Sclera Protects and contains internal parts Cornea Cornea is responsible for maximum refraction of incident light Aqueous Humour Prevents collapse of the eye due to atmospheric pressure changes Iris Iris controls the light entering the eye by  adjusting the size of pupil Crystalline Lens Focuses the light reflected by objects on the retina. Ciliary Muscles Alter focal length of the crystalline lens Retina Receives optical image and converts it to electrical impulses Vitreous Humour Maintains the shape of the eye Optic Nerve Carries electrical impulses to the brain. Brain interprets these impulses and produces the sense of vision.