Jim C Bradley
Member
- Messages
- 4,945
You better hope you get to need a third power because the only way you can avoid it is to die.
Think about that and enjoy,
Jim
As you get older your ability to control your focus drops off. It actually started about age 12. But you really didn't care if you could only focus up to 4 inches from your eyeballs instead of three and a half inches.
However, 4 inches becomes 5 and 5 becomes 6 and you still don't care. However when the nearest you can focus is 16 inches you suddenly notice that you have to hold things a little further away to see detail. That's when bifocals get entered into your life (age 43 and a half is the most common age to notice this).
Myrna just called dinner. Guess we will see if this will hold or vanish. On second thought I will send it and come back and add an edit later.
Enjoy
What it all boils down to: When you are young and wearing your distance glasses if you need them, you can see clearly from about 3 inches to the moon. As you age your ability to control your focus diminishes. If you are typical, how close you can focus has moved out far enough to bother your reading and other close tasks in your early 40s. You get glasses for close (bifocal or just reading glasses).
Since you are still alive, your ability to focus close becomes more difficult and you need a stronger reading Rx. The stronger Rx creates a shorter depth of field (photography people and optical people will know what that means). (Very brief: The stronger the lens the smaller the distance between how close it will focus and how far). At the same time, how close you can see through the top of the bifocals is moving away. How far away you can see through the bifocal is moving closer.
At a certain point (1.50 diopter difference between top and bottom bifocal powers) how far out you can see with the bifoclal and how near you can see through the top, no longer meet. This presents a blurred area. This blur is around arm's length (typical computer screen distance, end of screwdriver, head of nail, tip of gouge, etc.). A bit of time goes by and this situation drives you nuts so you go to the optometrist and he/she prescribes a third power to fill in the gap.
A lens to do that has two lines instead of the one line in a bifocal. There are newer lenses called Progressive Addition Lenses (PAL) that also solve the problem. For most people and most tasks the PALs work fine. If you have always had vision better than 20/20 (corrected or not) and you do detailed vision tasks you will notice that the PALs are not as quite as clear as the old two-line (trifocal) lenses.
My vision was always much sharper than 20/20. When I was in optometry school my sharpnes of distance vision was tested by about half of the PhDs in the world (there were only a couple dozen of them at that time). I was off of the theoretical chart. 20/8 was considered the limit. The 20/8 person can read at 20 feet, what the 20/20 person has to move up to 8 feet to read. I was better than that by a bit. I could read a freeway sign almost 4 times as far away as a 20/20 person.
So what happened is that each of these doctors thought that the other docs didn't do it right and they would test me---and get the same answer. All of the stuff was leading up to the next statement. I far prefer the trifocals to the PALs because, even at age 85 I see so much better with the trifocal than the PAL. There is a new method of making lenses, they are not molded nor are they ground; they are sculped using a laser. I have only tried two of these new lenses in the progressive form. I found one to be very good, the other was nothing to brag about. However, either of the two was better than the molded PALs.
Good Grief---it's shut up time again Bradley.
Now you can see why Carol Reed and I didn't get much looking at shop time---we were talking.
Enjoy,
Jim
Last edited:
