What are the Causes of Myopia (Short-Sightedness)?

In a perfect, healthy eye, the biological lens violently bends the incoming light rays so they physically crash and focus exactly on the Retina (the back screen of the eye). In a Myopic eye, the light rays bend too much. They crash and focus in front of the Retina, not on it. Because the image is formed before reaching the screen, the brain only receives a highly blurry picture of distant objects.

The eye doctor will tell you this happens for two massive biological reasons:

1. Elongation of the Eyeball (Too Long): This is the most common cause. As a child grows, their physical eyeball genetically grows too long (like an oval egg instead of a perfect round ball). Because the eyeball is too long, the back Retina screen is pushed too far away, causing the light to focus in the empty space in front of it.
2. Excessive Curvature of the Eye Lens (Too Thick): The biological eye lens becomes massively thick and violently curved. A thicker lens has massive optical power, bending the light far too aggressively and causing it to focus way too early.

To fix this massive optical failure, the doctor places a piece of curved glass called a Concave Lens (Diverging Lens) in front of the eye (spectacles). The concave lens mathematically spreads the light rays slightly apart before they enter the eye. This perfectly forces the thick eye lens to push the focus point further back, landing the image exactly on the Retina.