A normal eye cannot see objects clearly closer than 25 cm due to the limitations in its power of accommodation. Accommodation is the eye’s ability to change the curvature of its lens to focus on nearby objects. There’s a limit to how much the lens can curve or ‘accommodate’. Objects closer than 25 cm require the lens to curve beyond its capability, resulting in a blurred image as the eye cannot focus the light properly on the retina.
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Understanding the Limitations of the Human Eye
The Concept of Accommodation: The human eye has the remarkable ability to adjust its lens to focus on objects at varying distances, a process known as accommodation. This is achieved by changing the curvature of the lens, allowing us to see objects clearly both near and far.
The Near Point of the Eye
The closest distance at which the eye can focus on an object without strain is known as the near point. For a normal, healthy eye, this point is typically around 25 centimetres away.
Limitations in Accommodation
While the eye’s lens is flexible, there are limits to its accommodation ability. The lens can only curve to a certain extent, and this curvature is necessary to focus light correctly onto the retina for clear vision.
Difficulty with Objects Closer than 25 cm
When an object is closer than 25 cm, it requires the lens of the eye to curve more than its maximum capacity to focus light directly on the retina. This excessive demand exceeds the accommodative ability of the eye.
Resulting Visual Impairment
As a result, when objects are closer than 25 cm, the eye cannot bring them into sharp focus. The light rays from these close objects are not refracted sufficiently, leading to a blurred image on the retina.
Conclusion: The Eye’s Focusing Limit
Thus, the normal eye’s inability to see objects clearly closer than 25 cm is due to the physiological limitation in the lens’s ability to curve further. This limitation defines the near point of the eye and is a natural aspect of the eye’s optical system.