The scotopic vision is developed through the stimulation of

During the night,when light intensity is low,light is detected by .....

Good vision depends on adequate intake of carotene-rich food. Select the best option from the following statements:
$(1)$ Vitamin $A$ derivatives are formed from carotene.
$(2)$ The photopigments are embedded in the membrane discs of the inner segment.
$(3)$ Retinal is a derivative of vitamin $A$.
$(4)$ Retinal is a light-absorbing part of all the visual photopigments.

The visual acuity is the greatest at

In the human eye,the image formed on the retina is:

Which structure is covered by the iris?