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
Diaphragm (birth control) to test whether the diaphragm offers protection from HIV found that women provided with both male condoms and a diaphragm experienced the same rate of HIV infection as women provided with male condoms alone. Because pelvic inflammatory disease (PID) is caused by certain STIs, diaphragms may lower the risk of PID. Cervical barriers may also protect against human papillomavirus (HPV), the virus that causes cervical cancer, although the protection appears to be due to the spermicide used with diaphragms and not the barrier itself. Diaphragms are also considered a good candidate as a delivery method for microbicides (preparations that, used