Red eyes are one of those symptoms that make people feel instantly on edge. It’s visible, it can look dramatic and it’s hard to ignore in the mirror. The tricky bit is that “red eye” isn’t a diagnosis. It’s a sign. And the same red-looking eye can mean very different things depending on what else is going on.
In practice, we don’t just look at whether the eye is red. We look at where it’s red, whether it’s painful, whether light hurts, whether vision has changed, whether it’s one eye or both, whether you wear contact lenses, whether there’s discharge, whether the cornea looks clear and whether the pupil is behaving normally. That’s how we separate the common, self-limiting stuff from the situations that need proper assessment.
“Red eye is one of those symptoms where the details matter. Two people can both say ‘my eye is red’ and one ends up needing reassurance while the other needs treatment quickly – but both still need proper assessment to know what’s actually going on.” – Amiee, Dispensing Optician, Eyediology Styling Opticians
First – red flag situations (don’t wait it out)
If you have any of the following, don’t sit on it or try to push through for a few days:
- Moderate to severe pain (not just mild irritation)
- Light sensitivity (you want to keep the eye closed, bright light feels awful)
- Sudden blurred vision or a noticeable drop in vision
- A contact lens wearer with a painful red eye
- A chemical splash (cleaning products, hair dye, garden chemicals)
- A bad headache with nausea plus a red eye
- Halos around lights or a pupil that looks unusual
If you’re local, message us and we’ll advise you on the right next step. If symptoms are severe or worsening quickly, urgent care matters.
The most common red eye causes we see
1) Subconjunctival haemorrhage – the “burst blood vessel”
This is the one that looks like you’ve had a fright. A bright red patch on the white of the eye, sometimes spreading a bit over the first 24 hours.
What it usually feels like:
Most of the time it feels completely normal. Occasionally it’s mildly scratchy, but it shouldn’t be properly painful and vision should be fine.
Most of the time it feels completely normal. Occasionally it’s mildly scratchy, but it shouldn’t be properly painful and vision should be fine.
Why it happens:
We often hear it followed a cough, sneeze, heavy lifting, rubbing the eye or a minor knock – and sometimes there’s no clear trigger at all. It can also be more common if you’re on blood thinners or if blood pressure is running high.
We often hear it followed a cough, sneeze, heavy lifting, rubbing the eye or a minor knock – and sometimes there’s no clear trigger at all. It can also be more common if you’re on blood thinners or if blood pressure is running high.
What we do in practice:
We’ll check the eye surface is otherwise healthy, ask about any trauma, review medications and if it’s recurrent we’ll often suggest a blood pressure check. The key is making sure it’s truly a simple subconjunctival bleed and not part of a bigger story.
We’ll check the eye surface is otherwise healthy, ask about any trauma, review medications and if it’s recurrent we’ll often suggest a blood pressure check. The key is making sure it’s truly a simple subconjunctival bleed and not part of a bigger story.
What to do:
It usually clears on its own over 1–2 weeks, changing colour a bit like a bruise. Lubricating drops can help if it feels dry. If it’s recurrent, painful, after a significant knock, or you have visual symptoms, get it checked.
It usually clears on its own over 1–2 weeks, changing colour a bit like a bruise. Lubricating drops can help if it feels dry. If it’s recurrent, painful, after a significant knock, or you have visual symptoms, get it checked.
2) Conjunctivitis – not all “pink eye” is the same
Conjunctivitis means inflammation of the conjunctiva – the thin membrane over the white of the eye and inside the lids. The cause matters because the advice changes.
Viral conjunctivitis:
Often watery, gritty and can start in one eye then spread. It can be very contagious and can hang around longer than people expect.
Often watery, gritty and can start in one eye then spread. It can be very contagious and can hang around longer than people expect.
Bacterial conjunctivitis:
More likely to be sticky with thicker discharge and lashes stuck together in the morning. Still, not every sticky eye is bacterial, and not every bacterial case needs the same approach.
More likely to be sticky with thicker discharge and lashes stuck together in the morning. Still, not every sticky eye is bacterial, and not every bacterial case needs the same approach.
Allergic conjunctivitis:
Itching is the giveaway. Often both eyes, watery, seasonal and can come with hay fever symptoms.
Itching is the giveaway. Often both eyes, watery, seasonal and can come with hay fever symptoms.
What we do in practice:
We’re looking at the pattern of redness, the type of discharge, the eyelids and lashes, and importantly the cornea (the clear front window of the eye). If there’s pain, light sensitivity or blurred vision, we stop thinking “simple conjunctivitis” and start checking for other causes.
We’re looking at the pattern of redness, the type of discharge, the eyelids and lashes, and importantly the cornea (the clear front window of the eye). If there’s pain, light sensitivity or blurred vision, we stop thinking “simple conjunctivitis” and start checking for other causes.
What to do at home:
Good hygiene matters – hand washing, avoiding rubbing, not sharing towels, and binning old eye makeup. If we’re closed, your local pharmacist or GP nurse can be a good first stop for straightforward cases. If you wear contact lenses, stop wearing them until you’ve had advice and the eye is settled.
Good hygiene matters – hand washing, avoiding rubbing, not sharing towels, and binning old eye makeup. If we’re closed, your local pharmacist or GP nurse can be a good first stop for straightforward cases. If you wear contact lenses, stop wearing them until you’ve had advice and the eye is settled.
