet, which defines your ability to distinguish objects that differ in contrast.

This design is different from other charts. Acuity charts like Bailey-Lovie or ETDRS vary the size of the letters to measure sharpness of vision, not contrast sensitivity. The Vistech system uses patches or gratings across different spatial frequencies and contrasts, rather than triplets at a single contrast level. So the triplet-at-each-contrast arrangement is the hallmark feature of the Pelli-Robson chart.