An Exploration of the Eye

Light is Essential for Vision

External Anatomy of the Eye

Position of the Eyes Within the Skull

Muscles to Move the Eyeball

Intrinsic Eyeball: 3 Layers Fibrous layer Vascular layer Inner layer Lens Optic nerve (CN II) Cornea The 3 layers of the eyeball from superficial to deep are the fibrous, vascular & inner (retinal) layers.

Internal Anatomy

Opthalmoscope View

The Retina

Rods and Cones- 130 million Bright daytime light Color Vision 3 subtypes for Red, Green, Blue in MOST Humans 2 subtypes in animals (4 in trout!) Night vision Saturated during the day Classroom light = ½ rods, ½ cones

Images are projected on the retina upside down!

Upside down and backwards!

Nearsighted

Farsighted

Don’t yell out the number!

Pop Quiz!

Let’s Dissect!

Fibrous (Outer) Layer The fibrous (outer) layer of the eyeball consists of 2 continuous structures the sclera and cornea. The cornea is transparent and covers the anterior 1/6 of the eyeball. It is responsible for the refraction of light entering the eye The sclera is the tough white of the eye and covers the posterior 5/6 of the eyeball. The sclera provides shape and attachment sites for muscles. Cornea Sclera Main Menu

Vascular (Pigmented) Layer: Middle Layer The vascular (pigmented) layer (or the uvea/uveal tract) of the eyeball consists of the choroid, ciliary body & iris. Iris Ciliary body Choroid Main Menu

Vascular (Pigmented) Layer: Choroid Choroid The choroid consists of an outer pigmented layer (dark brown) and an inner highly vascularized layer which invests the posterior 5/6 of the eyeball. The choroid nourishes the retina. Main Menu

Vascular (Pigmented) Layer: Ciliary Body The ciliary body is both a muscular and vascular structure that connects the choroid and iris. It also provides attachment for the lens. Folds on its internal surface (ciliary processes) secrete aqueous humor that fills the anterior and posterior chambers The ciliary muscle is a smooth muscle innervated by parasympathetic fibers. Contraction & relaxation of this smooth muscle controls the thickness of the lens. This results in focus or accommodation. Cornea Iris Ciliary Body Main Menu Distant Vision Near Vision

Vascular (Pigmented) Layer: Iris The iris lies on the anterior surface of the lens, is a thin, contractile diaphragm with a central aperture known as the pupil. The pupil allows in varying levels of light. Two muscles in the iris control the size of the pupil: the sphincter (constrictor) pupillae & dilator pupillae The sphincter pupillae is smooth muscle innervated by parasympathetics while the dilator pupillae is also smooth muscle but its innervated by sympathetics. Sphincter pupillae Iris Ciliary body Dilator pupillae Main Menu

Inner (Retinal) Layer: Deep Layer Excitation Light Retina Main Menu

Inner (Retinal) Layer Excitation Light The retina consists of an outer pigmented and inner neural layers. The neural layer is the light-receptive layer and is composed of 3 types of neurons: rods & cones; bipolar neurons; and ganglion neurons. The axons of the ganglion neurons form the optic nerve (CN II). The pigmented layer consists of a single layer of cells that reinforce the light absorbing property of the choroid so to reduce the scattering of light in the eye. Pigmented layer Choroid Ganglion neurons Bipolar neurons Rods & Cones Main Menu Optic nerve

Inner (Retinal) Layer Fovea centralis Macula lutea (yellow spot) Optic Disk (blind spot) Central artery & Vein of the retina The fundus is the posterior part of the eyeball. The optic disc is the circular area where the optic nerve and central retina vessels are found. It has no photoreceptors and is insensitive to light (“blind spot”). The macula lutea is just lateral to the blind spot. At the center of the macula lutea there is a small depression called the fovea centralis. The fovea is the area of most acute vision. Fundus Medial Lateral Main Menu

Refractive Media: Cornea & Lens The cornea is largely responsible for refraction of light that enters the eye. It is transparent, avascular, and sensitive to touch. It is innervated by the (V1 fibers of the) ciliary nerves. The lens is posterior to the iris and is a transparent, biconvex structure that is enclosed in a capsule and attached by zonular fibers to the ciliary bodies. The convexity of the lens, particularly its anterior surface, constantly varies to focus near and distant objects on the retina. Cornea Lens Main Menu

Refractive Media: Aqueous Humor & Vitreous Chamber Aqueous humor is a watery solution produced by the ciliary processes that fills the anterior and posterior chambers and nourishes the cornea & lens. The anterior chamber is anterior to the iris. The posterior chamber is posterior to the iris. The vitreous chamber is located posterior to the lens and is filled with a watery, semi-gelatinous substance called the vitreous humor or body. The vitreous body holds the retina in place, supports the lens and transmits light. Vitreous chamber Anterior chamber Posterior chamber Main Menu