Sehklinik

Cornea

Corneal inflammation: when the red eye hurts and sees worse

One eye is red, it really hurts, light becomes uncomfortable — and vision is worse than yesterday. That is no longer the picture of conjunctivitis. When the cornea becomes inflamed, keratitis in medical terms, hours to days count rather than weeks: an infection can leave a scar in a short time, and if that scar lies in the visual axis, it stays. Anyone wearing contact lenses takes them out immediately and calls the same day.

Why a corneal inflammation is an emergency

The cornea is the clear window at the front of the eye — the curve a contact lens sits over. It contains no blood vessels, and its fibres lie in a highly ordered structure — together, those two things make it transparent. At the same time, as the strongest lens of the eye, it focuses the light. To that end it is densely threaded with fine nerves, more sensitive than almost any other tissue of the body. From both of those follows what distinguishes this condition from most red eyes: It hurts — and it does not always heal without a trace.

The medical name for inflammation of the cornea is Keratitis; in conversation most people say corneal inflammation. The same thing is meant. Unlike with conjunctivitis, 'wait and watch' is not a safe strategy here: a bacterial corneal infection can increase in area and depth within hours to a few days. What is left behind afterwards is not redness but clouding.

And where that clouding lies decides what you see. A scar at the edge of the cornea goes unnoticed by many people all their lives. The same scar in the visual axis — directly in front of the pupil — scatters the light, makes the image flat, produces glare against the light and reduces visual acuity. No drops can remove it later. That is why we treat the suspicion, not only the confirmation.

Call us the same day if any of these applies:

  • Pain in the eye — not burning, not itching, but pain
  • Vision is worse now, blurred or as if behind a veil
  • Marked light sensitivity, which makes you screw up your eye
  • A red eye and contact lenses — take the lens out at once and call us
  • A whitish or grey spot on the otherwise clear cornea
  • A yellowish level in the lower part of the anterior chamber of the eye
  • After an injury, especially with a branch, a twig, soil or plant material
  • With a known herpes disease of the eye and a red, painful eye again

A call that turns out to be unnecessary costs ten minutes. A corneal inflammation left too long can cost visual acuity. That calculation only works out one way.

Symptoms that distinguish keratitis from conjunctivitis

A great many people who come to us with a corneal inflammation first looked up 'conjunctivitis' at home — understandably, since both conditions produce a red, watering eye. The difference lies not in the colour but in three symptoms that do not belong to the conjunctiva: Pain, worsening vision and strong light sensitivity.

FeatureMore likely conjunctivitisMore likely corneal inflammation
SensationBurning, itching, a gritty feelingReal pain, often sharp and severe
VisionUnchanged, at most veiled by dischargeMarkedly worse, blurred, as if through frosted glass
LightMild sensitivityMarked light sensitivity, the eye screws shut
RednessEvenly across the whole white of the eye, stronger towards the lidsA deep, bluish-red ring directly around the cornea
CorneaClear and shinyPossible whitish or grey spot, a dull patch
DischargeWatery, mucous or purulent, lids stuck together in the morningDischarge says little here — anything from heavy watering to clearly purulent discharge is possible. What counts remains pain, vision and light sensitivity.
SideOften spreads to the second eye after one or two daysUsually one-sided — in the eye that wore the lens
Time frameWithout pain, light sensitivity or worsening vision, and without contact lenses: watching for one or two days is as a rule defensibleAssessment the same day

The one eye wearing a contact lens is the most telling sign of them all. A contagious conjunctivitis typically travels on; a keratitis stays where its cause sat. So if the lens-wearing eye goes red, you have pain, and the second eye stays quiet, the probability is high that the cornea is involved.

How a genuine conjunctivitis runs its course, which forms there are and how long it is contagious is set out in full on its own page: Conjunctivitis — symptoms, contagion and treatment. There you will also find what you can spare yourself. The reverse holds too: not every painful red eye is the cornea. An Inflammation inside the eye (uveitis) also causes pain, light sensitivity and worse vision — and is just as little a case for waiting. Which inflammation sits where is something the slit lamp separates in a few minutes; an overview of the other forms is given on the page Eye inflammation.

The forms of keratitis — and why telling them apart changes everything

'Corneal inflammation' says which tissue is inflamed, but nothing yet about what caused it. The treatment, however, hangs on exactly that: what works against bacteria does nothing against viruses, and what helps a viral form can leave an amoebic infection unnoticed for months. Determining the cause is therefore not an academic intermediate step but the actual point of the examination.

