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 on the iPad 3 and iPad 4. The contrast values are not valid for earlier versions.
This student version of the test has not been validated. The full, validated version, available from the Store, should be used for clinical trials, research, driver testing, disease evaluation, drug monitoring, etc.
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 tests using gratings.
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 0.6%, below that visible to the average patient.
This version of the iPad test presents one letter per 0.1 log unit step, two letters per page. Scores should be similar to those obtained with the Pelli-Robson Chart. The test uses the same 10-letter set as the Bailey-Lovie Visual Acuity Chart.
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