Answer: Amebic keratitis due to Acanthamoeba species. The double-walled cysts and trophozoites are characteristic:
Unfortunately this patient ended up undergoing 2 corneal transplants before she finally was cleared of infection. She now has near normal vision. Amebic keratitis can be very difficult to treat, since the presence of a single residual cyst is enough to allow for reactivation of infection after treatment or surgery.
Greater than 90% of cases in the U.S. are associated with contact lens use, as was the case with this patient.