2,701 articles
ORANGE study
The ORANGE study was a 2023 multicenter cohort study of 514 ICU patients showing that automated pupillometry, the Neurological Pupil index, predicts outcome after severe acute brain injury.
Orbicularis oculi muscle
Orbicularis oculi: sphincter-like facial muscle around the eyelids that closes the eye, aids tear drainage, divides into orbital, preseptal, and pretarsal parts, and is innervated by CN VII.
Orbit (anatomy)
Orbit (anatomy): the bony eye socket, formed by seven skull bones (frontal, ethmoid, lacrimal, palatine, maxillary, zygomatic, sphenoid), housing the globe, optic nerve, and extraocular muscles, with optic canal and orbital fissures.
Orbital cellulitis
Orbital cellulitis (postseptal cellulitis) is infection of the eye socket tissues behind the orbital septum, usually spreading from ethmoid or other paranasal sinusitis. Distinct from preseptal cellulitis; treated with IV antibiotics and surgery, it threatens vision and can cause cavernous sinus thrombosis.
Orbital fracture
Orbital fracture, including blowout fracture of the orbital floor or medial wall: break in the eye socket bones from blunt trauma, causing diplopia, enophthalmos, and V2 numbness; diagnosed by thin-cut CT, managed observationally or surgically.
Orbitofrontal cortex
Orbitofrontal cortex (OFC), ventral prefrontal cortex above the eyes; areas 11, 13, 14, 47/12; represents reward value and hedonic experience, supports decision making; damage causes impulsive, socially inappropriate behavior.
Orexin
Orexin (hypocretin): hypothalamic neuropeptide pair orexin-A/B that stabilizes wakefulness and suppresses REM; its loss causes narcolepsy type 1, and its receptors are drug targets for insomnia antagonists and 2026-approved narcolepsy agonists like oveporexton.
Organ (biology)
Organ (biology): a body structure made of two or more tissue types performing specific functions; from Greek organon (tool). Humans have eleven organ systems; organs include the heart, liver, brain, and skin.
Organ donation for heart transplantation
Organ donation for heart transplantation covers DBD and DCD donor selection, 4-hour cold ischemia limits, machine perfusion, NRP ethics, and DCD trial outcomes showing noninferior 6-month survival versus brain-death donors.
Organ of Corti
Organ of Corti: the mammalian cochlea's hearing sensory epithelium, on the basilar membrane under the tectorial membrane; one inner and three outer hair-cell rows, tunnel of Corti, described by Corti in 1851.
Organ procurement
Organ procurement: surgical removal of organs, corneas, or tissue from donors for transplant, performed in the U.S. by about 55 nonprofit OPOs under OPTN and CMS oversight, with strict preservation time limits.
Organ Size
Organ size: measurement of a bodily organ in volume, mass, or heaviness (MeSH D009929, formerly Organ Weight). Covers biological size regulation and clinical measurement by CT, MRI, and ultrasound.
Organ system
An organ system is a group of organs working together to carry out major body functions. The human body has eleven, including the nervous, cardiovascular, digestive, and respiratory systems.
Orthostatic proteinuria
Orthostatic (postural) proteinuria: excess urinary protein only when upright, normal when supine; benign condition affecting 2-5% of adolescents, diagnosed by first-morning urine testing, requiring no treatment.
Oscillopsia
Oscillopsia is the illusion that the visual world moves when it is still, caused by nystagmus, saccadic intrusions, or vestibulo-ocular reflex failure, most often in bilateral vestibulopathy, Ménière's disease, or neurological disease.
Osseointegrated prosthetic limb
An osseointegrated prosthetic limb is an artificial arm or leg attached directly to the skeleton by a titanium implant passing through the skin, replacing the socket.
Ossicles
Ossicles (auditory ossicles): the malleus, incus, and stapes, three tiny chained bones of the mammalian middle ear that carry and amplify eardrum vibrations to the oval window; smallest bones in the body.
Ossification
Ossification (osteogenesis): bone formation via intramembranous ossification (direct from mesenchyme; skull, face, clavicles) and endochondral ossification (cartilage template replaced; long bones), starting in the embryonic sixth to seventh week, plus pathologic heterotopic ossification.
Osteo-odonto-keratoprosthesis
Osteo-odonto-keratoprosthesis (OOKP, MOOKP), tooth-in-eye surgery: a two-stage operation using the patient's tooth root and alveolar bone to support a PMMA optical cylinder for end-stage corneal blindness, with 91% 18-year lamina retention in the UK cohort.
Osteoblast
Osteoblast: bone-forming cell that secretes osteoid and mineralizes it with hydroxyapatite; fates include osteocyte, bone lining cell, or apoptosis; regulated by RUNX2, osterix, Wnt signaling, and PTH.
Osteoclast
Osteoclast: multinucleated monocyte-lineage cell that resorbs bone via a sealing zone, ruffled border, and acid secretion, regulated by RANKL–RANK–OPG and targeted by denosumab.
Osteocyte
Osteocyte: the most abundant bone cell, an embedded former osteoblast forming the lacunocanalicular network; mechanosensor directing remodeling via sclerostin and RANKL, endocrine via FGF23.
Osteon
Osteon (Haversian system): the microscopic structural unit of compact bone, a cylinder of 4–20 concentric lamellae around a central Haversian canal carrying blood vessels and nerves, bounded by cement lines in secondary osteons and renewed by BMU remodeling.
Other parasomnias
Other parasomnias (ICSD-3; ICD-11 code 7B02) is the residual sleep-disorder category for parasomnias independent of sleep stage, including exploding head syndrome, sleep-related hallucinations, and sleep enuresis, distinct from NREM and REM parasomnias.
Otitic barotrauma
Otitic barotrauma (barotitis media, aero-otitis-media, ear squeeze) is ear injury from failed pressure equalization, usually via Eustachian tube dysfunction, affecting divers and aircrew; middle ear injury predominates, with pain above ~30 mmHg gradients.
Otitis
Otitis, or ear infection and inflammation, includes otitis externa (swimmer's ear), otitis media, otitis media with effusion, and labyrinthitis; most acute otitis media in children resolves without antibiotics.
Otitis externa
Otitis externa, commonly known as swimmer's ear, is inflammation of the external ear canal, often with infection, causing ear pain, itching, and discharge; it occurs in acute, chronic, and necrotising forms.
Otitis media
Otitis media, also called ear infection or middle ear infection, is inflammation of the middle ear behind the eardrum. Types include AOM, OME, and COME; five of six children are affected by age three, treated with watchful waiting, amoxicillin, or tympanostomy tubes.
Otolith
Otolith (otoconia): calcium carbonate crystals in the utricle and saccule of the inner ear's vestibular system, detecting linear acceleration and head tilt relative to gravity; distinct from semicircular canals, tested clinically by VEMP, vOCR, and SVV.
Otorrhagia
Otorrhagia (otorragia) is the medical term for bleeding from the ear, ICD-10 H92.2 and ICD-11 AB70.1, distinct from otorrhea and hemotympanum, caused by eardrum perforation, infection, trauma, or tumor.