What are contact lenses made of?
Contact lenses are made of one of three polymer families: hydrogel, silicone hydrogel, and rigid gas permeable plastic.
Hydrogel is a water-swollen plastic built on hydroxyethyl methacrylate — HEMA. According to Contact Lens Spectrum, Contact Lens Materials (Loretta B. Szczotka-Flynn, June 2006), Professor Otto Wichterle and his assistant Lím first synthesized HEMA and glycol diester in 1954, and their first material, the poly-hydroxyethylmethacrylate gel, contained about 40 percent water. That water is not incidental. In a conventional hydrogel it is the route oxygen takes to the cornea, which is why hydrogel materials are classified by how much of it they hold.
Silicone hydrogel is that same gel with silicone incorporated into the polymer. Oxygen travels through the silicone phase instead of through the water, which breaks the old link between high water content and high permeability. Contact Lens Spectrum records the first silicone hydrogel lens reaching the market in 1998, with a second manufacturer following in 2001.
Rigid gas permeable material is a firm plastic — modern designs are fluorosilicone acrylates — that does not hydrate and holds its own shape on the eye. It is the descendant of the silicone-acrylate materials that Contact Lens Spectrum, History of Contact Lenses: The World’s First Rigid GP Lens Material (Patrick J. Caroline and Craig W. Norman, August 2023) records as approved in 1982, which in turn replaced cellulose acetate butyrate, approved by the FDA in 1978 as the first rigid gas permeable contact lens material in the United States.
A fourth material, silicone elastomer, was approved in 1981 and survives in a narrow set of specialty applications. It is not one of the three families a routine order is written in.
Are contact lenses plastic or glass?
Contact lenses are plastic. Glass was the original material and has not been in general use since around 1940.
Contact Lens Spectrum (June 2006) dates the first documented contact lenses to 1887, when Müller made a glass scleral device as a protective shell, and 1888, when Fick made one for refractive correction. The first solid polymethyl methacrylate lenses appeared around 1940, and PMMA remained the primary material until the late 1970s.
Both of those materials failed for the same reason, and it is the reason the polymer families above exist. Contact Lens Spectrum (August 2023) states the problem directly: the obstacle facing the industry “was not manufacturing or lens design; instead, it was always the non-oxygen-transmitting materials,” and the lack of oxygen permeability in glass and PMMA “dramatically limited many patients’ wearing times due to the onset of hypoxia-induced corneal clouding.” Every material change since has been a change in how much oxygen reaches the cornea through the lens.
That is also why “plastic” is not a useful answer on its own. PMMA is plastic. So is a modern silicone hydrogel. The clinically meaningful question is not whether the lens is plastic but which polymer family it belongs to and what that family transmits.
What are the FDA contact lens material groups?
The US FDA sorts soft contact lens materials into five groups, by water content and by whether the polymer carries an ionic charge.
Review of Optometry, Understanding the Influence of Water Content in Soft Lenses (Langis Michaud, 15 August 2023) lists them:
| Group | Water content | Ionicity | What the grouping is for |
|---|---|---|---|
| I | Low, under 50 percent | Non-ionic | Least deposit-prone of the hydrogels |
| II | High, over 50 percent | Non-ionic | Higher water route for oxygen, no charge |
| III | Low, under 50 percent | Ionic | Charge attracts protein deposition |
| IV | High, over 50 percent | Ionic | Highest water and highest deposit tendency |
| V | Not defined by water | — | Created later, specifically for silicone hydrogel materials |
Group V is the one worth reading carefully. Groups I to IV are a two-by-two of water content against charge, and that structure only classifies a material whose oxygen performance depends on water. Silicone hydrogels do not, so they did not fit the scheme and a fifth group was added for them.
The groups are a materials classification, not a ranking, and not a substitute for a fitting. They tell you how a material is likely to behave with deposits and dehydration. They do not tell you which material a given eye should wear.
How are contact lenses made?
Three manufacturing techniques are in current use: lathe cutting, spin casting, and cast moulding.
Contact Lens Practice (Chapter 5, Soft Lens Manufacture) describes all three. In lathe cutting, a dry cylindrical button of polymer — a xerogel — is cut to shape and hydrated afterwards. Raw xerogel arrives as rods roughly 16 mm across and 400 mm long, sliced into buttons about 10 mm thick. The button is clamped to a back-surface lathe spinning at typically 8,000 to 12,000 rpm while a diamond-tipped tool cuts the posterior surface; modern lathes reach a surface tolerance of 8 to 15 nm. The cut dimensions are calculated dry, to allow for the expansion that comes when the lens is hydrated in unpreserved saline and autoclaved at 120 °C for at least 15 to 20 minutes.
The reason lathing survives is also the reason it matters chairside. It is the most expensive of the three, so it is “generally reserved for the production of custom-ordered or extreme-range lenses that contain design features not amenable to mass production” — high spherical power, high toric power, and aberration-correcting designs for an irregular cornea. When a parameter falls outside a stock range, lathing is usually what makes it exist.
In spin casting, liquid monomer is poured into a concave mould spinning about its own axis, and the back surface is formed by centrifugal force, surface tension and gravity rather than by a tool. One consequence is worth knowing: a faster spin shifts polymer mass toward the periphery and produces more minus power. Cast moulding, the third technique, forms the lens between opposing moulds and is the high-volume process behind stock disposable ranges.
Rigid lenses are lathe cut by the same method, minus the hydration step — the lens is cut to final shape and polished. The tolerances are tighter, and cutting and mounting temperatures are controlled more closely to preserve wetting behavior in high-permeability materials.
