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Spotting herpes simplex keratitis

Ophthalmologist Dr Scott Fraser on what you need to do to make sure you don’t miss the serious eye infection herpes simplex keratitis

Ophthalmologist Dr Scott Fraser on what you need to do to make sure you don't miss the serious eye infection herpes simplex keratitis

Worst outcomes if missed

Herpes simplex virus infections of the cornea can cause a profound impairment of vision in the affected eye. This occurs because of corneal scarring but the prolonged inflammation associated with HSK can also cause cataract and glaucoma.

Although this visual loss varies, the earlier the diagnosis is made and treatment started the better.

One way to ensure a poor outcome is to treat HSK with topical steroids but without antiviral cover. This is why only practitioners who are experienced in using a slit-lamp to examine the eye should prescribe ocular steroids.

Epidemiology

The herpes simplex virus is, of course, very common and most people are exposed to it during their lives – although most do not get keratitis. HSV-1 is found in the orofacial region and HSV-2 is sexually transmitted.

HSV-1 almost exclusively causes HSK and, although it is always worth being aware of the possibility, it is very unlikely you will come across type 2 affecting the eye.

As with other herpes viruses, HSV-1 lies dormant for months or years, allowing it to cause recurrent infections. Approximately 20,000 new cases of ocular HSV occur in the US annually, and more than 28,000 reactivations occur in the US annually.

Thus it is one of the commonest corneal disorders and the leading cause of cornea- related blindness in developed countries. Fortunately it is almost exclusively unilateral. Bilateral corneal involvement can occur but usually only in severely atopic patients.
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Symptoms and signs

The symptoms of HSK are the same as those of any keratitis:

• ocular pain

• reduced vision on the affected side

• unilateral photophobia

• watering.

Symptoms such as the above invariably warrant referral whether the infection is thought to be herpetic or not. As HSK is almost always unilateral, this is a further clue – as is a previous history of HSK.

Signs of HSK include the following:

• unilateral red eye

• reduced Snellen vision

• aversion to the examining light.

Classically, the corneal infection can be seen as a branching pattern (‘dendritiform') on the corneal surface. This is best seen by instilling fluorescein drops and shining a blue light – such as a Wood's light – on the cornea.

Repeated infections or a persistent infection may leave a white scar on the cornea, which invariably means vision is reduced.

Differential diagnosis

Any type of keratitis will cause the symptoms of pain, reduced vision and photophobia.

Unilateral symptoms do increase the likelihood that the infection is herpetic but many other corneal problems can be predominantly unilateral. For practical purposes, this does not really matter as if the patient describes keratitis symptoms they should be seen by an ophthalmologist the same day.

Dendritic ulcers of the cornea are most often mimicked by healing corneal abrasions. The white scar of late, untreated HSK can look very similar to bacterial keratitis. Once again, this needs same-day referral.

Photophobia, reduced vision and pain are also signs of uveitis and scleritis, but again these need specialist referral.

First-line investigations

HSK is essentially a clinical diagnosis based on symptoms of keratitis and perhaps a previous history of similar episodes. The most useful diagnostic tool is the use of 2% fluorescein drops with a blue light source to show up a dendritic ulcer.

Second-line investigations

Corneal scrapings can be taken to look for active virus but these are rarely done and are of limited value.

Dr Scott Fraser is consultant ophthalmologist at Sunderland Eye Infirmary

Competing interest: none declared

5 key questions Herpes Simplex Keratitis Five red herrings

1 Use of topical steroids in HSK will ease the patient's symptoms, so temporarily it will appear that things are improving.

2 Again, take care with contact lens wearers. They can get HSK but also may have corneal damage from their lenses or early microbial keratitis. If in doubt, get them seen by their optometrist or an ophthalmologist.

3 Healing corneal abrasions can look like dendritic ulcers – if the patient gives a good history of traumatic abrasion and their symptoms are improving it is unlikely to be a herpetic infection.

4 Snellen vision is not always a good guide to the seriousness of the ocular problem. If the patient gives a good history of a recent reduction in vision then believe them rather than the chart.

5 HSK can recur even if the patient has had a corneal graft. Once again, if the cardinal symptoms of keratitis are present, refer the same day.

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