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Eyeball: Anatomy, Red in Eyeball, Pain and Blood Explained
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Eyeball (noun, also called the globe): the eyeball is the nearly spherical organ of sight, about 24 mm from front to back in an adult, that sits in the bony eye socket (the orbit). It contains the cornea, iris, pupil, lens and retina, which together focus light and turn it into signals for the brain. Red in the eyeball is usually harmless (a burst surface vessel or mild irritation), but pain, light sensitivity or reduced vision with redness needs a doctor the same day.
Quick answer on red in eyeball: most red eyeballs come from infection, dry eye, conjunctivitis, blepharitis or a small burst blood vessel, according to the NHS. Our surgeons, Prof. Dr. Ahmet Satıcı, Doç. Dr. Muhammet Derda Özer and Op. Dr. Aysan Bayram, treat the underlying eye conditions; a painful red eye is never something to wait out.
Eyeball: key facts
- What it is
- The eye itself, without the eyelids, tear glands, muscles and socket around it
- Size
- About 24 mm front to back, 23.7 mm high and 24.2 mm wide; volume about 6.5 ml; full adult size is reached by about age 12
- Where it sits
- In the orbit, a bony socket made of seven bones with a volume of about 28 ml, so the eyeball fills only about a quarter of it
- Three coats (layers)
- Outer fibrous coat (clear cornea and white sclera), middle vascular coat or uvea (choroid, ciliary body, iris), inner coat (retina)
- Filling
- Watery aqueous humour at the front; jelly-like vitreous humour behind the lens
- Movement
- Six muscles outside the eyeball move it up, down, side to side and rotate it
- Specialist
- Ophthalmologist (eye doctor); at Laser Istanbul Clinic: Prof. Dr. Ahmet Satıcı, Doç. Dr. Muhammet Derda Özer (Doç. = Associate Professor) and Op. Dr. Aysan Bayram
What is the eyeball made of? Structure and layers
The eyeball is built in three coats, each with its own job, wrapped around two fluid-filled spaces.
| Part | What it is | What it does |
|---|---|---|
| Sclera | The tough white outer wall that covers nearly the whole surface of the eyeball | Protects the eye and gives it shape; the six eye muscles attach to it |
| Conjunctiva | A thin, clear membrane over the sclera and inside the eyelids | Protects and lubricates; this is where a "burst blood vessel" shows up |
| Cornea | The clear dome at the front | Does about 70% of the eye's focusing (AAO) |
| Iris and pupil | The coloured ring and the opening in its centre | The iris muscles widen or narrow the pupil to control the light reaching the back of the eye |
| Lens | Clear flexible disc behind the pupil | Adds about 30% of focusing and changes shape for near vision |
| Uvea (choroid, ciliary body, iris) | The middle coat, rich in blood vessels | Feeds the eye and makes the aqueous humour |
| Aqueous humour | Watery fluid in the front of the eye | Nourishes the cornea and lens and keeps eye pressure steady through constant production and drainage |
| Vitreous humour | Clear, jelly-like gel between lens and retina | Keeps the eyeball round |
| Retina | Light-sensitive tissue lining the back | Rods and cones turn light into electrical signals |
| Optic nerve | The cable leaving the back of the eyeball | Carries those signals to the brain |
The surface is also protected by the tear film, three layers (mucous, watery and oily) that keep the front of the eye smooth and moist.
At the back, rod cells use a light-sensitive pigment to see in dim light.
How does the eyeball work?
Light passes through the cornea, then the pupil, then the lens, which together focus it onto the retina. Photoreceptor cells in the retina convert it into electrical signals, and the optic nerve carries them to the brain, which turns them into the picture you see (National Eye Institute). Tears keep the front surface clear enough for this to work. Because the cornea and lens provide the focusing, small changes in their shape or clarity, or in the length of the eyeball, change how sharp vision is.
Red in eyeball: what causes the eyeball to turn red?
