Lea tests, developed by the world-renowned ophthalmologist Dr. Lea Hyvärinen, include a range of vision tests that are designed for persons who cannot read letters. The first test developed by Lea included symbols and was designed for pediatric testing. These symbols included an Apple, Pentagon, Square and Circle. Subsequent tests incorporated numbers that could be used to evaluate a wider range of the population, including adults. Preferential looking tests were also developed to test infant vision. A unique feature of these tests is that they were validated so that the size, shape and thickness of the letters provided visual acuity scores to match those provided by the standard visual acuity measurements. The tests are available in charts, pocket cards, and a variety of other formats. More recently, Lea incorporated different contrast levels in the tests, to make them more sensitive to a wider range of vision.