Eye Diseases Guide: Common Eye Conditions Grouped by Symptom

Eyes can go wrong in many different ways, and the same symptom can have very different causes. Blurry vision may be nothing more than an out-of-date glasses prescription, or it may be the first sign of cataract, diabetic eye disease or macular degeneration. A red eye is usually a harmless irritation or infection, but occasionally it signals inflammation or a pressure spike that threatens sight. Knowing which symptoms are routine and which are urgent can make a real difference.

This hub gives you an overview of the major eye conditions, grouped by the symptoms people most often notice: blurry vision, red eyes, eye pain, floaters and flashes, and poor night vision, plus conditions that cause few or no symptoms at all. Each section links to a detailed guide. It is designed to help you understand what might be going on and how quickly to seek help, not to replace a diagnosis by an optometrist or ophthalmologist.

How to use this guide

Find the symptom that best matches your experience, read the overview of possible causes, then follow the link to the detailed guide. Keep in mind that several conditions can occur together, and symptoms overlap. The table below gives a quick orientation.

Blurry or gradually worsening vision

Blur that develops slowly over months or years is the most common eye complaint. The cause is often simple, but it should always be checked, because several important diseases start this way.

Refractive errors

Short-sightedness, long-sightedness, astigmatism and the age-related near vision loss of presbyopia are the most common causes of blur. They are corrected with glasses, contact lenses or surgery. Blur that clears when you look through a pinhole is often refractive. See our guide to refractive errors.

Cataract

A cataract is a clouding of the eye's natural lens, usually related to ageing. It causes gradually blurred or hazy vision, glare from headlights and sunlight, faded colours and frequent prescription changes. Cataract surgery, which replaces the cloudy lens with an artificial one, is one of the most common and successful operations worldwide.

Age-related macular degeneration

Age-related macular degeneration (AMD) affects the macula, the centre of the retina responsible for detailed vision. It causes blurred or distorted central vision, with straight lines appearing wavy, and in later stages a dark or empty patch in the centre. Side vision is preserved. The wet form can progress quickly but often responds to injections into the eye, so sudden distortion needs urgent assessment. An Amsler grid can help you monitor changes at home between examinations.

Diabetic retinopathy

Diabetic retinopathy is damage to the retinal blood vessels caused by diabetes. It often has no symptoms in early stages; later, leaking vessels can cause swelling of the macula and blurred vision, and fragile new vessels can bleed, causing sudden floaters or vision loss. Annual diabetic eye screening and good control of blood sugar, blood pressure and cholesterol are key to prevention.

Other causes of blur

• Dry eye disease causes fluctuating blur that improves with blinking, along with grittiness and burning.
• Keratoconus, a progressive thinning and bulging of the cornea, causes worsening blur and distortion, usually starting in the teens or twenties.
• Amblyopia (lazy eye) causes reduced vision in one eye that started in childhood.
• Retinitis pigmentosa and other inherited retinal diseases cause slowly progressive loss of vision.
• Fluctuating blood sugar can temporarily change focus; see our article on blood sugar and blurry vision.

Red eyes

A red eye is caused by widened blood vessels on the surface of the eye or by bleeding under the conjunctiva. Most red eyes are harmless and settle within days, but some need prompt treatment.

Common, usually non-urgent causes

• Conjunctivitis (pink eye): redness with discharge, grittiness and sticky lids. It can be viral, bacterial or allergic. Vision is normal.
• Eye allergies: itchy, watery, red eyes, often with sneezing, seasonal or triggered by pets or dust.
• Blepharitis: chronic inflammation of the eyelid margins with crusting, burning and red lid edges.
• Dry eye: redness with burning, grittiness and paradoxical watering.
• Pterygium and pinguecula: raised yellowish or fleshy growths on the white of the eye that can become inflamed, linked to sun exposure.
• Subconjunctival haemorrhage: a bright red patch from a burst blood vessel; painless, harmless and usually clears within two weeks, but recurrent cases or those on blood thinners need review.

Red eye that needs urgent care

• Uveitis: inflammation inside the eye causing redness around the cornea, aching pain, light sensitivity and blurred vision. It can be linked to autoimmune diseases and needs prompt treatment to prevent complications.
• Corneal ulcers and keratitis: painful red eye with light sensitivity, blurred vision and sometimes a white spot on the cornea. Contact lens wearers are at particular risk.
• Acute angle-closure glaucoma: a very painful red eye with blurred vision, haloes around lights, headache, nausea and vomiting. This is an emergency.
• Scleritis: deep, boring eye pain that may wake you at night, with a dusky red eye, often associated with autoimmune conditions.