A red eyeball means the tiny blood vessels on the white of the eye are swollen, or one has bled. The NHS says a red eye is "often caused by an infection or dry eyes, but there are lots of possible causes." The most common ones are:
| Cause | What it usually looks and feels like | How serious |
|---|---|---|
| Conjunctivitis (pink eye) | Both eyes red, burning or gritty, watering, sticky discharge; viral, bacterial or allergic | Usually mild; most cases clear within two weeks (NHS) |
| Dry eye | Red, gritty, stinging eyes, often worse on screens or in wind or air-conditioning | Common and treatable |
| Blepharitis | Red, swollen lid edges with crusting; eyes look red and irritated | Chronic but manageable |
| Burst blood vessel (subconjunctival haemorrhage) | A bright red patch on the white of the eye, usually painless | Usually harmless |
| Eyelid problems | Styes, lid swelling and turned-in lashes irritating the surface | Varies |
| Contact lens problems | Red, sore eye in a lens wearer | Can be a corneal infection: urgent |
| Keratitis or corneal ulcer | Red, painful eye, light sensitivity, sometimes a white spot on the cornea | Urgent; can damage vision |
| Uveitis or scleritis | Deep, aching red eye, often with light sensitivity | Urgent; needs specialist treatment |
| Acute angle-closure glaucoma | Very red eye, intense pain, headache, haloes round lights, nausea | Emergency |
The pattern matters more than the colour. A red eye with no pain and normal vision often settles by itself; the NHS advises not touching the eye and stopping contact lens wear until it clears. A red eye with pain, light sensitivity or changes in vision is different.
Why is there blood on my eyeball?
A bright red patch on the white of the eye is most often a subconjunctival haemorrhage: a small blood vessel in the conjunctiva has broken and blood has collected between the conjunctiva and the sclera. According to the American Academy of Ophthalmology (AAO), it is usually harmless and often heals on its own, and the usual triggers are coughing, sneezing, straining or rubbing the eye. Less often it is linked to diabetes, high blood pressure or blood-thinning medicines such as aspirin, warfarin (Coumadin), clopidogrel (Plavix), apixaban (Eliquis) and rivaroxaban (Xarelto).
- Looks: the only sign is a red spot, sometimes with very mild irritation. As it heals it can turn pink, orange, yellow or even black before clearing.
- How long: from a few days to a few weeks (AAO); EyeWiki gives 1 to 4 weeks depending on size.
- Treatment: usually none; artificial tears ease any irritation.
- See a doctor if: it keeps coming back, you take blood thinners and bleed repeatedly, or it follows an injury. After a blow, blood covering the whole white of the eye can be a sign of a ruptured globe, so it needs an urgent examination.
Blood can also collect inside the eye, in front of the iris and behind the cornea. This is called a hyphema; it is most often caused by a blunt injury, brings blurred vision, pain or light sensitivity, and needs prompt medical attention because of the risk of rebleeding and raised eye pressure in the first five days.
Warning signs: red eyeball with any of these means urgent care
The NHS tells people to get urgent or emergency help for a red eye if there is:
- very severe pain, or pain when looking at light
- changes in vision such as wavy lines, flashing lights or loss of vision
- a severe headache with nausea
- a very dark red eye
- an injury, embedded object or chemical splash
- one pupil bigger than the other
- a red eye while wearing contact lenses (take them out and get checked)
Eyeball pain: left eyeball pain, eye socket pain and pain around the eye
Pain in the left eyeball has the same range of causes as pain in the right: the side is not the clue, the accompanying signs are. The same is true for eye socket pain in one eye. These are the main causes, from common to urgent.
| Where it hurts | Likely causes | What else you may notice |
|---|---|---|
| On the surface, gritty or stinging | Dry eye, conjunctivitis, scratched cornea, foreign body | Redness, watering, light sensitivity |
| Deep, dull, boring ache, worse when you move the eye | Scleritis (inflamed white of the eye), optic neuritis | Violet-red eye in scleritis; sudden blurred vision and washed-out colours in optic neuritis |
| Pain around the eye socket and cheekbone | Sinusitis; a blow to the face (orbital floor fracture) | Blocked nose, discharge, pressure in cheeks and forehead; after injury, double vision, cheek numbness, a sunken eye |
| Pain in the eye socket and brow bone | Sinusitis (frontal sinus), cluster headache, migraine, eye strain | Forehead pressure; a red, watering eye and drooping lid on the same side in cluster headache |
| Severe pain with a red eye, haloes and nausea | Acute angle-closure glaucoma | Emergency: call 999 or go to A&E |
| Pain with a swollen red lid, bulging eye and fever | Orbital cellulitis | Emergency: hospital treatment with intravenous antibiotics |
| New headache in someone over 50, with jaw pain when chewing or scalp tenderness | Giant cell arteritis | Emergency: untreated, vision loss can become permanent |
A few of these are worth knowing in more detail.
