A 19-year-old medical student comes to see you in casualty. He had been out partying the night before and unfortunately slept with his contact lenses in. The following morning, he woke up and showered without removing his lenses. He comes to see you with photophobia and a red eye. You ask him to take out his lenses and put on his glasses: his best corrected VA is 6/60, and he has a large epithelial defect and a hypopyon.
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1. What is the most likely diagnosis?
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Correct answer: Contact lens-associated keratitis is the most likely diagnosis. One needs to scrape the infiltrate with a 21 or 23 gauge needle for two reasons:
a. So microbiology can identify the pathogen involved.
b. Physical removal of the infiltrate can aid penetration of the topical antibiotic and improve the effectiveness.
The most common pathogen in contact lens wearers is Pseudomonas aeruginosa, hence a quinolone is usually prescribed as first-line treatment. The idea is to sterilise the environment, so for 48 hours, patients are instructed to instil one drop hourly. The patient is then reviewed to see the response: at this stage, steroids are considered to limit the extent of inflammation and potential scarring (the so-called healing phase).
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2. How can you explain the hypopyon?
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Correct answer: A hypopyon is a collection of white blood cells in the anterior chamber. Only fungal infections have the capability to penetrate the Descemet’s membrane and subsequently enter the anterior chamber. So in bacterial keratitis, a sterile hypopyon develops.
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3. What are the biggest risk factors for developing this condition, and what should you tell your patient?
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Correct answer: The biggest risk factor in developing microbial keratitis is sleeping in contact lenses. Important general advice to contact lens wearers includes:
- Limit the use of lenses to 5 days a week.
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Aim to switch to daily disposables.
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Do not leave the lens case in the bathroom (to avoid water splashing into the case).
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Do not sleep, swim or shower whilst lenses are in the eye.
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4. With the history in mind, what other diagnosis should be in your mind? What signs should you look for?
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Correct answer:
Acanthamoeba is a free-living amoeba found in tap water, swimming pools and soils. Exposure to any of the above whilst wearing contact lenses puts one at risk of acanthamoeba keratitis, which is a sight-threatening condition.
Look for the following signs, and always keep a low threshold for diagnosis:
- Disproportionate pain to clinical signs
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Radial keratoneuritis, whereby infiltrates settle around corneal nerves.
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Dense ring infiltrate at the stromal level.
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5. What are the indications for admitting a patient into hospital with this condition?
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Correct answer: Only admit patients into hospital if they are physically unable to administer their own drops (especially in elderly patients) or there is a question of compliance (e.g. in patients with mental illness).
Nine months later, he comes back to the anterior segment clinic. He has a large anterior stromal scar over the visual axis. Management options are discussed.
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6. Name the layers of the cornea. Which layers heal from scarring?
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Correct answer: Epithelium, Bowman’s layer, stroma, Descemet’s layer and endothelium. If any inflammation occurs in any layer deeper than and including Bowman’s layer, the cornea will heal with scarring. If this is centred on the visual axis, patients will complain of blurred vision.
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7. What are his surgical options?
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Correct answer:
Whilst not to be taken lightly, surgery is an option for this young man. The two procedures available are:
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Penetrating keratoplasty (PK):
- This is a full-thickness corneal graft, the traditional mode of treatment.
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In 1905, it was the first successful organ transplant carried out in humans.
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The limitations of the procedure include:
- Approximately 20% of patients have immunological reactions, which compromise endothelial function.
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Prolonged immunosuppression is required.
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There is a fairly long postoperative recovery time.
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Deep anterior lamellar keratoplasty (DALK):
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DALK consists of removing all the diseased corneal stroma up to the layer of Descemet’s membrane.
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Fresh donor cornea is prepared by the surgeon, and the anterior part is sutured to the recipient.
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Hence, it would be useful in this patient where the scar is in the anterior stroma and the endothelium is normal.
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The advantages compared to PK include:
- Reduced risk of rejection
- Reduced risk of irregular astigmatism
- Shorter postoperative recovery (sometimes within the week)
- Shorter requirement of topical steroids.
