Palytoxin Keratitis/Keratoconjunctivitis (Coral Keratitis)
Palytoxin Keratitis/Keratoconjunctivitis (Coral Keratitis)
Palytoxin keratitis or keratoconjunctivitis (sometimes called coral keratitis) describes the effects of topical palytoxin exposure on the eye. It was first described in 1993, but a majority of cases (twelve out of sixteen) have been published since 2015. Systemic effects of palytoxin exposure include bitter or metallic taste, lethargy, shortness of breath, and death from respiratory/cardiac failure
Palytoxin (PTX) is a large complex polyether non proteinaceous toxin with a molecular weight of 2680 kDa found in several marine organisms, most commonly soft corals, such as zoanthids. It was first described in Hawaii in 1971.. These corals are often found in home aquariums as a result of their beauty and relatively easy maintenance. Though not all corals of the genus are affected, it is impossible to know without extensive testing and all should be assumed to carry the toxin. This knowledge in the aquarium community is present but limited. Exposure to PTX results in differing presentations based on the initial site or organ that is contaminated. Inhalational exposure is the most common as a result of patients pouring boiling water over aquarium rocks to remove the fast-growing organism and resultant aerosolization of PTX in the steam. Ocular exposure is the rarest presentation and occurs when the coral squirts toxin directly into the eye, aquarium or ocean water is splashed onto the face, or after the eye is rubbed by hands that have touched the coral without protection. Palytoxin and other analogs have been detected in sea anemone, polychaete worm, dinoflagellates, alga, crab and fish.
Histopathology of corneal specimens that underwent transplantation for perforation revealed severe keratolysis, acute and chronic keratitis (though with a relative low number of inflammatory cells), and stromal scarring.
Though the effects of PTX have not been specifically documented in corneal cells, a number of its cellular mechanisms of action have been published in the literature. PTX is a vasoconstrictor and also functions as a Na+/K+ ATPase disruptor allowing free flow of cations across the cell membrane; this can lead to cell death. In addition, PTX can cause disruption of actin microfilaments which delays the wound healing process. These and associated inflammatory effects, likely lead to the death of corneal epithelial cells, cytoskeletal disruption of underlying stroma, and resultant ulceration and potential perforation as seen in many cases.
Preventative measures may include wearing personal protective equipment (mask, gloves, goggles) while working with coral as well as limiting exposure
There are no confirmatory imaging or studies to assess human exposure to PTX, and diagnosis is clinical, based on a clear history of potential exposure to PTX and appropriate symptomatology. Due to its general rarity, a detailed history and strong clinical suspicion are essential. Ocular pH is usually normal, but may be elevated initially. Cultures for infectious causes are often normal.
History of likely exposure to PTX through direct inoculation of the eye itself, contact with PTX contaminated water or rubbing the eye with PTX contaminated hands is necessary. Patients usually experience immediate burning pain and other non-specific symptoms including decreased visual acuity, photophobia, and a foreign body sensation. Also systemic symptoms include dyspnea, chest pain, cough, tachycardia, nausea/vomiting, headaches, fever, myalgia, and weakness .
Findings on slit lamp exam vary, but the most commonly reported signs include conjunctival injection, ring-shaped inflammatory infiltrates, and folds in Descemet’s membrane. Other findings on slit lamp exam may include eyelid swelling, diffuse epithelial erosions, anterior chamber reactions, partially avascular conjunctiva, iritis, bullae rupture, white spots on the limbus, limbal cell failure; “crystalline-appearing” foreign bodies, anterior chamber inflammatory changes, and tarsal conjunctival hemorrhages.
As a result of the nonspecific presentation, the differential is extensive. The consulting physician should consider infectious keratoconjunctivitis and appropriate cultures should be taken. However, a positive culture should not exclude the diagnosis if there is a strong temporal relationship between exposure and symptoms, especially given the possibility of secondary infectious keratitis. PTX keratitis has been noted to present similar to other rare conditions including other toxic exposures, ophthalmia nodosa from mechanical irritants (e.g., tarantula or caterpillar hair)4, and topical NSAID toxic keratolysis.
There are no treatment protocols or grading scales in the established literature for PTX keratitis. However, anecdotal evidence from published case reports has led to specific recommendations. Removal of any toxin in the eye with irrigation or instillation of artificial tears is the most important first step and should be performed immediately upon diagnosis; this includes immediate clean removal of any contact lens as concentration and exposure time may be increased with contact lens use.
Mild cases may be treated with early, aggressive topical steroids (e.g., 1% prednisolone acetate at least six times daily). Moderate cases can benefit from prophylactic antibiotics and prednisolone acetate 1% hourly, with ascorbic acid, oral steroids and doxycycline as other added possibilities. Severe cases may need surgery for the management of associated complications.
As with medical management, there are no guidelines on surgical approaches to ocular PTX exposure, and surgery should be considered on a case by case basis. Amniotic membrane transplant, tarsorrhaphy, and epithelialization stimulating eyedrops have been documented in cases with persistent epithelial defects; corneal transplants may be a consideration in cases of ulceration and corneal perforation; other cases of residual scarring have been treated with scleral contact. In the worst manifestations of PTX exposure, corneal perforation has been treated with urgent bilateral sequential penetrating keratoplasty and anterior lamellar patch grafting .
Systemic symptoms can occur with ocular exposure. Therefore, patients with a metallic taste and nausea or vomiting should be considered for systemic toxicity.
Prognosis is largely determined by the patient’s initial exposure (i.e., concentration, length of time, etc.) and time to treatment with steroids. All patients with mild symptoms who were quickly identified and treated with steroids returned to baseline visual acuity within days to months. Conversely, patients with more severe initial presentations, systemic manifestations, and those who eventually required surgical intervention faired much worse with best corrected visual acuity at follow up being substantially reduced.
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