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 articleMELAS stands for Mitochondrial Encephalomyopathy, Lactic Acidosis, and Stroke-like episodes. It is a rare genetic condition that affects how the tiny “power plants” inside our cells—called...
Read articleFatal Familial Insomnia (FFI) is an ultra-rare, inherited prion disease. A single change in the PRNP gene (classically D178N with methionine at codon 129) makes the...
Read articleTuberous sclerosis complex (TSC) is a genetic condition in which harmless-looking overgrowths of tissue (called hamartomas) can develop in many organs. The problem starts when changes...
Read articleSinus pericranii (SP) is a rare problem with veins in the skull. In SP, there is an unusual “shortcut” vein that connects veins inside the skull...
Read articleOphthalmic Manifestations of SIBO (Small Intestinal Bacterial Overgrowth) means there are too many bacteria in the small intestine. Those bacteria can deactivate bile acids (they “deconjugate” them),...
Read articleKawasaki disease is an inflammatory illness that mainly affects young children. It causes inflammation in blood vessels all over the body. Doctors call this a systemic...
Read articleHeparin-Induced Thrombocytopenia (HIT) is a dangerous immune reaction to the blood thinner heparin. Your immune system makes antibodies that stick to a normal platelet protein called...
Read articleDiGeorge syndrome is a genetic condition that a baby is born with. It happens when a tiny piece of DNA is missing from chromosome 22. Doctors...
Read articleSystemic capillary leak syndrome (SCLS) is a very rare condition where the tiniest blood vessels in the body (the capillaries) suddenly become “leaky.” When this happens,...
Read articleOphthalmic delusional parasitosis is a mental health condition where a person has a fixed, unshakable belief that parasites (like insects, worms, or mites) are living in...
Read articleAn ophthalmic artery pseudoaneurysm is a small, dangerous bulge that forms in the ophthalmic artery, the blood vessel that supplies the eye and the tissues around...
Read articleOphthalmia nodosa is eye inflammation that happens when tiny hairs or spines from certain insects—most often caterpillars—or spiky plant fibers get into your eye. These hairs...
Read articleOne-and-a-Half Syndrome is a special eye movement problem caused by a small injury in the brainstem (the “pons”). It knocks out almost all side-to-side eye movement....
Read articleAn oncocytoma is a tumor made of special cells called oncocytes. Oncocytes are cells that look pink and grainy under the microscope because they are packed...
Read articleAfrican River Blindness, also called onchocerciasis, is a long-lasting infection caused by a tiny worm named Onchocerca volvulus. People get it when blackflies that live and...
Read articleOnchocerciasis is a long-lasting infection caused by a tiny worm called Onchocerca volvulus. People get this worm when blackflies bite them many times over months or...
Read articleOculopharyngeal Muscular Dystrophy—usually shortened to OPMD—is a genetic muscle disease that mainly weakens the muscles of the eyelids (“oculo-”) and the throat (“pharyngeal”). People typically begin...
Read articleOculopalatal tremor is a movement disorder where the eyes move back and forth in a smooth, slow, repetitive way, and the soft palate inside the mouth...
Read articleOculomotor synkinesis is a problem where different eye and eyelid parts move together even when they should move separately. It happens because the third cranial nerve...
Read articleOculomotor apraxia (often shortened to OMA) is a problem with starting quick eye movements on purpose. These quick eye movements are called saccades. Saccades are the...
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