Q. How many Retinal Screeners does it take to change a lightbulb?

A. Two. One to change the lightbulb, and one to move it to the side for the nasal view.

But that aside, here's a little anecdote I was lucky enough to hear today...

A small boy walks into his parents' bedroom late one night and finds them making love. He sees what they're doing, but decides to keep quiet, and creeps back out of the room without saying a word. The next morning at breakfast, his father calls him over and says "Son, I saw you come into the bedroom last night, and I was proud of your tact and discretion. As a reward, I'm giving you a pocket watch that my father gave to me". He hands his son a beautiful gold watch.

The next day at school, the boy shows the watch to his best friend, and recounts the story of how he got it. The friend is naturally impressed, and says "I'm going to try that myself!"

So the next night, the friend gets up and walks ino his parents' bedroom, where they too are making love. His father sees the boy at the foot of the bed and says "What do you want, son?". The boy replies "I want a watch". So his Dad says "Well, pull up a chair, but shut the door - there's a draught going straight up my backside".

I've cleaned that up considerably. The original was so fruity it would count as one of your five a day. But here's the real punchline:

That joke was told to me today by one of my patients, shortly after I'd administered the eye drops. I think he was trying to put me through as much pain as I'd put him through. I wouldn't mind, but he made the story last a good five minutes, and performed it as though he was doing an open mic slot at the Comedy Store. He even did the whole routine on his feet. I've never seen anyone take stand-up comedy so literally. I kept looking around for a red buzzer like they have on Britain's Got Talent.

But here's the second punchline:

The chap was 87, and my oldest patient of the day.

I don't know what they're putting in the water around here, but they need to stop before the man gets an agent. Whatever happened to pensioners who just sit quietly in a corner, dribbling?