Over 100 million Americans wear some form of corrective eyewear, and yet many people don’t understand how these simple pieces of plastic improve their vision, and by extension their quality of life. Last week, on the Cohen’s Fashion Optical Twitter feed, we posted a video explaining how contact lenses are made, and this week you get a peek inside how prescription glasses are made.
Recently, on NPR, Ira Flatow interviewed Dr. Larry Enright, who is the general manager at PerfeRx Optical, a Massachusetts-based optical laboratory that makes eyeglass lenses. Here are some of his insights into the science of sight:
1. The lab receives a hockey puck-shaped hunk of plastic called a lens blank from the factory. The blank is formed by pouring molten plastic into different molds. Each mold has a separate curve to make it easier to grind that particular prescription.
2. The prescription is created by the curve of the front of the lenses and the back of the lenses added together. For example, if a patient has a prescription of + 2.00 and the blank from the factory has a curve of +6.00 on the front of the lens, the optical lab technician would cut a curve of -4.00 into the back of the lenses with a lathe generator.
3. After adjusting the curve of the lens, the technician is left with something that looks like a giant contact lens. Then, depending on the size of the frame you’ve chosen, they’ll cut that orb down even further.
4. Since the lens carved with a diamond-embedded blade, it needs to be polished as it goes through the manufacturing process. A soft felt pad and a cold water treatment give the lens a smoother finish.