ask the labs
Frequently Asked Questions
Alex Yoho, ABOM
Lab executives tell us there are certain questions that are asked more consistently than others. This month, we’ll take a look at two topics that labs are asked about on almost a daily basis.
STARBURST EFFECTS
Q Sometimes patients with AR coatings complain of starburst effects, often in the shape of a cross, coming off lights when driving at night. What is causing this?
A The starburst effect that wearers of AR experience at night from the headlights of oncoming vehicles is a result of the lens being over flexed at some point. The over flexing of the lens actually causes the hard coat (scratch-resistant coating) on the AR lens to shatter (referred to as crazing by labs), similar to a piece of glass that has shattered.
When the light hits this shattered hard coat, the reflections create the starburst effect noticed by individuals when driving at night. These fine cracks in the hard coat are not acceptable and are very hard to see with the naked eye. Labs and ECPs alike should do a cosmetic inspection of the lens using a halogen lamp to identify any crazing before delivery of the eyewear to the customer.
The over flexing or crazing of the lens can happen during several processes at the finishing stages of the eyewear in the lab. These stages include blocking, edging, deblocking, inserting, and adjusting—basically anywhere the lens gets pressure applied to it. Though easier said than done, the key is to reduce or eliminate as much of this as possible.
— Marty Kratzer,
production manager,
Duffens Optical,
Lenexa, Kans.
| PAL for everything |
|---|
| Q Is there any one progressive lens for all activities including driving, reading, watching television, and using the computer? A The very nature of the design of a regular progressive renders it difficult to use for computing. The intermediate area on all progressives is fit at the pupil height, just below the patient’s viewing horizon during a straight-ahead gaze. In order to see the computer monitor clearly, the patient must cock his or her head back to view the screen through the intermediate area. One solution is to sell the patient a progressive that will correct all of his or her visual needs except computing. In addition to that PAL, your patient needs a pair of dedicated computer glasses. The intermediate area in a computer-style lens is very large and is higher in the lens, eliminating neck strain. The bottom of the lens has full reading power so the keyboard will be in perfect focus. Some computer lenses even have distance correction in the top, if the patient tilts his or her head down slightly. This feature will allow your patient to walk around the office wearing glasses without feeling dizzy. — Mike Sutherlin, vice president, Sutherlin Optical, Kansas City, Mo. |
If you have a question you’d like to have answered in Ask the Labs, send it to Susan P. Tarrant. Email: Susan.Tarrant@WoltersKluwer.com. An archive of past Ask the Labs columns can be found on the Eyecare Business website at EyecareBusiness.com.
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