Elschnig pearls are clusters of regenerating lens epithelial cells that form after cataract surgery on the posterior (back) capsule of the lens. They are a ...

Elevated intraocular pressure (IOP) means that the fluid pressure inside the eye is higher than normal. The eye maintains its shape and internal environment by ...

Every eye makes a clear fluid called aqueous humor. This fluid drains out through channels that eventually empty into the episcleral veins, small veins on the ...

Eight-and-a-Half Syndrome is a rare neurological condition caused by a small but specific injury in the back (dorsal) part of the pons, which is a section of ...

Ehlers-Danlos Syndrome (EDS) is a group of inherited (passed in families) disorders that make the body’s connective tissue weaker than normal. Connective ...

Eczema herpeticum is a serious skin infection caused by the herpes simplex virus (mostly HSV-1, sometimes HSV-2) that spreads rapidly over areas of broken or ...

Ectropion is a condition where the eyelid, most often the lower eyelid, turns outward away from the eyeball instead of sitting gently against it. Because the ...

Ectopia lentis means that the natural lens inside the eye is out of its normal place. Normally, the lens sits behind the pupil, held in place by tiny fibers ...

Ectasia after LASIK is a rare but serious problem where the cornea (the clear front window of the eye) becomes weaker, thinner, and bulges outward after laser ...

Eccrine sweat gland carcinoma is a very rare type of skin cancer that starts in the eccrine sweat glands—the glands all over the body that make watery sweat to ...

Eccrine hidrocystomas are harmless, small fluid-filled cysts that form when sweat produced by the eccrine glands gets trapped and builds up in the duct, ...

Eales Disease is a rare eye condition that mainly affects the small veins in the outer (peripheral) part of the retina, the light-sensing layer at the back of ...

Dysthyroid optic neuropathy is a serious problem that happens in some people with thyroid eye disease (also called Graves’ orbitopathy). In this condition, the ...

Dysphotopsia means unwanted visual images or disturbances that a person sees, usually after cataract surgery when an artificial lens (intraocular lens, IOL) is ...

Dysmorphology syndromes in the eye means conditions where the eye's shape, structure, or parts develop in an unusual or abnormal way, often from birth. These ...

Dyslexia is a learning difference that mainly affects a person’s ability to read, spell, and sometimes write. It is not a sign of low intelligence. Instead, ...

A dysembryoplastic neuroepithelial tumor (DNET) is a rare, slow-growing, benign (WHO grade 1) brain tumor that arises from cortical tissue and contains both ...

Dupilumab-induced conjunctivitis is an inflammation of the eye’s conjunctiva (the clear tissue covering the white part of the eye and the inside of the ...

Duane Retraction Syndrome (DRS) is a condition someone is born with (congenital) that affects how the eye moves side to side. Normally, muscles and nerves work ...

Dry eye after LASIK is a condition where the eyes feel dry, uncomfortable, or irritated following laser vision correction surgery called LASIK. It happens ...

Dry Eye Syndrome (also called Dry Eye Disease or DED) is a common condition where the front surface of the eye does not stay properly wet. Tears are needed to ...

Dry eye in Sjögren’s syndrome is a condition where the eyes become very dry, uncomfortable, and sometimes damaged because a person’s immune system attacks the ...

Drug-induced corneal disease means damage to the clear front part of the eye (the cornea) caused by medicines. These drugs can be taken by mouth, injected, or ...

Drug-induced acute angle closure glaucoma (DI-AACG) is a sudden, serious eye problem caused by certain medications. In this condition, the angle between the ...

Uveitis means inflammation inside the eye, especially of the uveal tract (the iris, ciliary body, and choroid), but the inflammation can involve other parts ...

Drug-induced maculopathy means damage to the macula—the central part of the retina that gives us sharp, detailed vision—caused by medications or systemic ...

Cataract means the natural lens inside the eye becomes cloudy, so light cannot pass clearly and vision becomes blurred, dim, or distorted. It usually happens ...

Doyne Honeycomb Retinal Dystrophy (DHRD), also known as Malattia Leventinese or Familial Dominant Drusen, is a rare inherited eye disease that slowly damages ...

