Question

when does the focal length of eyes increases or decreases ?​

Answer 1

Answer:

Increases

Explanation - When the muscles are relaxed, the lens becomes thin. Thus, its focal length increases. The image is formed on the retina even on increasing the distance of an object from the eye. For this eye, the lens becomes thinner and its focal length increases as the object are moved away from the eye

Answer 2

Answer:

This is the answer:

Explanation:

The ability of the eye lens to adjust its focal length is called accommodation.

Damage to or malfunction of any part of the visual system can lead to significant lossof visual functioning. For example, if any of the structures involved in the transmissionof light, like the cornea, pupil, eye lens, aqueous humour and vitreous humour orthose responsible for conversion of light to electrical impulse, like the retina or eventhe optic nerve that transmits these impulses to the brain, is damaged, it will resultin visual impairment.You might have experienced that you are not able to see objectsclearly for some time when you enter from bright light to a room with dim light. Aftersometime, however, you may be able to see things in the dim-lit room. The pupil ofan eye acts like a variable aperture whose size can be varied with the help of the iris.When the light is very bright, the iris contracts the pupil to allow less light to enterthe eye. However, in dim light the iris expands the pupil to allow more light to enterthe eye. Thus, the pupil opens completely through the relaxation of the iris.The eye lens is composed of a fibrous, jelly-like material. Its curvaturecan be modified to some extent by the ciliary muscles. The change in thecurvature of the eye lens can thus change its focal length. When themuscles are relaxed, the lens becomes thin. Thus, its focal lengthincreases.  This enables us to see distant objects clearly. When you arelooking at objects closer to the eye, the ciliary muscles contract. Thisincreases the curvature of the eye lens. The eye lens then becomes thicker.Consequently, the focal length of the eye lens decreases.  This enablesus to see nearby objects clearly.The ability of the eye lens to adjust its focal length is calledaccommodation.  However, the focal length of the eye lens cannot bedecreased below a certain minimum limit.  Try to read a printed pageby holding it very close to your eyes. You may see the image being blurredor feel strain in the eye. To see an object comfortably and distinctly, youmust hold it at about 25 cm from the eyes.  The minimum distance, atwhich objects can be seen most distinctly without strain, is called theleast distance of distinct vision. It is also called the near point of the eye.For a young adult with normal vision, the near point is about25 cm. The farthest point upto which the eye can see objects clearly iscalled the far point of the eye. It is infinity for a normal eye. You maynote here a normal eye can see objects clearly that are between 25 cmand infinity.Sometimes, the crystalline lens of people at old age becomes milky andcloudy. This condition is called cataract. This causes partial or completeloss of vision. It is possible to restore vision through a cataract surgery.