The question is asking which parameter remains constant when different objects at different distances are seen by the eye. The correct answer is option 3, the radii of curvature of the eye lens.

To understand this, we need to look at how the eye forms an image. When an object is at different distances from the eye, the eye lens adjusts its shape to focus the light rays onto the retina. This adjustment is done by changing the curvature of the lens.

The focal length of the eye lens (option 1) changes as the lens adjusts its shape to focus the light rays. So, the focal length is not a constant parameter in this case.

The object distance from the eye lens (option 2) changes as different objects are at different distances. Therefore, this is also not a constant parameter.

The image distance from the eye lens (option 4) is the distance between the lens and the formed image. As the object distance changes, the image distance also changes accordingly. So, this parameter is not constant.

However, the radii of curvature of the eye lens (option 3) do not change when different objects are seen at different distances. The eye lens maintains a consistent shape, regardless of the object distance. Therefore, option