Lymphedema-Distichiasis Syndrome (LDS) is a rare inherited condition in which two main problems appear together: lymphedema (swelling, usually of the legs, ...

A Dome-Shaped Macula (DSM) is a special shape change in the central part of the retina (the macula) where, instead of being flat or slightly concave, it bulges ...

Distichiasis is a condition where a person has an extra row of eyelashes. Instead of the normal single line of lashes at the lid margin, there is a second row ...

An intraocular lens (IOL) is an artificial lens implanted inside the eye to replace the eye’s natural lens, most commonly during cataract surgery. A dislocated ...

Glaucoma is a group of eye diseases that slowly damage the optic nerve, usually by pressure or reduced blood flow inside the eye. When the optic nerve is ...

The superior ophthalmic vein (SOV) is the main vein that drains blood from the eye and the tissues around the eye back toward the brain. When this vein becomes ...

Diffuse Unilateral Subacute Neuroretinitis (DUSN) is a rare eye infection caused when a tiny worm (a nematode) gets into the layers under the retina of one eye ...

Diffuse Lamellar Keratitis (DLK) is a sterile (non-infectious) inflammatory condition that affects the cornea after lamellar refractive surgeries such as ...

A visual hallucination is when a person sees something that is not actually there. It is a perception with no external visual stimulus — for example, seeing ...

Dry Eye Disease (DED) is not just “dry eyes” like when you are tired—it is a long-lasting problem of the front surface of the eye. According to the ...

Optic neuritis means the optic nerve—the nerve that carries vision signals from the eye to the brain—becomes inflamed. This inflammation can damage the nerve ...

Diabetic retinopathy is an eye disease that happens when long-term high blood sugar from diabetes damages the tiny blood vessels in the retina, the ...

Diabetic papillopathy is a condition seen in people with diabetes where the head of the optic nerve (the “optic disc”) becomes swollen or puffy. This swelling ...

Diabetic Macular Ischemia (DMI) is a complication of diabetic eye disease where the tiny blood vessels supplying the central part of the retina (the macula) ...

Diabetic Macular Edema is swelling in the central part of the retina called the macula, caused by leakage of fluid from tiny, damaged blood vessels in people ...

Descemet’s membrane is a thin, strong layer at the back of the cornea. It sits just under the innermost cells of the cornea (the endothelium) and helps keep ...

A dermoid cyst is a benign (non-cancerous) lump that forms because of cells that are in the wrong place during early development. These cells are usually from ...

A dermis fat graft is a piece of a person’s own skin (without the top layer) plus the fat beneath it, taken from one part of the body and moved to another to ...

Dermatomyositis is a rare disease where the body’s own immune system attacks the muscles and the skin. It causes muscle weakness and a special kind of skin ...

Dermatochalasis is a medical term that means too much loose skin on the eyelids. Most often it happens on the upper eyelids but can also affect lower lids. The ...

Demyelinating optic neuritis is inflammation of the optic nerve caused by loss or damage of its myelin sheath—the protective coating that helps nerve signals ...

Demodex infestation, also called demodicosis, happens when tiny mites named Demodex that normally live on human skin grow too many in number or trigger ...

Idiopathic Intracranial Hypertension is a condition where the pressure inside the skull (intracranial pressure) is too high, but doctors can’t find a tumor, ...

Mohr-Tranebjærg syndrome (MTS), also called Deafness–Dystonia–Optic Neuronopathy (DDON) syndrome, is a rare, inherited disease that slowly damages nerves in a ...

Deafness-Dystonia-Optic Neuronopathy syndrome, also called Mohr-Tranebjærg syndrome (MTS), is a rare genetic disease that slowly damages nerves in different ...

Dead Bag Syndrome is a rare, late problem that happens years after cataract surgery. In cataract surgery, the cloudy natural lens of the eye is removed and an ...

Dacryocystitis is an infection or inflammation of the tear-drainage sac (the lacrimal sac) that sits just beside the bridge of your nose. Tears normally flow ...

A dacryocele is a soft, cyst-like swelling that forms where the tear-drainage sac sits beside the nose because the tear duct is blocked at both ends, trapping ...

