Sunday, August 09, 2009

glasses for computer use

If you want glasses simply for helping other programmers, get a pair
of single-vision glasses for the over-the-shoulder distance. Here are
two ways to figure out what prescription you need. You'll need to know
about how far it is from your eyes to the screens you can't read, and
you'll need your "driving" prescription.

Method 1. Use the following guideline: If the screens you have to read
are 3 feet away, add +1.00 diopter to your driving glasses
prescription's spherical correction. If the screens are 2 feet away,
add +1.50 diopters. If they are 1.5 feet away, add +2.00 diopters.
Most likely they are no closer than that, given that your computer
glasses aren't working for this.

Method 2. Put on your driving glasses and visit the reading glasses
section of your local drug store. With luck, they will have glasses in
every strength from +1.25 to +2.50 (in increments of 0.25). Try on
various strength reading glasses *over* your driving glasses until you
can read at the over-the-shoulder distance. Whatever works is what you
need to add to the spherical correction of your driving glasses.

IMPORTANT: Be sure you're adding a positive number to your driving
prescription, not a negative number. You're a programmer, so I'm sure
you know that when you add +1.00 to the number -2.25, you get -1.25,
*not* -3.25!

If you want a single pair of glasses that will allow you to help
others, but also to see your own screen, for days when you're back and
forth a lot, I suggest getting a pair of "monovision" glasses, with
one lens optimized for over-the-shoulder and one lens optimized for
your own screen. In other words, add +1.5 (or whatever you got above)
to the spherical correction of your driving prescription for one eye
only. Choose the eye based on which eye has the best view of the
screen when you're doing the over-the-shoulder thing.

For the record, I teach Computer Science and have to do a lot of over-
the-shoulder myself, but I also have to see students from the front of
the classroom. So my monovision glasses have one lens of "driving"
prescription and one lens of "over-the-shoulder" prescription. My
guess is that you want one over-the-shoulder lens and one "your own
computer" lens.

If your two prescriptions have slightly different PD values, don't
worry about it. Either will work - my pick would be the larger of the
two (probably the driving prescription).