A lens wearable in an eye of a user can indicate intraocular pressure of the eye. The wearable lens includes a substrate containing anthocyanins. The substrate is formed by polymerization of a hydrophilic monomer and a hydrated polymer under the effects of a photoinitiator and a cross-linking agent. The anthocyanins in the substrate change color according to the pH of the eye, and the pH of the eye is determined according to the intraocular pressure of the eye.
