Vision

Accessory Structures of the Eye Only about 17% of the eye is visible About 2.5 cm in diameter Accessories / external features of the eye: Palpebrae - eyelids; evenly distribute tears across the surface of the eye to keep it moist Palpebral fissure – cleft between upper/lower eyelid Lacrimal caruncle – contains sebaceous/sweat glands Lateral / medial canthus – 2 points where the upper/lower eyelid meet Eyelashes Tarsal glands – secretes oily substance that keeps eyelids from sticking together Conjunctiva – thin mucous membrane that covers the eye / lubricates eye and contains vessels

Lacrimal Apparatus Produces, distributes, and removes tears Lacrimal gland – tear gland Provide most of the volume of tears that cover surfaces / supply nutrients and oxygen / contain antibacterial lysozyme Lacrimal canaliculi – where tears drain  lacrimal sac  nasolacrimal duct Lacrimal fluid contains lysozyme  fluid moves across eyeball surface and enters two openings in medial canthus  superior / inferior lacrimal puncta  lacrimal canals  lacrimal sac  nasolacrimal tract drains the tears into the nasal cavity

INTERNAL EYE Fibrous tunic – dense connective outer layer tissue Sclera – white part of the tunic that covers the eye Corneal lambus – the border between sclera and cornea; contain canal of Schlemm, Cornea – NOT covered by sclera, transparent tissue where light enters the eye Vascular tunic (uvea) Iris (anterior) Lens (posterior to iris) – focuses light Ciliary body – where iris attaches Pupil Choroid (posterior) – melanin that absorbs light and prevents against reflection Neural tunic (aka retina) Pigemented part (outer layer) Neural part – contains light-sensitive photoreceptors Aqueous humor – maintains intraocular eyepressue and supplies nutritents to lens/ cornea Vitreous body – holds retina against choroid and prevents collapse

How does the pupil change size? Pupillary sphincter muscles / pupillary dilator muscles Parasympathetic vs Sympathetic innervation

Cellular Organization of the Retina Neural part of the retina contains the photoreceptors And 2 types of sensory neurons  bipolar cells and ganglion cells Photoreceptors Rods – motion detection Cones – visual acuity Light  pigemented area  neural part  photoreceptors  bipolar cells  ganglion cells axons converge at optic disc Amacrine cells – communication between bipolar and ganglion cells Horizontal cells – inhibit or facilitate communication b/w photoreceptors and bipolar cells Macula lutea – contains many cones Fovea (center of ML) – sharpest vision at this point / no rods here

Diseases of the Eye Glaucoma Diabetic Retinopathy Conjunctivitis Macular Degeneration Sty

Refractive Problems https://www.youtube.com/watch?v=Po7K0Va8BUs

Visual Pathways Begin with photoreceptors  visual cortex of cerebral hemispheres 130 million photo receptors and 6 million bipolar cells / 1 million ganglion cells Convergence – increases effeciency of information transmitting but you lose specificity M cells monitor rods  provide information about general form of an object and motion P cells monitor cones  provide information about shape, form, color  cones provide more precise information

Visual Pathway Bipolar cells and ganglion converge at optic disc  optic nerve  optic tract  lateral genicular nucleus Projection fibers  visual cortex https://www.youtube.com/watch?v=ni6RjkjdQyk