What does the material decide about the parameters you order?
Material decides which base curves and diameters exist to be ordered, and in a rigid lens it also changes the power.
A soft lens drapes. Its back surface is not the shape it was cut to once it is on the eye, so a manufacturer does not need — and does not offer — a continuous range of radii. It publishes two or three base curves and one or two diameters per design, and the fit is chosen from that short list. Read Base Curve of Contact Lenses and Diameter of Contact Lenses for what those two values do once they are chosen.
A rigid lens does not drape. It keeps its own back surface, so base curve is worked out from keratometry across a continuous range, and the tear layer trapped between the lens and the cornea becomes a lens of its own — which changes the power that has to be ordered. That path is on RGP Contact Lens Parameters and Starting Power, and the arithmetic is on the RGP Power Calculator.
Same eye, same refraction, two different parameter sets, because of what the lens is made of. That is why material sits on this inventory at all: it is not a comfort preference expressed after the parameters are chosen, it is a constraint that exists before them.
Does the material change the power you convert?
No. Converting a spectacle sphere to the corneal plane is optics, not chemistry — the material does not appear in the arithmetic.
Vertex compensation depends on the power and on the distance the lens moves, not on what the lens is made of. A −6.00 D spectacle sphere becomes the same corneal-plane value in a hydrogel, a silicone hydrogel or a rigid lens. Convert it on the Contact Lens Conversion Calculator, and read Vertex Distance of Contact Lenses for why the plane change happens at all.
What the material does change is what happens to that converted number afterwards. It limits which powers are manufactured at all, so the converted value is rounded into an available step. In a rigid lens it is displaced again by the tear layer. And in every material the ordered power sets the lens thickness — read Center and Edge Thickness of Contact Lenses — which is the divisor in oxygen transmissibility.
Where material stops and oxygen transmissibility begins
What a material transmits — Dk, Dk/t, water content, modulus, and hydrogel against silicone hydrogel — is one page across, on Oxygen Transmissibility and Dk/t of Contact Lenses.
That split is deliberate. This page answers what the polymer is. That page answers what a specific lens, at a specific ordered power, delivers to the cornea — a different question, because thickness changes with power and thickness is the divisor.
This site is manufacturer-agnostic and does not publish material specifications by brand or SKU, here or there. A permeability figure is a property of a material as measured by a particular laboratory method, and published values for a single material have varied by more than 60 percent between methods. Reproducing a vendor's number under our own heading would present a marketing figure as a clinical constant. Material is chosen with a practitioner, against the eye in front of them.
Starting contact lens parameters still require on-eye fit
A material named on a box is a starting parameter, not a finished prescription.
Which polymer family suits an eye depends on findings this site cannot see: tear film, corneal oxygen demand, deposit history, wearing pattern, and how the lens behaves after it settles. The families above narrow the field. They do not choose within it.
Patient aside (Grade 8–9)
Contact lenses are made of soft, water-containing plastic or of firm, oxygen-permeable plastic. They are not glass. You cannot pick a material from a chart — the material has to suit your eyes, and an eye-care practitioner decides that after trying a lens on you.
Read Starting Contact Lens Parameters Are Not a Prescription for the bound that applies across this site. Convert spectacle prescription to contact lens parameters for power. Fit base curve and diameter on eye. Verify power with over-refraction after the trial lens. Contact lens parameters at the corneal plane stay unfinished until that sequence is done.
Sources
Clinical and historical claims on this page are attributed to the publications below.
- Szczotka-Flynn LB. Contact Lens Materials: A Brief History of Contact Lens Materials. Contact Lens Spectrum, June 2006— first documented glass lenses, Müller 1887 and Fick 1888; first solid PMMA lenses around 1940, primary material until the late 1970s; Wichterle and Lím synthesized HEMA and glycol diester in 1954; the first poly-HEMA gel about 40 percent water; open rotating-form casting from 1961; lathing the dry polymer and swelling it afterwards, patented as xerogel, 1963; CAB approved 1978; silicone-acrylate 1979; silicone elastomer 1981; first silicone hydrogel 1998.
- Caroline PJ, Norman CW. History of Contact Lenses: The World’s First Rigid GP Lens Material. Contact Lens Spectrum, August 2023;38:52— glass and PMMA as non-oxygen-transmitting materials, and hypoxia-induced corneal clouding limiting wearing times; CAB Dk 3.75 to 5.90 × 10⁻¹¹; CAB approved by the FDA in 1978 as the first GP contact lens material; silicone/acrylate materials approved 1982.
- Contact Lens Practice, Chapter 5, Soft Lens Manufacture — lathe cutting, spin casting and cast moulding as the three techniques in current use; xerogel rods about 16 mm across and 400 mm long, buttons about 10 mm thick; back-surface lathe at 8,000 to 12,000 rpm; 8 to 15 nm surface tolerance; hydration in unpreserved saline and autoclaving at 120 °C for at least 15 to 20 minutes; lathing reserved for custom-ordered or extreme-range lenses; spin speed shifting polymer to the periphery and producing more minus power; rigid lathing without the hydration step.
- Michaud L. Understanding the Influence of Water Content in Soft Lenses. Review of Optometry, 15 August 2023— US FDA groups I to IV by water content and ionicity, and Group V created for silicone hydrogel materials. Attributed identically on Oxygen Transmissibility and Dk/t of Contact Lenses so the two pages agree.
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