Ocular myiasis is a disease of the organ of vision caused by the introduction of various parasites into the eye cavity. The main cause of ocular myiasis is the penetration of a fly larva or gadfly into the structures of the eyeball. There are superficial and deep ophthalmomiases. Clinical manifestations are diverse and depend on the type of pathology. Diagnostics consists in collecting anamnesis, conducting visual examination, visometry, tonometry and biomicroscopy. Treatment of ocular myiasis depends on the type and depth of penetration of the fly larva into the eye cavity, can be conservative or surgical. With early treatment and adequate therapy, the prognosis is favorable.
Ocular myiasis (myiasis – from the Greek myia – fly) is a parasitic disease of the eye and its appendages that occurs when larvae of flies or gadflies penetrate into the tissues. Eye diseases caused by fly larvae have been known for a long time. The sacred books of the Hindus and Chinese manuscripts describe ocular myiasis of humans and animals. Infection occurs both directly by laying eggs or larvae on the conjunctiva or near the eyeball, and indirectly through dirty hands or bites of infected insects. Ocular myiasis caused by parasitization of fly larvae are diverse in localization, pathogenesis and species composition of flies.
The main reason for the development of ocular myiasis is the penetration of fly larvae or gadflies into the eye cavity or its appendages through wound surfaces. Female flies of the family Muscidae, Calliphoridae and Sarcophagidae usually lay eggs in accumulations of meat waste, animal corpses, excrement, manure, etc. Attracted by the smell of rotting tissues, flies can lay eggs on open wounds, in festering eyes. Larvae of cavity gadflies parasitize in the cavities of the nose, larynx and sinuses of the forehead of animals. Female horse and sheep gadfly spray larvae into people’s faces on the fly. Once in the human eye, the larva causes suppuration, blindness may occur. Migrating inside the nasal cavity, the larvae destroy the mesh bone and can reach the brain.
Ocular myiasis caused by the larvae of the Wolfart fly is the most severe. When larvae develop in the female’s body, she lays them (120-190 copies) in the eye area. Larvae cannot penetrate through intact skin, but at the slightest abrasions or scratches they are introduced into the body. With the help of special mouth hooks, they mechanically violate the integrity of the tissue, while damage to muscles and other structures occurs by special digestive enzymes. Penetrating into the muscle tissues, the larvae eat them down to the bone, resulting in periosteal necrosis, complicated by osteomyelitis. The development of larvae takes 5-7 days, after which the pre-pupae fall out of the wound and pupate in the soil. Especially painful is the migration of larvae in the tissues before pupation.
Clinical manifestations depend on the type of ocular myiasis (external or internal).
Orbital (external) ocular myiasis includes myiasis of the eyelid, larval conjunctivitis, conjunctival larval granuloma and destructive ocular myiasis. With myiasis of the eyelid or myiasis furunculosis, after the introduction of a fly larva into the skin of the eyelid, a furuncle-like tumor with an opening occurs. The patient may complain of swelling in the eyelid area, soreness during palpation. After 1.5-2 weeks, the larva is removed through the hole in the boil to the outside for further maturation. Larval conjunctivitis manifests itself 10 hours after infection. When examined by an ophthalmologist, a sharp blepharospasm, severe redness, thickening and swelling of the conjunctiva of the eye are determined. Clinical symptoms disappear after removal of larvae.
Conjunctival larval granuloma occurs when the larva is inserted under the conjunctival membrane. An inflammatory granuloma is formed, during examination, sharp soreness in the tumor area, hyperemia and swelling of the conjunctiva are revealed. Destructive ocular myiasis is characterized by the ingestion of a large number of fly larvae under the conjunctival membrane, followed by complete destruction of the muscles, other soft tissues and bones of the eye. Causes pain in the affected eye in combination with severe inflammatory processes in the orbital region.
Intraocular ophthalmiasis can be internal anterior or internal posterior. Internal anterior ocular myiasis develops when a fly larva or gadfly penetrates into the anterior segment of the eyeball. Examination reveals changes characteristic of iridocyclitis: the eyeball is irritated, painful on palpation, the moisture in the anterior chamber is cloudy, the pupil is more often narrowed. Internal posterior ocular myiasis proceeds in a variety of ways, possibly asymptomatic. It is most often manifested by the development of uveitis with loss of vision. The phenomena of chorioretinitis with retinal hemorrhages can be detected on the fundus. In severe cases, retinal detachment or optic nerve atrophy are possible.
Complications of ocular myiasis include the development of severe forms of uveitis, neuritis (sometimes up to atrophy of the optic nerve), corneal opacification (before the formation of a corneal cataract). Osteomyelitis of the orbital bones, eyeball atrophy and meningitis may occur.
Diagnosis and treatment
Standard examination methods are used for diagnosis: patient interview, thorough visual examination, visometry, tonometry, ophthalmoscopy, fundus biomicroscopy using a slit lamp and an aspherical lens.
Conservative and surgical techniques are used in the treatment process. Conservative methods consist in removing the larva with tweezers (if it is on the surface). Surgical methods involve making an incision in the inflamed area and extracting the parasite. After removal of the larva, the wound is washed with an antiseptic solution until the inflammation completely subsides, antibacterial ointments are applied to the incision area. Inside, anti-inflammatory drugs are prescribed.
Prevention of infection of people with fly larvae includes carrying out complex (sanitary and hygienic and extermination) measures to destroy insects in settlements and places of livestock (farms, pastures, etc.). It is necessary to use protective equipment to protect food products in homes and at work from infection with their eggs (larvae) of flies. Protection of premises from insect penetration and protection of people from fly attacks are required, especially in livestock areas.
An important measure in the prevention of ophthalmiasis is compliance with sanitary and hygienic requirements in contact with pets, livestock. When people return from tropical regions, in case of tumors and infiltrates in the eye area, it is necessary to immediately consult an ophthalmologist. When larvae are detected, they are immediately removed, the places of their introduction are disinfected.