Case Study

Internal Posterior Ophthalmomyiasis: A Case Report

A tricky case of parasitic infection requires an innovative surgical approach.

Nicolay Umanets, MD • Natalia Pasyechnicova, MD • Galina Levitskaya, MD

Ophthalmomyiasis is a parasitic disease caused by penetration of the larvae of flies and gadflies into the eye globe tissues. It affects humans either directly — laying eggs or depositing larvae on or near the conjunctiva or on the eyeball — or indirectly, through dirty hands or the bites of infected insects.

There are a large variety of clinical manifestations of ophthalmomyiasis. Internal posterior ophthalmomyiasis is characterized by a different clinical course from asymptomatic ophthalmomyiasis, with accidental discovery to sudden loss of vision due to severe uveitis and retinal detachment. In the subretinal space, larvae can grow to up to 3-5 mm.

Oxygen contained in the choroid can maintain the viability of the larvae for some time. The larvae's movement in the subretinal space causes pathognomonic symptoms of posterior intraocular ophthalmomyiasis: a hypopigmented line with pigment clumps and tiny subretinal hemorrhages.

According to the literature, the larvae in the human body rarely reach the second stage of their development. Intraocular ophthalmomyiasis is found mainly in children due to their thinner and more supple sclera, which facilitates the possibility of the larvae penetrating the eye. The place of introduction of the larvae cannot usually be detected. The larvae penetrate from the outside, causing a small, subconjunctival hemorrhage, which is rapidly absorbed.

We present here a clinical case of intraocular posterior ophthalmomyiasis in a child.

CASE STUDY

A seven-year-old Caucasian girl was hospitalized in the pediatrics department of the Filatov Institute of Eye Diseases and Tissue Therapy with complaints of redness and low vision in the left eye. We learned from the case history that, two weeks earlier, she experienced redness of the left eye and a sense of pricking. Anti-inflammatory therapy was prescribed by a local physician. Later, when visual acuity decreased dramatically — down to 20/200 — opacity of the vitreous body was diagnosed. The child was sent to the Filatov Institute.

The right eye was clinically normal. The left eye showed a mild, mixed conjunctival injection, with no abnormalities in the anterior segment, a clear lens and intensive opacity in the vitreous. In the outer-inferior part of vitreous cavity, we found a white, moving foreign body with low fundus visualization.

The patient's intraocular pressure was normal, and her VA was 20/400. The initial diagnosis was indolent uveitis, with a suspicion of intraocular helminthiasis.

On ultrasound scan, in the lower inner quadrant at eight o'clock in the equatorial zone, a foreign structure was detected (size 1.4 x 1.5 mm; length 8.2 mm), changing position with eye movement. The retina was attached (Figure 1).

Figure 1. B scan exam of the left eye. In the lower inner quadrant in equatorial zone, a mobile foreign structure was detected.

A diagnosis of acute uveitis was made, with intraocular posterior ophthalmomyiasis. Ultrasound scans a few days later showed an increase in the size of the larva; its diameter was 1.8 mm, and its length had increased 10.5 mm. These facts proved its vitality.

Surgical Technique

The operation of choice was vitrectomy. The main goal of the surgeon during vitrectomy is to remove the larva without damaging its outer shell to avoid contact of the contents of the parasite with the vitreous cavity and to prevent postoperative infectious complications.

We performed standard three-port 20-gauge vitrectomy, with subtotal excision of the posterior hyaloid membrane. At this stage of the operation, it was difficult to remove the vitreous body because of free movement of the larvae in response to the work of the aspiration-irrigation system. For better visualization of the posterior hyaloid membrane and for anti-inflammatory effect, we injected triamcinolone acetonide into the vitreous cavity.

After removal of opacities, we found a retinal break on the attached retina (the site of the larva's penetration), and hypopigmented stripes indicating movement of the larva in the subchorioidal space.

The first step in removing the larva was that it was fixed by the aspiration cannula and tucked up for expansion to a 2-mm sclerotomy (Figure 2). Next, we carefully removed the larva from the vitreous cavity with vitreal forceps, without damaging its integrity (Figure 3), and we placed it in physiological solution for further identification. As the final step, we performed endolaser coagulation around the retinal break and closure of the sclerotomy.

Figure 2. The larva was fixed by aspiration cannula.

Figure 3. The larva was removed from the vitreous cavity with vitreal forceps.

In the postoperative period, the patient received local antibacterial and anti-inflammatory therapy. She was discharged on the seventh day after surgery with a visual acuity of 20/24. On discharge from the institute, the left eye was calm, the cornea was clear, the anterior chamber was of average depth, there was moderate residual mydriasis, the lens was transparent, the content of the vitreous cavity was transparent and the optic disc was pale pink with clear margins.

In the macular area, there were minor degenerative changes, downward and outward from the optic disc — a light yellow stripe with pigmented edges. The retina was attached. The extracted object was identified as the larva of a spotted flesh fly (Wohlfahrtia magnifica).

DISCUSSION

According to data from the literature on the surgical treatment of intraocular ophthalmomyiasis, much attention has been paid to the diversity of clinical manifestations, ranging from mild symptoms such as eye redness to severe uveitis and panophtalmitis with total retinal detachment. An interesting fact is that the larvae can migrate between cavities of the eye, from the anterior chamber and vitreous cavity in subchorioidal space.

The surgical approach is determined individually, depending on the location of the larvae and on the clinical manifestations. Undoubtedly, the main tactic is to remove the larvae without damaging their integrity and to avoid contact of the contents of the parasite with eye tissues, to prevent the development of severe inflammatory complications. If the larvae are in the subretinal space, retinotomy must be performed for recovery.

In our case, the larva was in the third stage of development. It was mobile and had dimensions that did not allow us to fix it with vitreal forceps, so it became necessary to move it with the aspiration cannula to an expanded sclerotomy and to extract it from the vitreous cavity. This original technique was applied to remove the larva, and it is the most gentle and clinically justified way.

The patient had a normal fundus after the operation. A light yellow stripe with pigmented edges started from the optic disc and ended with a break on the attached retina, indicating that the parasite migrated along the optic nerve through the subchorioidal space in the vitreous (Figure 4).

Figure 4. A photo of the posterior pole of the left eye three days after vitrectomy. A light yellow stripe with pigmented edges started from the optic disc and ended with a break on attached retina.

CONCLUSION

Intraocular posterior ophthalmomyiasis is a rare pathology, and it is more common in countries with hot climates.

We have described this interesting clinical case because it occurred in Eastern Europe, demonstrating the need for attention to parasitic diseases of the eye. If ophthalmomyiasis is suspected, it is necessary to perform vitrectomy as soon as possible to prevent complications associated with the prolonged stay of larvae in the eye. RP