Browse plain-English disease and condition guides, including symptoms, causes, diagnosis, treatment options, prevention, and when to seek medical care.
Persistent Hyperplastic Primary Vitreous (PHPV)—now more often called Persistent Fetal Vasculature (PFV) is a congenital (present at birth) eye condition. In a developing baby, the eye has...
Read articleAblepharon-Macrostomia Syndrome (AMS) is an extremely rare, autosomal dominant genetic disorder characterized principally by absent or underdeveloped eyelids (“ablepharon”) and an unusually wide, fish-like mouth (“macrostomia”)...
Read articleAcanthamoeba keratitis is a rare but potentially sight-threatening corneal infection caused by the free-living amoeba Acanthamoeba, which is found ubiquitously in soil, fresh water, and even...
Read articleAccommodative esotropia is a common form of childhood strabismus in which one or both eyes turn inward (esodeviation) because of excessive focusing (accommodation) linked to farsightedness...
Read articleAchromatopsia is a rare eye condition that affects how a person sees color. People with achromatopsia typically have trouble seeing colors or can only see them...
Read articleAchromatopsia is a rare, inherited vision disorder that causes a complete or partial inability to see color. People with achromatopsia rely almost entirely on their rod...
Read articleAchromatopsia 2 (ACHM2) is a genetic eye condition that starts from birth. It mainly affects the cone cells in the retina, which are the light-sensing cells...
Read articleAcquired Developmental Prosopagnosia, often referred to as ADP, is a condition that affects a person’s ability to recognize faces. It’s a complex condition, and in this...
Read articleAcquired ectropion uveae (AEU) is a condition in which the pigmented posterior layer of the iris—normally hidden on the back surface—becomes adherent to and everts onto...
Read articleAcquired oculomotor nerve palsy is a non-congenital condition in which the third cranial nerve (oculomotor nerve) becomes damaged after birth, leading to dysfunction of most extraocular...
Read articleAcquired ophthalmoparesis is a condition characterized by weakness or paralysis of one or more extraocular muscles—those that control eye movements—due to processes that occur after birth....
Read articleAcquired Orbital Dysmorphia (AOD) is a medical condition that affects the structure and appearance of the eye socket and surrounding areas. In simpler terms, it means...
Read articlePersistent pupillary membrane, often shortened to PPM, is a harmless remnant of the fine, web-like blood vessels that cover a baby’s pupil before birth. During normal...
Read articlePersistent Postural-Perceptual Dizziness (PPPD) is a long-lasting balance disorder. People feel dizzy, unsteady, or as if they are moving when they are actually still. These symptoms...
Read articlePersistent Hyperplastic Primary Vitreous (PHPV)—now more often called Persistent Fetal Vasculature (PFV) is a congenital (present at birth) eye condition. In a developing baby, the eye has...
Read articlePeroxisomal ocular diseases are eye problems that happen because tiny cleaning-and-building stations inside our cells—called peroxisomes—do not work properly. Peroxisomes help the body break down very-long...
Read articlePeripheral Ulcerative Keratitis (PUK) is a serious eye condition where the edge of the cornea (the clear front window of the eye) becomes inflamed, thins out,...
Read articlePeripheral retinal degenerations are age- and structure-related changes that happen in the outer (side) parts of the retina—the light-sensing tissue that lines the back of your...
Read articlePeripheral Exudative Hemorrhagic Chorioretinopathy — usually shortened to PEHCR — is an eye condition that happens in the peripheral retina (the outer edges of the back...
Read articlePeripapillary Pachychoroid Syndrome is an eye condition. It sits inside the “pachychoroid” family of disorders. “Pachy” means thick. “Choroid” is the blood-vessel layer under the retina....
Read articlePeripapillary Intrachoroidal Cavitation, often shortened to PICC, is a pocket or hollow inside the choroid (the vascular layer under the retina) that forms right next to...
Read articlePeripapillary hyperreflective ovoid mass-like structures (PHOMS) are a pattern doctors see on a special eye scan called optical coherence tomography (OCT). They sit next to the...
Read articlePeriorbital (or periocular) necrotizing fasciitis is a rare but extremely dangerous skin and soft-tissue infection that attacks the tissue layers just under the skin around the...
Read articlePeriocular atypical mycobacterium infection means an infection caused by non-tuberculous mycobacteria (NTM) in the skin and soft tissues around the eye. “Periocular” or “periorbital” means the...
Read articlePeriocular dermatitis, also called periorbital dermatitis or eyelid eczema, is a skin problem that happens on the thin skin around your eyes. “Peri-” means “around.” “Ocular”...
Read articlePerifoveal Exudative Vascular Anomalous Complex (PEVAC) is a mouthful that describes a very specific problem with a tiny blood vessel near the very center of sight (the...
Read articlePentosan polysulfate maculopathy is an eye disease that can happen in some people who take the bladder-pain medicine pentosan polysulfate sodium (PPS) (brand: Elmiron). The macula...
Read articlePellucid marginal corneal degeneration (PMD) is a clear-looking but structurally thinned belt of cornea near the lower edge of the eye. This thinning makes the cornea...
Read articlePelizaeus–Merzbacher disease (PMD) is a rare, inherited brain white-matter disorder. “White matter” is the wiring of the brain. It is covered by myelin, which works like...
Read articlePeduncular hallucinosis is a rare brain condition that causes vivid, detailed visual hallucinations. People often see bright, colorful, moving scenes, people, animals, or small figures. The...
Read articlePediatric uveitic glaucoma is optic-nerve damage from long-lasting or repeated eye inflammation in a child, often with high eye pressure (IOP). The inflammation can clog or...
Read articlePenetrating keratoplasty, often called PK or full-thickness corneal transplant, is an eye surgery where a surgeon removes a circular piece of the patient’s cloudy or damaged...
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