I'm new here.  Thank you in advance for your responses!

Mom has major cognitive disorder, along with various physical ailments.  She still enjoys a lot of what life has to offer and has been pretty stable.  However, she was recently diagnosed with wet AMD.  She has lost most of the vision in her left eye.  We may be able to stall the progression in her right eye.  The treatment involves putting various drops in her eye, including numbing, and then a needle.  Mom needs to cooperate to get this essential treatment, but won't allow the doctor to treat her.  She never appreciated people telling her what to do and that aspect of her personality certainly hasn't changed.  I understand her anxiety and concern.  What can my Dad and I do to help facilitate this treatment?  Your suggestions are welcome!

My uncle had the same situation with macular degeneration.  They could not do anything for the one eye, but they gave him shots for awhile and put him on PreserVision for the other eye.   That helped stabilize the "good" eye until he had majory surgery and they took him off the vitamin and mineral mixture for about nine days.  He suffered substantial loss of vision while he was off PreserVision.  I think PreserVision is for dry eye macular degeneration so it may not be an alternative in your mother's case.

https://www.aao.org/eye-health/diseases/vitamins-amd 

My father was horrified when he realized he would go blind without the injections. One eye had little vision left (he could only see the big E) before he was diagnosed with wet macular degeneration in both eyes.

Think of it this way. If you believe that caregiving for a demented LO is difficult, imagine what what it would be like if your mother were blind.  Tell your mother that. "Mom, you will go blind if you don't let the doctor give you the injections. If you go blind because you refuse to get the injections,  Dad and I will no longer be able to care for you at home."