What is Palytoxin Keratitis (Soft Coral and Microalgae Keratitis)?
Palytoxin (PTX) is a large, naturally occurring poison first found in soft corals, specifically those of the Palythoa genus. This toxin has since been discovered in a variety of marine creatures, like microalgae. PTX is a highly dangerous compound not made up of proteins, with a lethal dose of 150 nanograms per kg of body weight in mice if administered directly into the bloodstream. It is among the biggest nonpolymeric (not made up of repeating small units) natural products. This toxin was first fully produced in a lab in 1994, long after its initial discovery.
The toxin comes from parts of the coral cells known as nematocysts that release thread-like structures with sharp ‘barbs’ that can pierce tissue upon touching it. These soft corals are often found in aquariums because of their beauty and easy upkeep.
Although not every species is known to produce a toxin, it’s generally impossible to pinpoint the precise genus and species, hence, all should be treated as potentially toxic.
Breathing in, swallowing, or getting the toxin on the skin can lead to fatal whole-body effects, but recently, a few cases have mentioned eye-related effects that range from superficial tiny dot-like injuries to both corneas melting and then subsequently breaking.
What Causes Palytoxin Keratitis (Soft Coral and Microalgae Keratitis)?
Exposure to PTX, or palytoxin, often happens when breathing in the vapors while cleaning or removing coral from home aquariums. Due to their high growth rate, Zoanthids – a type of coral that can contain this toxin – often need to be removed from certain parts of the aquarium. This is usually done by boiling the coral in water or scraping them off the rocks. The problem occurs when the steam or tiny water droplets from this process are inhaled, causing symptoms like a runny nose, coughing, and difficulty breathing. Moreover, handling the coral without any protection can lead to swelling, skin redness, and other systemic symptoms, even if the skin is not broken.
Even though it’s less common, palytoxin can harm the cornea, which is the clear layer at the front of your eye. This usually happens in one of three ways: either by direct contact with water that has been contaminated with the toxin, by rubbing the eye with a hand that’s been contaminated, or by directly touching the eye with the toxin.
Risk Factors and Frequency for Palytoxin Keratitis (Soft Coral and Microalgae Keratitis)
Zoantharia, a type of marine life, is commonly found in the tropical and subtropical oceans like Hawaii, western American coastline from Florida to Brazil, many Atlantic islands, Japan, and Australia. They live in shallow parts of the ocean with a hard bottom, up to 12 meters deep. As a result, if your eyes are exposed to the water where these animals live, you might also be exposed to PTX. However, it’s worth noting that zoantharia can easily be bought online, and most of the documented cases involve people who keep them in an aquarium.
Keratoconjunctivitis is an inflammation of the cornea and conjunctiva, which can be caused by many different things. Since the cause can vary, so does the data on how common it is. However, keratoconjunctivitis associated with PTX, a substance found in Zoantharia, is relatively rare and there are no studies or estimates on how common it is to our knowledge.
Signs and Symptoms of Palytoxin Keratitis (Soft Coral and Microalgae Keratitis)
PTX-associated keratoconjunctivitis is a condition related to toxic exposure to the eyes. The symptoms vary, but commonly include extreme eye pain, red eyes, vision loss, a metallic taste, light sensitivity, and the feeling of something stuck in the eye. If you have these symptoms, it’s important to share all the details of recent activities, like hobbies and travel experiences, with your doctor. These factors can play a crucial role in identifying the cause of your symptoms.
Doctors perform a thorough eye examination for patients with symptoms that suggest toxic eye exposure. Observable signs can differ from one patient to another. However, common findings include an inflamed, red conjunctiva, and a distinctive ring-like inflammation in the eye. These signs can be detected during the initial examination.
