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How do contact lenses work?

How do contact lenses work?

So how do contacts really work to correct our vision? It’s amazing how a small, curved, gel-like lens can sit on our eyes and help us to see.

We’ve brought in one of our experts and in-house optician Anita, to explain to you how contact lenses actually work to correct our vision.

Contact lenses work just like glasses - except they are made from light and flexible plastic polymers called hydrogels. However, because of its close proximity to the eye, the optic zone of contact lenses (the part of the lens that contains the corrective power for your vision) is made much smaller than the optic zone of glasses lenses that correct your vision.

The shape of contact lenses is important for fitting correctly on your eye but also it affects how the lenses work. Contact lenses are made to capture and reflect light in the correct way so that your eyes process light normally. It redirects the light into a single focal point onto the retina which fine-tunes your vision. 

With good vision, light enters the cornea and focuses onto a single point on the retina at the back of the eye. However, vision issues occur when the cornea is unable to focus properly therefore contact lenses correct this in various ways:

  • Short-sightedness (Myopia)

This is where you can see up close but your vision at a distance is blurry. This occurs when the eyeball is too long which leads to light focusing in front of the retina.

  • Long-sightedness (Hyperopia)

Hyperopia is also known as farsightedness. This means that your distance vision is fine, but objects up close will be blurry. This occurs when the eyeball is too short, so light focuses behind the retina.

The shape of contacts lenses are therefore measured in diopters so if you are shortsighted, your prescription will have a minus sign and if you are long-sighted, it will have a plus sign. This exact diopter measurement depends on how impaired your vision is in each eye.

Contact lenses don’t come in a ‘one size fits all’ as all of us have different sized and shaped corneas. For example, some of us may have rugby ball shaped eyes instead of round; this is referred to as astigmatism. The axis of the contact lens for someone with astigmatism will therefore be different from sphere-shaped lenses as these will be made as toric contacts to fit the cornea correctly and correct astigmatism.

The inside curvature of a contact lens needs to stick correctly to the cornea in order to correct your vision, therefore, it is important for an optician to correctly measure the shape of your eye during an eye exam so that your lenses are tailored specifically to you. The natural moisture of your eye then helps to keep the contact lens in place on your eyeball so that it doesn’t fall out or move around.

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