Your eye focuses distant objects in front of the retina instead of on it, so far things blur, near things stay sharp.
Rays converge in front of the retina, before the image can form, so distant objects blur.
Think of your eye like a camera that's slightly 'over-zoomed'. In a myopic eye, either the eyeball is a little too long, or the lens curves a bit too much. Both mean light from far-away objects bends too early and meets at a point before it reaches the retina, so by the time it actually hits the retina, the image has already spread back out into a blur.
Nearby objects are unaffected because their light rays are already diverging more when they enter the eye, so they still land correctly on the retina.
The fix: a concave (diverging) lens placed in front of the eye spreads the light out slightly before it enters, pushing the focus point back exactly onto the retina.
Key exam points
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Defects of Vision: Myopia & Hypermetropia with Numericals, CBSE Physics · CBSE Physics