Bacterial keratitis

The most common infectious form in our consultations — and almost always in people who wear soft contact lenses. The rapid onset is typical: within a day pain, redness and light sensitivity become markedly stronger, vision clouds over, and often a whitish spot appears on the cornea. Some pathogens that thrive in the moist environment of lens cases and water are regarded as particularly aggressive and can damage the cornea deeply within a short time. Treatment is with antibiotic eye drops, in very close succession to begin with — hourly at first, in severe cases at night as well — and with checks at intervals of hours to days, until the finding is reliably receding.

Viral keratitis, herpes in particular

A great many people carry the herpes simplex virus without noticing; it can lie dormant in nerve ganglia and reach the eye from there. Herpes keratitis is therefore typically not a new infection but a reactivation — and that is why it comes back. Triggers can be fever, heavy UV exposure, stress, other illnesses or weakened immune defences. Characteristic is a branching pattern in the corneal epithelium, reminiscent of a small twig, which can be made visible with dye; noticeably often the sensation in the eye is reduced at the same time, so that the symptoms seem milder than the finding is.

Why steroids are dangerous here: Steroid eye drops damp down the inflammatory reaction — the redness recedes, the eye feels better. They do not slow the multiplication of the virus; they can encourage it. A small finding can turn into an extensive ulcer while everything looks like improvement. Where herpes is suspected, antiviral treatment therefore comes first; if deeper layers of the cornea are involved as well, steroids can be part of the treatment — but then only on an ophthalmologist's prescription, in combination, and under close monitoring. Old bottles of drops from the medicine cupboard have no place with a painful red eye.

Adenoviruses, the commonest cause of the highly contagious form of conjunctivitis, can involve the cornea as well. After the redness has settled, fine opacities then often remain for weeks to months, which are perceived as a veil and as glare and usually disappear again on their own.

Acanthamoeba keratitis

Acanthamoebae are tiny single-celled organisms found in tap water, swimming pools, lakes, hot tubs and soil. For a healthy eye they are not an issue — for an eye with a contact lens they very much can be. The typical history is always the same: showered in lenses, swam in them, rinsed the case with tap water or stored lenses in it. Characteristic is pain markedly stronger than the visible finding would lead you to expect, and a course over weeks rather than days.

This form is rare, but it is often taken for herpes at first and treated accordingly — which costs time. Identifying it requires special investigations, the treatment is protracted, and it belongs at a centre specialising in it. When we have this suspicion, we tell you so plainly and arrange the onward care, instead of making attempts of our own.

Fungal keratitis

Rare in Switzerland. It occurs above all after injuries with organic material — the branch while trimming the hedge, the twig on a run through the woods, soil while gardening — and also with weakened immune defences and after prolonged use of steroid drops. The insidious course is typical: over days to weeks it slowly gets worse rather than rapidly getting bad, which tempts people to wait too long. The treatment is antifungal, takes a long time and needs patience on both sides.

Not every keratitis is an infection

The cornea can also become inflamed without any pathogen. A severely disturbed tear film irritates and mechanically damages the surface; anyone who has had dry eyes for months often shows fine defects spread across the whole cornea at the slit lamp. Anyone who has worked at welding without protection, or spent a day in the snow without glasses, knows what follows: hours later severe pain begins, because UV light has damaged the topmost cell layer. And if the lids do not close completely at night — for instance with an eyelid malposition — the cornea dries out in its lower part and becomes inflamed. If instead the upper lid sits too high, rather than the closure failing, that is a finding of its own with causes of its own: an upper lid that sits too high and does not close fully at night. These forms are not infections, but they need assessing just as much: an irritated, damaged surface can also become secondarily infected. You will find an overview of the other conditions of this layer — from a change in its shape to clouding — on the page Cornea, including Keratoconus.

Contact lenses: the most important risk factor

Contact lenses are a good and safe aid — when the rules are kept. Most of the bacterial corneal infections we see, however, have something to do with them. The reason is simple: the lens lies directly on the cornea, reduces the supply of oxygen, alters the tear film and offers germs a surface they can hold on to. Add a small injury to that surface and the way is clear for an infection.

Water and contact lenses do not go together. That is the most important rule, and it is the one broken most often — usually without ill intent, because 'tap water is clean, after all' sounds plausible. But drinking-water quality does not mean germ-free for the eye: tap water can contain bacteria and acanthamoebae that are harmless in the stomach and are not on the cornea.

  • Do not shower in lenses — not even 'just briefly' and with your eyes shut.
  • Do not swim in lenses, neither in the indoor pool nor in the lake. If there is no way around it: tight-fitting goggles over daily lenses that you throw away afterwards.
  • Never rinse the case or the lenses with tap water — only with fresh lens solution.
  • Never top up the lens solution, but replace it completely every time. 'Topping up' only dilutes the used solution.
  • Replace the case regularly, roughly every three months, and after emptying it let it dry open, with the opening facing down.
  • Wash and dry your hands, before you handle lenses.
  • No saliva, to moisten a lens. The mouth and the eye are two very different environments.

