Ocular involvement of oak processionary caterpillar hairs: Clinical outcome up to one year

Purpose: To evaluate a consecutive series of patients that presented with ocular findings after contact with the oak processionary caterpillar (OPC) during an epidemic reproduction of the OPC in Germany in 2019 and to assess the 1-year outcome of those eyes with persisting OPC hairs in the cornea.

Methods: Retrospective analysis of 11 eyes (11 patients) that presented in June/July 2019 with acute ocular symptoms after outdoor activity or caterpillar nest removal. Evaluation of patients charts and slit-lamp images up to one year. Assessment of the incidence of patients with OPC-associated ocular complaints in the subsequent years (2020-2023).

Results: All patients had conjunctival injection, foreign body sensation, pain, itching and/or burning sensation. In 9/11 eyes, multiple caterpillar hairs could be detected in the superficial and deeper cornea. Hair removal was attempted in 8/9 eyes; in one eye hair removal was impossible due to its deep stromal location (lost-to-follow-up). Entire hair removal was successful in 2/9 eyes, hence, six eyes with persisting hairs within the cornea were followed. Stromal haze developed adjacent to the hairs in all eyes and individual hairs disappeared (n = 4) and/or showed migration within the cornea (n = 3). Until 2023, the number of patients with OPC-associated ocular complaints decreased continuously.

Conclusions: Ophthalmologists should be aware of the possibility of caterpillar hairs in patients with acute eye symptoms after outdoor acitivities, especially in early summer; the incidence may fluctuate, though. Hair removal is recommended to avoid possible intraocular migration, still residing hairs did not cause any serious long-term complications in our cohort.

Key messages: What is known Within the late spring and early summer season, mass reproduction of the oak processionary carterpillar (OPC) can lead to an increased number of patients with OPC-related eye complaints (pain, itching and burning sensation) caused by OPC hairs within a very short period of time. Within that season, people should be (more) actively sensitized to avoid trees with OPC hairs, take precautions and avoid eye rubing when having complaints What is new Complete surgical removal of the hairs can be difficult and is often unsuccessful due to their tiny size and often stromal location most possibly resulting from eye rubbing In the longer-term, residing hairs have shown to develop haze adjacent to the hair, migrate within the cornea or disappear/resolve. Since this may go along with an inflammatory reaction, long-term follow-up and topical steroids may be useful.