Human health and medicine

Phosphoribosylpyrophosphate synthetase superactivity

Phosphoribosylpyrophosphate synthetase superactivity (PRS superactivity, PRPS1 superactivity) is a rare X-linked purine metabolism disorder causing hyperuricemia, gout, and uric acid stones, with a severe early-onset form adding deafness and neurologic impairment.

Phossy jaw

Phossy jaw (phosphorus necrosis of the jaw) was an occupational osteonecrosis of match-factory workers exposed to white phosphorus fumes; about 11% of the exposed developed it, it killed roughly 20%, and it ended after the 1906 Berne Convention.

Photic retinopathy

Photic retinopathy, also called solar retinopathy or eclipse retinopathy, is retinal damage caused by intense light exposure, most often from sungazing, eclipse viewing, welding arcs, or laser pointers.

Photic sneeze reflex

The photic sneeze reflex (PSR), also known as ACHOO syndrome or sun sneezing, is involuntary sneezing triggered by bright light, affecting an estimated 25% of people and inherited in an autosomal dominant manner.

Photic stimulation

Photic stimulation, or intermittent photic stimulation (IPS), is an EEG activation test in which strobe flashes provoke the photoparoxysmal response, used to diagnose photosensitive epilepsy.

Photo-allergic contact dermatitis

Photo-allergic contact dermatitis (PACD, photoallergic eczema) is a type IV hypersensitivity skin reaction to a light-activated contact allergen, mainly sunscreens and topical NSAIDs, diagnosed by photopatch testing and distinguished from phototoxic dermatitis by delayed onset and sensitization.

Oct 22, 2026

Photoacoustic nanoprobes

Photoacoustic nanoprobes are nanoparticles, typically tens to hundreds of nanometers, that serve as contrast agents in photoacoustic imaging, adding molecular specificity and functional readouts beyond endogenous absorbers like hemoglobin.

Photoacoustic Techniques

Photoacoustic techniques (optoacoustic techniques) are diagnostic and investigative methods using sound waves generated by absorption of electromagnetic radiation, chiefly laser-based biomedical imaging combining optical contrast with ultrasound resolution, from Bell's 1880 effect to PACT and PAM systems.

Photoacoustic tomography

Photoacoustic tomography, also called photoacoustic computed tomography, is a biomedical imaging method combining ultrasound resolution with optical contrast from hemoglobin, reaching centimeter depths for breast cancer imaging.

Oct 22, 2026

Photoaffinity labeling

Photoaffinity labeling (PAL) is a chemical biology technique in which a probe with a photoreactive group binds its target, and light triggers a covalent bond, enabling target identification and binding-site mapping.

Photoaging of the skin

Photoaging of the skin: UV radiation-driven premature skin aging, mainly UVA (95% of terrestrial UV) and UVB, causing wrinkles, lentigines, solar elastosis, immunosuppression; treated with sunscreens and topical retinoids.

Photobiomodulation therapy

Photobiomodulation (PBM) therapy, long known as low-level laser therapy and marketed as red light therapy, uses low-power red or near-infrared light to relieve pain and reduce inflammation.

Photodynamic therapy

Photodynamic therapy is a treatment in which a photosensitizing drug activated by light and oxygen generates reactive oxygen species that destroy target cells, with FDA approval for several cancers.

Photofluorography

Photofluorography (fluorography, mass miniature radiography) photographs the X-ray image on a fluorescent screen onto small 7x7 or 10x10 cm film; used for mass TB chest screening from the 1940s, later replaced by digital radiography.

Photoimmunotherapy

Photoimmunotherapy, often called NIR-PIT, is a cancer treatment in which antibody-dye conjugates bound to tumor cells are activated by near-infrared light, killing them within minutes.

Photokeratitis

Photokeratitis (ultraviolet keratitis, arc eye, snow blindness) is a painful, usually bilateral corneal epithelial injury from UV exposure, with delayed onset 6-12 hours and self-healing within 24-72 hours.

Photomicrography

Photomicrography: photographing magnified images through a microscope; distinct from microphotography. Pioneered by Talbot (1830s) and Woodward (1870s sunlight apparatus); now digital, with QC metrics, OME metadata standards, and contests like Nikon Small World.

Photon-counting computed tomography

Photon-counting computed tomography (PCCT) is a CT technique whose detectors count individual X-ray photons, sharpening resolution and separating materials; the first clinical scanner, the Siemens NAEOTOM Alpha, was FDA-cleared in 2021.

Photophobia

Photophobia is abnormal light sensitivity causing eye discomfort or pain, a symptom of migraine (85-90% of patients), dry eye, blepharospasm, and TBI, mediated by melanopsin ipRGCs and treated by addressing the cause plus FL-41 tinted lenses.

Photoplethysmogram

Photoplethysmogram (PPG): noninvasive optical signal of arterial blood volume changes, basis of pulse oximetry and wearable heart-rate sensors; transmission or reflectance mode, green/red/IR light, used for heart rate, SpO2, rhythm screening.

Photoreceptor cell

Photoreceptor cells (rods and cones) are retinal neurons that convert light into electrical signals via a G-protein phototransduction cascade; rods detect single photons in dim light, cones mediate bright-light, color, high-acuity vision.

Photoreceptor disk component PRCD

PRCD (photoreceptor disc component) is a 54-amino-acid, ~6 kDa rhodopsin-binding protein of unknown function found only in photoreceptor outer segment discs; its C2Y mutation causes canine progressive rod-cone degeneration and human retinitis pigmentosa 36.