Yes it is ethical. Given that even with the most gifted of physicians about 10% of diagnosis are "wrong" it is ethical, proper and customary.
Besides there is always the issue of "how many guttatta make Fuchs' Dystrophy" many of us, especially as we age, develop bumps on the back of the cornea (guttatta) while one ophthalmologist may think the number normal for the age another might diagnosis Fuch's it is not a yes-no type of diagnosis, neither is cataract, neither is glaucoma.
It would be a mistake to call what happened a mistake. It's "lawyer think"
JCH III MD
Guttata are stage 3+, corneal thickness 645. Is that in the range that is considered normal?