of the patient guessing the images. Parents and caregivers may test their child's eyesight from home to identify potential vision problems that require an eye care professional. Testing a child age three and older can be accomplished using the Tumbling E chart to play the "pointing game". For this test, the child sits in a chair 10 feet from the chart, gently holding an eye cover over one eye. The parent or caregiver points to each E, starting with the largest E. The child then points in the direction the E is facing (up, down, left, right). The smallest line with Es identified by the child can be recorded. The various directions the E can face should be reviewed with the child prior to home testing. Home tests are not as accurate as exams conducted by professional ophthalmologists. At home eye tests should not replace a visit to a professional eye care physician. Alternatives Computer-based alternatives to the eye chart have been developed, but are not very common prior to smart phones with high display resolution and DPI becoming popular. They have several potential advantages, such as a more precise measurement, less examiner-induced bias and randomized optotypes. If the person, particularly a young child, is unable to cooperate with visual acuity testing via an eye chart, practitioners can be alerted to possible deficits in visual acuity by asking parents whether the child appears to see well. A clue is that the child may hold objects close to the face when attempting to focus. Refractive error can be estimated via photography, a technique called photoscreening. Technical details Optotype Crowding Research has shown that optotype "crowding" reduces visual acuity at the fovea (as opposed to eccentric visual acuity) once the optotype characters are closer than 4.4 bar widths apart. This is referred to as the "critical spacing" for optotype letters at the fovea. For periphery visual acuity, the critical spacing is much greater, such that optotype characters closer than 15-20 bar widths apart negatively affect visual acuity. See also Golovin–Sivtsev table Landolt C Lea test Monoyer chart Snellen chart References Diagnostic ophthalmology Optometry Ophthalmic equipment