Dacryoadenoma is a rare benign lacrimal gland tumor best managed by early recognition and complete surgical removal. Supportive care—including lifestyle, diet ...

Dacryoadenitis means inflammation of the lacrimal gland. “Dacryo-” refers to tears, and “-adenitis” means gland inflammation. So it literally means the tear ...

Cytomegalovirus (CMV) anterior uveitis is an eye disease in which a very common herpes-family virus infects or re-activates inside the front part of the uveal ...

Cystoid Macular Edema is a build-up of watery fluid inside the tiny layers of the macula—the spot in the very center of the retina that gives you sharp, ...

Cystinosis is a rare inherited disease caused by mutations in the CTNS gene that prevents the normal removal of a small amino acid called cystine from inside ...

Cysticercosis of the eye is an infection where the larval stage of the pork tapeworm (Taenia solium), called Cysticercus cellulosae, lodges in or around the ...

Synophthalmia is an extremely rare and severe birth defect in which the two eyes are fused into one or are so closely set that they appear as a single eye—this ...

Synophthalmia (pronounced sin-off-THAL-mee-ah) is a very rare and severe birth defect in which the two developing eyes fail to separate and instead grow ...

Cyclopia (sometimes called cyclocephaly or synophthalmia) is the most extreme facial expression of a brain‐formation error known as alobar holoprosencephaly. ...

Glaucoma is a group of eye diseases that slowly damage the optic nerve, usually because of elevated pressure inside the eye (intraocular pressure, IOP). Over ...

A cyclodialysis cleft is an abnormal separation between the ciliary body and the scleral spur in the eye. The ciliary body normally attaches to the scleral ...

Cushing’s syndrome is the condition caused by having too much cortisol in the body over time. Cortisol is a stress hormone made by the adrenal glands; when its ...

Crystalline retinopathy is not one single disease. It is a family of rare eye problems in which tiny, shiny crystals build up inside the layers of the ...

Cryptophthalmos is a rare congenital eye condition where the eyelids fail to form properly, and skin is continuous over the eye, hiding the palpebral fissure ...

Cryptococcal choroiditis is an uncommon fungal infection in which Cryptococcus neoformans or C. gattii—yeast-like fungi usually found in bird droppings and in ...

Crunch Syndrome—also called the anti-VEGF crunch phenomenon—is a serious, sight-threatening complication that can appear days to weeks after an injection of an ...

Crossed Quadrant Homonymous Hemianopsia—sometimes nick-named the “checkerboard visual-field defect”—is an exceptionally rare pattern of visual-field loss in ...

Corneal collagen cross-linking (CXL) is a medical procedure used to strengthen the cornea, usually to slow or stop progressive thinning or bulging in ...

Crocodile shagreen of the cornea is a benign, usually harmless degenerative finding that gives the cornea a faint, polygonal, “crocodile skin” appearance. Most ...

Crocodile shagreen (also called crocodile shagreen of Vogt or simply crocodile shagreen of the cornea) is a harmless age-related change that makes the front ...

Craniosynostosis means that one or more of the flexible seams (called cranial sutures) in a baby’s skull close much earlier than they should. When the closure ...

Follicular dendritic cell sarcoma (FDCS) is a rare malignant tumor arising from follicular dendritic cells—specialized cells that reside in the germinal ...

Cranial neuritis means inflammation of one or more of the twelve cranial nerves that come directly out of the brain or brainstem. When a cranial nerve becomes ...

Cranial Nerve IV palsy—often called trochlear nerve palsy or superior-oblique muscle palsy—is a problem with the fourth cranial nerve, the tiny motor nerve ...

COVID-19 associated orbital mucormycosis is a severe, rapidly progressing fungal infection of the nasal, sinus, and orbital (eye socket) region caused by molds ...

COVID conjunctivitis is inflammation of the conjunctiva (the clear membrane covering the white of the eye and inner eyelids) caused directly or indirectly by ...

Cotton wool spots are small, fluffy, white patches seen on the retina (the light-sensing layer at the back of the eye) during a dilated eye exam. They are not ...

Steroid glaucoma is a type of open-angle glaucoma that appears after the eye or the whole body is exposed to corticosteroid medicines. These medicines—such as ...

