Medical terms, defined.

Nuclear cataract is an age-related opacification and sclerosis of the central (nuclear) lens, the most common type of senile cataract. It causes progressive blurry distance vision, glare, and "second sight" (transient improvement in near...

Cortical cataract is an opacity of the peripheral lens cortex that appears as radial, wedge-shaped "spokes" pointing toward the center. It is classically associated with diabetes mellitus and aging, and it often causes glare and monocula...

Age-related macular degeneration (AMD) is the leading cause of irreversible central vision loss in people >50 years in developed countries. It affects the macula and presents as painless central vision loss with metamorphopsia (distortio...

Posterior subcapsular cataract (PSC) is a lens opacity at the posterior pole of the lens, just beneath the posterior capsule. It is classically associated with chronic corticosteroid use, diabetes, ocular inflammation (uveitis), radiatio...

A pinguecula is a benign, yellowish-white, raised conjunctival degeneration on the bulbar conjunctiva adjacent to the limbus (usually nasal), caused by chronic UV exposure, wind, and dust. Unlike a pterygium, it does NOT extend onto the...

Pterygium is a benign, wedge/wing-shaped fibrovascular conjunctival growth that extends from the bulbar conjunctiva (usually nasal side) onto the cornea. It is strongly associated with chronic UV exposure, wind, and dust, and can cause i...

Normal-tension glaucoma (NTG; low-tension glaucoma) is a form of primary open-angle glaucoma with characteristic optic neuropathy (cupping, neuroretinal rim loss) and visual field defects despite untreated IOP consistently ≤21 mmHg. Open...

A chalazion is a painless, firm, chronic granulomatous inflammatory nodule of the eyelid caused by obstruction of a meibomian (tarsal) gland with lipid leakage into surrounding tissue. It differs from a hordeolum (stye), which is an acut...

A hordeolum (stye) is an acute, painful, localized abscess of the eyelid caused by infection (usually Staphylococcus aureus) of an eyelash follicle/gland of Zeis or Moll (external) or a meibomian gland (internal). It presents as a tender...

Posterior uveitis is inflammation of the choroid and/or retina (choroiditis, chorioretinitis, retinochoroiditis, retinitis), posterior to the vitreous base. It presents with floaters and painless blurred vision, often without a red eye o...

Anterior uveitis (iritis/iridocyclitis) is inflammation of the iris and/or ciliary body, the most common form of uveitis. It presents with a painful, photophobic, red eye (ciliary flush), miosis or irregular pupil, and cells/flare in the...

Marcus Gunn pupil is a relative afferent pupillary defect (RAPD): when a light is swung from the normal eye to the affected eye, both pupils paradoxically dilate instead of constricting. It indicates unilateral or asymmetric optic nerve...

Cholesteatoma is a destructive, expanding mass of keratinizing stratified squamous epithelium (keratin debris) in the middle ear/mastoid. Despite the name, it is not a tumor and contains no cholesterol. It presents with chronic painless,...

Bitemporal hemianopia is loss of the temporal (lateral) half of the visual field in both eyes, caused by a lesion at the optic chiasm that damages the crossing nasal retinal fibers. The classic cause is a pituitary adenoma (adults) or cr...

Amblyopia ("lazy eye") is a unilateral (occasionally bilateral) reduction in best-corrected visual acuity caused by abnormal visual development in early childhood, without a structural ocular lesion explaining it. The most common causes...

Homonymous hemianopia is loss of the same half of the visual field in both eyes (e.g., right temporal + left nasal field), caused by a lesion posterior to the optic chiasm. The lesion is contralateral to the field defect, and the most co...

Vestibular schwannoma (acoustic neuroma) is a benign Schwann cell tumor of the vestibular portion of CN VIII, arising at the cerebellopontine angle. It presents with unilateral sensorineural hearing loss, tinnitus, and disequilibrium. Bi...

