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 articleUsher syndrome is a genetic condition that a person is born with. It mainly affects hearing, vision, and sometimes the balance system of the inner ear....
Read articleNeurodegenerative diseases are long-lasting conditions where nerve cells (neurons) in the brain and spinal cord are damaged or die earlier than they should. Because neurons control...
Read articleUrrets-Zavalia syndrome is a rare complication after eye surgery where the black center of the eye (the pupil) becomes stuck in a large, round, and non-reactive...
Read articleUpper eyelid retraction means the upper lid sits too high on the eye. In normal, relaxed gaze, the upper lid usually covers the top 1–2 millimeters...
Read articleUpper eyelid blepharopathy means “a disease or dysfunction of the upper eyelid,” most often showing up as eyelid margin inflammation (blepharitis), meibomian gland dysfunction (MGD), crusting,...
Read articleBilateral pigmentary retinopathy means that both eyes show abnormal pigment changes in the retina, the light-sensitive layer at the back of the eye. The pigment cells...
Read articleUnilateral Pigmentary Retinopathy (UPR) describes a retina-degenerating condition in one eye that looks and behaves like retinitis pigmentosa (RP), but with the other eye normal. The...
Read articleBilateral coronal synostosis means both coronal sutures—the flexible seams running from ear to ear across the top of a baby’s skull—fuse too early. In a newborn...
Read articleUnilateral coronal synostosis means one of the baby’s two coronal sutures (the joints that run from ear to ear across the top of the skull, just...
Read articleSudden visual loss means your eyesight drops quickly over minutes, hours, or a few days. You may notice a dark curtain, a gray shadow, foggy or...
Read articleUltramarathon-induced corneal edema is a temporary swelling of the clear front window of the eye (the cornea) that happens during or soon after very long, hard...
Read articleTINU syndrome is a rare inflammatory disease that affects both the kidneys (specifically the tiny tubes and the tissue around them—this part is called tubulointerstitium) and...
Read articleTubulointerstitial Uveitis is known as tubulointerstitial nephritis and uveitis (TINU) syndrome—a disorder where the kidneys’ tubules/interstitium are inflamed (tubulointerstitial nephritis) and the eye’s uveal tract is...
Read articleTuberculosis uveitis (often called ocular TB) is inflammation inside the eye that happens when your immune system reacts to germs from Mycobacterium tuberculosis (the bacteria that...
Read articleTrochleitis means inflammation around the trochlea, the tiny pulley of cartilage at the inner-upper corner of the eye socket where the superior oblique tendon glides. When...
Read articleTrisomy 21, commonly called Down syndrome, is a genetic condition where a person has three copies of chromosome 21 in their cells instead of the usual...
Read articleTrisomy 13—also called Patau syndrome—is a genetic condition in which a person has three copies of chromosome 13 in their cells instead of the usual two....
Read articleTrigeminal trophic syndrome is a rare skin and nerve disorder that appears after damage to the trigeminal nerve (the 5th cranial nerve that carries feeling from...
Read articleA trifocal intraocular lens (IOL) is a clear, foldable lens implant placed inside your eye during cataract surgery (or sometimes refractive lens exchange when there is...
Read articleA trichilemmoma is a benign (non-cancerous) skin growth that comes from the outer root sheath of a hair follicle—the sleeve of cells around the hair inside...
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