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Medical Forum / General / Vision / February 2007Progressive advice
Well, I got my progressives, and I think I'm adapting fine. Small problem, though. Things are fine at far, but at near, I need to turn my head to the right to focus. Is this how these things are supposed to work, or is a center off? How off does a center need to be to notice stuff like this? The optician isn't in today, but he measured my PD by marking up the blanks in the frames with a marker while I looked at his eyes. The glasses were ordered to 31/31. When I noticed the head turn at home, I measured my own PD, and sure enough, my eyes are about 3 mm off center. Today I went to ask the optician about this. He wasn't there, but they measured my PD with their optical device, and it was 33/30.5 (right/left). I'm wondering if the doc just measured between the dots and divided by 2 to generate the blanks. If he did, would this explain the required head turn at near? Or, is this just the nature of the beast, and I'll eventually adapt?  SignatureScott Reverse name to reply > Well, I got my progressives, and I think I'm adapting fine. Small problem, > though. Things are fine at far, but at near, I need to turn my head to the [quoted text clipped - 15 lines] > Scott > Reverse name to reply Yes, 3mm off on PD could make a big difference. It should be measured separately for each eye. Have them measure one more time and then ask for a remake. They get a free remake from the lab/manufactureris if there is a fitting or Rx error. The remake is built into the cost of the lens, which is one reason it costs so much. >> Well, I got my progressives, and I think I'm adapting fine. Small >> problem, though. Things are fine at far, but at near, I need to turn [quoted text clipped - 25 lines] > error. The remake is built into the cost of the lens, which is one > reason it costs so much. Thanks. Do they built a little vergence into the PD for the prescription? The eye that bothers me more is 30.5, and the doc called for 31, so it doesn't seem all that far off. If you need to subtract a tad for vergence, though, things seem to make sense. SignatureScott Reverse name to reply > Thanks. Do they built a little vergence into the PD for the > prescription? The eye that bothers me more is 30.5, and the doc called > for 31, so it doesn't seem all that far off. If you need to subtract a > tad for vergence, though, things seem to make sense. The reading area of a progressive lens does converge (gets closer to your nose) as you get lower into the reading area. This is needed to enable binocular vision at closer distances. However this is done automatically in the lens design (unless someone requests something other than the default offset). 1/2 mm error should probably not make a difference, but being off 3 mm in the PD on the other side may actually be causing the problem with your eye on side with the nearly-correct measurement. This is because the eyes attempt to work together with binocular vision and your other eye may be the dominant eye. However, it is really hard to speculate if that is the real problem and this is just conjecture. Just make sure they re-measure the PD and the fitting height accurately, and get a lens remake. When they measure you, make sure that eyes of the person doing the measurements are at the same level as your eyes and that your head is level. You must insist on this to get a good fitting. >Well, I got my progressives, and I think I'm adapting fine. Small problem, >though. Things are fine at far, but at near, I need to turn my head to the >right to focus. Is this how these things are supposed to work, or is a >center off? How off does a center need to be to notice stuff like this? Scott, It depends on the lens design and Rx. I can consistently get it +/- 1mm per eye (from the dispensing table, to the lab, and back to the table), and will usually reject 2mm wide or narrow. Vertical meridian (seg height) should be central pupil or -1mm. >The optician isn't in today, but he measured my PD by marking up the blanks >in the frames with a marker while I looked at his eyes. If done properly, this can be more accurate than using a pupilometer. >The glasses were >ordered to 31/31. Keep in mind that this doesn't mean that's what was received. For example, they may be 30/32, or xx/xx. >When I noticed the head turn at home, I measured my own >PD, and sure enough, my eyes are about 3 mm off center. Not unusual, certainly not enough to let the circus know your in town. >Today I went to >ask the optician about this. He wasn't there, but they measured my PD with >their optical device, and it was 33/30.5 (right/left). Bingo. If you received 30/32 then the Rt eye is 4mm narrow (ouch) and the left is 1.5mm wide. >I'm wondering if >the doc just measured between the dots and divided by 2 to generate the >blanks. If he did, would this explain the required head turn at near? Maybe. PDs ~must~ be monocular, and the frame must be pre-adjusted for back vertex distance, panto, nose pad/bridge fit, and temple splay, even if the frame goes back on display. If the frame isn't adjusted properly before the measurements will be, to some degree, incorrect. >Or, is this just the nature of the beast, and I'll eventually adapt? Confirm that the fitting cross for each eye is central pupil +1.5mm/-1.5mm. If it's not, then make it so. Regards, Robert Martellaro ~~~~~~~~~~~~~~~~~~ Optician/Owner Roberts Optical Wauwatosa Wi. ~~~~~~~~~~~~~~~~~~ "Science is a way of trying not to fool yourself." - Richard Feynman
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