Corticobasal Degeneration (CBD) is a rare, progressive brain disease that slowly damages specific brain cells, leading to problems with movement, thinking, and ...

When an eye-surgeon finishes cataract or corneal-transplant surgery, they often inject a small jet of balanced salt solution into the edges (stroma) of the ...

A corneal epithelial defect is a localized area where the outermost layer of the cornea (the epithelium) has been interrupted or lost. This break in the ...

Corneal edema is swelling of the cornea, the clear, dome‑shaped front surface of the eye that helps focus light onto the retina. In corneal edema, excess fluid ...

Corneal donation diseases encompass a spectrum of serious corneal disorders in which damage or degeneration of the cornea—the clear, dome-shaped “window” at ...

A corneal dermoid is a benign, congenital growth on the surface of the eye composed of normal skin-like tissue in an abnormal location. These lesions, also ...

Corneal dellen are small, localized areas of thinning on the edge of the clear front window of the eye (the cornea). They appear as saucer‑shaped depressions ...

The cornea is the clear, dome‑shaped window at the front of your eye. Corneal biomechanics is the study of how this window bends, stretches, and returns to ...

Corneal allograft rejection is an immunologic response in which the recipient’s immune system specifically attacks donor corneal tissue, leading to ...

Corneal Allogenic Intrastromal Ring Segments (CAIRS) are tiny arc‑shaped implants carved from donor (allogenic) corneal stroma. These segments are inserted ...

Whorl keratopathy—also known as vortex keratopathy or cornea verticillata—is a pattern of fine, golden‑brown or grayish opacities in the basal layer of the ...

Cornea verticillata—also known as vortex keratopathy or whorl keratopathy—is a pattern of fine, golden‑brown or gray opacities arranged in a characteristic ...

Cornea transplantation–induced glaucoma is a form of secondary glaucoma that arises after corneal graft procedures such as penetrating keratoplasty (PKP), ...

Cornea plana is a rare congenital eye disorder in which the transparent, dome‑shaped front window of the eye (the cornea) is abnormally flat. Instead of the ...

Cornea farinata is a benign, degenerative condition of the cornea characterized by innumerable, fine, dust‑like opacities located in the deep posterior stroma ...

Functional Neurological Symptom Disorder (FNSD) is a condition where individuals experience real neurological symptoms—such as weakness, tremors, or ...

Conversion disorder, also known as Functional Neurological Symptom Disorder (FNSD), is a psychiatric condition in which patients experience genuine ...

Convergence Insufficiency (CI) is a common binocular vision disorder in which the eyes have difficulty turning inward together when looking at nearby objects. ...

Convergence ability refers to the coordinated inward movement of both eyes so that the visual axes intersect at a near point, allowing clear and single ...

Contact lens complications occur when the tissues of the eye react negatively to the presence or improper use of contact lenses. These reactions can range from ...

Conjunctivochalasis is an eye condition in which the conjunctiva—the clear membrane covering the white part of the eye—becomes loose and redundant, creating ...

Conjunctival telangiectasia is a condition characterized by the dilation of tiny blood vessels—typically measuring 0.5 to 1.0 mm in diameter—on the surface of ...

Conjunctival Reactive Lymphoid Hyperplasia (CRLH) is a benign lymphoproliferative disorder characterized by a polyclonal proliferation of lymphoid tissue in ...

Conjunctival papilloma is a benign (non‑cancerous) growth that arises from the surface cells of the conjunctiva, the thin, clear membrane covering the white ...

Conjunctival melanocytic tumors are abnormal growths of the pigment-producing cells (melanocytes) that reside in the thin, clear membrane covering the white of ...

Conjunctival lymphoma is a malignant tumor arising from the lymphoid tissue located in the conjunctiva, the thin membrane covering the white part of the eye ...

Conjunctival lymphangiectasia is an uncommon eye condition characterized by the visible swelling and dilation of lymphatic vessels within the conjunctiva—the ...

Conjunctival keloid is a rare, benign ocular condition characterized by the excessive growth of scar tissue on the conjunctiva, the clear membrane covering the ...