He is suffering from Myopia( short sightedness )
as
he is unable to see objects distinctly that are placed within 50 cm........


This defect can be corrected by using Concave lens. .. ...

Defect of Eye: Myopia (Nearsightedness)

Myopia, commonly known as nearsightedness, is a refractive error of the eye that causes distant objects to appear blurry or out of focus, while objects closer to the eye remain clear. This condition occurs when the shape of the eye elongates, causing light rays to focus in front of the retina instead of directly on it.

Causes:
Myopia can be caused by several factors, including:
1. Genetic predisposition: If parents or close relatives have myopia, there is a higher likelihood of developing the condition.
2. Environmental factors: Excessive near work, such as reading or prolonged use of digital devices, can contribute to the development or progression of myopia.
3. Eye strain: Poor lighting or prolonged periods of focusing on near objects can strain the eyes and contribute to myopia development.

Effects:
In the case mentioned, where the person is unable to see objects distinctly placed within 50cm from their eye, it indicates a significant degree of myopia. The person can see nearby objects clearly as light rays from those objects converge correctly on the retina. However, for objects placed farther away, the elongated eye shape causes the light rays to focus in front of the retina, resulting in a blurred image.

Treatment:
Myopia can be corrected using various methods, including:
1. Eyeglasses: A prescription for concave lenses is provided to help diverge the incoming light and focus it correctly on the retina, allowing for clear distance vision.
2. Contact lenses: Soft or rigid gas-permeable contact lenses can be prescribed to provide clear vision without the need for eyeglasses.
3. Refractive surgery: Procedures such as LASIK or PRK reshape the cornea to correct the refractive error permanently.

Prevention:
While myopia cannot be completely prevented, there are measures that can help reduce the risk or progression of the condition:
1. Outdoor activities: Spending time outdoors, especially during childhood, has been associated with a reduced risk of myopia development.
2. Proper visual habits: Taking regular breaks during near work, maintaining good lighting conditions, and holding books or screens at an appropriate distance can help prevent eye strain and potential myopia progression.
3. Regular eye check-ups: Routine eye examinations can help detect myopia early and allow for timely intervention.

By addressing the myopic refractive error through appropriate corrective measures, the person can regain clear and sharp distance vision, enabling them to see objects distinctly beyond the 50cm limit.