Keratoendotheliitis fugax hereditaria (often shortened to KEFH) is a rare, inherited eye condition. People get short, repeat attacks where the clear window of ...

Keratoconus (pronounced keh-rah-toe-KOH-nus) is an eye condition where the cornea—the clear, dome-shaped “front window” of your eye—gets thinner and bulges ...

Keratoacanthoma (KA) is a fast-growing bump on the skin that looks like a small dome with a central “plug” of hard, yellow-brown material called keratin ...

Kearns–Sayre syndrome (KSS) is a rare mitochondrial disease—meaning the tiny “power plants” in our cells (mitochondria) don’t make enough energy. Classic KSS ...

Kawasaki disease (often shortened to “KD”) is an illness in young children that causes swelling and irritation of blood vessels (a “vasculitis”). It usually ...

Kasabach-Merritt Phenomenon (KMP) is a dangerous blood-clotting problem that happens in babies and young children who have a special kind of blood-vessel ...

Kabuki syndrome is a rare genetic condition present from birth. It affects how a child’s face, body, brain, and several organs develop and work. The name comes ...

Juvenile xanthogranuloma (JXG) is a benign (non-cancerous) skin condition in babies and young children. It belongs to a family of diseases called ...

Juvenile open-angle glaucoma (JOAG) is a glaucoma that shows up after early childhood (usually in the pre-teen, teen, or young-adult years) and before age ~40. ...

Juvenile idiopathic arthritis–associated uveitis — often shortened to JIA‑U — is inflammation inside the eye that happens in some children who have juvenile ...

“Junctional scotoma of Traquair” is a specific visual field loss pattern that happens when a lesion (often a tumor, cyst, aneurysm, or inflammation) sits right ...

A scotoma means a blind spot or patch of missing vision. You already have a normal “blind spot” where the optic nerve leaves the eye, but a pathologic scotoma ...

Joubert syndrome (JS) is a rare genetic condition that affects how the brain develops before birth. The main problem is in the back part of the brain called ...

Ivacaftor is a medicine used for cystic fibrosis (CF). In some children and teens who take ivacaftor (by itself or combined with other CF drugs), doctors have ...

An iris varix is a stretched-out, widened vein inside the colored part of your eye (the iris). Think of it as a tiny “varicose vein” of the iris. It usually ...

The iris is the round, colored part of your eye (brown, blue, green, etc.). It works like a camera aperture. A small ring of muscle inside the iris makes the ...

Iris Retraction Syndrome (often shortened to IRS) is a rare eye condition. In plain terms, it means the colored part of the eye (the iris) bends backward ...

Iris melanoma is a cancerous growth made from pigment cells (called melanocytes) in the iris, the colored ring at the front of your eye. These melanocytes ...

An iris cyst is a small, thin-walled, fluid-filled sac that forms in or behind the iris. Most iris cysts are benign (non-cancerous). Many cause no trouble and ...

An iris AVM is an abnormal shortcut (shunt) between an iris artery and an iris vein. Instead of blood flowing from arteries → tiny capillaries → veins, the ...

“Iris and ciliary body metastasis” means a cancer from somewhere else in the body has spread to the front part of the eye. The iris is the colored ring that ...

Iridoschisis is a rare eye condition where the colored part of your eye (the iris) literally splits into two layers. The thin front layer of the iris weakens, ...

Secondary glaucoma means glaucoma that happens because of another eye problem, a disease elsewhere in the body, a drug, or an injury. In simple words: the ...

Primary glaucoma is a group of eye diseases that slowly injure the optic nerve without another eye problem causing it (that’s why we call it “primary”). The ...

ICE syndrome is a rare eye condition where a thin cell layer on the back of the cornea (the corneal endothelium) starts acting abnormally. These cells creep ...

Your cornea is the clear front window of the eye. It has a smooth dome shape and steady thickness so it can bend (focus) light properly. Ectasia means abnormal ...

Iodine” is a natural trace mineral that your thyroid and every cell in your body needs to live. Because iodine is tiny and essential, the immune system does ...

An inverted papilloma is a non-cancerous (benign) growth made of the lining cells of the nose and nearby drainage passages. When it grows inside the lacrimal ...

