double vision

Whilst visiting Louisa the other day she handed me a letter and asked if I could read it to her.


'It's about my eyes' she said. 'I am having my an operation on them, so hopefully I will be able to read it myself soon.'


I opened the envelope and started to read the information out loud. It was standard stuff about what to do on the day of the operation; Time and date; What to bring; where to park;  post op treatment etc.
I had read two pages and just turned over the third page to read when I stopped in my tracks.


'Have you had any trouble with double vision Louisa? I enquired
'No?'
'Are you sure?'
'Yes I'm having a cataract removed in my left eye'
'And that hasn't caused any double vision?'
'No. Why?
'Well they've sent you two identical letters in the same envelope.'