- Coexistent signs like swollen eyelids and surface abrasions to the eye
- Erosion to the clear, front surface of the eye (Cornea)
- Reactions in the space filled with fluid right behind the cornea (Anterior chamber)
- Areas of conjunctiva (the clear, thin tissue that covers the front of the eye) without blood vessels
- Inflammation of the iris (colored part of the eye)
- Breaking of fluid-filled blisters resulting in surface scratches on the eye
- Damage to the area where the white of the eye and the cornea meet, resulting in corneal thinning and excess growth of the conjunctiva
- Surface abrasions and inclusions in the clear, outermost layer of the eye, with crystal-like foreign bodies
- Changes indicating inflammation in the anterior chamber
- White spots on the junction between the cornea and the white of the eye
- Tiny red dots caused by minor bleedings in the clear tissue covering the white of the eye and the inner surface of the eyelids
Since the symptoms and signs can vary greatly and PTX-associated keratoconjunctivitis itself is relatively rare, it’s important to provide a thorough history and maintain high clinical suspicion for an accurate diagnosis.
Testing for Palytoxin Keratitis (Soft Coral and Microalgae Keratitis)
Diagnosing PTX keratoconjunctivitis, a type of irritation in the eye, can be challenging because there is no specific lab test or imaging technique for it. Health care professionals base their diagnosis mainly on symptoms and the patient’s recent history of being in water that likely contains PTX.
High-performance liquid chromatography (a lab technique used to separate mixtures) was used in isolated cases to identify PTX in some public health scenarios. Still, currently, no test can measure toxicity levels in a person, that is, we cannot isolate PTX in a patient as part of a diagnosis.
In some cases, the pH (a measurement of acidity or alkalinity) of the affected eye was high but turned to normal after rinsing with special salt solutions. Still, in other reports, the pH was found to be neutral, not elevated. In one instance, a patient was tested for autoimmune associations, which can sometimes cause symptoms similar to PTX keratoconjunctivitis, but the results were negative.
Due to the potential severe effects (including lethality) from eye exposure to PTX, further testing may be required if the patient complains of signs like a bitter or metallic taste, lethargy, nausea, vomiting, muscle cramps, or problems with breathing. Tests may include an electrocardiogram (a test that checks your heart’s electrical activity) and monitoring of the respiratory function. In one case, a patient with these symptoms had increased levels of creatine kinase and had a urine test positive for myoglobin, suggesting a condition called rhabdomyolysis, which is a problem with muscle degradation.
Treatment Options for Palytoxin Keratitis (Soft Coral and Microalgae Keratitis)
There are no set-in-stone treatment plans for the medical or surgical care of PTX associated keratoconjunctivitis because there are very few reported cases in medical literature. That said, some recommendations have been made based on the inflammation seen in most cases and the positive response to certain treatments.
First, it’s crucial to rid the eye of the toxin causing the issue as quickly as possible. This is best done by washing the eye or applying artificial tears. In some instances, the toxin may also have been distributed to both eyes, so it’s important to clean each eye separately. The use of contact lenses can increase the toxin’s concentration and exposure time, so it is beneficial to take out the contact lenses immediately.
After the eyes have been thoroughly washed, certain treatments may help. For milder cases, the current recommendation is aggressive corticosteroid treatment (a type of medication often used to reduce inflammation) and preventive antibiotic treatment. Antibiotics help prevent infections while your body heals. These recommendations stem from the fact that these types of treatments have had positive effects in all reported cases where they were used early on.
For more moderate or severe cases, current recommendations advise the use of preventive antibiotics in combination with regular intake of corticosteroids, oral doxycycline (an antibiotic), and ascorbic acid (Vitamin C).
For the most severe cases, treatment is determined individually, but often includes some form of surgical treatment alongside medication. Some possible options include amniotic membrane transplant, tarsorrhaphy (a procedure where the eyelids are partially sewn together), or special eye drops that stimulate the growth of new skin. In cases where the cornea has ulcerated (suffered a deep, typically circular, open sore) to the point of perforation, a corneal transplant might be considered. In instances where scarring remains after treatment, rigid or scleral contact lenses or a corneal transplant may be needed. In the past, two cases of corneal perforations were resolved using sequential penetrating keratoplasty (a corneal transplant surgery) in one case, and anterior lamellar patch grafting (a type of corneal transplant surgery) in the other.
