Glasses

Glasses, also known as eyeglasses or spectacles, are visual-perception devices consisting of clear or tinted lenses mounted within a frame that positions them in front of the eyes. Supported by a bridge across the nose and by temples resting over the ears, they serve both functional and aesthetic purposes. Traditionally associated with correcting visual impairments, glasses have diversified significantly and now occupy important roles in personal protection, sports, style and specialised optical applications.
Originating centuries ago as simple corrective aids, glasses have become highly engineered devices designed to manipulate light, protect vision and enhance visual comfort. Modern lenses are commonly manufactured from plastic and polyethylene materials, though glass continues to be used for certain specialist purposes. Frames may be produced from metals, plastics or composite materials, with fashions varying widely across cultures and historical periods.

Functions and Uses

Glasses fulfil a variety of distinct purposes depending on the characteristics of the lenses and the environments in which they are used. Corrective glasses address refractive errors; safety glasses protect against physical hazards; and sunglasses shield the eyes from excessive brightness and ultraviolet radiation. In addition, certain glasses are intended solely for cosmetic or aesthetic use, reflecting trends in fashion and personal identity.
Many users employ accessories such as straps to secure the glasses during sport, or neck cords to prevent occasional-use glasses from being misplaced or damaged. In some cases, glasses are also integrated with other assistive devices, including hearing aids.

Corrective Lenses

Corrective lenses are designed to modify the path of incoming light so that images focus correctly on the retina. They address a range of refractive errors, including myopia, hypermetropia and astigmatism. Over time, the eye’s natural ability to adjust focus diminishes, leading to presbyopia—a common age-related condition from around forty onwards—requiring additional near-vision correction.
Lenses are produced according to a prescription issued by an ophthalmologist or optometrist. A lensmeter may be used to verify the power of existing lenses. Corrective eyeglasses significantly improve the quality of life by enhancing clarity of vision and reducing strain-related symptoms such as headaches and squinting.
Common corrective lens types include:

• Single-vision lenses, which have a uniform refractive index.
• Bifocal and trifocal lenses, which provide two or three refractive zones for different distances.
• Progressive lenses, which offer a continuous gradient for smooth focusing.
• High-index lenses, which are thinner and lighter due to enhanced refractive efficiency.

Reading glasses serve as convenient near-vision aids and are often sold without prescription, though they do not correct asymmetrical refractive errors or astigmatism. Individuals requiring full correction must therefore obtain a recent personalised prescription.
In some jurisdictions, people with poor eyesight have corrective-lens restrictions on driving licences, obliging them to wear suitable glasses when operating a vehicle. Militaries and prisons may issue government-standard spectacles, such as GI glasses or institutional clear frames.
Alternative corrective devices include adjustable-focus eyeglasses, which can substitute for bifocals or allow low-cost universal dispensing, and pinhole glasses, which rely on small apertures rather than lenses to increase depth of field. However, pinhole glasses have practical limitations and are not widely used.

Safety Glasses

Safety glasses provide protection from physical hazards and are an essential component of personal protective equipment. Constructed with break-resistant plastic lenses, they shield the eyes from debris, chemicals, blood and other materials that may cause injury or irritation. Side shields are common, improving coverage beyond the frontal field.
They are mandatory in many occupational settings, including construction, manufacturing, machining workshops and laboratory environments. In medical practice, dentists and surgeons in several countries are required to wear safety glasses to prevent exposure to bodily fluids.
Specialised models include welding goggles, sometimes known as flash goggles, which incorporate darker lenses to shield against intense light produced during welding. Nylon frames are frequently used in sports safety eyewear because of their strength, flexibility and light weight.

Sunglasses

Sunglasses are designed to improve comfort and protect against bright visible light and damaging ultraviolet radiation. For adequate UV protection, lenses generally require a UV400 filter, which blocks the full harmful spectrum. Many sunglasses are also polarised, using filters that eliminate horizontally polarised glare from reflective surfaces such as water or roads. This provides clearer vision in outdoor environments, although polarisation may interfere with the visibility of liquid-crystal displays and can affect altitude perception for pilots.
Sunglasses can also serve cosmetic purposes, often used to conceal the eyes or to satisfy fashion preferences. Styles such as tea shades and mirror-shades have become cultural symbols. Individuals with photophobia, including those with migraine-related light sensitivity, often wear tinted or precision-filtered glasses even indoors.
Prescription sunglasses combine corrective power with sun protection. Clip-on lenses and oversized wraparound sunglasses offer alternatives for users who require regular corrective glasses. Contact-lens wearers may simply pair their lenses with standard sunglasses.

Specialised and Mixed-Function Glasses

A wide array of specialist eyewear has been developed for specific environments and technologies. For example, 3D glasses enable stereoscopic viewing in cinemas and virtual-reality settings. In some sports, particularly squash, specially designed protective glasses prevent impact injuries.
Mixed-function designs include double-frame or flip-frame glasses, which feature a movable secondary frame connected by a linkage mechanism. These allow users to alternate instantly between different lens types—such as switching between sun lenses and corrective lenses—making them particularly practical for drivers entering tunnels or individuals who move frequently between light conditions. Such designs may also accommodate presbyopic combinations that can be repositioned without removing the glasses.