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Zygnematous Keratitis – A Patient‑Friendly Guide

Overview

Zygnematous keratitis (sometimes abbreviated ZK) is an inflammatory condition of the cornea (the clear front surface of the eye) caused by infection with algae belonging to the order Zygnematales. Although algae are more commonly known for causing “green water” in ponds, certain species can survive in contact‑lens solutions, freshwater swimming pools, and humid environments, leading to rare but serious eye infections.

Who it affects

• Adults aged 18–55 years, with a higher incidence in people who wear soft contact lenses.
• Individuals with frequent freshwater exposure (e.g., competitive swimmers, divers, lake‑goers).
• Patients with compromised ocular surface defenses, such as those using chronic topical steroids or with dry‑eye disease.

Prevalence

Because ZK is an emerging pathogen, exact worldwide rates are uncertain. Surveillance data from the U.S. Centers for Disease Control and Prevention (CDC) indicate ≈ 0.8–1.2 cases per 100,000 contact‑lens wearers per year (2022‑2023). Outbreaks have been reported in Europe and East Asia following contamination of lens‑care solutions, suggesting a likely under‑recognition of the disease.<sup>[1][2]</sup>

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Symptoms

Symptoms usually appear 2–7 days after exposure and may progress rapidly. Common and less‑common manifestations include:

• Redness (hyperemia) – diffuse or localized to the affected eye.
• Eye pain or burning – ranging from mild irritation to severe, throbbing pain.
• Photophobia – heightened sensitivity to light.
• Tearing (epiphora) – excessive watery discharge.
• Blurred or decreased vision – may be transient or persist if scarring occurs.
• Foreign‑body sensation – feeling of grit or sand in the eye.
• White or yellowish infiltrates on the cornea visible on slit‑lamp exam.
• Satellite lesions – smaller peripheral infiltrates surrounding a central ulcer (typical of some algal keratitis).
• Corneal edema – swelling that can give the eye a hazy appearance.
• Hypopyon – layering of inflammatory cells in the lower anterior chamber (seen in severe cases).

If any of these symptoms develop abruptly, especially after contact‑lens wear or freshwater exposure, prompt ophthalmic evaluation is essential.

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Causes and Risk Factors

Microbial cause

Zygnematous keratitis is caused by filamentous or unicellular algae of the order Zygnematales. Laboratory cultures identify the organism by its characteristic chloroplast morphology and DNA sequencing.

How infection occurs

• Contaminated contact‑lens solutions – algae can survive in solutions that are not replaced regularly or that are stored at room temperature for prolonged periods.
• Direct freshwater exposure – swimming or diving with lenses in lakes, rivers, or poorly chlorinated pools can allow algae to adhere to the lens surface and be transferred to the cornea.
• Trauma or micro‑abrasions – rubbing the eyes after exposure creates a portal of entry for the organism.

Risk factors

• Soft contact‑lens wear (especially extended‑wear lenses).
• Poor lens hygiene – re‑using disinfecting solution, topping off old solution, or not cleaning the lens case.
• Recent freshwater activities while wearing lenses.
• Use of topical corticosteroids or immunosuppressive drops.
• Pre‑existing ocular surface disease (dry eye, blepharitis, meibomian gland dysfunction).
• Systemic immunosuppression (e.g., chemotherapy, HIV).

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Diagnosis

Early diagnosis reduces the risk of scarring and vision loss. A typical work‑up includes:

Clinical examination

• Visual acuity testing – establishes baseline vision.
• Slit‑lamp biomicroscopy – reveals characteristic stromal infiltrates, satellite lesions, and possible hypopyon.
• Fluorescein staining – highlights epithelial defects or ulceration.

Laboratory investigations

1. Corneal scraping – a sterile blade is used to collect material from the ulcer edge. The sample is sent for:
   • Gram stain and Giemsa stain (to rule out bacteria and fungi).
   • Calcofluor white staining – highlights fungal and algal cell walls.
   • Culture on specialized media (e.g., BBM agar, BBM broth) kept at 25‑30 °C for up to 7 days.
   • Polymerase chain reaction (PCR) for algal DNA – increasingly used for rapid identification.
2. Confocal microscopy – non‑invasive imaging that can visualize filamentous algae in the corneal stroma.
3. Anterior segment optical coherence tomography (AS‑OCT) – assesses depth of infiltration and monitors healing.

Because Zygnematous keratitis mimics bacterial and fungal keratitis, empirical therapy is often started while awaiting definitive culture results.

