Focusing and rods and cones

difference between cones and rods

Focusing?

● Image formation on the retina involves the refraction of light rays by the cornea and lens, which focus an inverted image on the central fovea of the retina.

How the lens changes shape in order to focus?

Near and far:

● For viewing near objects, the lens becomes rounder (increases its curvature) : ciliary muscles contract and suspensory ligaments relax.

● For viewing far objects, the lens becomes flatter (decreases its curvature) : ciliary muscles relax and the suspensory ligaments become taut.

Accomodation:

• The adjustment the lens makes to accomodate near and far vision.

• It is a reflex reaction and the ciliary muscles change the shape of the lenses to focus on near or far vision.

Blind spot:

An area of thedretina where the optic nerve is located where there is no sensory reception (absence of rods and cones)

Rods?

• Located primarily around the periphery of the retina

• Respond to/subjected to low intensity light.

• Responsible for contrast, shapes/shadows/movement, peripheral vision.

Cones?

• Located primarily at the centre of the back of the eye in the “fovea centrals”

• High intensity light (recieve the most light because of where its located)

• Responsible for detail, visual acuity/sharpness, mainly responsible for colour vision.