Inverse Bell’s Phenomenon is a rare eye movement problem that happens when you try to close your eyes.Normally, when we close our eyes — especially tightly — ...

Invasive fungal infection of the orbit and sinuses” means a fungus has moved past the surface lining of the nose and sinus cavities, grown into the deeper ...

Intumescent cataract means a swollen cataract. The natural lens inside the eye takes up extra water (fluid) and thickens. Because the lens is thicker and ...

Intravascular Papillary Endothelial Hyperplasia (IPEH) is a benign (non-cancerous) growth that forms inside a blood vessel. It appears when the inner lining ...

Intratunnel phacofracture is a way to remove a cataract (a cloudy natural lens) during manual small-incision cataract surgery (MSICS). Instead of breaking the ...

An IKC is a benign (non-cancerous) pocket filled with keratin—a soft, cheesy or flaky protein that skin makes—sitting inside the tarsal plate (the firm ...

Posterior capsular rupture means a tear in the thin, clear back wall of the eye’s natural lens “bag.” During cataract surgery, surgeons remove the cloudy lens ...

Iris prolapse is a condition where a part of the iris — the thin, colored, circular part of the eye that controls how much light enters — slips or bulges out ...

Intraoperative Floppy Iris Syndrome (IFIS) is a problem that can happen during cataract surgery. The iris is the colored ring in your eye that controls the ...

A circumscribed choroidal hemangioma is a benign (non-cancerous) blood-vessel tumor that grows inside the choroid, the spongy, vascular layer underneath your ...

Diffuse choroidal hemangioma is a birth-related (congenital) cluster of extra blood vessels inside the choroid, which is the thin, spongy, reddish layer of ...

Retinal vasoproliferative tumor (often shortened to VPT) is a rare, usually benign (non-cancer) lump that grows in the peripheral retina (the outer edge of the ...

Coats’ disease is a rare eye condition where some of the tiny blood vessels in the retina (the “film” at the back of the eye that senses light) are abnormal, ...

Ocular ischemic syndrome is a problem where the eye doesn’t get enough blood for a long time. Most of the time this happens because the big neck artery that ...

A choroidal vasoproliferative tumor—more commonly called a retinal vasoproliferative tumor (VPT)—is a benign (non-cancer) lump made mostly of new blood vessels ...

Von Hippel-Lindau (VHL) disease is a rare genetic condition that makes the body grow tumors and fluid-filled cysts in many organs. Most of the tumors are ...

A retinal angioma, also known as a retinal capillary hemangioma, is a rare, non-cancerous (benign) growth made up of extra blood vessels in the retina—the ...

Wyburn-Mason syndrome, also called Bonnet–Dechaume–Blanc syndrome, is a very rare condition present at birth in which blood vessels form direct connections ...

A racemose hemangioma (RH) is a fast-flow vascular malformation, not a true tumor. Doctors also call it a retinal or iris arteriovenous malformation (AVM) when ...

A vasoproliferative tumor of the retina (VPT) is a rare, benign growth made up of abnormal blood vessels within the retinal tissue. These tumors typically ...

Cavernous Hemangioma of the Retina is a rare, benign (non-cancerous) vascular hamartoma that forms clusters of thin-walled, blood-filled sacs within the ...

A retinal capillary hemangioma is a non-cancerous growth made up of tiny blood vessels in the light-sensitive layer at the back of the eye called the retina. ...

Choroidal hemangioma is a harmless, noncancerous growth made up of extra blood vessels in the choroid, the layer of blood‐rich tissue found between the retina ...

An intraocular vascular tumor is an abnormal, benign or malignant growth of blood‐vessel cells inside the eye. These tumors arise from the vascular (blood ...

An intraocular paraganglioma is a very rare tumor that starts inside the eye. It grows from a type of nerve cell called a chromaffin cell, which normally helps ...

Intraocular Leiomyoma is a rare, non-cancerous tumor made of smooth muscle cells that grows inside the eye. It most often comes from the uveal tract—the ...

Retinoblastoma is a rare cancer that starts in the retina, which is the light-detecting layer at the back of the eye. It most often affects young children, ...