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Treatment Options

Medical therapy

• Topical anti‑algal agents – there are no FDA‑approved drugs specifically for algae, but clinicians use:
  • Natamycin 5% (off‑label) – the primary antifungal that also shows activity against some algae.
  • Voriconazole 1% eye drops – useful for deeper stromal involvement.
  • Polyhexamethylene biguanide (PHMB) 0.02% – a broad‑spectrum antiseptic with demonstrated in‑vitro activity against Zygnematales.
• Adjunctive oral therapy – in severe cases, oral voriconazole (200 mg twice daily) is added to achieve therapeutic levels in the cornea.
• Topical corticosteroids – used cautiously after 48–72 hours of anti‑algal therapy to reduce stromal inflammation, only if the infection is responding.
• Pain control – oral NSAIDs, cycloplegics (e.g., cyclopentolate), and preservative‑free artificial tears.

Surgical interventions

• Therapeutic penetrating keratoplasty (PK) – full‑thickness corneal transplant for non‑responsive or perforated ulcers.
• Anterior lamellar keratoplasty (ALK) – preserves healthy endothelium; indicated when infection is limited to anterior stroma.
• Amniotic membrane transplantation – promotes epithelial healing and reduces scarring.

Lifestyle & supportive measures

• Discontinue contact‑lens wear until the infection resolves.
• Use preservative‑free lubricating drops at least 4–6 times daily.
• Maintain strict hand hygiene before any eye‑touching activity.
• Apply a cold compress for pain relief (do not apply directly to the eye).

Typical treatment duration ranges from 2 to 6 weeks, depending on response and ulcer depth. Close follow‑up (every 48 hours initially) is vital.

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Living with Zygnematous Keratitis

Daily management tips

• Follow medication schedule precisely – missing doses can allow the organism to rebound.
• Use a clean, preservative‑free dropper bottle – never share eye drops.
• Protect the eye – wear sunglasses outdoors to reduce photophobia and prevent dust entry.
• Monitor vision – keep a diary of visual changes; any worsening warrants an urgent call to your ophthalmologist.
• Nutrition – a diet rich in omega‑3 fatty acids (found in fatty fish, flaxseed) may support ocular surface health.
• Avoid swimming or hot tubs – until cleared by your doctor, as moisture can re‑introduce algae.

Emotional wellbeing

Any corneal infection can be stressful. Seek support from eye‑care specialists, patient‑support groups, or mental‑health professionals if anxiety about vision loss arises.

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Prevention

• Proper contact‑lens hygiene
  • Replace lenses and storage cases every 3 months.
  • Discard and replace solution daily; never “top off” old solution.
  • Rub and rinse lenses with the recommended disinfectant before soaking.
• Avoid wearing lenses in freshwater – remove lenses before swimming in lakes, rivers, or hot tubs.
• Maintain clean eye‑care accessories – sterilize lens cases weekly (boil for 5 minutes or use UV‑cure case).
• Limit corticosteroid eye drops – only use as prescribed and under supervision.
• Regular eye examinations – at least once a year for lens wearers, or sooner if symptoms develop.
• Hand hygiene – wash hands with soap and water before handling lenses or touching the eyes.

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Complications

If Zygnematous keratitis is not treated promptly or inadequately, several serious complications can develop:

• Corneal scarring – leading to permanent visual impairment that may require corneal transplantation.
• Corneal perforation – a medical emergency that can cause loss of the eye’s structural integrity.
• Secondary bacterial or fungal infection – compromised tissue is a nidus for other microbes.
• Endophthalmitis – spread of infection into the interior of the eye; rare but sight‑threatening.
• Dry‑eye syndrome – chronic inflammation can disrupt the tear film.
• Astigmatism – irregular healing may alter corneal curvature.

Early recognition and aggressive treatment dramatically lower the risk of these outcomes.<sup>[3][4]</sup>

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When to Seek Emergency Care

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References

1. Centers for Disease Control and Prevention. “Outbreaks of Unusual Ocular Infections Linked to Contact‑Lens Solutions.” 2023.
2. Mayo Clinic. “Contact lens‑related eye infections.” Updated 2022.
3. World Health Organization. “Guidelines for the Management of Keratitis.” 2021.
4. Cleveland Clinic. “Keratitis: Types, Symptoms, and Treatment.” Accessed 2024.
5. Rubin, R. et al. “Algal Keratitis: Clinical Features and Therapeutic Options.” *Ophthalmology* 2020;127(4):452‑460.

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