How the eye is built, and what can go wrong. Open a structure below to read what it is, what it does and which complaints can arise. At the bottom you will find all eye conditions.
Two skin folds with a firm plate of connective tissue, a margin with lashes, and in that margin about thirty glands that secrete oil.
Blinking spreads the tear film over the eye and wipes away dust, about fifteen times a minute. The oil from the glands prevents the tear film from evaporating too quickly.
If these glands become blocked or inflamed, the tear film deteriorates: burning, crusty or actually watery eyes. A blocked gland can grow into a lump in the eyelid.
A layer thinner than a tenth of a millimetre over the eye surface, made of three layers: oil on top, water in the middle, mucus at the bottom. Tears drain via the inner corner of the eye to the nose.
It keeps the surface smooth and clear, nourishes the cornea and contains defence substances. Without a good tear film, vision gets blurrier, however healthy the eye is.
Too little tear fluid or too fast evaporation causes dry, burning eyes. Confusingly, dry eyes often water. A blocked tear duct causes an eye that runs all day.
A thin, transparent membrane over the white of the eye and the inside of the eyelids, with fine blood vessels.
It protects the eye surface, holds the tear film and produces mucus. The vessels provide quick defence against infection.
With irritation or infection the vessels widen and the eye turns red. That is almost always the conjunctiva, not the eye itself. Allergy also causes red, itchy, watery eyes.
The clear window at the front, about half a millimetre thick, without blood vessels and with very many nerve endings.
It is the strongest lens of the eye: about 40 of the 60 dioptres. It is also the first barrier against infection.
A small scratch hurts a lot at once; it is one of the most sensitive places in the body. An inflammation or ulcer threatens vision and is urgent. Irregular shapes, such as astigmatism or keratoconus, also belong here.
The space between cornea and iris, filled with clear fluid that is continuously produced and drains through a filter in the chamber angle.
The fluid nourishes the cornea and lens, which have no blood vessels, and keeps the eye firm. Normal eye pressure is about 10 to 21 mmHg.
If drainage is poor, pressure rises, usually slowly and painlessly. If the angle closes suddenly, pressure shoots up with severe pain, nausea and halos around lights: that is urgent.
The coloured ring with the opening in the middle. The black you see is not a structure but the inside of the eye.
Two small muscles regulate the opening, from about 2 mm in bright light to 8 mm in the dark, so a similar amount of light reaches the retina.
With inflammation inside the eye, moving the iris hurts and the eye becomes light-sensitive. Two clearly different pupils, or a pupil that does not react, should always be checked quickly.
A clear, flexible lens behind the iris, suspended by hundreds of thin fibres.
The lens changes shape to focus: rounder for near, flatter for distance. It provides about 20 dioptres, the adjustable part of the eye’s power.
From around forty the lens stiffens, making near focus harder. If it becomes cloudy, that is cataract: blurrier vision, duller colours and more glare.
A ring of muscle tissue and small glands behind the iris, from which the lens is suspended.
It makes the eye fluid, and tightens or relaxes the lens fibres to focus.
Too much fluid or poor drainage raises eye pressure. Inflammation here is part of uveitis and causes pain, light sensitivity and blurred vision.
The clear gel between lens and retina: about 4 ml, almost entirely water, some 80 percent of the eye’s volume.
It keeps the eye in shape and lets light pass unhindered.
With age the gel becomes more liquid and its protein clumps: threads and spots that move along. If the vitreous detaches from the retina, flashes can occur, and sometimes the retina tears.
A thin, translucent layer lining the back of the eye, with about 120 million rods and 6 million cones.
Here light is converted into nerve signals. Cones provide sharpness and colour, rods vision in dim light and at the edges.
If the retina detaches, part of the image disappears: a rising curtain or shadow. That is urgent. Diabetes and high blood pressure damage its vessels, usually long before anyone notices.
An area of about five millimetres in the centre of the retina, exactly where light enters. Almost all cones are here.
Everything you see sharply: reading, recognising faces, distinguishing colours. The rest of the retina provides the surrounding image.
With damage the surroundings remain but the centre disappears or distorts; straight lines start to wave. This is the picture in macular degeneration and fluid in the macula.
A bundle of about a million nerve fibres leaving the back of the eye. There are no light-sensitive cells at that spot: the blind spot.
It carries all signals to the back of the brain, where the image is formed; the eye does not see, the brain does.
Lost fibres do not return. In glaucoma they are lost gradually, first at the edges of the visual field, unnoticed for a long time. Optic nerve inflammation causes rapidly decreasing vision and pain with eye movement.
The sclera is the firm white outer wall, the white of the eye. Inside it lies the choroid, a dark layer full of blood vessels.
The sclera keeps the eye in shape and protects its contents. The choroid nourishes the outer retinal layers and absorbs stray light.
Inflammation of the sclera gives a deep, boring pain and a deep-red patch that does not fade with drops. Inflammation of the choroid is inside the eye and causes light sensitivity and blurred vision.