Interstitial keratitis is when the middle layer of the cornea (called the stroma) becomes inflamed without any open sore on the surface or back of the cornea. ...

Internuclear ophthalmoplegia (INO) is an eye movement problem caused by damage to a special pathway in the brainstem called the medial longitudinal fasciculus ...

Internal limiting membrane dystrophy (ILMD), also called Familial Müller Cell Sheen Dystrophy, is a rare inherited eye condition that affects the very inner ...

Intermittent exotropia is a common eye alignment problem where one eye occasionally drifts outward, away from the nose, while the other eye remains focused ...

Intermediate uveitis is when the middle part of the eye (the vitreous gel and the pars plana just behind the iris) becomes inflamed. This means the tissues in ...

Interface Fluid Syndrome (IFS) is a rare eye condition that happens when clear fluid collects in the thin space between layers of the cornea after surgery. In ...

An infraorbital rim tear is a cut or split in the bone or soft tissue just below the eye socket. This area—the infraorbital rim—is the bony edge that forms the ...

Inferior oblique myokymia is a rare eye movement disorder where a small muscle under the eye (the inferior oblique muscle) twitches by itself without you ...

Infectious crystalline keratopathy (ICK) is a rare, slow-growing infection of the cornea. It was first described in 1983 by Gorovoy and colleagues after they ...

Infantile esotropia is a form of eye misalignment that appears in the first six months of life. In this condition, one or both eyes turn inward toward the nose ...

Incontinentia Pigmenti (IP) is a rare genetic skin disorder that also affects the teeth, eyes, hair, nails, and sometimes the brain. It is caused by a change ...

Inclusion body myositis (IBM) is a muscle disease that develops slowly and mainly affects adults over the age of 45 or 50. In IBM, two harmful processes happen ...

Inborn Errors of Galactose Metabolism (I.E.G.M.) are rare genetic conditions that affect how the body processes a sugar called galactose (a simple sugar found ...

A periorbital hematoma, often called a “black eye,” is a collection of blood in the tissues around the eye. It looks like bruising—dark blue, purple, or black ...

Traumatic enophthalmos is when an eye appears to have “sunken in” after an injury. In medical terms, it’s the posterior displacement of the eyeball within its ...

Chemical and thermal injuries to the ocular adnexa are serious eye emergencies that affect the tissues surrounding the eyeball—chiefly the eyelids, ...

Orbital compartment syndrome is an emergency condition in which the pressure inside the eye socket (the orbit) rises so quickly and so high that blood cannot ...

Limbic ischemia happens when blood does not reach parts of the limbic system in the brain. The limbic system includes structures like the hippocampus ...

Ptosis, also called blepharoptosis, means the upper eyelid droops too low when the eye looks straight ahead. When this drooping happens after an injury, it is ...

A degloving injury happens when a large section of skin and the fat underneath is torn away from the deeper layers of muscle, bone, or connective tissue. This ...

Orbital emphysema is a condition in which air becomes trapped within the soft tissues of the eye socket (orbit). Picture the orbit as a hollow house around ...

An orbital blow-out fracture is a break in one or more of the thin bones forming the walls of the eye socket, known as the orbit. Unlike fractures involving ...

Orbital rim fractures are breaks in the solid bones that form the border, or “rim,” of the eye socket. These fractures happen when a force hits the side of the ...

Canalicular lacerations are tears or cuts in the small tubes (canaliculi) that drain tears from the eye into the nasal cavity. These tiny ducts lie just inside ...

Eyelid lacerations happen when the delicate skin and soft tissue of the eyelid are cut or torn open. These injuries can range from small nicks to deep wounds ...

An eyelid contusion, often called a “black eye,” is a bruise of the soft, thin skin and underlying tissues around the eye. It happens when a blunt object ...

Ocular adnexal trauma refers to any injury affecting the structures around the eyeball—namely the eyelids, lacrimal (tear) apparatus, conjunctiva, orbital soft ...

IgG4-related orbital inflammation is a specific form of a wider condition called IgG4-related disease (IgG4-RD). In IgG4-RD, certain immune cells (called ...

Idiopathic Neuroretinitis is an inflammation of the optic nerve head (optic disc) and adjacent retina for which no clear cause can be found. It typically ...

