I understand that surgery is generally a taught skill, but is it one that everyone can learn? Are there people who simply lack the manual dexterity/ fine motor skills to perform the more complex opthamologic procedures (retina surgery, etc)?
Yes. Most people can learn surgery. The hardest things about surgery are knowing when to perform surgery on a patient, how to manage complications, how to deal with surprises during the case, and how to manage the patient as a whole patient.
Yes. There are some people who lack the manual dexterity/fine motor skills to perform surgery; however, these are few, and according to Dr. Nerad (Oculoplastics surgeon at Iowa), in his 20+ years of teaching, he has yet to encounter a resident that he cannot teach.