Anterior Ophthalmomyiasis Interna: An Ophthalmic Emergency

Ophthalmomyiasis is the infestation of the eye by the larval form (maggots) of flies of the order Diptera. Involvement may include eyelids and conjunctiva (ophthalmomyiasis externa), or the larva may invade inside the eye (ophthalmomyiasis interna).¹ Ophthalmomyiasis interna may be further subdivided into anterior and posterior based on the larva being in the anterior or posterior segment of the eye, respectively.² However, posterior migration of an anterior larva has been previously reported³ and also occurred in our patient. Unpredictable behavior of the larva inside the eye results in difficulty in making treatment decisions.

A 12-year-old boy had redness and mild pain in his left eye for the past 8 days. At initial examination, visual acuity was 20/20 OD and 20/25 OS. Examination results of the right eye were unremarkable, whereas the left eye showed mild ciliary injection, deep anterior chamber with 2+ cells, and a white 6-mm larva attached to the iris at the 11-o’clock position (Figure 1). No entry site was found. Direct ophthalmoscopy through the undilated pupil showed a normal retina. Three hours later while the patient was being prepared for surgery, the larva left the anterior chamber. Careful examination showed a full-thickness hole (iridotomy) in the peripheral iris produced by the larva, through which it had migrated posteriorly between the iris and zonulae. The patient was closely followed up for emergency removal of the larva in case of remigration of the larva into the anterior chamber. Two days later, the larva moved into the vitreous cavity and floated freely (Figure 2). After 3 days, it was very close to the retina and produced retinal hemorrhages. Pars plana deep vitrectomy was performed and the larva was removed completely and sent in normal saline for parasitologic studies. Three days later, the patient developed retinal detachment and underwent another surgery to reattach the retina. Parasitologic studies showed a stage 1 larva belonging to blowflies (Diptera: Calliphoridae). After 6 months, the retina was attached and best-corrected visual acuity was 20/200 due to posterior subcapsular cataract.

Ophthalmomyiasis interna is a rare disease caused by larvae of Diptera flies.² These larvae penetrate the sclera and migrate into the eye.¹ However, the entry site is usually not apparent.² In most cases the larvae are found in the posterior segment appearing as posterior uveitis, retinal detachment, and subretinal migratory tracks.^1,2 Anterior ophthalmomyiasis interna is less common and appears clinically as anterior uveitis.² Usually there is only 1 larva inside the eye; however, 2 larvae in the same eye³ and bilateral involvement⁴ have also been reported.

Prognosis of vision in these patients varies greatly. The causes of decreased vision in patients with ophthalmomyiasis interna include uveitis, subretinal migratory track crossing the macula, retinal detachment, retinal and vitreous hemorrhage, invasion to the optic nerve, and resulting optic atrophy.^1,2 Early removal of larvae decreases the potential of vision loss.¹ However, the decision to remove the larva must be made on an individual basis. For a mobile subretinal larva, argon laser photocoagulation has been recommended, obviating the need for deep vitrectomy.¹ For an immobile subretinal larva with scar tissue, no treatment is needed.³ In the case of retinal damage, the subretinal larva is best removed by pars plana vitrectomy and retinotomy.^1,5 Because of the unpredictable behavior of larva inside the eye and potential complications of vitreoretinal surgery, we recommend dealing with the anterior chamber larva emergently and removing it through a limbal incision as soon as possible to prevent posterior migration. Additionally, it is recommended not to use pilocarpine to constrict the pupil as it may cause moving and posterior migration of the larva.³

Correspondence: Dr Sharifipour, Department of Ophthalmology, Ahvaz Jundishapour University of Medical Sciences, Imam Khomeini Hospital, Azadegan Street, Ahvaz, Iran (sharifipourf@yahoo.com).

Financial Disclosure: None reported.

Additional Contributions: Bijan Abazar, MD, Babak Vazirian, PhD, and Mahmood Rahdar, PhD, provided help in the parasitologic studies.