The lens fine-tunes the focus of light onto the retina, forming a clear image of objects at different distances.

The cornea is the outermost transparent layer that refracts light entering the eye and begins the focusing process.

The nearest distance at which objects can be seen clearly without strain, typically about 25 cm for a young adult.

Myopia, or near-sightedness, is when a person can see nearby objects clearly but not distant ones, resulting from the image being focused in front of the retina.

Myopia can be corrected using concave lenses that diverge light rays before they enter the eye.

Hypermetropia, or far-sightedness, is when a person can see distant objects clearly but has difficulty with close ones, due to the image being focused behind the retina.

Hypermetropia can be corrected using convex lenses that converge light rays before they enter the eye.

Presbyopia is the age-related loss of elasticity in the eye lens, making it difficult to focus on nearby objects.

Bifocal lenses, which combine concave and convex lenses, are commonly used to correct presbyopia.

Atmospheric refraction is the bending of light rays as they pass through layers of air at different temperatures, affecting how we perceive celestial objects.

Twinkling occurs due to atmospheric refraction, which causes the apparent position of stars to fluctuate as their light passes through varying air densities.

Dispersion is the splitting of white light into its component colors (spectrum) upon passing through a prism or water droplets.

VIBGYOR is an acronym for the colors of the spectrum: Violet, Indigo, Blue, Green, Yellow, Orange, and Red.

A rainbow forms when light is refracted and dispersed by water droplets in the atmosphere, creating a spectrum of colors in the sky.

The iris controls the size of the pupil, regulating the amount of light entering the eye.

Cataracts cause a cloudy lens, resulting in blurred vision, which can be corrected through surgery.

It is the minimum distance (around 25 cm) at which the eye can see objects clearly without strain.

The curvature changes through the action of ciliary muscles, allowing the eye to focus on objects at various distances.

The far point is the farthest distance at which objects can be seen clearly, typically at infinity for a normal eye.