"A lens just popped out of my glasses,"

the Senior Cat told me.
He sounded more than a little anxious about this - as well he might. The Senior Cat doesn't see that well even with his glasses these days.
He has worn glasses since early childhood. His eyesight has been such that sport was a mystery to him. He could never see the ball even when it was coming directly towards him. 
When he dutifully went off to enlist in the armed services (non-combat please) they took one look at him and said, "Not with that eyesight and those flat feet." They may have been desperate - but not that desperate.
He wore the same pair of sturdy frames for years. Last year the optician insisted the frames had to be changed. They could not, they claimed, fit the new prescription into the old frames. The Senior Cat sighed and bought new frames. They looked almost identical to the old frames but - they are not as sturdy.
I took them up to the optician once and asked them to fix them because a lens had popped out. Yes, they had twisted slightly. 
Over the past week the Senior Cat has been complaining that "the table is sloping". I told him it wasn't. He insisted it was. He even went to get the spirit level from his workshop to show me. It was not sloping. 
I was worried, particularly when he seemed dramatically clumsier than usual. I was actually very worried. There had to be something wrong. 
As nothing else had changed I assumed that there had been a sudden and dramatic change in his  ieyesight. Middle Cat was about to phone the eye specialist he sees for his glaucoma and ask for an appointment.
And then...a lens popped out again. He takes them off for his afternoon catnap of course. I came home just as he was getting up. He came out and sat in his chair to clean the lenses - and said one had come out. He couldn't see it.
I hunted and hunted. I got him to take his pullover off in case it had got caught in that. No. I got the torch and looked under his chair. No easy feet and a reminder that I need to vacuum under there and not just around it. I took everything on the big wicker container next to his chair off. No, it wasn't there. 
I wasted twenty minutes searching - and not finding. He insisted that he had "felt it pop out" when he was cleaning them. I went towards the bedroom to look there but he called me back. It was not in the bedroom. I hunted some more. He told me to stop.
I finished making him a cup of tea and, when he was sitting there drinking it, I prowled off to the bedroom.
Yes, there was the lens - where I thought it might be. He took it with an embarrassed sort of purr and fitted it back in. He cleaned both lenses and put his glasses on.
The table was no longer sloping. I had actually thought it might not be. While I had been hunting my thought had been that perhaps the lens had just shifted slightly at first but not enough to pop out. That would have made a difference.
I will have to make a trip to the optician. The Senior Cat will not have to make a trip to the specialist.