Sinusitis causes "pain, swelling and tenderness around your cheeks, eyes or forehead," along with a blocked nose and thick discharge (NHS). It is a very common reason for pain around the eye socket and cheekbone or the brow bone, and often follows a cold. See a GP if it lasts more than three weeks or keeps returning.
Scleritis causes a dull, boring pain that is worse on eye movement and often worse at night, and it can spread to the ear, scalp, face or jaw. Up to half of cases are linked to a general inflammatory disease such as rheumatoid arthritis, so it needs prompt assessment (EyeWiki).
Optic neuritis is inflammation of the optic nerve. It typically brings sudden blurred or "foggy" vision, pain when moving the eye and washed-out colours, and mostly affects adults aged 18 to 45. It can be the first sign of multiple sclerosis, so see a doctor straight away.
Cluster headache is sharp, burning or piercing pain on one side of the head around the eye, with a red, watering eye, a drooping or swollen lid and a sweaty face. Attacks last from 15 minutes to 3 hours (NHS).
Orbital cellulitis is an infection of the tissues behind the eyeball, most often spreading from the sinuses (about 90% of cases, EyeWiki). Pain on eye movement, a red swollen lid, a bulging eye, fever and double vision make it a medical emergency.
Orbital floor fracture can follow a punch or sports injury: look for double vision (especially looking up or down), cheek numbness and a sunken eye. The EyeWiki guidance is to avoid blowing the nose for 4 to 6 weeks after such an injury.
Pulsating eyeball: why does my eye pulse or throb?
A pulsating or throbbing feeling in the eye is most often eyelid twitching (myokymia), not the eyeball itself. Eyelid myokymia is usually benign and settles on its own within minutes to weeks. Recognised triggers include stress, tiredness, caffeine, alcohol, lack of sleep and long screen time, and some medicines. See a doctor if it lasts for several weeks or longer, spreads beyond the eyelid, affects both sides or comes with other nerve symptoms (EyeWiki).
A throbbing pain behind the eye can also come from sinusitis, migraine or cluster headache (see above). Rarely, a truly pulsing, bulging eyeball with a red eye, a whooshing sound and double vision points to an abnormal artery-to-vein connection behind the eye called a carotid-cavernous fistula, which needs urgent imaging and treatment. If your eye looks as if it is bulging or pulsing, do not wait.
Is an eyeball transplant possible? What would it cost?
No: a whole-eye transplant cannot restore sight today, so there is no standard treatment or price. The obstacle is the optic nerve. The eye has to be reconnected to the brain through this nerve, and the nerve cells do not regrow across a join.
In November 2023, surgeons at NYU Langone Health in New York carried out the first whole-eye transplant in a human, as part of a 21-hour partial face transplant for a man who had lost his left eye in a high-voltage accident. The donor eye's blood vessels and retina looked healthy afterwards, but the recipient has not regained sight through it, and the team described it as proof that the operation can be done, not as a cure for blindness.
What is routine is a corneal transplant, which replaces only the clear front window of the eye with donor tissue, not the eyeball. It is a different operation, used for keratoconus, scarring and corneal swelling, and recovery is measured in months. Because whole-eye transplants are experimental, there is no price to quote; any provider advertising an "eyeball transplant" for a fee should be treated with great caution.
