some afflictions can be an eye-opener. Photograph: Getty Images

“Can Chlamydial Conjunctivitis Result from Direct Ejaculation Into the Eye?” ask Simon Rackstraw, ND Viswalingam and Beng T Goh of the Moorfields Eye Hospital in London. That question forms the title of a study they published in 2007 in the International Journal of STD and Aids. Drs Rackstraw, Viswalingam and Goh describe the plights of four patients, and disclose the detective work involved in diagnosing and treating them.

Conjunctivitis, whether caused by the sexually-transmitted disease chlamydia or by some other irritant, also goes by the name “pink eye”. It’s a catch-all description for inflammation of the conjunctiva, the membranes that line the eyelid and the surface of the eye.

The doctors finger the bacterium chlamydia trachomatis as the likely culprit in as many as 9% of the severe conjunctivitis cases seen by casualty departments. they imply that most doctors would blindly – and perhaps wrongly – assume that manual transmission was involved: that patients had rubbed their own eyes with their own hands after those hands had come in contact with infected fluids, either their own or those of a partner.

The mechanical aspect of their tales had a dull sameness. One patient said that “symptoms in her right eye started a week following sexual intercourse with a known male partner who had ejaculated into the eye”. another, a man, “had a casual encounter four months previously and recalled this partner ejaculating into his eye during oral sex”.

The Sherlock-Holmesian big clue, the study relates, was that “none of the patients were found to have chlamydia detected within the genital tract on testing, but all gave a history of a recent sexual partner having ejaculated into the affected eye”.

But the story remains incomplete, because “unfortunately, in these cases we were unable to test the sexual partners to see if they had chlamydia”.

The doctors reached a sort of conclusion, undoubtedly meant to guide the thoughts of any medical personnel who might have limited understanding as to the ways one can contract conjunctivitis. “It is likely”, they write, “that this mode of transmission is underestimated, as a history of ejaculation into the conjunctiva is not normally asked for.”

(Thanks to Ivan Schwab and Maarten Keulemans for bringing this to my attention.)

• Marc Abrahams is editor of the bimonthly Annals of Improbable Research and organiser of the Ig Nobel prize