Who's right? (Dispute with my dad)

[Bulldog]

Back in July, my parents went on a two-week mission trip to Peru. They have three dogs and they live about 20 minutes away from me. I agreed to take care of the dogs and other general house-sitting duties (mail, newspapers) at no charge. They are my parents, after all.

One night my fiancee went out with her sisters so I just stayed at the house and slept there, in the recliner. I wear contacts and have glasses for late night/first thing in the morning. I took off the glasses and put them on the table next to the recliner. In the morning when I woke up, the youngest dog had destroyed the glasses, chewing the earpieces and lenses.

When they got back, I told my mom about it and she said they'd pay for a replacement pair. I held off because my bi-annual eye exam was in October, and I wanted to wait until after any change in prescription to get them. It's annoying not having glasses, but I managed.

Fast forward to present day. I went to Costco and got the cheapest glasses I could--$40 frames, $90 total. I stopped in at my dad's drycleaners today and told him he owed me the $90. Well, he's not paying. He thinks it is my fault for leaving the glasses where the dog could get them.

Who should pay?