The "Do You See What I See?" Story

It was an ordinary day.  Checking out my email on my MacBook Air when I heard a knock at the back door.  Turned to look and saw a delivery person had just dropped off a package.  About a year ago I would have had to be wearing my glasses to do both looking at my computer and looking out the back door a short time later.  I wore photo-gray glasses that had seamless bifocals at the bottom of them.  Each lens was different since I needed help with distance in the one eye as well as needing help with seeing close in the other eye.  Then I had needed cataract surgery on my left eye.  Doctor Jones, a former high school student of mine, asked if I would like to be able to see both close-up as well as long distances without having to wear glasses.  That was a no-brainer!  Since my cataract surgery, I can still see close-up in my right eye, as I had in the past, but now my left eye can see distances without the help of glasses.  Being able to do so is known as monovision and I love it!  But, I read this morning that it is not for everyone, since it can interfere with depth perception.  And, if you look at a moving object, the impact of depth perception is much worse than commonly acceptable.  And, for those that are affected, it can cause a public safety hazard.  Suppose a motorist slows down as they enter an intersection because a cyclist is riding from left to right in cross traffic.  If someone with monovision is driving and the bike is traveling 15 miles per hour, it will seem to be as much as 9 feet farther away from the car than it actually is.  The illusion could cause the motorist to engage in what is called "casual braking" rather than coming to a full stop, thus hitting the cyclist as a result.  And, if the cyclist is moving faster that 15 mph, the result becomes even greater.  What is really scary is that the illusion is new, and puzzling, to scientists.  Potentially it could cause serious public safety issues.  For me, that is not the case; luckily!  I have no problem with depth perception, but evidently it happens enough with monovision that it is a problem.  It is estimated that about 10 million people in the United States have had their eyesight corrected to achieve monovision.  Usually it is done with contacts, but can be done, as with me, with lens implants during cataract surgery.  Monovision lenses have been known to cause a slight decline in depth perception because they compromise a person's ability to see in stereo.  When an object appears sharp in one end and blurry in the other, the brain suppresses the blurry image to some degree.  The viewer is less able to "triangulate" and has more of a problem telling how far away the object may be.  But, it is said to only be a problem if the object is in motion.  A pendulum in a large clock, when moving from side to side, may appear as if it is swinging forward and backward.  The reason is the brain can process blurry images several milliseconds faster than it handles sharply focused images.  Actually, I'm not sure if I understand this, but that's what I read.  For me, at first it was hard to get used to having an object blurry in one eye while sharp in the other.  As I sit here typing these words on my computer, if I look at it with my left eye, I can't read it, but it is perfectly clear with my right eye.  With both eyes open it looks clear, but with the slightest fuzzy effect.  If I'm not thinking about it, it looks perfect.  I guess it is hard for my brain to adjust to the fact that I have two different focal points, but it works.  I do realize that I'm lucky, since it works for me, but perhaps not the person next to me with monovision.  I guess I'm the lucky one since I no longer have to wear glasses.  My only problem now it to remember to wear sunglasses when I am outside in bright daylight.  When I wore glasses my photogray glasses took care of that.  Always something to worry about, isn't there!  It was another extraordinary day in the life of an ordinary guy.