IGCSE Biology – BIO-IGCSE-05 – Revision
Summary on Eye Structure, Nervous System,
Hormones & Homeostasis
Cornea - Transparent layer forming the front of the eye
Pupil - Dark circular opening in the centre of the eye which lets light through
Iris - Coloured ring of tissue which controls the amount of light entering the eye by changing the size
of the pupil
Lens - Biconvex transparent body situated behind the iris that focuses light on the retina
Choroid - Dark pigmented vascular layer which stops light being reflected around the inside of the
eye
Sclera - Tough outer coat of the eye
Retina - Light-sensitive layer at the back of the eye where light energy is transduced into the electrical
energy of nerve impulses
Fovea - A small depression in the centre of the retina where a high concentration of cone cells can be
found
Optic Nerve - Transmits impulses from sensory neurones in the retina to the brain
Ciliary muscles - Circular muscles that relax or contract to enable the lens to change shape for
focussing
Suspensory ligaments - A series of fibres that hold the lens of the eye in place
Blind spot - The one area of the retina where an image cannot be formed as there are no rods or cones;
this is where the optic nerve leaves the eye
Refraction - When light is bent. For example in the human eye at the air/cornea boundary and again at
the lens
Circular muscles - Muscles found in the iris that contract in bright light and relax in dim
light
Summary on Eye Structure, Nervous System,
Hormones & Homeostasis
Cornea - Transparent layer forming the front of the eye
Pupil - Dark circular opening in the centre of the eye which lets light through
Iris - Coloured ring of tissue which controls the amount of light entering the eye by changing the size
of the pupil
Lens - Biconvex transparent body situated behind the iris that focuses light on the retina
Choroid - Dark pigmented vascular layer which stops light being reflected around the inside of the
eye
Sclera - Tough outer coat of the eye
Retina - Light-sensitive layer at the back of the eye where light energy is transduced into the electrical
energy of nerve impulses
Fovea - A small depression in the centre of the retina where a high concentration of cone cells can be
found
Optic Nerve - Transmits impulses from sensory neurones in the retina to the brain
Ciliary muscles - Circular muscles that relax or contract to enable the lens to change shape for
focussing
Suspensory ligaments - A series of fibres that hold the lens of the eye in place
Blind spot - The one area of the retina where an image cannot be formed as there are no rods or cones;
this is where the optic nerve leaves the eye
Refraction - When light is bent. For example in the human eye at the air/cornea boundary and again at
the lens
Circular muscles - Muscles found in the iris that contract in bright light and relax in dim
light
