• The human eyeball measures only about 25 millimeters in diameter.
  • The outer parts of the eye include the eyelids, the conjunctiva, the lacrimal glands, and the lacrimal sac. Three layers of tissue form the wall of the eyeball: (1) the sclera and the cornea, (2) the uveal tract, and (3) the retina.
    EYES, human eye
  • The iris is the colored disc that lies behind the cornea. Its colour comes from a brownish-black substance called melanin.
  • At the centre of the iris is a round opening called the pupil, which looks like a black circle. The pupil regulates the amount of light that enters the eye.
  • The retina makes up the innermost layer of the wall of the eyeball.
  • The point where the optic nerve enters the eye is known as the blind spot. It has no rods or cones and therefore cannot respond to light.
  • Light rays are absorbed by pigments in the retina’s rods and cones. The pigments consist of protein and vitamin A. Vitamin A helps give the pigments their co lour.
  • Cataract is opacifcation of lens.
  • Aqueous humour is a thin, clear, liquid fulling the space between the lens and the cornea.