Dark field microscopy in the context of Scattering

An optical mouse is a computer mouse which uses a light source, typically a light-emitting diode (LED), and a light detector, such as an array of photodiodes, to detect movement relative to a surface. Variations of the optical mouse have largely replaced the older mechanical mouse design, which uses moving parts to sense motion.

The earliest optical mice detected movement on pre-printed mousepad surfaces. Modern optical mice work on most opaque diffusely reflective surfaces like paper, but most of them do not work properly on specularly reflective surfaces like polished stone or transparent surfaces like glass. Optical mice that use dark field illumination can function reliably even on such surfaces.

Syphilis (/ˈsɪfəlɪs, ˈsɪfɪlɪs/) is a sexually transmitted infection caused by the bacterium Treponema pallidum subspecies pallidum. The signs and symptoms depend on the stage it presents: primary, secondary, latent or tertiary. The primary stage classically presents with a single chancre (a firm, painless, non-itchy skin ulceration usually between 1 cm and 2 cm in diameter), though there may be multiple sores. In secondary syphilis, a diffuse rash occurs, which frequently involves the palms of the hands and soles of the feet. There may also be sores in the mouth or vagina. Latent syphilis has no symptoms and can last years. In tertiary syphilis, there are gummas (soft, non-cancerous growths), neurological problems, or heart symptoms. Syphilis has been known as "the great imitator", because it may cause symptoms similar to many other diseases.

Syphilis is most commonly spread through sexual activity. It may also be transmitted from mother to baby during pregnancy or at birth, resulting in congenital syphilis. Other diseases caused by Treponema bacteria include yaws (T. pallidum subspecies pertenue), pinta (T. carateum), and nonvenereal endemic syphilis (T. pallidum subspecies endemicum). These three diseases are not typically sexually transmitted. Diagnosis is usually made by using blood tests; the bacteria can also be detected using dark field microscopy. The Centers for Disease Control and Prevention (U.S.) recommends for all pregnant women to be tested.