Dr. Karishima Khilar
Interactive model

Cataract, explained

One model of the eye, in eight steps: how a healthy lens focuses light, how a cataract clouds it, and how surgery replaces it.

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What the model shows

A horizontal section through an eye, 24 mm long, on an optical bench. Light comes in from the left, as from an eye chart 6 metres away.

How a healthy eye focuses

The cornea and the lens bend light so that it meets at one point on the retina. The cornea gives most of the focusing power (about 43 dioptres). The lens gives the rest (about 20 dioptres).

What a cataract does

A cataract is a cloudy lens. The cloudy lens scatters light, so the image on the retina becomes blurred, dim and yellow. Vision falls slowly, for example from 20/20 to 20/40, and then to 20/200.

How the surgery is done

  1. A 2.2 mm cut in the clear cornea lets in the instruments.
  2. A round 5.5 mm opening is made in the front of the lens capsule (capsulorhexis).
  3. An ultrasound probe breaks the cloudy lens into pieces and removes them (phacoemulsification).
  4. A folded 6 mm acrylic lens is injected into the empty capsule, where it unfolds.

After surgery

The new lens is clear, so light focuses on the retina again. Its power is chosen before surgery from measurements of the eye.

For education only
The vision values in the model are typical examples, not a diagnosis. The instruments are drawn slimmer than they are in real life. If your vision changes, see an ophthalmologist (eye doctor).