Vision

Surface Anatomy of the Eye Eyebrows divert sweat from the eyes and contribute to facial expressions Eyelids (palpebrae) blink to protect the eye from foreign objects and lubricate their surface Eyelashes detect and prevent foreign objects

Conjunctiva A mucous membrane lining the inside of the eyelids and the anterior surface of the eyes Conjunctivitis (“pinkeye”): inflammation of the conjunctival sac Latin con = with, and junctus = joined (cf. junction)

The Lacrimal Apparatus Lacrimal Apparatus: – lacrimal gland – lacrimal sac – nasolacrimal duct Rinses and lubricates the conjunctival sac Drains to the nasal cavity where excess moisture is evaporated

Extrinsic Eye Muscles Lateral, medial, superior, and inferior rectus muscles (recall, rectus = straight); superior and inferior oblique muscles

Eye Movments

CN II - Optic nerve, vision CN III - Oculomotor, 5 muscles, Autonomic to pupil CN IV - Trochlear, superior oblique CN V - Trigeminal, ocular sensation CN VI - Abducens, lateral rectus CN VII - Facial, obicularis oculi Cranial nerves & eye

Autonomic Regulation of the Iris

Pupil Constricts Pupil Dilates

Internal Anatomy of the Eye Anterior Segment contains the Aqueous Humor – Iris – Ciliary Body – Suspensory Ligament – Lens Posterior Segment contains the Vitreous Humor Latin humor = liquid

Ciliary process at the base of the iris produces aqueous humor Scleral venous sinus returns aqueous humor to the blood stream Positive pressure from aqueous humor, generally above 6 mm Hg, is needed to keep the retina attached to the back of the eye and to nourish the cornea and lens which have no blood vessels. But if the fluid cannot drain!? Circulation of the Aqueous Humor

15 Glaucoma – any disturbance that increases aqueous humor volume and pressure which causes pain – ultimately the vitreous humor crushes the retina causing blindness

Internal Anatomy of the Eye--Tunics Fibrous tunic: sclera & cornea Vascular tunic: choroid layer Sensory tunic: retina

The Two Layers of the Retina Outer pigmented layer absorbs light to prevent light scattering inside Inner neural layer has the photosensory cells and various kinds of rneurons in three layers

Neural layer Organization in the Retina Photoreceptors: rods (for dim light) and cones (3 colors: blue, green and red, for bright light) Bipolar cells are connecting interneurons Ganglion cells’ axons become the Optic Nerve

The Optic Disc Axons of ganglion cells exit to form the optic nerve Blood vessels enter to serve the retina by running on top of the neural layer The location of the “blind spot” in our vision

20 blind spot octopusvertebrate