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 articleOptic nerve sheath decompression is a delicate eye-orbit surgery that a specialist eye surgeon performs to protect vision when pressure inside the head is harming the...
Read articleOptic nerve hypoplasia (ONH) is a birth difference of the eye–brain connection. The optic nerve is the “cable” that carries visual signals from the eye to...
Read articleOptic Nerve Head Drusen (ONHD) are tiny, rock-like (often calcified) deposits that sit inside the optic nerve head (the “disc” you see at the back of...
Read articleOptic nerve head avulsion means the optic nerve fibers are torn away from the back of the eye right at the optic nerve head (the “optic...
Read articleThe optic nerve is the “cable” that carries visual signals from your eye to your brain. In some babies, a part of the tissue near the...
Read articleAn optic disc melanocytoma (ODM) is a small, very dark brown or black growth made of pigment cells (melanocytes) that sits on the optic disc (the...
Read articleAn optic disc hemorrhage is a small spot of bleeding on or next to the optic disc. The optic disc is the place in the back...
Read articleOptic disc drusen are tiny, hard, pebble-like deposits that sit inside the “head” of the optic nerve where it enters the back of the eye (the...
Read articleOptic atrophy means the optic nerve is damaged and has lost healthy fibers, so the nerve cannot carry visual messages from the eye to the brain...
Read articleOpsoclonus-Myoclonus Syndrome (OMS)—also called opsoclonus-myoclonus-ataxia syndrome (OMAS) or Kinsbourne syndrome. Opsoclonus-Myoclonus Syndrome (OMS) is a rare problem of the nervous system. It has three hallmark features:...
Read articleRecurrent Painful Ophthalmoplegic Neuropathy (RPON) is a rare condition in which a person has two or more attacks of a unilateral (one-sided) headache together with weakness...
Read articleOphthalmomyiasis means fly larvae (maggots) invade the eye or the tissues around the eye. It is uncommon, but it can harm vision if it is not...
Read articleRift Valley fever (RVF) is a viral disease that mainly affects animals (like sheep, goats, cattle, camels, and buffalo) but can also infect people. It is...
Read articleLeptospirosis is an infection caused by spiral-shaped bacteria called Leptospira. These bacteria live in the kidneys of many animals and come out in their urine. People...
Read articleKyasanur Forest Disease (KFD) is a viral hemorrhagic fever that people get after a bite from an infected tick in or near forested areas. The virus...
Read articleThrombotic thrombocytopenic purpura (TTP) is a rare, life-threatening blood disorder. Tiny clots form inside many of the body’s smallest blood vessels. These clots use up platelets...
Read articleSpinocerebellar ataxia (SCA) is a large family of inherited brain disorders in which the cerebellum—the brain’s “coordination center”—and its connections slowly wear out over time. Because...
Read articleObstructive sleep apnea is a sleep disorder where your throat repeatedly narrows or closes while you sleep. Air has trouble getting into your lungs. This causes...
Read articleFacioscapulohumeral dystrophy (FSHD) is a genetic muscle disease. The name tells you which muscles are hit first: the face (facio-), the shoulder blades (scapulo-), and the...
Read articleCreutzfeldt-Jakob disease (CJD) is a rare, fast-moving, and always fatal brain disorder. It happens when a normal body protein called prion protein changes shape into a...
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