Our article on red eye: harmless or an emergency? walks through the differences in more detail.

Eye pain and discomfort

Eye discomfort ranges from a mild gritty feeling to severe, deep pain. Superficial irritation usually points to the surface of the eye or lids; deep pain and light sensitivity suggest something inside the eye or around the optic nerve.

• Stye and chalazion: a stye is a painful, red lump at the lid margin caused by infection of a gland; a chalazion is a firmer, usually painless lump from a blocked oil gland. Warm compresses help many cases.
• Foreign body or corneal abrasion: sharp pain, watering and a feeling of something in the eye. Embedded objects or high-speed injuries need urgent assessment; see our guide to eye emergencies and first aid.
• Optic neuritis: pain on moving the eye with blurred or dim vision and faded colours in one eye, often in young adults; it can be associated with multiple sclerosis.
• Thyroid eye disease: gritty, aching eyes, puffy lids, bulging eyes and sometimes double vision in people with thyroid conditions, especially Graves disease.
• Ocular migraine and visual aura: shimmering zigzag patterns or blind spots lasting up to about an hour, often followed by headache. A first episode, or aura in only one eye, should be medically assessed.
• Digital eye strain: tired, aching, dry eyes and headaches after prolonged screen use.

Floaters, flashes and shadows

Floaters are small dots, threads or cobwebs drifting across your vision, most noticeable against a bright background. Flashes are brief sparks or arcs of light, often at the edge of vision. Both are usually caused by age-related changes in the vitreous gel, which shrinks and can separate from the retina (posterior vitreous detachment). This is common after the age of 50 and in people with myopia.

• Floaters and flashes: long-standing floaters are usually harmless, but a sudden increase needs examination.
• Retinal detachment: the retina lifts away from the back of the eye, causing a shadow or curtain spreading across vision, often preceded by new floaters and flashes. It is a medical emergency, and early surgery gives the best chance of preserving sight.
• Bleeding inside the eye (vitreous haemorrhage), for example from diabetic retinopathy, can cause a sudden shower of dark floaters or smoky vision.

Poor night vision and glare

Difficulty seeing in dim light or at night can be a simple matter of uncorrected prescription, but it can also be the first sign of a lens or retinal problem.

• Night blindness (nyctalopia): a symptom rather than a disease, with causes including cataract, myopia, retinitis pigmentosa and vitamin A deficiency.
• Cataract: glare and haloes from headlights are classic early symptoms.
• Retinitis pigmentosa: an inherited condition that typically begins with night blindness and gradual loss of side vision.
• Uncorrected myopia and astigmatism often worsen at night, when larger pupils increase blur. Our article on night driving vision explains more.
• Previous refractive surgery or dry eye can cause haloes and starbursts around lights.

Silent conditions: no symptoms until late

Some of the most important eye diseases cause no noticeable symptoms until significant, often irreversible damage has occurred. Regular eye examinations are the only way to catch them early.

• Glaucoma: a group of diseases damaging the optic nerve, often but not always linked to raised eye pressure. The common open-angle form causes slow loss of side vision that people do not notice until it is advanced. Treatment with drops, laser or surgery can slow or stop further loss, but cannot restore lost vision.
• Diabetic retinopathy: early stages are silent; screening detects changes before vision is affected.
• Early AMD: often detected during routine examinations before symptoms appear.
• Eye tumours: rare, but some, such as choroidal melanoma, are found incidentally during dilated examinations.

See our guide to eye examinations for what is checked and how often you should go.

Other conditions worth knowing about

Lowering your risk of eye disease

Not all eye disease can be prevented, but several measures make a real difference:

• Have regular eye examinations, more often if you have diabetes, high myopia or a family history of glaucoma.
• Do not smoke: smoking increases the risk of cataract and AMD.
• Manage blood sugar, blood pressure and cholesterol.
• Wear sunglasses with UV protection and protective eyewear for risky work and sports.
• Practise good contact lens hygiene and never sleep or swim in lenses unless specifically advised.
• Eat a balanced diet rich in leafy green vegetables and fish; see our guide to nutrition for eye health.

When to see a doctor

Book a routine appointment with an optometrist or ophthalmologist for gradual changes in vision, persistent irritation, lumps on the eyelid that do not settle, or if you have not had an eye examination in the past two years. Children should have their vision checked according to local screening recommendations.