3) Dry eye and irritation – the sneaky one
Dry eye can look red, feel tired, sting, feel gritty, or paradoxically feel watery (reflex tearing is common). People often describe it like this:
- “My eyes feel tired by mid-afternoon”
- “My vision goes in and out on screens”
- “It feels like there’s something in my eye but there isn’t”
- “I keep blinking to clear it”
Why it happens:
Screens, air con, heating, contact lenses, eyelid inflammation, hormonal changes, some medications – and just the reality of modern life. Dry eye is rarely one single cause, which is why random drops sometimes don’t touch it.
Screens, air con, heating, contact lenses, eyelid inflammation, hormonal changes, some medications – and just the reality of modern life. Dry eye is rarely one single cause, which is why random drops sometimes don’t touch it.
What we do in practice:
We look at the tear film, lid margins and oil glands, and we check for surface staining and inflammation. The goal is to work out what’s driving it for you, not just label it “dry”.
We look at the tear film, lid margins and oil glands, and we check for surface staining and inflammation. The goal is to work out what’s driving it for you, not just label it “dry”.
What helps:
A proper plan is usually a mix of the right lubricants (not all drops are equal), lid care if needed, and practical changes around screens and environment. Sometimes we also need to treat inflammation – that’s when it stops being a “just use drops” situation.
A proper plan is usually a mix of the right lubricants (not all drops are equal), lid care if needed, and practical changes around screens and environment. Sometimes we also need to treat inflammation – that’s when it stops being a “just use drops” situation.
If you want a practical run-through of drops, allergies and what’s worth trying (and what’s usually a waste of money), this is a good starting point:
https://www.eyediologyopticians.co.uk/dry-eye-irritation-allergies-and-eye-drops/
https://www.eyediologyopticians.co.uk/dry-eye-irritation-allergies-and-eye-drops/
And if you feel like you’ve been stuck in a loop with dry eye for ages, our dry eye assessment explains what we actually check and why:
https://www.eyediologyopticians.co.uk/the-eye-examination/dry-eye-syndrome-assessment/
https://www.eyediologyopticians.co.uk/the-eye-examination/dry-eye-syndrome-assessment/
4) Uveitis (iritis)
Often one eye, sore, light-sensitive and sometimes blurry. The redness can look more concentrated around the coloured part of the eye. This needs assessment – it’s not something to guess at with over-the-counter drops.
5) Keratitis / corneal ulcer (especially contact lens wearers)
If you wear contact lenses and you have a painful red eye, we take that seriously. Corneal infections can worsen quickly and can threaten vision if not managed promptly. Even if it started as “a bit irritated”, the combination of contact lenses + pain is a different category.
If you’re a lens wearer, this guide is worth having saved somewhere so you’re not relying on half-remembered advice:
https://www.eyediologyopticians.co.uk/the-ultimate-contact-lenses-wear-and-care-guide/
https://www.eyediologyopticians.co.uk/the-ultimate-contact-lenses-wear-and-care-guide/
6) Acute angle-closure glaucoma
Uncommon, but important not to miss. Symptoms can include severe eye pain, headache, nausea, halos around lights and sudden blurred vision. This needs urgent care.
7) Scleritis
A deeper, more painful red eye – often described as a deep ache rather than surface irritation. This is another one that needs proper assessment.
8) Chemical injury
Rinse immediately and thoroughly (for a long time, not a quick splash) and seek urgent assessment. Early management makes a real difference.
A quick note about who you’re speaking to (and why it helps)
When you message us, you’re often speaking to our Dispensing Opticians – the same people you think of as your “glasses stylists”. We’re not optometrists so we can’t diagnose, but we’re trained to understand signs and symptoms and advise you on the right next step if an optometrist isn’t available straight away. Sometimes that’s booking in with us, sometimes it’s pharmacy or GP, and sometimes it’s urgent care. It can save you time and stress so it’s worth noting.
A quick note about who you’re speaking to (and why it helps)
When you message us, you’re often speaking to our Dispensing Opticians – the same people you think of as your “glasses stylists”. We’re not optometrists so we can’t diagnose, but we’re trained to understand signs and symptoms and advise you on the right next step if an optometrist isn’t available straight away. Sometimes that’s booking in with us, sometimes it’s pharmacy or GP, and sometimes it’s urgent care. It can save you time and stress so it’s worth noting.
What we actually check in clinic for a red eye
A proper red eye assessment usually includes:
- a careful history (onset, pain, light sensitivity, discharge, contact lenses, trauma, chemicals)
- vision check
- a close look at lids, conjunctiva and cornea under magnification
- fluorescein dye if we need to check for surface damage
- pupil reactions
- eye pressure when appropriate
- treatment advice and follow-up based on what we see (and referral if needed)
A lot of the time the outcome is reassurance – and that’s a good outcome. But we want that reassurance to be earned, not guessed.
When to message us
If you’re unsure, message us on WhatsApp with:
- which eye
- when it started
- pain level (0–10)
- any light sensitivity
- any vision change
- whether you wear contact lenses
- a clear photo in good light
Please keep in mind that we are a small independent practice, and are not a substitute for urgent care. If we’re unavailable or unable to see you, you should always seek medical advice from an alternate professional at another practice or through emergency services such as Moorfields Eye Hospital. This article is for information purposes only and accurate diagnoses can only be completed when a genuine in person assessment has taken place. It is not a substitute for in person care.
Book an eye test at Eyediology (Commercial Street, East London): https://www.eyediologyopticians.co.uk/book-an-eye-test-london/
Blackheath Eyecare bookings: https://www.blackheatheyecare.co.uk/book-an-eye-examination/
Blackheath Eyecare bookings: https://www.blackheatheyecare.co.uk/book-an-eye-examination/
If you’d like us to cover more causes (there are plenty), we’ll do a follow-up article.
