Are segs for st28 bi-focals to be measured at the top of seg line or the center of seg line?
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Are segs for st28 bi-focals to be measured at the top of seg line or the center of seg line?
The center is supposed to be in vertical line with the center of the pupil therefore it is in the center of the line.Quote:
Originally Posted by 24416355
Should be a straight line unless you are putting them in crooked.
Actually you measure from the seg line to the deepest part of the frame, even if this is outside the seg line.
Chip
Yes, top of seg to bottom of lens !!!
Are you asking where the seg should be alined in lay out, or measuement on patient?
Because if you are laying out a FT (any size ) then you line it up by the corners of the seg.
..... and then it could be that I am just stupid and not understanding your question.
This is the right answer and here is why:Quote:
Originally Posted by ASenior
First I am assuming that you are pointing out that the line has width. In that case it doesn't matter if it is the top, bottom or middle; as long as you are consistant between left and right. The width of the line is less than a 1/3mm, so don't worry.
Second, I believe that you are talking about the aspect that the seg line appears to be curved down in the middle, especially on plus lenses. You must use the curved up edges because you need two points to make a straight line. If you use the bottom of the seg, it could be tilted. Use the two outer point in order to ensure that it is straight.