Adie (tonic) pupil is a unilateral, dilated pupil with light-near dissociation (poor/sluggish light response, slow tonic constriction to accommodation/near) caused by damage to the postganglionic parasympathetic fibers of the ciliary gan...

Acoustic neuroma (vestibular schwannoma) is a benign Schwann cell tumor of CN VIII (usually the vestibular division) at the cerebellopontine angle. It presents with unilateral sensorineural hearing loss, tinnitus, and disequilibrium. Bil...

BPPV is the most common cause of peripheral vertigo, caused by displaced calcium carbonate crystals (otoconia/canaliths) in the semicircular canals, most often the posterior canal. It presents with brief (<1 minute) episodes of rotatory...

Presbycusis is age-related, progressive, bilateral, symmetric sensorineural hearing loss that begins with high-frequency sounds. It is the most common cause of hearing loss in adults and results from cumulative degeneration of cochlear h...

The Rinne test compares air conduction (AC) to bone conduction (BC) using a 512 Hz tuning fork, placed first on the mastoid and then in front of the ear canal. Normally AC > BC (positive Rinne). BC > AC (negative Rinne) indicates conduct...

Benign Paroxysmal Positional Vertigo (BPPV) is the most common cause of peripheral vertigo, caused by displaced otoconia (canaliths) in the semicircular canals, most often the posterior canal. It presents with brief (<1 min) episodes of...

Conductive hearing loss (CHL) is reduced sound transmission through the external or middle ear (canal, tympanic membrane, ossicles), with a normal inner ear and cochlear nerve. Hallmarks: Rinne negative (BC > AC) in the affected ear, Web...

The Weber test is a bedside tuning fork test (512 Hz) placed at the midline forehead/vertex to assess for lateralization of sound, helping distinguish conductive from sensorineural hearing loss. Sound lateralizes to the AFFECTED ear in c...

Labyrinthitis is inflammation of the membranous labyrinth (cochlea + vestibular apparatus), most often viral (post-URI), causing acute vertigo WITH sensorineural hearing loss and/or tinnitus. It differs from vestibular neuritis, which ca...

Vestibular neuritis is an acute, usually viral (presumed HSV-1 reactivation) inflammation of the vestibular portion of CN VIII, causing sudden severe vertigo, nausea/vomiting, and gait instability lasting days, WITHOUT hearing loss or ti...

Laryngitis is inflammation of the larynx (especially the vocal folds) causing hoarseness or voice loss. Acute laryngitis is most often viral and self-limited (<3 weeks); chronic (>3 weeks) is linked to GERD/LPR, smoking, and vocal abuse,...

An esophageal web is a thin, membranous mucosal fold (epithelium + lamina propria, no muscularis) that protrudes into the esophageal lumen, most often in the upper (cervical) esophagus anterior wall. It causes intermittent solid-food dys...

A Schatzki ring is a thin, mucosal ring of tissue at the squamocolumnar junction of the distal esophagus, usually associated with a small hiatal hernia. It is a common cause of intermittent, nonprogressive solid-food dysphagia (classical...

An esophageal ring is a thin, concentric, mucosal narrowing of the distal esophagus. The classic type is the Schatzki ring (lower esophageal B-ring) at the squamocolumnar junction, associated with a hiatal hernia. It presents with interm...

Ludwig angina is a rapidly progressive, potentially fatal bilateral cellulitis of the submandibular, sublingual, and submental spaces, most often from an infected mandibular molar (2nd/3rd). It presents with fever, floor-of-mouth swellin...

Peritonsillar abscess (quinsy) is a collection of pus between the palatine tonsil capsule and the pharyngeal constrictor muscle, and it is the most common deep neck space infection in adolescents and young adults. It is a complication of...

Curling ulcer is an acute stress-related gastric or duodenal mucosal ulcer occurring after severe burns (classically >30-50% TBSA). It results from mucosal ischemia and hypoperfusion from hypovolemia. It is classically located in the sto...

