The answers provided are established first principals of medicine and physiology and clinical practice. Both have been firmly established since the late 19th Century. Contemporary medical research publications assume knowledge of these facts and are mot helpful. – Robert Carnes Jun 27, 2021 at 1:22
Looks like my “references” never made into an edited post. For physiology of the eye, the standard first-year medical school text is good enough: Hall and Guyton, “Medical Physiology.” For use of cycloplegics and fundascopic exams of the retina, almost any clinical practice manual, but “Harrisons Principals of Internal Medicine” details the range of diseases and conditions discoverable on fundascopic exam. Beyond that, tapping all this on my iphone is more exhausting than passing over a question for something more critical to life and limb. – Robert Carnes Jun 27, 2021 at 1:45
Otherwhere, Carey Gregory commented that he downvoted "-1 for a complete lack of references."
It's consistent to downvote, but keep, another answer, whilst deleting mine for the same reason of lacking references. Meantime, I shall add references after my holiday.