The wearing time is not a recommendation but a limit. Change monthly lenses after the month, throw daily lenses away in the evening, even if they still feel fine — an older lens carries more deposits and more germs. Just as non-negotiable: do not sleep in lenses, and that includes the nap on the sofa and the short sleep on a plane. Overnight the cornea gets noticeably less oxygen, and the tear film no longer rinses — wearing lenses overnight is regarded as one of the strongest risk factors for a bacterial corneal infection.

And the rule that counts when it matters: If an eye goes red, the lens comes out immediately — and it does not go back in until the eye has been examined. Wearing the lens for another day 'for reassurance', because you see badly without it, is the step that turns a beginning inflammation into a serious one. Please bring your lenses, case and care products to the appointment; if there is any doubt, we examine those as well.

What does not help — and what harms

With a painful red eye, reaching for a home remedy or the leftover packet is understandable. Here, both only cause delay.

  • Steroid eye drops without a confirmed diagnosis. That is the single most dangerous mistake in this condition: they take away the redness while an infection carries on undisturbed.
  • Antibiotic drops left over from the last episode or from a relative's cupboard. Opened bottles are, moreover, often colonised with germs themselves.
  • Camomile tea compresses and eye baths. Camomile is a common contact allergen and irritates further; an eye bath washes nothing out of the cornea.
  • Taping the eye shut or covering it, to give it rest. With a contact lens-associated infection that is not a good idea — moist and warm are exactly the conditions in which germs multiply.
  • Rubbing. It soothes for seconds and damages the surface further.
  • Waiting until a consultation suits you better. The one point on this page that really counts.

What does make sense is little, and it is simple: lens out, leave the eye alone, sunglasses against the light sensitivity, a painkiller you are used to if you need one — and call. Moisturising drops with no active ingredient do no harm, but they are no substitute for an assessment.

How we assess: slit lamp, staining and swab

The examination begins with your history, and in this condition that is unusually informative: since when, which eye, contact lenses yes or no and how worn, contact with water, injury, earlier episodes in the same eye, existing conditions and medicines. Then we measure visual acuity — not as a formality, but as a baseline against which the further course can be measured.

At the slit lamp the cornea is examined layer by layer with a narrow slit of light. We assess where the inflammation sits, how large it is, how deep it reaches and — the decisive question — whether it lies in the visual axis. At the same time we look into the anterior chamber of the eye: cells there, or even a level of pus, point to a severe course.

With a dye (fluorescein) we then stain the surface. Under blue light, places where the topmost cell layer is missing light up — making visible what could only be guessed at before: the branching defect of herpes, the round loss of substance over an infiltrate, the fine dots of a dried-out eye. Where herpes involvement is suspected we also test the sensitivity of the cornea.

With a swab we take material directly from the affected spot and send it to the laboratory — for culture and, depending on the question, for identification of the pathogen by PCR. Not every small, superficial inflammation needs this. It makes sense above all with larger or central findings, in contact lens wearers, in courses that do not respond to the treatment started, and always where an unusual pathogen is suspected. Bring your lenses and case with you: a pathogen can be identified from those as well.

Why that is better than drops on suspicion: Targeted treatment hits the pathogen you actually have. Drops chosen blind can work against one pathogen and achieve nothing against the next — and the days on which they do not work are exactly the days on which the inflammation goes deeper. Because results take time, with a finding that needs treatment we of course start immediately and adjust as soon as the laboratory answers. Referring physicians reach us directly for cases like these — the ways to do that are set out under Referring physicians.

Treatment and course

Treatment is pathogen-specific: antibiotic where the cause is bacterial, antiviral for herpes, antifungal where fungi are involved, and with a special, protracted treatment for acanthamoebae. That is not a nicety for a specialist audience — it is the reason the assessment comes before the treatment.

With infectious forms the start is typically intensive: eye drops in very close succession, hourly at first and, in severe cases, at night as well. That is demanding, and it is the part where a treatment fails if nobody explains beforehand why it is necessary. As soon as the finding recedes, the frequency is reduced step by step. Pupil-dilating drops against the pain and moisturising preparations to care for the surface can be used in addition.

Close monitoring is part of the treatment, not of the aftercare. At the start we often see you again daily or every second day, measure visual acuity again and compare the size and depth of the finding with the day before. That makes it apparent early whether the treatment is working or whether it has to be changed. Contact lenses stay out completely during this time — in the healthy eye as well, if the cause lay in how they were handled. Opened lenses, the case and care products you replace afterwards.

