The light sensitivity of the retina depends upon a pigment called visual purple which is derived from vitamin 'A', Retina can also be affected by strong light, systemic diseases like diabetes, hypertension, etc. Infections like tuberculosis also affect it. Systemic diseases can affect the third component or the optic nerve. Infections, alcohol,tobacco, certain drugs especially anti tubercular drugs. The lids protect it from foreign bodies and injuries.
Tears act as lubricant, and cleansing as well as antiseptic agents.
They also provide nourishment to the cornea. The she oft pupil becomes small in strong light thus cutting off excess light reaching the retina. To avail services of these vital organs for a longer time it is essential to take proper care of your eyes. Use dark glasses. Looking at solar eclipse can cause burn on the retina.