Soft Contacts
The method used for making contact lenses often is dependent upon the type of contact lens. There are three chief contact lens types: soft, gas permeable or hybrid lenses.
Soft contact lenses are made in order to retain their flexible properties that make them comfortable on the eye. The process begins with a plastic polymer that absorbs water (known as hydrophilic). Then, the materials are either cut into a button shape with a computer-controlled cutting tool (in the lathe cutting process) or injected into a mold placed under pressure (injection molding). The contacts are shaped into the standard oval shape and hydrated in order to retain flexibility and softness to the touch. Each contact is manufactured to match a common lens power, size, curve and edging. The lenses are then stored in plastic packaging that contains a sterile saline solution meant to mimic similar properties to that of human tears.
The injection molding process is the more popular of the two procedures, as it is more cost-effective than cutting the contacts into a shape. The finished product is a contact that is 1/3 to 1/2 water.
Gas Permeables
Gas-permeable lenses are less flexible than soft contact lenses. Instead of a hydrophilic plastic, these lenses are made of an oxygen-penetrating plastic so that oxygen is better able to reach the eye (which can result in a more comfortable wearing experience). These lenses are custom-made to the eye. Therefore, an eyecare professional must measure the shape and cornea of the eye. The plastic is first formed into a rod that is cut into a button shape. The specifications for a patient, particularly the eye's corneal curvature, are then inputted into a computer and cut to specifications using a lathe. The contacts are then shipped to the eyecare professional where they are soaked in a solution to enhance their softness.
Hybrid
Hybrid contact lenses represent an even cross between the two previously mentioned types of contacts: soft and gas permeable. The inner portion is gas-permeable materials, while the outer is the hydrophilic soft contact material. These contacts are first cut with a lathe out of their respective materials, then bonded together to create a single lens. The lenses are then hydrated with a specialized solution.
