The Chemistry of Contact Lenses

The Chemistry of Contact Lenses

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Today’s episode shows us the chemicals literally hidden right before our eyes: the chemistry of contact lenses!

The first contact lenses were these uncomfortable slices of glass that covered much of the eye, and could only be used for a few hours.

Lenses were subsequently made of synthetic polymers , or plastic. Later, poly-methyl methacrylate lenses, which is to say “acrylic”, became popular. They were smaller, adapted to the cornea, but  still very stiff, uncomfortable and unstable, which made it a common sight to see users looking for them on all fours on the floor.

These problems were solved through a chemical modification: the poly-methyl methacrylate was replaced by poly-hidroxyethil methacrylate, a very big word that means a strong and clear but much more malleable acrylic polymer.

But the main problem of contact lenses was still not solved: they were impermeable to oxygen.

The cornea has no blood vessels, and therefore it is not blood that supplies nutrients and oxygen to its cells. Nutrients are transported by the lacrimal fluid and the vitreous humor of the eye, while the oxygen reaches the cells of the cornea directly through contact with the air. Because they were totally impermeable to oxygen, acrylic lenses could only be used for a few hours.

More recently however, chemical laboratories have developed a solution to this problem: the hydrogel, a gelatinous material composed of a network of insoluble polymers containing large amounts of water. This material is highly hydrated and very comfortable for the eyes and, above all, is permeable to oxygen in the air. As a result, current hydrogel contact lenses can be used for long periods.

Long periods with chemistry right in front of your eyes!

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Química 2011 Science Office Universidade de Aveiro QREN Compete