Dad’s New Bifocals
For those readers not old enough to know what bifocals are, some explanation is in order. Each human eyeball has a tiny donut-shaped muscle group surrounding the cornea that expands and contracts to change the focal length of the lens. It responds spontaneously, refocusing as the eye encounters objects both near and far away. At least that is the way it works up to the age of 40 or so, at which time it abruptly stops working. When you see someone holding a newspaper at arms-length, you can be pretty sure they are over 40 and have not yet come to grips with this reality.
When this happens we are said to suffer from presbyopia. Doctors tell us that the onset of this condition is one of the most accurate predictors of age – and it happens to everyone.
That’s also when people start buying reading glasses, or in more recent times getting laser surgery. But in the distant past, it was customary for ophthalmologists or optometrists to prescribe glasses that included a lens for distance viewing and a second lens in the lower half of the frame to correct for close viewing. That additional lens is called a bifocal because it offers a “second view”. It adds higher magnification to bring things into focus and makes them appear larger and closer than they actually are.
While driving a car with them, we can glance up at a stoplight, then down at the speedometer without moving our head, and both things stay in focus. We can read a book by glancing down through the bifocal, then glance up at the TV through the lower magnification lens and everything seems fine. At least until we try to walk down a flight of stairs, or encounter other things that seem to have been altered in size – that can lead to trouble.
Our depth perception is affected because that results from the brain’s ability to triangulate using the parallax angle between the two eyes, combined with a few other things, including our ability to recognize familiar objects in the field of view and judge their distance from their relative size, particularly in the far-field. That means making things appear larger has the effect of making them appear closer as well, so glancing down through the bifocal as we approach a flight of stairs makes them seem closer, and that can be problematic.
Where Dad began to run into trouble was with things seeming to be larger than the actual size. Having been recently fitted for his first pair of bifocals, he was overjoyed with his ability to read newspapers and do other things that the new glasses made possible, but a problem developed.
As he told the story, the problem arose when he walked into the men’s room of the local Savings And Loan (aka Building & Loan) in Three Rivers. He approached the urinal in the usual manner and after a couple of minutes, glanced down through the bifocals. Startled at what he saw, he said to himself, “what the hell – that is not mine”, then stuck it back in his pants and pissed down his pants leg.