All these measures aim to recover the full function and health of the eyes and to prevent any further complications.
What else can Palytoxin Keratitis (Soft Coral and Microalgae Keratitis) be?
When patients come in with symptoms that are unclear, it’s important for doctors to consider a range of possible diagnoses. A common guess in these situations is a type of eye infection called keratoconjunctivitis. To confirm this, doctors might order different lab tests like bacterial, viral, fungal, and amoebic cultures. But sometimes, even with positive results, a diagnosis can only be made by looking at the timeline of symptoms and exposure to infection.
Other possibilities that doctors should keep in mind include exposure to harmful substances. For example, one patient had been exposed to water from his coral fish tanks and sap from plant debris. There are also cases where symptoms are similar to those caused by ocular irritants like caterpillar or tarantula hair stuck in the eye, known as ophthalmia nodosa. Unlike keratoconjunctivitis, this condition is caused by physical damage and inflammation, not infection. Another thing to watch out for is damage to the cornea caused by prolonged use of topical non-steroidal anti-inflammatory drugs (NSAIDs). This can also present with a corneal ulcer like some ocular PTX exposure cases.
- Ocular irritation caused by physical objects
- Keratoconjunctivitis (eye infection)
- Corneal damage due to prolonged use of topical NSAIDs
What to expect with Palytoxin Keratitis (Soft Coral and Microalgae Keratitis)
The outcome or progress of the condition known as eye exposure largely depends on the initial magnitude of exposure, time taken to start treatment with steroids, and any loss in visual clarity or acuity. Patients who had a minimal exposure and minor symptoms, and were promptly treated with steroids, usually improved within a matter of days to months.
However, patients who were severely exposed, had symptoms affecting the entire body, had a visual acuity worse than 20/200 (meaning their vision was poor), or had to undergo surgery, often had a more challenging outcome. In these cases, there have been reports of permanent corneal scarring and growth of new blood vessels in the eyes, failure of limbal cells (cells in the eyes that help in healing) with overgrowth of the conjunctiva (the clear tissue covering the front of the eye), and permanent vision loss. For some patients, their best-corrected vision (the sharpest, clearest vision attainable, through either natural or artificial means) was still poor, being equal to or worse than 20/100, even after treatment.
Possible Complications When Diagnosed with Palytoxin Keratitis (Soft Coral and Microalgae Keratitis)
Not properly diagnosing or treating PTX keratoconjunctivitis can result in lasting damage to the eyes. Some serious complications include the cornea (the clear front surface of the eye) weakening and breaking open or limbal stem cells (cells that help repair the eye) failing. These problems mostly occur because of the initial exposure to the irritant and delay in diagnosis. Usually, most affected people experience minor exposure without any lasting damage.
Possible Long-Term Vision Issues:
- Cornea weakening and breaking open
- Failure of limbal stem cells, needed for eye repair
Preventing Palytoxin Keratitis (Soft Coral and Microalgae Keratitis)
Many people who buy and sell fish tank decorations, like corals, don’t seem to know that they can expose themselves to harmful substances. Some people who love aquariums and share their experiences on websites and blogs do talk about these risks. To avoid skin, eye, or breathing problems from these toxins, people should wear safety gear when taking care of these creatures. This can include eye protection, like goggles, tough rubber gloves that won’t tear if you touch something sharp, and a special kind of air mask that uses activated charcoal to filter the air.
Apart from wearing protective gear, some people suggest turning off equipment like protein skimmers, air bubblers, or other water pumps, while you’re touching or moving the coral. This can help to decrease the chance of the toxin spreading through the air.
Some have even sworn by the idea that the best way to deal with these kinds of coral, called zoanthids, is to let a trained expert handle taking them out of the tank. After the coral is removed and disposed of, the water can be cleaned of over 99% of the toxins by treating it with activated charcoal.
Efforts around public health, like teaching people about these risks or overseeing how these corals are bought and sold, may help increase awareness about this potential problem and prevent future situations.
