This iPad-based letter contrast sensitivity test is similar in principle to the well-established Pelli-Robson Chart and Mars Letter Contrast Sensitivity Test.
The letters have all been calibrated for the Retina Display.
The iPad test presents two letters per page and in 0.1 log unit steps. Thus scores should be equivalent to those obtained with the Pelli-Robson Chart. The test uses the same 10-letter set as the Bailey-Lovie Visual Acuity Chart.
Letter contrast sensitivity testing is fast to administer and easy for patients to understand, due to its similarity to visual acuity charts. Letter-based tests have been shown to be more repeatable than printed tests using gratings and are widely used in large clinical trials supported by the US National Institutes of Health.
Unlike other tests, the test requires no external lighting and runs on the ubiquitous iPad without need for special software or calibration. The test utilizes the high quality iPad screen to produce letters with contrasts as low as 0.5%, below that visible to the average patient.
An un-validated student version with one letter per contrast level is also available from the iTunes store.
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