Eye glasses have been improving people’s vision since they were first invented, almost eight centuries ago. Their invention was revolutionary and has allowed people to do things they couldn’t previously do, such as drive a car or read a book. Eye glasses use the same principle that the human lens uses, and they work by augmenting the lens function.
The human lens is found between the retina (the layer of cells at the back of your eye) and the cornea (the front of the eye). The eye lens is convex in shape and works with the cornea to focus images and project them onto the retina. The retina then reacts to the image, sending signals to the brain.
There are different conditions that cause the eyes to focus images incorrectly. It could be that the lens may have lost, or is in the process of losing its ability to curve, or there may be a problem with the cornea. These problems result either in the eyes being unable to focus on distant objects (nearsightedness), closer objects (farsightedness), or it may cause images to be distorted (astigmatism).
The first step when making prescription glasses is determining the strength of the correction needed, or the prescription. This is normally done in the doctor’s office with a simple eye test. Once the prescription is determined, the numerical value is sent off to the laboratory to aid in the creation of lenses for eye glasses.
In the laboratory, the prescription eye glasses start off as lens blanks, which are either made from a plastic or glass disc that is about four inches wide and up to one and one-half inches thick. The blank lens has a flat back surface and a curved front surface. The lab technician takes the lens blank that is close to the required prescription thickness and puts it into a machine that grinds it to the required curve. The thickness of the chosen blank lens is determined by the curve needed to fill a prescription and by the type of material the lens is made of. The grinding process requires painstaking precision to ensure that the eye glasses are made to the exact prescription and that they are made without scratches that can affect their function.
After the lenses are ground, they are edged to fit the frame the patient chose. At this point in the manufacturing process, the eye glasses are tinted or coated for UV protection by inserting them into a tinting solution. This is followed by a groove being cut into the lenses to ensure they fit into the frame.
Next, the lenses are inserted snugly into the frame. The lenses are either heated or treated with chemicals to make them flexible for easy insertion. The glasses are also checked for any imperfections at this point. The prescriptive strength is also double checked. The glasses are then cleaned, packaged then delivered to the eye doctor’s office for the patient.