How do contact lenses work?

• Prescription contact lenses correct vision much like regular eye glasses – by bending the light entering the eye, so that it becomes focused accurately onto the retina.
• Although they are known as ‘contact’ lenses, the lenses themselves do not stick directly to the eyeball. Rather, contact lenses stay in ‘contact’ with the eye by floating on the tear film layer which covers the cornea.
• Contact lenses are not all the same. There are many types of contact lenses, designed to fit different needs, worn in different ways, and made with different materials.

When light passes from one medium to another (e.g. from air to glass), it bends and changes direction. This phenomenon is called ‘refraction’. Glasses lenses use refraction to their advantage by bending the light at the front of the eye, to focus it precisely onto the retina. Different types of vision errors (myopia, hyperopia, astigmatism, and more) are corrected by tailoring the shape, curvature, and thickness of the lens to match the amount of refraction needed.

Contact lenses used for vision correction work on the same basic principle as glasses lenses, but with some minor differences. Glasses lenses are held within a frame positioned in front of the eyes, while contact lenses sit directly on the tear film covering the cornea. As a result, contact lenses move in unison with eye movement, without a glasses frame obstructing the view. Despite their small size, contact lenses can be purposed to fit a wide range of optical needs using different designs, curvatures, and thicknesses.

A contact lens does not stick directly to the eye’s cornea. Rather, it sits on a thin layer of tears called the tear film, which covers the cornea and acts as a thin cushion between the lens and the eye.1 

The natural surface tension of the tear film acts as a glue to hold the lens onto the surface of the cornea.2  When a contact lens is placed on the eye, tears spread underneath and over the lens, forming a thin and even layer around it. The attraction between water molecules in the tears further helps keep the lens close to the eye.3,4  At the edge of the lens, capillary action creates a suction effect that adheres the lens to the eye.

Soft contact lenses are especially effective at staying on the eye, thanks to their flexible material helping them adjust to the shape of your cornea.

There are a range of contact lens options. The main purpose is to correct eyesight, but contact lenses are also used to treat eye diseases, prevent injury, improve appearance, and much more.

Contact lenses can be divided according to material: soft lenses, rigid gas permeable lenses (RGP). The first contact lenses were originally manufactured from glass until the introduction of a hard plastic material known as PMMA (polymethyl methacrylate) in the 1930s.5  These gave way to more breathable materials that better supported eye health and comfort, such as RGP lenses and soft lenses.

Soft contact lenses are a very popular option for their versatility and high comfort. They can correct a variety of vision problems and fit a wide range of prescriptions. However, most soft contact lenses are disposable. This means that the lenses degrade over time and need to be replaced regularly to avoid complications like eye discomfort or infection. Disposable soft lenses are categorised based on how often the lenses need to be replaced: single-use (“dailies”), weekly/fortnightly/monthly, or extended wear.

RGP lenses are made from more durable materials and can potentially offer sharper vision than soft lenses, especially for patients with eye conditions like keratoconus. Additionally, rigid contact lenses play a very important role in specialty eye care, such as slowing the worsening of myopia (near-sightedness) in children.

The cornea is the clear surface at the front of the eyeball, serving as the eye’s outermost lens and focusing the entrance of light. It needs oxygen to stay healthy, and most of this oxygen comes directly from the air.

When a contact lens is worn on the eye, it reduces the flow of oxygen to the cornea, similar to wearing a mask over the nose and mouth. Over long periods of contact lens wear, such as extended daytime wear, or overnight wear, this can cause eye swelling, redness, or long-term effects on eye health. Therefore, choosing a high-quality, breathable contact lens (e.g. silicone hydrogel material) is important for maintaining healthy and comfortable wear.6,7 

Contact lenses are safe for children when they are properly fitted and used with good hygiene and handling habits. Research suggests that the risk of eye infection among children aged 8–12 who wear soft contact lenses may even be lower than that reported in teenagers and adults.8