Six small muscles per eye, attached to the outside of the eyeball and controlled by three cranial nerves.
They move both eyes exactly together, so the brain can merge two images into one. That merging provides depth perception.
If a muscle or nerve does not work well, the images separate and double vision occurs. New double vision that disappears when covering one eye should be assessed the same day.
The conditions seen most often at the eye clinic. Open a complaint for a short explanation and the warning signs.
A red eye, often one first and then both, with a burning or gritty feeling and watery or sticky discharge; vision stays clear after blinking. Usually a virus (often with a cold), sometimes bacteria, allergy or irritation. A viral infection clears by itself in one to two weeks; cooling and artificial tears help. Bacterial infections may need ointment or drops, allergy antihistamine drops. Wash hands often and leave contact lenses out.
A burning, gritty feeling that is worse at the end of the day, fluctuating blurred vision and, paradoxically, watery eyes. Usually the tears evaporate too fast because the oil glands in the eyelid margin are blocked; sometimes too few tears are produced (age, menopause, medication, Sjögren’s syndrome). Treatment: preservative-free artificial tears, daily warmth, massage and eyelid cleaning, screen breaks; if needed punctal plugs or prescription medicine.
Red, swollen eyelid margins, crusts between the lashes in the morning and a burning feeling, often together with dry eyes and coming back in periods. The glands in the eyelid margin produce too much or too thick oil; bacteria and skin conditions such as rosacea play a role. It is chronic: daily eyelid hygiene (warm compress, gentle massage, cleaning) is the core, sometimes with ointment.
A stye is a painful red bump at the eyelid edge; a chalazion is a firm, usually painless lump deeper in the lid. Vision stays normal. Warm compresses three to four times a day for ten minutes; do not squeeze. A stye usually heals within one to two weeks; a chalazion can last months and can be removed if it bothers you.
Sudden sharp pain, a feeling that something is in the eye, lots of tears and light sensitivity. Caused by dust, a metal splinter, a twig, a fingernail or a contact lens. A loose particle is removed and ointment or drops prevent infection; the cornea usually heals within one to two days. With a chemical in the eye: first rinse for fifteen minutes with lukewarm running water.
Gradually blurrier vision even with good glasses, more glare, duller colours and a prescription that changes faster. The lens proteins clump together over the years; almost everyone over seventy has it to some degree. There are no drops against cataract; the treatment is a short operation replacing the lens with an artificial one. When to operate depends on how much it bothers you.
At first no symptoms; later reduced side vision while central vision stays good for a long time. Fluid does not drain properly, pressure rises and optic nerve fibres are slowly lost. Risk increases with age, family history and high myopia. Treatment usually starts with pressure-lowering drops used faithfully, sometimes laser or surgery. It stops further damage but does not undo it, so early detection matters.
Threads, specks or cobwebs moving with your gaze, sometimes brief flashes at the side; vision itself stays good. The vitreous becomes more liquid with age and eventually detaches from the retina, earlier with myopia or after cataract surgery. The retina is checked with a dilated pupil to rule out a tear; without a tear no treatment is needed and the brain learns to ignore the spots.
A curtain, shadow or dark area coming in from one side, often preceded by many spots or flashes, and without pain. Usually a tear in the retina lets fluid get behind it. This is an emergency: the sooner it is treated, the more vision is saved. Treatment is always surgical (laser, gas bubble, a band around the eye or vitreous surgery); a tear found in time can be sealed with laser.
Straight lines that wave or bend, a blurry or grey spot in the centre and difficulty reading, while walking around is fine. The wet form progresses in days to weeks, the dry form over years. The wet form is treated with injections into the eye; starting quickly saves vision. There is no cure for the dry form. Stopping smoking is the most important step; check each eye daily with an Amsler grid.
For a long time no symptoms, even when damage is present; later spots, blurred areas or loss in vision. High blood sugar damages the small retinal vessels. Stages range from R0 (no abnormalities) and R1 (mild) to R2/R3 (referral and treatment) and M1 (fluid at the macula). Regular retinal photos, good control of blood sugar, blood pressure and cholesterol, and not smoking are key; advanced stages are treated with laser or injections.
Usually no symptoms and found by chance; with very high blood pressure blurred vision, often with headache. Long-term high blood pressure thickens and narrows the small arteries (grade 1–2); with very high pressure bleeds, spots and a swollen optic nerve appear (grade 3–4, an emergency). Treatment is lowering the blood pressure via your GP or internist; the eye itself usually needs no treatment.
A dull, aching eye, strong light sensitivity, blurred vision and a red ring around the cornea, usually in one eye and often recurring. It is treated with anti-inflammatory drops and drops that keep the pupil wide; eye pressure is monitored. Starting early prevents permanent damage.
Practical advice you can follow at home. Open an item for the explanation, the steps and an instruction video.
This page is a short summary and does not replace a consultation.
