What Causes Thinning Of Optic Nerve Along With Black Circle Around The Nerve?

Can taking Glaucoma eye drops damage your eye if you don t actually have Glaucoma? I have family history of Mom, brother & cousin w/ glaucoma. My pressure has always measured within normal limits. Today the doc noted thinning of optic nerve, took a photo which revealed no damage, but significant thinning. He showed me a red and a black circle around the nerve, stating he estimated something which should be 40%, appeared on visual exam a yr ago to be ~60%, and photo this year is 80%. He prescribed Latanoprost 0.0005% OU daily, hoping to block further thinning, but stated clearly I do not have Glaucoma Dx. He suspects the pressure is up sometimes when not being checked. Is that reasonable? What are symptoms if there is too little fluid? Side effects? I am healthy, otherwise, don t take any Rx, but do have dry eye syndrome, treated w/otc drops. Also have amblyopia w/o central vision in L eye. Am 70, female, Caucasian, retired RN.