Assembly Line

How contact lenses are made

A soft lens is molded around a stand-in liquid, and water takes its place later so the lens swells predictably.

stations
6
things upstream
18
raw sources
9
steps from the ground
5

The short version

Most soft lenses are cast. A liquid mix of water-loving monomers and an inert diluent is confined between two mold halves whose surfaces control the lens shape, then cured into a solid. The halves separate, the diluent is replaced with water so the lens swells to size, and it is inspected and packaged.

  1. Mix the monomers

    Hydrophilic monomers are blended with an inert diluent and a catalyst. Replacing that diluent with water later keeps the lens from swelling unpredictably, a problem with older methods.

    Goes in
    Silicone

  2. Fill the mold halves

    A small dose of liquid is trapped between two mold halves whose surfaces set both optical faces.

  3. Cure into a lens

    The monomer polymerizes in the mold and turns into a solid lens shape. Older routes use a spinning mold, or cut a dry button on a lathe and polish it.

  4. Open the mold

    The halves are separated, leaving the lens ready for its soak.

  5. Hydrate in water

    Water replaces the diluent and the lens swells into its soft gel. Makers call this step time consuming and difficult to control, so much patent work has gone into it.

    Goes in
    Water

  6. Inspect and package

    Each wet lens is inspected for flaws and sealed into its final package.

End of the lineContact lens

Worth repeating

  • Contact lenses were used by over 150 million people worldwide in 2012.
  • Leonardo da Vinci's 1508 notes described a water-filled glass hemisphere worn over the eye, but he did not propose it as a way to correct vision.
  • Cosmetic lenses that change eye color accounted for only 3% of contact lens fits in 2004.

Back to the ground

Follow every input upstream and contact lens starts as these 9 raw sources.

WaterSilica sandQuartzCoalTimberNatural gasRock saltSulfurAir

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Neon sign 9 stations · 24 raw sources Remote control 7 stations · 27 raw sources Drumstick 8 stations · 8 raw sources Ski 8 stations · 24 raw sources Leather handbag 6 stations · 20 raw sources Olive oil 6 stations · 1 raw source

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Sources

Cite this page: "How contact lenses are made." Assembly Line, 2026-11-03. https://assemblyline.org/make/contact-lens

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