Are fish eyeballs good for you? Fish eyeball nutrition and benefits
There is no good evidence that eating fish eyeballs does anything for your own eyes. Fish eyes are eaten in several cuisines and are rich in fats, and the retina is full of the omega-3 fat DHA: DHA makes up about 60% of the polyunsaturated fats in the retina. That is why the idea is popular, but it does not follow that eating DHA improves your eyes.
- The best-known trial, the National Eye Institute's AREDS2, found that adding omega-3 supplements to the standard formula had no additional effect on the risk of advanced age-related macular degeneration, and that omega-3 supplements had no effect on cataract or AMD.
- A systematic review found no significant visual-field benefit from DHA in retinitis pigmentosa.
- We found no study that looks at eating fish eyeballs for eye health, so any claim about "fish eyeball benefits" is unproven.
- The nutrition is in the fish itself. The NHS advises at least one 140 g portion of oily fish a week (salmon, sardines, mackerel, trout, herring); girls and women who may become pregnant, and pregnant or breastfeeding women, should have no more than two portions of oily fish a week.
Eat fish for general health if you enjoy it; do not expect it to protect your eyesight. If you are worried about macular degeneration or dry eye, an eye examination is worth more than any diet change.
How is the eyeball examined?
Eye doctors examine the eyeball from the front surface to the retina and optic nerve. Most tests are quick and painless:
- Visual acuity and refraction: reading letters and checking your glasses prescription.
- Slit-lamp examination: a microscope with a thin beam of light that shows the cornea, iris, lens and front of the eye in cross-section; it finds scratches, ulcers, inflammation and blood in the eye.
- Tonometry: measures eye pressure, important for glaucoma.
- Dilated retinal examination and OCT scan: show the retina, macula and optic nerve in detail.
- Corneal topography and tomography: map the front and back surface and thickness of the cornea.
- Eye ultrasound and visual field tests: used when the view into the eye is blocked, or to check how much side vision you have.
At Laser Istanbul Clinic, a full pre-operative examination with scans is part of every treatment in Istanbul, and your surgeon can review scans you already have before you travel.
When to see a doctor about your eyeball
Get same-day or emergency care (NHS 111, urgent eye service or A&E) if you have:
- a painful red eye, especially with light sensitivity or nausea
- sudden loss of vision, flashing lights, wavy lines or a curtain over your sight
- an eye injury, a chemical splash, or blood covering the whole white of the eye after a blow
- red eye with a swollen lid, bulging eye or fever
- intense eye pain with haloes round lights
- one pupil larger than the other
- a new headache over the age of 50 with jaw pain or scalp tenderness
- a red, sore eye while wearing contact lenses
Book an appointment soon if you notice:
- redness that lasts more than about a week, or comes back repeatedly
- repeated bleeds on the white of the eye
- eyelid twitching that lasts weeks or spreads
- eye pain or pressure that is mild but persistent, or sinus symptoms that last over three weeks
- gritty, dry eyes that do not improve with lubricating drops
If you already have a diagnosis, such as glaucoma, uveitis or retinal disease, and want another specialist's opinion before surgery, you can send your scans for review before you travel.
Frequently asked questions
The eyeball is the eye itself: a nearly round organ about 24 mm across that sits in the bony eye socket. It has three layers (sclera and cornea, uvea, and retina) and is filled with aqueous and vitreous fluid.
The most common causes are conjunctivitis, dry eye, blepharitis, an infection or a small burst blood vessel. If the eye is red but not painful and your vision is normal, it often settles on its own. Redness with pain, light sensitivity or blurred vision needs a doctor the same day.
Usually a tiny vessel in the conjunctiva has burst, often after coughing, sneezing, straining or rubbing. This subconjunctival haemorrhage looks alarming but is usually harmless and clears in 1 to 4 weeks. See a doctor if it recurs, if you take blood thinners, or if it follows an injury.
Dry eye, conjunctivitis, a scratched cornea, sinusitis, migraine, optic neuritis, scleritis and glaucoma can all cause it, and the side of the face makes no difference. Pain with redness, nausea, haloes, vision loss or pain on eye movement needs prompt examination.
Most often it is eyelid twitching (myokymia) triggered by stress, tiredness, caffeine or screen time, and it settles within minutes to weeks. A truly pulsing, bulging, red eye is rare but needs urgent assessment.
