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Editor,—Intraocular filariasis is an uncommon disease in civilised countries. In only a few cases has the worm been surgically removed from the posterior portion of the eye and identified.1 In this report we describe a patient who had a filaria-like worm in an epimacular and/or submacular lesion, which was successfully removed surgically.
A 38 year old woman complained of decreased visual acuity in her left eye of 5 days’ duration. Her medical history was unremarkable. The patient had two pet dogs, and she had not travelled to foreign countries in recent years. On examination, her corrected visual acuity was 20/20 in the right eye and 20/100 in the left. No inflammation was present in the anterior segment or vitreous cavity bilaterally. Ophthalmoscopic examination disclosed a white worm, approximately 3 disc diameters in length, equivalent to about 4.5 mm, moving slowly in the macula at the epiretina. Epiretinal and intraretinal haemorrhages were observed in and around the macular region. The body of the worm was tapered at one end and slightly rounded at the other (Fig 1). A round, preretinal haemorrhage was observed on a branch of the superonasal retinal artery, which could have been the route of entry into the eye.
Numerous subretinal hypopigmented tracks with small haemorrhages were noted in the superior retina, and perivascular haemorrhages were observed around the inferior branch of the central retinal vein (Fig2). Fluorescein angiography showed numerous hyperfluorescent tracks without dye leakage. The patient’s blood test revealed a slightly elevated white blood cell count (10 200 ×106/l; normal <9000) and elevated IgE in the serum (680 U/ml; normal <250).
On the following day pars plana vitrectomy was performed and the worm was found partially migrated into the subretinal space of the macula. The worm was aspirated successfully through a 20 gauge silicone tipped needle and submitted for parasitological study; however, it was lost during transportation to a different laboratory. Parasitological study of the patient’s serum detected an antibody toDirofilaria. Six months after surgery, the patient’s visual acuity was still 20/50. Ophthalmoscopically the hypopigmented tracks had faded, and mildly irregular pigment was observed at the deep retina in the macular lesion. Cone and rod electroretinograms to full field stimuli were normal bilaterally.
Our patient owned two dogs, and her ocular findings could be differentiated from toxocariasis, in which only larvae ofToxocara canis can infect humans. The length of the Toxocara larva is about 400 μm, and grows no longer. Although no direct microscopical evidence ofDirofilaria infection was obtained in our patient, a positive antibody to Dirofilariain the serum indicated its infection. There have been many reports of intraocular filariasis; however, the filariae were removed and identified in only six of 56 cases reviewed by Beaver in 1989.1 Direct parasitological microscopic examination is necessary for accurate diagnosis, but serological study can be helpful, as shown in the present case.
Various types of management for intraocular parasites have been reported. Direct photocoagulation to the worm body has been successfully reported in cases with filaria-like worms2 3and in one case with insect parasites.4 It has been suggested that photocoagulation denatures the parasite proteins and mitigates the immune reaction.2 4 If the parasite is located in the posterior pole of the retina, however, photocoagulation may cause permanent visual impairment, and surgical removal should be selected. Furthermore, photocoagulation would make parasitological identification impossible. Preretinal or subretinal parasites were retrieved successfully by pars plana vitrectomy in several reported cases.5 6 In the present case, the visual acuity was still 20/50 6 months postoperatively. The migrating worm may have caused considerable damage to macular function, therefore, we believe that intraocular parasites should be removed as soon as possible.
The authors are grateful to Dr Keizo Yamaguchi for parasitological examination and Mr Shingo Yamazaki for fundus photographs.