ANSI standards say i can have up to 2 degrees of tilt in my multifocal lenses. how do i go about measuring those 2 degrees? ive looked all over for a layout chart and can find nothing on the web.
ANSI standards say i can have up to 2 degrees of tilt in my multifocal lenses. how do i go about measuring those 2 degrees? ive looked all over for a layout chart and can find nothing on the web.
Just search for pantoscopic tilt instead.
Here's some info: https://www.odob.health.nz/wp-conten...f-D-Wilson.pdf
that has nothing to do with what i was asking. i'll give you an example.
Lets say i have a freshly edged and mounted pair of bifocals. everything checks out on the lensometer. all my axis's and powers are spot on. BUT! the bi-focal segment is crooked by an undetermined amount. how would i go about measuring how far off of the 180 that segment is? or am i just coming at this all wrong?
Ohh... But if the axis checks out for the distance part, doesn't that say that you mounted the bifocal segment of the lens correctly? If you rotate one, you have to rotate the other. The only option is a manufacturing defect on the bifocal blank (either on the axis of astigmatism or on the bifocal segment).
Can you turn the lens in the frame at all? In this scenario I would try getting the bifocal seg straight and then see if the cyl is within tolerance. If you can't simultaneously get the bifocal and cyl to be correct, that sounds like a manufacturing/surfacing error, as vfpamp said.
If you needed a precise measurement for determining how crooked a seg is, I'd just take it over to the lensometer and mark the 180 line on the mounted lenses and use a protractor to find the angle of the seg.
I usually just hold a PD ruler across the top of both segs and make sure they are parallel to eachother. If they are way off to the point of needing a remake, it's usually plainly obvious without needing to use a tool or measure it.
All these are manufacturing/lab standards, not dispensing standards.
B
The reference in Europe is EN ISO 2187 and give you all the information
I don't think anyone has answered the OP's question, so I'll take a stab. ANSI HORIZONTAL SEGMENT TILT < 2 DEGREES CROOKED......I asked and answered this question of myself a while back with trigonometry knowing that the dots are 34 mm apart.....and the answer is slightly over a 1 mm vertical height difference between the nasal dot and the temporal dot. I used tangent (2 degrees = 0.0349066 radians) = x / 34...therefore x = 1.2 mm
The line at the top of a FT28 is 26 mm long....so the difference in vertical height to be within 2 degrees tolerance from nasal side of seg line to temporal side would be (26/34) x 1.2 mm = 0.9 mm
A protractor is your easiest bet.
I'm Andrew Hamm and I approve this message.
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