How Lenses Are Made

Ophthalmic Lenses are designed to refract light so that it reaches the retina. It is necessary for light rays to focus on each retina, in the back of our eyes, in order for us to see. When the eye’s own optical system cannot refract light onto the retina, ophthalmic lenses are needed.

The main job of the ophthalmic lens is to manipulate light. Lenses are used for many reasons. The main reasons they are prescribed is for safety, vision and comfort. Different materials are used for specific purposes and visual needs. The following list is an example of what ophthalmic lenses do:

1. Refract light rays to reach the retina
2. Reflect uncomfortable or dangerous light rays
3. Reflect annoying glare and reflections
4. Absorb light for comfort or safety
5. Transmit light for better vision
6. Block dangerous light and blinding glare

The design and production of lenses is a complex art and science. Glass and Plastic-type lenses, with the exception of polycarbonate, are made from a molding process. First, the lens designer calculates the best curvatures necessary for superior optical quality. Then, a computerized program attached to a digital file and lathe cuts the inside/top surface of the mold. This could be a single curvature for single vision lenses, or multiple curves for an aspheric lens or a progressive addition lens. Then, the back of the mold is attached and liquid plastic (monomers and polymers) are added. After the annealing and cooling process is complete, the lens is ready to be surfaced. Surfacing a lens means cutting curves into the back side to create the prescribed numbers, or spectacle Rx. In simple spherical curves, a steeper curve yields a stronger prescription and a flatter curve yield a weaker prescription. Once polished, the finished lens is ready to be edged for the shape of the frame or eyewire. Many coatings and filters can be added to the lens to manipulate light in different ways. A vacuum-sealed process is necessary for coatings to adhere properly. Examples of coatings are ultra violet filters, tints, anti-reflective coatings, mirrors and more.

The most common reason lenses are prescribed is for vision. Three factors determine the prescription in a lens. They are the material (index of refraction), thickness, and curvature. In theory, lenses are considered as being prisms attached, base to base or apex to apex. A convex lens (prisms base to base) magnifies images, and is used for the correction of Hyperopia or Presbyopia. A concave lens (apex to apex) minifies images, and is used for the correction of Myopia. Cylinder (toric) lenses are also used for the correction of astigmatism, and have different powers in different zones of the lens.
Technology and science have improved the way lenses are made and it keeps getting better. Shamir Insight’s team of optical scientists are dedicated to improving lens designs to deliver the best possible vision ever, recreating perfect vision.