Ophthalmologymiddle twist
A 31-year-old cyclist has had a gritty, watering right eye since riding home in a strong wind two days ago. It hurts most each time he blinks. Visual acuity is 6/6 in both eyes and the eye is diffusely red. Fluorescein staining shows several fine parallel scratches running vertically across the cornea, with no white infiltrate and no branching pattern. The anterior chamber looks clear and the pupils are equal. Which one of the following bedside steps is most likely to reveal the cause?