This iPad-based pediatric contrast sensitivity test is similar in principle to the well-established Pelli-Robson Chart,. It uses the HOTV symbols which have been used in major NIH-funded clinical studies including the Visual in Preschoolers Study and the Amblyopia Treatment Study.
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.
Unlike printed charts, the test requires no external lighting and uses the 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. Validation of this format has been published in Optometry and Vision Science.
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 only four letters—H, O T, V—making it appropriate for pediatric and non-verbal patients.
Two versions of the test are included for testing of two eyes.
The letters have all been calibrated for the Retina Display.
Other vision tests also available from the iTunes store.