"Worm in the eye": the rationale for treatment of DUSN in south India
K Myint1, R Sahay2, S Mon1, V R Saravanan2, V Narendran2 and B Dhillon1
1 Eye Pavilion, Royal Infirmary of Edinburgh, Edinburgh, UK 2AravindEyeHospital, Coimbatore, India
Correspondence to:
Dr Kyaw Myint
Princess Alexandra Eye Pavilion, Chalmers Street, EdinburghEH3 9HA, UK; kmyintuk{at}yahoo.co.uk
ABSTRACT Aim: To discuss the rationale for different techniques of treatmentfor DUSN (diffuse unilateral subacute neuroretinitis) and theireffectiveness in two patients from south India.
Methods: Two rare cases of live worms in DUSN from India arereported, where filarial Brugia malayi is endemic. Both casespresented with progressive unilateral loss of vision with nohistory of animal contact. They were 40 year old, apparentlyhealthy men. In case 1, the worm (1500–2000 µm)was easy to identify with wriggling movements among crisscrossingdiffuse subretinal tracks. The worm was destroyed by a singleshot of laser to its advancing end, which was followed by oralsteroid to control the inflammation caused by the dead worm.In case 2, the worm was small and difficult to identify. Initiallydiffuse neuroretinitis was diagnosed and treated with intravenousmethylprednisolone and oral corticosteroid. A week later, asmall live worm (400–600 µm) was found and subsequentlydestroyed by laser photocoagulation followed by a combinationof anthelminthics.
Results: The patients’ vision had improved to 6/60–6/36from counting fingers after a few weeks.
Conclusion: The role of a combination of laser treatment, systemicsteroid, and anthelminthics is discussed.
Intraocular parasitic infections are uncommon, with most cases reported from countries in endemic areas. In Thailand, Gnathostoma and Angiostrongylus are the most common nematodes reported in the eye. These parasites may localize to the anterior chamber, the vitreous or the retina. Ocular inflammation can be induced, particularly upon the death of the organism. Parasites can migrate actively within the eye, creating visual symptom and damaging ocular tissue.
One therapeutic approach is surgical removal, either via limbal paracentesis in the case of anterior chamber parasite, or vitrectomy in posterior segment location. Laser photocoagulation has also been used to eliminate the nematode in treating these infections.
Case Reports and Technique
In the first case demonstrated in this video the parasite is localized within the subretinal space. The patient was a 34 year-old man who presented with blurred vision in the affected eye for 3 days, accompanied by severe headache. The vision in this eye was counting fingers, with moderate iritis and an afferent papillary defect. The fundus showed vitritis, multifocal choroiditis and swollen optic disc. In the second case the parasite was found within the vitreous; in both cases, we used laser to treat the nematode. Argon laser was aimed directly at the parasite, using a spot size of 200 um, power of 500 mW, and duration of 0.1 second. Fifty to seventy-five burns may be necessary to successfully immobilize and kill the parasite. Since most of the worm is transluscent, we initiated treatment by focusing at pigmented areas in its body. Once it began to be photocoagulated, it turned to a white color and stuck to overlying or underlying tissue, thus making the following laser treatment easier.
In both cases the patients received a single dose of IV dexamethasone prior to the laser procedure to minimize uveitis caused by necrosis of the worm. High dose oral prednisone and intensive topical prednisolone acetate were used in the post-treatment regimens. In the case of the patient with the subretinal parasite, minimal post-laser inflammation was controlled by the steroid regimen, and at 2 months follow-up he recovered a visual acuity of 20/80. No follow-up data were available for the second case.
Comment
Previously, the conventional treatment for intraocular parasite was surgical removal. Vitrectomy surgery for posterior segment parasite is complicated to perform, takes longer surgical time, and in some cases the worm may elude capture, creating serious ocular complications.1,2 There have been several reports of using laser to treat intraocular parasites.3 This approach is non-invasive, fast, and relatively safe in the treatment of smaller worms in the posterior segment. Adjuvant high-dose systemic and topical corticosteroid therapy are advocated to minimize the risk of post-treatment uveitis. In both sub-retinal and intravitreal locations the laser can be effective in killing the worms without serious adverse effects, with one case of good visual recovery seen here.
References
Biswal J, Gopal L, Sharma T, et al. Intraocular gnathostoma spinigirum. Clinicopathologic study of two cases with review of literature. Retina 1994;14:438-44.
Orirala GK, Raju V, Pradesh A. Nematode in the anterior chamber. ArchOphthalmol 2003;121:1338-39.
Martidis A, Greenburg PB, Rogers AH, et al. Multifocal electroretinography response after laser photocoagulation of a subretinal nematode. Am J Ophthalmol 2002;133:417-9.