Robbie is at an age where eye sight decline is normal.
The last visit I had to the optician, they said that 46 was the average age at which decline starts.
Robbie is 51 so should EXPECT to be experiencing a potential decline.
Robbie is attributing a correlation as causation.
Until there's a scientific study that confirms more concerning data than one man starting to lose his sight at a typical age for losing his sight, I'd take what Robbie says as
A FUCKING LOAD OF ABSOLUTE BOLLOCKS.