High Index Lens Becoming More Curved
Hi Everyone,
I have a customer who purchased glasses from me about 6 months ago. I fit him with 1.67 high index plastic lenses. The base curve of the demo lenses in the frame were 6. The customer liked the "wrap around" feel of the glasses and so I had his RX ground on a steeper base curve (clocked at 5 at dispense) than he was previously wearing (clocked at 3.5). The center thickness of his new lenses was 1 millimeter.
The RX is:
OD) -6.00 -0.25 x 135
OS) -4.25 -2.00 x 180
He brought the glasses in a few weeks ago because they'd become more curved causing blurred vision. The lenses HAVE in fact become more curved. The right lens clocks at 6.25 and the left 8.5. Any thoughts as to why the lenses (especially the left) would curve so much more than the original curve of the frame??
The lab is suggesting new lenses (same material) with a center thickness of at least 2 mm.
I'm just wondering if anyone else has had this problem and what your thoughts are.
Thanks,
Hip Chic
Can only be..................
Quote:
Originally Posted by
hip chic
The right lens clocks at 6.25 and the left 8.5. Any thoughts as to why the lenses (especially the left) would curve so much more than the original curve of the frame??
An increase in the left base curve of 3.5 Diopters (50%) over a period of 6 month without doing anything to them can only be the work of the Hi Index fairy.
Craze....................
When lenses have AR and would change curvator shape, the AR would automatically craze and delaminate and be ready for the garbage,
Put a 6 base in the frame!
Quote:
Originally Posted by
hip chic
Hi Everyone,
I have a customer who purchased glasses from me about 6 months ago. I fit him with 1.67 high index plastic lenses. The base curve of the demo lenses in the frame were 6. The customer liked the "wrap around" feel of the glasses and so I had his RX ground on a steeper base curve (clocked at 5 at dispense) than he was previously wearing (clocked at 3.5). The center thickness of his new lenses was 1 millimeter.
The RX is:
OD) -6.00 -0.25 x 135
OS) -4.25 -2.00 x 180
He brought the glasses in a few weeks ago because they'd become more curved causing blurred vision. The lenses HAVE in fact become more curved. The right lens clocks at 6.25 and the left 8.5. Any thoughts as to why the lenses (especially the left) would curve so much more than the original curve of the frame??
The lab is suggesting new lenses (same material) with a center thickness of at least 2 mm.
I'm just wondering if anyone else has had this problem and what your thoughts are.
Thanks,
Hip Chic
We base curve match all of our jobs and in a thick frame like Chrome Hearts zyl, the heat will cause the lens to be overtaken by the frame curve. If you put them in a 6 base to start; all problems will vanish.
Just remember to compensate for the curve and if you use the Autograph Attitude on a 6 base, you should have a job optically and cosmetically correct.
It needs to be edged on a machine without wheels to ensure the curve/bevel are correct; this is essential on a 6 base thick zyl for cosmetics.
Hope it helps and how is Rochester!
Craig
Confirm warpage by using lens clock and
check the vertical (90th) meridian. If the curve there is not as steep, the lenses are warping, for the reasons listed above.
Barry