Human eye can see objects at different distances with contrasting illuminations. This is due to

The ability of the human eye to see objects at varying distances is primarily due to the mechanism of accommodation [1]. This process involves the adjustment of the eye's focal length by changing the curvature of the crystalline lens [1][2]. The ciliary muscles play a critical role; when they relax, the lens becomes thin, increasing the focal length for distant vision [2]. Conversely, when focusing on nearby objects, the ciliary muscles contract, making the lens thicker and decreasing the focal length [2]. Additionally, the eye manages contrasting illuminations through the iris and pupil, which regulate the amount of light entering the eye [4][5]. While myopia (near-sightedness) and hypermetropia (far-sightedness) are refractive defects that impair this ability, accommodation is the natural physiological function that enables clear vision across a range of distances [1][3].

Sources

1. [1] Science , class X (NCERT 2025 ed.) > Chapter 10: The Human Eye and the Colourful World > What you have learnt > p. 170
2. [2] Science , class X (NCERT 2025 ed.) > Chapter 10: The Human Eye and the Colourful World > 10.1.1 Power of Accommodation > p. 162
3. [4] Science , class X (NCERT 2025 ed.) > Chapter 10: The Human Eye and the Colourful World > 10.1 THE HUMAN EYE > p. 161
4. [5] https://pmc.ncbi.nlm.nih.gov/articles/PMC6634360/
5. [3] Science , class X (NCERT 2025 ed.) > Chapter 10: The Human Eye and the Colourful World > Figure 10.3 > p. 164