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Medical Forum / General / Vision / August 2005Self-measuring P.D.s
Anyone have a good method of self-measuring P.D.s? I'm talking binocular as opposed to monocular, and accuracy to within +- 2 mm or so would be acceptible. I'm looking for something that is quick, easy, doesn't cost much, and could be sent through the mail. I sometimes get questions from people in distant places that would be better handled if I knew their p.d. Oh, and it's got to be easier than using a mm ruler, which I have trouble even teaching to my employees due to the parallax problems. w.stacy, o.d. Dear Wiliam, I can take a simple metric scale and look at a "target" in the distance and read about 63 mm. It does depend on the accuracy you require. Using the same idea, you could use small sliding apetures on a metric scale that the person would look through, and that they would adjust themselves. This could be done at a reasonable cost. Best, Otis > Dear Wiliam, > > I can take a simple metric scale and > look at a "target" in the distance > and read about 63 mm. There is the little problem of parallax and explaining how to avoid parallactic error to a person from a distance... w.stacy, o.d. > Anyone have a good method of self-measuring P.D.s? I'm talking > binocular as opposed to monocular, and accuracy to within +- 2 mm or [quoted text clipped - 7 lines] > > w.stacy, o.d. Much better to have a friend do it, I would think, but I imagine a mirror would work as well. Look in mirror. Close one eye. Look straight at your pupil Set rule index in center of pupil, with rule extending over the other pupil. Hold head very still from now on Open the closed eye Close the open eye Look into pupil Take measurement at center of pupil. I'd do this a bunch of times, and take the mean. I suppose you can also measure monocular PD in much the same way.  SignatureScott Reverse name to reply I know how to do that, and would add other instructions to your list if I were going to have someone try it that way, but I was hoping for a simpler solution that any idiot could do. I'm tallking "fool proof" if you know what I mean. Some kind of simple device, nearly as simple, maybe simpler, than a ruler. I suppose I could have them poke holes in a piece of paper while looking through one of them... naw, forget it. Too dangerous for the people I'm talking to... w.stacy, o.d. > Much better to have a friend do it, I would think, but I imagine a mirror > would work as well. [quoted text clipped - 20 lines] > I'd do this a bunch of times, and take the mean. I suppose you can also > measure monocular PD in much the same way. Dear William, You might supply a chart with the average PD for a person. You know that the average for an adult is 63 mm. I would bet there is a chart that relates PD to child's age. At least the person would have a ball-park number to compare his results against. I can look out the window at a point about 50 yards away and "switch eyes", from left to right, and get about 63 mm. Not accurate as I am doing it, but with some refinement I think it would work. The real question is one of "accuracy" or range of acceptable values -- and that would take some testing by the person (and you) concerned with the issue. There are NO fool-proof methods. In fact, I think you could sell such a device, and I would support you (and recommend it) if you did. I would consider it to be like a low-cost blood-pressure guage. To be used "independently", or under guidance. Sounds like a product. Dr. W. Stacy's PD device. Best, Otis I doubt it's worth taking to market, but the normal range of adult p.d.s is from about 50 mm to about 80 mm, for children from about 40 mm to 60 mm, and accuracy within 1 or 2 mm is needed for a lot of applications. I can think of no use for "average" p.d.s, except to market "one size fits all" glasses, another thing I would never indulge in. w.stacy, o.d. >Dear William, > [quoted text clipped - 30 lines] > > > Anyone have a good method of self-measuring P.D.s? I'm talking binocular > as opposed to monocular, and accuracy to within +- 2 mm or so would be [quoted text clipped - 6 lines] > > w.stacy, o.d. Here's a method that's simple, but specs need to be worn: Have a Sharpie or other permanent marker in hand. Cover/close one eye while viewing a distant object with the other, head held straight on. Bring tip of marker toward lens so that the object is obscured and dot the lens. Repeat with other eye closed. Measure the distance from dot to dot across the front of the frame. --LB, O.D. >Have a Sharpie or other permanent marker in hand. >Cover/close one eye while viewing a distant object with the other, head [quoted text clipped - 6 lines] >--LB, O.D. > Amazing, I tried this with the help of my buddy and it is 63 mm for me. What is PD required for? > Here's a method that's simple, but specs need to be worn: > Have a Sharpie or other permanent marker in hand. > Cover/close one eye while viewing a distant object with the other, head [quoted text clipped - 3 lines] > Repeat with other eye closed. > Measure the distance from dot to dot across the front of the frame. > --LB, O.D. Thats the way they do it at my place, except don't use a permanent marker, use something easily removed from lens when done, to avoid scratching. Also covering eye is better than closing. George |
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