Answer: Amebic keratitis, Acanthamoeba species
This case is diagnosed by finding the characteristic cysts and trophozoites of Acanthamoeba. As mentioned by Lukus and Arthur, the trophozoites show a small nucleus with large central nucleolus (karyosome) and the cysts have a characteristic wavy/crenated double wall that give them a 'star-like' appearance. The trophozoite I've shown below may be in the process of excysting since there seems a remnant of the outer double wall present.
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