E chart

When Snellen hook ( named after the Dutch ophthalmologist Herman Snellen; synonym: E- hook ) is a test figure in the form of a great Latin E, where all three bars have a length of 5 d. The bar and space width are the same size and amount per 1 d Thus, the Snellen hook is as long as high. Because he is not around as opposed to the Landolt ring, coming only four positions into consideration, namely, top, right, bottom or left. Therefore, the probability of a " geratenen " result is also twice as large.

With a vision test the examinee should recognize where the opening of the Snellen hook is pointing. Application, it is used primarily for ophthalmologists to check the visual acuity of illiterate or small children. In particularly difficult cases, the device under test is a model of the hook, called Sehzeichengabel placed in the hand which is then to be held as the character is viewed. The handling is not ideal for children, but more revealing than the test with Sehtafelbilder, which rather the sense of form is checked.

Even if the candidate is not able to resolve the gaps, so he can feel one side darker than the other. Therefore, the optotypes used only for non- expert's visual acuity test. It can also lead to differences in the test results if you are in a " series" presents the optotypes "single" or.

A modification of Snellen hook, the Pflueger hooks dar. In this the middle bar to the extent of its thickness is shorter than the top and bottom.