Photoreception (the eye)

Sclera

Outer layer

White fibrous layer

Shape and Protection

Cornea

Front of sclera

Refracts (bends) light to pupil

Receives nutrients from aqueous humour

Aqueous Humour

Behind cornea

Provides nutrients and maintains intraocular pressure

Choroid

Second Layer

Blood vessels (provide oxygen) and pigmented granules (prevent stray light from bouncing inside the eye)

Iris

Front of choroid layer

Has muscles that control the size of the pupil, regulating the amount of light that enters the eye. (constrict and dilate)

Pupil

Opening of the eye, allowing light to enter

Black hole

Size of pupil determined by the iris - light adaptation

Constriction/dilation is influenced by para and sympathetic nervous system

Vitreous humour

Transparent gel like fluid that fills the large chamber behind the iris

maintains the shape of the eye

Facilitates light transmission to the retina

Lens

Refracts light to focus images on the retina

image is inverted on the retina

Ciliary muscles

Shape of lens changes to adjust focus for near or distant objects.

This is known as accommodation

Suspensory ligaments

Connect the ciliary muscles to the lens, helping to maintain its position and enabling adjustments in shape for focus.

Keeps it all in place

Near point accommodation

Far = background = flat lens

Close = pencil = curved lens

Retina

Innermost layer of the eye

Contain photoreceptors: Rods & Cones, which convert light energy into nerve impulses to the optic nerve and then occipital lobe.

Blind Spot

Where the optic nerve exists to the brain

and lacks photoreceptors, resulting in a gap in the visual field.

Fovea Centralis

The small depression in the retina where visual acuity is highest. It contains a high density of cones and is responsible for sharp central vision.

Rods

Low intensity light

Discriminates shades of gray

Shape and movement only

Multiple rods connect to one bipolar cells which makes it unable to have detailed vision

Rods contain rhodopsin

Rhodopsin

In dim light - inhibitory neurotransmitters

In bright light - it breaks down

Made up of vitamin A, opsin and retinal

Peripheral vision

Cones

Require high intensity light to determine color

and fine detail. They are concentrated in the fovea centralis and are crucial for daylight vision.

1:1 ratio with bipolar cells

Defective - color blindness

Binocular Vision

Left goes to right, right goes to left

Cataracts

Clouding the lens

Diabetes and hypertension

Degradation of the proteins in the lens

Treatment: Often replacing of the lens

Glaucoma

Increased pressure build up that creates damage to the optic nerve

Eye drops, meds, laser therapy, surgery

Astigmatism

Abnormally shaped cornea

Lenses or surgery

Myopia

Near sighted ness

Only able to focus on close up images

Causes by elongated eyes

Images land in front of the retina

Corrected by concave lenses or lasik

Hyperopia

Farsightedness

Only see far away good

Images land behind the retina

Treated with convex lenses