Human eye The upper end of the range is given in terms of normal visual performance as 10 cd/m (100,000,000 or one hundred million candelas per square meter). The eye includes a lens similar to lenses found in optical instruments such as cameras and the same physics principles can be applied. The pupil of the human eye is its aperture; the iris is the diaphragm that serves as the aperture stop. Refraction in the cornea causes the effective aperture (the entrance pupil) to differ slightly from the physical pupil diameter. The entrance pupil is typically about 4 mm in diameter, although it
The Seeing Eye through the training of guide dogs in the United States. Eustis and Humphrey began to research and modify their own training in which they trained several German shepherds to guide humans. In April 1928, Frank met his first ever Seeing Eye dog named Kiss. He changed her name to Buddy and named all his future Seeing Eye dogs (he had six in total) Buddy. The name is now retired by The Seeing Eye. Frank and Buddy had to go through a six-week training that not only created a strong bond, but also taught them to work as a team to