Describe the functions of the various parts of the human eye.

K.C.S.E Biology Q & A - MODEL 2003PP1QN18

Describe the functions of the various parts of the human eye.

answers

Sclerotic layer – (made up of collagen fibres thus) protects the eye  maintains shape of eyeball.
Cornea

• Allows light to enter the eye
• Refracts light towards retina

Conjunctive - Protects cornea
Eyelids

•  Protects cornea from mechanical & chemical damage / protects eye form entry of foreign particles.
• protects retina from bright light (by reflex action)

Choroids

• (Contains black pigment which)prevents reflection of light within the eye / absorbed light.
• Nourishes the eye / retina / supply oxygen / remove CO2

Ciliary muscles

•  Alter shape of lens during accommodation
•  Ciliary body produces aqueous humour.

Suspensory ligaments – adjusts shape of lens during accommodation
Lens – Refracts light rays / focuses light on retina
Vitrerous aqueous humour once.
Aqueous Humour – Nourishes cornea / lens Refracts light
Irus – ( pigmented thus) – gives the eye its colour / absorbs light controls amount of light entering the eye / adjusts size of pupil impulses.
Pupil – light enters the eyes through pupil.
Retina – has photoreceptor cells / rods / cones / image formation ;l generates impulses.
Fever / yellow spot – visual acuity / most sensitive part of retina with only cones.
Blind spot – point where nerve fibre emerges from the optic nerve / where the optic nerve leaves the eye / point where blood vessels & nerve fibres enter the eye.
Optic nerve – transmit impulses to brain.