Esophageal squamous cell carcinoma (ESCC) is a malignancy of the esophageal squamous epithelium, typically in the upper and middle thirds. It is the most common esophageal cancer worldwide. Major risk factors are alcohol, tobacco, hot be...

Vocal cord paralysis is loss of motor function of one or both vocal folds due to injury to the vagus nerve or its branch, the recurrent laryngeal nerve (RLN). Unilateral paralysis presents with hoarseness and breathy voice; bilateral par...

Cushing ulcer is a stress-related gastric (or duodenal/esophageal) ulcer that occurs after traumatic brain injury, intracranial hemorrhage, or neurosurgery. It's caused by elevated intracranial pressure driving vagal stimulation, which i...

Gastrointestinal stromal tumor (GIST) is the most common mesenchymal tumor of the GI tract, arising from the interstitial cells of Cajal (pacemaker cells) and driven by gain-of-function mutations in KIT (CD117) or PDGFRA. It most often o...

Familial adenomatous polyposis (FAP) is an autosomal dominant syndrome caused by germline APC (tumor suppressor, chromosome 5q21) mutations, producing hundreds to thousands of colorectal adenomatous polyps beginning in adolescence. Witho...

HNPCC (Hereditary Non-Polyposis Colorectal Cancer), now called Lynch syndrome, is an autosomal dominant disorder caused by germline mutations in DNA mismatch repair (MMR) genes (MLH1, MSH2, MSH6, PMS2). It causes early-onset (<50 y) prox...

Hereditary nonpolyposis colorectal cancer (HNPCC), now called Lynch syndrome, is an autosomal dominant disorder caused by germline mutations in DNA mismatch repair (MMR) genes (MLH1, MSH2, MSH6, PMS2) or EPCAM deletions. It causes early-...

HCC (hepatocellular carcinoma) is the most common primary malignancy of the liver, arising from hepatocytes, typically in the setting of cirrhosis (HBV, HCV, alcohol, NASH/MASLD) or aflatoxin exposure. It presents with a liver mass and e...

Seborrheic keratosis is a very common benign epidermal tumor of older adults, presenting as tan-to-brown/black, waxy, "stuck-on" papules or plaques with a verrucous surface. It is not premalignant, but sudden eruption of many lesions (Le...

Internal hemorrhoids are symptomatic vascular cushions of the anal canal located ABOVE the dentate (pectinate) line, covered by columnar (insensate) mucosa and supplied by visceral innervation. They classically present with painless brig...

Bowen disease is squamous cell carcinoma in situ (full-thickness epidermal dysplasia without breach of the basement membrane). It presents as a slowly enlarging, erythematous, scaly, well-demarcated plaque on sun-exposed skin, and it can...

PSC most commonly = Primary Sclerosing Cholangitis: a chronic cholestatic liver disease with idiopathic inflammation and fibrosis of intra- and extrahepatic bile ducts, producing "beading" on cholangiography. Strongly associated with ulc...

PBC (primary biliary cholangitis, formerly "primary biliary cirrhosis") is an autoimmune, T-cell–mediated destruction of small intrahepatic bile ducts, classically in middle-aged women. It presents with fatigue, pruritus, and cholestatic...

Alopecia areata is an autoimmune, non-scarring hair loss disorder in which T cells attack anagen hair follicles, causing well-circumscribed round/oval patches of hair loss. Exclamation-point hairs are pathognomonic, and it is associated...

Tinea cruris ("jock itch") is a dermatophyte infection of the groin and upper inner thighs, most commonly caused by Trichophyton rubrum and Epidermophyton floccosum. It presents as a pruritic, erythematous, sharply demarcated annular pla...

Verruca vulgaris (common wart) is a benign, hyperkeratotic epidermal papule caused by HPV, most commonly types 1, 2, 4, 27, and 57. It is spread by direct contact or autoinoculation (Koebner phenomenon). Most resolve spontaneously, espec...