Opinions on vet, negligence?

Hello,

We've recently had an experience that has left us questioning proper action. This is a long story, but we would appreciate advice.

In this past August, we noticed our 11 yr. old dog's sclera was red & irritated. He suffers from inhalant allergies. I called the vet & he did an opthamology exam & said it was from allergies. He gave prescription eye drops & allergy meds. A few weeks later, there was still no improvement, so the vet did another exam & switched us to different eye drops. Two more times between then & this month we called him back because the eye wasn't improving & actually was getting worse. After the 3rd visit, the eye started looking larger, so I started researching & came across glaucoma. On the 4th exam, I brought up glaucoma, but the vet insisted it was still allergies. I said that I was going to schedule an opthamology exam at a teaching college to do the pressure test for glaucoma. I mentioned that we were leaving town & asked if it was something we should do right away, or could it wait until after our trip. He again insisted it was allergies & that I should wait until the end of the winter allergy season.(This whole time, our dog was eating, drinking, playing as normal) The day before we left on our trip, the vet came to drop off refills on the allergy meds. The very next day, at our vacation destination, we took our dog for a walk & twice he walked into me, which was unusual. But, I thought maybe it was because we were in a new place & too many new smells. The next morning when we woke up, we noticed that he was squinting his bad eye & couldn't seem to keep it open. The concierge found an emergency hospital for us & we took him there. The e-vet came in the room, took one look at our dog, & said it was glaucoma. Upon testing, his pressure was 75 (as opposed to 15 normal average) & that he had lost the vision in that eye. They kept him there over night on iv meds to try to relieve the pressure, to no avail. We checked out, picked him up first thing, & drove 8 hours directly to the university's veterinary animal hospital. They tried different meds to reduce the pressure, but nothing worked. That & the fact the eye was no longer visual left us no choice but to have him undergo surgery to remove his eye. Had this been caught at an earlier stage & had he not lost the vision in his eye, there were options to prolong the life of the eye. Laser surgery, surgery to place shunts, topical meds.
Needless to say, we are overcome with guilt. Not just the loss of his eye, the thought of all the pain he must have been in due to the pressure makes us feel sick. We should've taken action, not just relied on the vet. But...I was the primary care giver this past year for my Mom, who was bed-bound total care. I went up against drs all time who just wanted to write her off, demanding tests when they insisted nothing was wrong, questioning everything & one. I lost my Mom anyway, I guess the drs were right about her decline, & so when this issue with our dog arose, I decided maybe I should trust someone with the degree. No excuse really, ultimately he is our furbaby & we are responsible.
The bottom line is, this vet saw our dog 5 times (4 exams & the day before he went blind just dropping off meds) about his eye. Even when asked about the possibility of glaucoma, he insisted it was just allergies. We really feel he should share the blame. Misdiagnosis, negligence?
Any thoughts, opinions, or advice would be so greatly appreciated. Thanks for reading if you made it this far