ask the labs
Sun Effects and Processing Pointers
by Karlen McLean, ABOC, NCLC
EYES WIDE SHUT
Q Can UV rays enter the eyes while they're closed, such as when taking a nap at the beach or during sleep at night?
A While it's likely that UV rays can enter the eye through the thin exterior lid, the exact amount of UV that can pass through the eyelid is unknown.
The delicate skin of the eyelids may be especially susceptible to UV damage, and long term exposure could lead to problems such as skin cancer.
That said, it's important to wear UV-blocking lenses like polarized and photochromic lenses when outdoors to protect the eye and the skin around the eye.
When no UV rays are present, such as at night while you're sleeping, there is no risk of exposure.
—Carole Bratteig, manager, training and education, Transitions Optical
PADDING THE ORDER
Q Why are edging pads so crucial to the edging process?
A Edging pads are more complex than they appear. The edging process is rigorous and the pad is solely responsible for preventing lens slippage. Pads must withstand the high torque forces applied to the lens during edging.
Further, the pad's adhesives must adhere to each lens without removing coatings or leaving residue. The foam core base of edging pads cannot be too stiff or it will strain the adhesive, but foam substrates that are too soft can stretch too much, causing slippage. For a blocking pad to work, it must completely bond to the lens and the edging block.
Make sure the lens is thoroughly clean, properly match the block to the curvature of the lens, and then select blocking pads that are specially engineered for the lens material and coatings.
—Geoffrey D. King, SecurEdge product manager, Saint-Gobain Performance Plastics
| FREE-FORM Factoid |
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| Q What are the steps in processing a free-form PAL, and what are the steps in processing a single vision free-form PAL? A From our standpoint, the lenses are processed through the lab identically, whether it's single vision or a progressive. The difference is the point file created by the software to be passed to the generator. The calculations for one will be a progressive and the other for single vision. The same semi-finished blanks can be used for either design. The job is then taped, blocked, generated, and polished on the free-form line. The tools on the polisher are soft foam to accommodate polishing the multiple curves versus the old hard tools. This is usually all done on an automated line, and once the job is placed on the conveyer for taping, it's not touched again until it's finished the surfacing process. —Jerry Thornhill, technical services manager, Shamir Insight |
If you have a question you'd like to have answered in Ask the Labs, send it to Karlen McLean. Email: karlen.mclean@wolterskluwer.com. Fax: 215-367-2155. An archive of past Ask the Labs columns can be found on the Eyecare Business website at www.eyecarebusiness.com.
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