Glasses

Glasses, also known as eyeglasses or spectacles, are vision eyewear used for many different purposes.

They consist of clear or tinted lenses mounted in a frame. This frame typically uses a bridge to rest over the nose. It also features hinged arms called temples that rest over the ears for support.

While many people use them to correct their vision, others wear them for cosmetic reasons or as personal protective equipment. They are essential tools for health, safety, and even entertainment.

Corrective lenses work through a process called refraction.

Refraction is the bending of light as it passes through a medium, such as a lens. When a person has a refractive error, light does not focus correctly on the retina, which is the light-sensitive layer at the back of the eye. Lenses bend the incoming light to ensure the image lands sharply on the retina. This process can alleviate conditions like myopia, which is nearsightedness, or hypermetropia, which is farsightedness. It can also correct astigmatism. Lenses are often custom-made to match a specific prescription from an eye doctor.

There are several distinct types of corrective lenses designed for different needs. Single vision lenses have a uniform refractive index, meaning they bend light the same way across the entire surface. For people dealing with presbyopia, lenses can be more complex. Presbyopia is a condition, common in people over forty, where the eye's crystalline lens loses elasticity. This makes it harder to focus on objects close to the eye. To help, bifocal glasses provide two different refractive indices for different distances. Trifocal glasses provide three, while progressive lenses use a continuous gradient to transition between focus levels.

Safety glasses serve as a vital form of personal protective equipment (PPE).

These are often made with break-proof plastic lenses to shield the eyes from foreign debris or hazardous splatters. Construction workers, machinists, and lab technicians use them to prevent injury from flying particles. In Canada, dentists and surgeons are required to wear them to protect against infection from bodily fluids. Some safety glasses even include side shields or a wraparound design for extra coverage. There are even specialized "flash goggles" used in welding to protect against intense light.

Sunglasses are designed to manage light levels and protect against radiation.

They help prevent damage from excessive ultraviolet (UV) light. To be effective, many sunglasses include a UV-400 blocker to cover the dangerous parts of the light spectrum. Some lenses feature polarization, which uses filters to remove horizontally polarized light rays. This eliminates glare from surfaces like water, though it can sometimes make it difficult for pilots to judge altitude. Another interesting type is photochromic glasses. These lenses are clear indoors but automatically turn into sunglasses when they contact UV light.

Specialized glasses exist for unique visual tasks, such as 3D viewing.

3D glasses create the illusion of depth by providing each eye with slightly different visual information. Anaglyph glasses use different colored filters, like red and blue, to achieve this. Other systems use polarized filters or electronic active shutters. Beyond movies, glasses can also provide magnification through bioptics. These are small telescopes mounted on or behind regular lenses to assist people with vision impairments. Some even use high-refractive index materials to remain lightweight and thin.

Throughout history, glasses have evolved alongside technology.

After the transistor was developed in the 1940s, engineers created combined eyeglass-hearing aids. These allowed a hearing aid to be concealed within the thick-rimmed temple pieces of the frames. While these fell out of fashion after the 1970s, they represent an early step in integrating assistive technology into eyewear. Today, glasses remain a massive industry, utilizing materials like plastic, metal, and glass to serve functions ranging from medical necessity to high fashion.