Thealoz Duo contains sodium hyaluronate with natural disaccharide trehalose, which creates an "artificial tear" to protect cell membranes from extreme dryness, the manufacturer said.

Thea Pharmaceuticals stressed the addition of trehalose provides a “significantly greater improvement” in dry eye symptoms, compared with hyaluronic acid alone.

A 300 drop bottle of Thealoz Duo – available in the preservative-free "ABAK" bottle – retails for £13.99, while 30 unit doses retail for £9.99. Both products are available on prescription.

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