This does not mean, however, that all calves will develop pinkeye in both eyes. The mortality rate of pinkeye is less than one percent. Severe cases that go untreated could progress to involvement of the optic nerve with subsequent encephalitis. Bilateral blindness in a young pastured animal could result in death from starvation. The incubation period or time from infection to clinical disease is usually two to three days but may range up to 21 days.
Initial signs are moist eyes and slight constriction of the pupil.
Photophobia, or sensitivity to light, is demonstrated by the animal turning away from light, blinking, or keeping the eye closed. In a short time tears begin to overflow, there is distinct constriction of the pupil, and a haze on the cornea, usually centrally. Then lacrimation becomes copious and a vesicle forms on the cornea which later ruptures and leaves a clear punched out ulcer. Enlarged blood vessels appear at the periphery of the cornea at seven to ten days and may completely encircle the cornea as the infection progresses. As the acute inflammation subsides, the ocular discharge may become more purulent.