An idiopathic aneurysm is an unusual bulging or ballooning of a blood vessel wall that happens without any identifiable cause, such as trauma, infection, or ...

Idiopathic vasculitis is a condition in which the body’s blood vessels become inflamed for reasons that doctors cannot fully explain. In very simple English, ...

Idiopathic retinitis means the retina (the light-sensing layer at the back of your eye) is inflamed, and doctors cannot find any known infection, autoimmune ...

Idiopathic multifocal choroiditis (IMFC) is a rare, chronic eye disease where many small, inflamed spots develop deep in the back of the eye, especially in the ...

Idiopathic Intracranial Hypertension (IIH) is a condition where the pressure inside the skull (intracranial pressure) is higher than normal, even though there ...

Hypotropia in Thyroid Eye Disease (TED), also known as Graves’ orbitopathy, is when one eye is pulled downward relative to the other due to inflammation and ...

Hypotony maculopathy is an eye condition where the pressure inside the eyeball (intraocular pressure or IOP) falls so low that it damages the macula, the ...

Hypnic headache, often called “alarm clock headache,” is a rare primary headache disorder that happens only during sleep and consistently awakens people, ...

Hypertropia is a kind of eye misalignment (strabismus) in which one eye points higher than the other. This happens because the muscles or nerves that move the ...

Hypertropia is a form of eye misalignment where one eye drifts upward compared to the other. When both eyes look at the same point, one eye points higher than ...

Hypertelorism is a condition present at birth in which the distance between the two eye sockets (orbits) is larger than usual. In very simple English, imagine ...

Hyperopia, also known as farsightedness, is a common refractive error of the eye in which light entering the eye focuses behind the retina rather than directly ...

Hydroxychloroquine toxicity happens when the medicine hydroxychloroquine builds up in the body to levels that cause harm. Hydroxychloroquine is a drug often ...

Hurricane keratopathy is a condition that affects the clear front part of the eye called the cornea. In this condition, the cells on the surface of the cornea ...

Human T-cell Lymphotropic Virus Type 1 (HTLV-1) associated uveitis is an eye inflammation caused by infection with HTLV-1, a retrovirus that primarily infects ...

A meniscus tear—sometimes called a horseshoe tear because the meniscus is a small, horseshoe-shaped piece of cartilage in your knee, or a flap tear when a ...

Horner syndrome is a condition that happens when the nerve pathway that controls certain eye and facial functions is damaged. This pathway is called the ...

Homocystinuria (pronounced “home-oh-sis-tin-YOOR-ee-uh”) is a genetic disorder. It happens when one of the enzymes needed to break down homocysteine—an ...

HLA-B27-Associated Acute Anterior Uveitis (HLA-B27 AAU) is a sudden inflammation of the front part of the eye—the iris (colored part) and ciliary body (just ...

HIV-associated facial lipoatrophy is a condition in which people living with HIV lose fat in their faces. This can make cheeks look hollow, temples appear ...

Central Serous Chorioretinopathy—often shortened to CSCR or just “central serous”—is an eye disease in which clear fluid leaks out of the small blood vessels ...

Central Retinal Vein Occlusion means that the single large vein that drains blood out of the retina – the light‑sensitive “film” at the back of your eye – has ...

Central neurocytoma (CN) is a rare, slow‑growing brain tumour that starts from immature nerve‑like cells (neurons) inside the fluid‑filled cavities of the ...

Your fovea is the tiny, bowl-shaped pit in the very center of the macula—the macula being the central patch of retina that lets you read, drive, and recognize ...

Central Cloudy Dystrophy of François is a very rare stromal corneal dystrophy first described in 1955. In this condition, the central part of each cornea ...

Central Areolar Choroidal Dystrophy is a rare, inherited eye condition that slowly erodes the very heart of your central retina (the macula). In CACD, the ...

Cavernous Sinus Syndrome (CSS) is a collection of signs and symptoms that appear when the structures running through, or lying next to, the cavernous sinus ...

A cataract is any cloudiness or opacity inside the eye’s natural lens. In children the condition is especially serious because the developing brain relies on ...