Surface anatomy

Layers of the eyeball

Conjunctiva

• The palpebral conjunctiva forms the deepest layer of the eyelid
• It is a thin mucous membrane, which is reflected onto the sclera of the eyeball (bulbar conjunctiva)

Fibrous layer

• Outermost layer which consists of the sclera and cornea
• Sclera provides attachment for the extraocular muscles
• Light entering the eye is partially (2/3) refracted by the cornea

Uvea (vascular layer)

• Iris - pigmented membrane with a central opening (the pupil) which adjusts its size in response to light
  • Regulates the amount of light that reaches the retina
  • The diameter of the pupil is altered by smooth muscle fibres within the iris, which are innervated by the autonomic nervous system
• Ciliary body - adapts the shape of the lens, anchors the lens and produces aqueous humor
  • Comprised of two parts, the ciliary muscle and ciliary processes
  • The ciliary muscle consists of a collection of smooth muscles fibres which are attached to the lens of the eye by the ciliary processes
• Choroid - layer of connective tissue and blood vessels which provides nutrition and gas exchange to the outer layers of the retina

Inner layer

• The fundus of the eye is the interior (posterior) surface of the eye opposite the lens where light is focused and includes the retina, optic disc, macula, fovea, and posterior pole
• Retina: light detecting component of the eye
  • 10 layers of cells in 4 main layers:
    • Retinal pigment epithelium (RPE) (most posterior, separates choroid from retina proper)
    • Rods and cones (photoreceptors)
    • Bipolar neurons
    • Ganglion neurons - axons of the ganglion cells form the optic nerve
  • Layers are inverted in the sense that the light sensing cells are in back of the retina, so that light has to pass through layers of neurons and capillaries before it reaches the rods and cones