How long it takes depends on the pathogen, on how far it extends and on when the treatment began. Superficial bacterial courses usually settle markedly within a few days under effective treatment; deeper findings, herpes courses involving the corneal tissue, and fungal and acanthamoeba infections need weeks to months. A duration can only be named responsibly against the finding. What we can promise is that you hear from us what we see — including when it goes more slowly than hoped.

Scars and visual acuity — what has to be said honestly

The cornea does not heal the same way everywhere. Its topmost cell layer, the epithelium, renews itself reliably: a pure surface defect usually closes within days and leaves nothing behind. If the inflammation reaches deeper, into the load-bearing corneal tissue, that is different. This tissue owes its clarity to a highly ordered fibre structure; repair tissue is disordered — and disordered fibres scatter light. That is precisely what a scar is.

Whether a scar impairs vision is decided above all by where it lies. At the edge of the cornea it often goes unnoticed for a lifetime. Directly in front of the pupil, in the visual axis, the same scar can permanently reduce visual acuity, make the image flat and cause glare against the light, at night and when driving. That cannot be undone with drops later, and nobody should tell you otherwise.

How a corneal inflammation turns out depends qualitatively on several things: on the pathogen and how aggressive it is; on the size, depth and location of the finding; on how early effective, targeted treatment began; on whether the treatment was carried through consistently and monitored; and on accompanying factors such as existing conditions, a disturbed tear film, incomplete eyelid closure or weakened immune defences. We do not quote percentages for this — they depend so strongly on the individual case that any figure promises more than it can keep.

Of these factors exactly one is in your hands, and it is the most effective: the moment at which you call. An inflammation treated early and in a targeted way is far more likely to stay superficial — and what stays superficial as a rule heals without lasting clouding.

If a troublesome scar does remain, that is not the whole of it. Some opacities grow paler over months. Irregularities of the surface can in part be evened out with rigid contact lenses, once the eye has settled completely. For pronounced central scars there is the possibility of a corneal transplant; that is a planned procedure at a centre specialising in it, and not a routine measure to be held out lightly. If it comes to that, we discuss it openly, with all the advantages and disadvantages — and with the question of whether it is worth the effort to you.

Costs & health insurance

What does the insurer pay for — and what not?

A corneal inflammation is an illness, and assessing and treating it are medical treatments. Where there is a medical indication this runs through basic health insurance (OKP); your deductible and co-payment apply as at any doctor's appointment. What is not included we tell you beforehand — in an emergency, though, only after the eye has been dealt with.

ServiceCoverageWhat this means for you

Emergency assessment for a red, painful eye

Basic insurance (OKP)

Examination at the slit lamp, visual acuity, staining of the cornea and the doctor's assessment — where there is a medical indication, a service covered by basic health insurance. That the assessment shows 'only' a harmless cause in the end changes nothing about that.

Swab and identification of the pathogen in the laboratory

Basic insurance (OKP)

Culture and, where necessary, molecular identification are covered where the question calls for them. The laboratory's bill can come separately from ours; it too runs through your deductible and co-payment.

Prescribed eye drops and medicines

Basic health insurance (covered preparations)

You collect them at the pharmacy; what you pay towards them depends on your deductible. Individual special preparations, of the kind needed for rare pathogens, are not covered by basic insurance in every case — we tell you before you fetch them.

Close follow-up checks

Basic insurance (OKP)

The short-notice reviews are part of the treatment, not an additional service. They are the reason a change of treatment can be made in time.

New contact lenses, care products, lens fitting

Self-pay service

You replace lenses, case and solution after a corneal inflammation in any event — as your usual visual aid they are at your own expense. The case is different if a scar or an irregular cornea remains after an inflammation: rigid specialist lenses are then a medically justified visual aid, to which basic health insurance contributes a limited amount at the applicable rates. What applies in your case we clarify beforehand.

Come in when in doubt, even if you are unsure whether it is 'bad enough'. With pain, light sensitivity, worse vision or a red eye while wearing contact lenses the rule is: call today, not tomorrow. Outside consulting hours the ophthalmic emergency service applies — contact it, or go directly to the emergency department of an eye hospital.

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Medically reviewed by PD Dr. med. Dietlind Friedrich · Last reviewed

Frequently asked questions

A painful red eye is not a case for waiting.

Call and describe your symptoms to us. Where a corneal inflammation is suspected we see you the same day — all the more so with contact lenses.

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+41 44 500 69 00 — Mon–Fri 08:00–12:00 / 13:00–17:30. Outside consulting hours the ophthalmic emergency service applies — contact it, or go directly to the emergency department of an eye hospital. Or Request an appointment online.