Human health and medicine

Ophidiophobia

Ophidiophobia, also called ophiophobia, is the specific phobia of snakes, an anxiety disorder affecting 2–3% of people; treated mainly with exposure therapy and studied through preparedness and snake detection theories.

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.

Ophthalmic artery

Ophthalmic artery: first branch of the internal carotid artery, supplying the eye and orbit via the central retinal and ciliary arteries; variant origins in 2–3%, occlusion is a sight-threatening emergency.

Ophthalmic zoster

Ophthalmic zoster, also called herpes zoster ophthalmicus (HZO), is shingles of the eye caused by reactivation of varicella-zoster virus in the ophthalmic branch of the trigeminal nerve.

Ophthalmodynamometry

Ophthalmodynamometry (ODM) measures retinal vessel blood pressure by pressing on the eye while observing the central retinal vessels; developed by Bailliart (1923), used for carotid disease, later displaced by Doppler sonography.

Ophthalmologic Surgical Procedures

Ophthalmologic surgical procedures cover cataract extraction, glaucoma filtration and MIGS, corneal transplantation, and vitreoretinal surgery, from ancient couching to phacoemulsification, IOLs, femtosecond lasers, and robotic systems.

Ophthalmological Diagnostic Techniques

Ophthalmological diagnostic techniques (MeSH D003941) are methods for diagnosing eye and vision disorders: comprehensive eye exams, tonometry, ophthalmoscopy, OCT, ultrasound, angiography, and AI-based retinal analysis.

Ophthalmologists

Ophthalmologists, or eye M.D.s, are medical doctors specializing in medical and surgical eye care; distinct from optometrists (O.D.), they train via residency and fellowship, hold ABO certification, and face projected global workforce shortfalls.

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).

Ophthalmomandibulomelic dysplasia

Ophthalmomandibulomelic dysplasia (OMM syndrome, Pillay syndrome, OMIM 164900) is an extremely rare autosomal dominant malformation syndrome with corneal-opacity blindness, temporomandibular fusion, and arm anomalies; three cases in one family, gene unidentified.

Ophthalmoparesis

Ophthalmoparesis, also called ophthalmoplegia when complete, is weakness of the extraocular muscles causing diplopia and ptosis; causes span brain, cranial nerve, neuromuscular junction (myasthenia gravis), and muscle (thyroid eye disease, CPEO).

Ophthalmoscopes

Ophthalmoscopes: instruments for viewing the eye's fundus. Invented by Helmholtz (1850/1851); types include direct (handheld, 15x, erect image), binocular indirect (head-mounted, 20D lens, inverted 3D view), and scanning laser ophthalmoscopes.

Ophthalmoscopy

Ophthalmoscopy (funduscopy) is examination of the eye's fundus, retina, optic disc, choroid, and vessels, by direct, indirect, or slit-lamp methods; invented by Helmholtz in 1850.

Opiate Substitution Treatment

Opiate substitution treatment, also called opioid agonist maintenance treatment (OAMT), is long-term methadone or buprenorphine treatment for opioid dependence; methadone retains patients better, both cut mortality sharply.

Opicapone

Opicapone (Ongentys) is a third-generation, once-daily, peripheral reversible COMT inhibitor used with levodopa/carbidopa for OFF episodes in Parkinson's disease; approved in the EU (2016), US (2020), and Japan (2020).

Opioid

Opioids: natural, semi-synthetic, and synthetic drugs (morphine, oxycodone, fentanyl, heroin) that bind mu, delta, kappa, and nociceptin receptors to relieve pain; small chronic-pain benefits, overdose and addiction risks, naloxone and OUD treatments.

Opioid epidemic

Opioid epidemic: the US overdose crisis since the mid-1990s, in three waves (prescription opioids from 1999, heroin from 2010, illegally made fentanyl from 2013), causing roughly 806,000 opioid overdose deaths from 1999 to 2023, with deaths declining since 2023.

Opioid epidemic in the United States

Opioid epidemic in the United States: a public health crisis since the mid-1990s in three waves (prescription opioids, heroin, illicit fentanyl), causing about 806,000 opioid overdose deaths 1999-2023, peaking near 110,000 total overdose deaths in 2022, then falling 27% in 2024.

Opioid overdose

Opioid overdose: life-threatening respiratory depression from opioids (fentanyl, heroin, oxycodone, methadone), marked by pinpoint pupils, unconsciousness, and slowed breathing; reversible with naloxone. Covers mechanism, risk factors, naloxone, mortality trends, and prevention.

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.

Sep 29, 2026

Opioid rotation

Opioid rotation, also called opioid switching or sequential opioid trials, is substituting one opioid painkiller for another to balance pain relief against side effects, needed by 20–44% of patients on opioid therapy.

Opioid use disorder

Opioid use disorder (OUD), also called opioid addiction, is a chronic treatable condition defined by DSM-5 criteria: at least 2 of 11 within 12 months. Treated with buprenorphine, methadone, or naltrexone; about 5.7 million US cases in 2023.

Opioid-induced delirium

Opioid-induced delirium (ICD-11 6C43.5) is acute disturbed attention and awareness during opioid intoxication, withdrawal, or use; risk is dose-dependent, highest with meperidine and methadone, managed by dose reduction or opioid rotation.

Opioid-induced mood disorder

Opioid-induced mood disorder (ICD-11 6C43.70) is mood symptoms, depressive, manic, or mixed, arising during or soon after opioid intoxication or withdrawal, distinguished from primary mood disorders by timing and course.

Opioid-induced psychotic disorder

Opioid-induced psychotic disorder (ICD-11 6C43.6; ICD-10-CM F11x50/51/59) is psychosis during or soon after opioid intoxication or withdrawal, rare with μ-agonists, mostly reported after abrupt opioid cessation.

Opipramol

Opipramol (Insidon) is an atypical tricyclic anxiolytic-antidepressant developed in the 1960s, acting via sigma receptors without serotonin/noradrenaline reuptake inhibition; approved in Germany for somatoform disorders and generalized anxiety disorder, not marketed in the US.

Opisthorchiasis

Opisthorchiasis is a foodborne parasitic disease caused by liver flukes of the genus Opisthorchis, acquired by eating raw or undercooked freshwater fish; chronic infection can cause bile duct cancer.

Opisthotonos

Opisthotonus (opisthotonos): severe backward arching of the neck and trunk from involuntary extensor paraspinal muscle contraction; symptom of tetanus, strychnine poisoning, dystonia, seizures, or functional disorders; described since Hippocrates.

Opitz GBBB syndrome

Opitz G/BBB syndrome, also called Opitz-Frias or hypertelorism-hypospadias syndrome, is a midline malformation disorder; the X-linked form is caused by MID1 variants at Xp22.2, causing hypertelorism, hypospadias, laryngeal clefts, cleft lip/palate, and heart defects.