1,240 articles
Oligodendrocyte precursor cell
Oligodendrocyte precursor cells (OPCs), also called NG2 glia or polydendrocytes, are CNS glia that generate myelinating oligodendrocytes, receive synaptic input, remodel synapses, support the blood-brain barrier, and drive remyelination in multiple sclerosis.
Oligodendroglioma
Oligodendroglioma, also known as an oligodendroglial tumor, is a brain tumor defined by an IDH mutation and 1p/19q codeletion, most common between ages 35 and 44 and often first causing seizures.
Oliver Sacks
Oliver Sacks (1933–2015), British-born neurologist and author in New York, wrote Awakenings and The Man Who Mistook His Wife for a Hat; known for narrative case histories, L-dopa work at Beth Abraham, and later accuracy controversies.
Olivocochlear system
Olivocochlear system: brainstem-to-cochlea efferent pathway from the superior olivary complex, divided into medial (MOC, outer hair cells, cholinergic gain reduction) and lateral (LOC) divisions, studied via otoacoustic emissions for protection and speech-in-noise roles.
Onda 10
Onda 10 (no.10, CVCL_3075) is a human glioblastoma/anaplastic glioma cell line established by Onda et al. from the left parietal lobe of a 62-year-old Japanese man, TP53-mutant, GFAP-positive early on, distributed as JCRB IFO50368.
Ophthalmic Administration
Ophthalmic administration: delivering drugs to the eye via topical, intravitreal, periocular, systemic, intracameral, and suprachoroidal routes, shaped by ocular barriers and low topical bioavailability.
Ophthalmology
Ophthalmology, the medical and surgical specialty for eye and visual system disorders; ophthalmologists train 12-13 years, board certified since 1916, distinct from optometrists (OD).
Opioid receptor
Opioid receptors (MOP/MOR, DOP/DOR, KOP/KOR, and the opioid-related NOP) are Gi/o-coupled GPCRs for endorphins, enkephalins, and dynorphins, mediating analgesia, reward, and respiratory depression; key targets of morphine, fentanyl, naloxone, and biased agonists like oliceridine.
Opsin
Opsin: light-sensitive seven-transmembrane GPCR apoprotein that binds retinal via a Schiff base; forms rhodopsin and visual pigments (Type II animal opsins), distinct from Type I microbial opsins used in optogenetics.
Optic chiasm
Optic chiasm: brain-base structure where optic nerves partially decussate, nasal retinal fibers crossing (about 53:47 crossed-to-uncrossed), enabling binocular vision; pituitary tumor compression causes bitemporal hemianopia.
Optic disc
Optic disc (optic nerve head): retinal site where ganglion cell axons exit as the optic nerve; no photoreceptors, so it forms the blind spot; central retinal vessels pass through it; key glaucoma and papilledema landmark.
Optic disc swelling
Optic disc swelling (disc edema, papilledema when from raised intracranial pressure) is axoplasmic-stasis swelling of the optic nerve head, distinguished from pseudoedema such as optic disc drusen by OCT and fundus findings.
Optic nerve
Optic nerve (cranial nerve II, nervus opticus): the CNS white-matter tract of about 1.2 million retinal ganglion cell axons carrying vision from retina to chiasm and brain; myelinated by oligodendrocytes, afferent limb of the light reflex, limited regeneration.
Optic nerve avulsion
Optic nerve avulsion (ONA, Evulsio nervi optici) is traumatic disinsertion of optic nerve fibers at the lamina cribrosa after blunt ocular trauma; rare, causes permanent severe vision loss, no effective treatment.
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.
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 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.
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.
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.
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.