Sinusitis is the most common cause. A blow to the face can fracture the floor of the socket, causing double vision and cheek numbness. See a doctor urgently if the eyelids swell, the eye bulges or your vision changes.
Not in a way that restores sight. A first whole-eye transplant was performed in New York in November 2023, but the recipient has not regained vision through it because the optic nerve cannot yet be reconnected. Corneal transplants, which replace only the clear front of the eye, are a standard operation.
There is no evidence that eating them benefits your eyes. DHA is concentrated in the retina, but trials of omega-3 supplements have not shown protection against macular degeneration or cataract. Eating oily fish once a week is sensible for general health.
Sources for the facts on this page
- NHS. Red eye. https://www.nhs.uk/conditions/red-eye/
- NHS. Conjunctivitis. https://www.nhs.uk/conditions/conjunctivitis/
- NHS. Sinusitis. https://www.nhs.uk/conditions/sinusitis/
- NHS. Glaucoma (acute angle-closure symptoms). https://www.nhs.uk/conditions/glaucoma/
- NHS. Cluster headaches. https://www.nhs.uk/conditions/cluster-headaches/
- NHS. Fish and shellfish: nutrition (oily fish, omega-3). https://www.nhs.uk/live-well/eat-well/fish-and-shellfish-nutrition/
- American Academy of Ophthalmology. Parts of the eye. https://www.aao.org/eye-health/anatomy/parts-of-eye
- American Academy of Ophthalmology. What is subconjunctival hemorrhage? https://www.aao.org/eye-health/diseases/what-is-subconjunctival-hemorrhage
- National Eye Institute. How the eyes work. https://www.nei.nih.gov/learn-about-eye-health/healthy-vision/how-eyes-work
- National Eye Institute. About AREDS and AREDS2. https://www.nei.nih.gov/research/clinical-trials/age-related-eye-disease-studies-aredsareds2/about-areds-and-areds2
- EyeWiki (AAO). Subconjunctival Hemorrhage. https://eyewiki.aao.org/Subconjunctival_Hemorrhage
- EyeWiki (AAO). Hyphema. https://eyewiki.aao.org/Hyphema
- EyeWiki (AAO). Scleritis. https://eyewiki.aao.org/Scleritis
- EyeWiki (AAO). Orbital Cellulitis. https://eyewiki.org/Orbital_Cellulitis
- EyeWiki (AAO). Orbital Floor Fractures. https://eyewiki.aao.org/Orbital_Floor_Fractures
- EyeWiki (AAO). Eyelid Myokymia. https://eyewiki.aao.org/Eyelid_Myokymia
- EyeWiki (AAO). Giant Cell Arteritis. https://eyewiki.org/Giant_Cell_Arteritis
- EyeWiki (AAO). Carotid Cavernous Fistula. https://eyewiki.aao.org/Carotid_Cavernous_Fistula
- Wikipedia. Human eye (dimensions, volume, three coats; cites the primary literature). https://en.wikipedia.org/wiki/Human_eye
- Wikipedia. Orbit (anatomy) (seven bones, volume about 28 ml). https://en.wikipedia.org/wiki/Orbit_(anatomy)
- Wikipedia. Optic neuritis (symptoms, age range, link to multiple sclerosis). https://en.wikipedia.org/wiki/Optic_neuritis
- Wikipedia. Eye transplantation (NYU Langone whole-eye transplant, November 2023; cites Reuters, 9 Nov 2023). https://en.wikipedia.org/wiki/Eye_transplantation
- Wikipedia. Docosahexaenoic acid (DHA in the retina). https://en.wikipedia.org/wiki/Docosahexaenoic_acid
Red, painful or blurred eye, or a diagnosis you want checked?
Send us your scans or eye report. One of our surgeons, Prof. Dr. Ahmet Satıcı, Doç. Dr. Muhammet Derda Özer or Op. Dr. Aysan Bayram, will review them and tell you which treatments may suit your eyes, with no obligation. A painful red eye or sudden loss of vision is an emergency: see a doctor near you first.
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