Monochromacy (from Greek mono, meaning "one" and chromo, meaning "color") is the ability of organisms or machines to perceive only light intensity, without respect to spectral composition (color). Organisms with monochromacy are called monochromats. Many mammals, such as cetaceans, the owl monkey and the Australian sea lion (pictured at right) are monochromats. In humans, absence of color vision is one among several other symptoms of severe inherited or acquired diseases, including achromatopsia or blue cone monochromacy, together affecting about 1 in 30,000 people. The affected can distinguish light, dark, and shades of gray but not color. Humans
Human vision relies on a duplex retina, comprising two types of photoreceptor cells. Rods are primarily responsible for dim-light scotopic vision and cones are primarily responsible for day-light photopic vision. For all known vertebrates, scotopic vision is monochromatic, since there is typically only one class of rod cell. However, the presence of multiple cone classes contributing to photopic vision enables color vision during daytime conditions. Most humans have three classes of cones, each with a different class of opsin. These three opsins have different spectral sensitivities, which is a prerequisite for trichromacy. An alteration of any of these three cone opsins can lead to colorblindness. Anomalous Trichromacy, when all three cones are functional, but one or more is altered in its spectral sensitivity. Dichromacy, when one of the cones is non-functional and one of the red-green or blue-yellow opponent channels are fully disabled. Cone Monochromacy, when two of the cones are non-functional and both chromatic opponent channels are disabled.
Patellar tendinitis, also known as jumpers knee, is an overuse injury of the tendon that straightens the knee. Symptoms include pain in the front of the knee. Typically the pain and tenderness is at the lower part of the kneecap, though the upper part may also be affected. Generally there is no pain when the person is at rest. Complications may include patellar tendon rupture.Risk factors include being involved in athletics and being overweight. It is particularly common in athletes who are involved in jumping sports such as basketball and volleyball. The underlying mechanism involves small tears in the tendon connecting the kneecap with the shinbone. Diagnosis is generally based on symptoms and examination. Other conditions that can appear similar include infrapatellar bursitis, chondromalacia patella and patellofemoral syndrome.Treatment often involves resting the knee and physical therapy. Evidence for treatments, including rest, however is poor. Recovery can take between months and persist over years. It is relatively common with about 14% of athletes currently affected; however research reflects that more than half of athletes with this injury end their careers as a result. Males are more commonly affected than females. The term "jumpers knee" was coined in 1973. Signs and symptoms
People report anterior knee pain, often with an aching quality. The symptom onset is insidious. Rarely is a discrete injury described. Usually, the problem is below the kneecap but it may also be above.