The Eye: Anatomy and Functions

Study Notes

Tunics of the Eye

The eye consists of three main tunics: fibrous (provides protection), vascular (supplies blood), and nervous (contains receptors).

Fibrous Tunic

The fibrous tunic is the outer layer of the eye, composed of the cornea and sclera.
The cornea is transparent, curved, and has a low water content, serving to focus light on the retina.
The sclera is a firm, white dense connective tissue that maintains the shape of the eyeball and protects its inner structures.

Vascular Tunic (Uvea)

The vascular tunic is composed of the choroid, ciliary body, and iris.
The choroid is a highly vascular dark brown membrane that provides nutrients to the retina.
The ciliary body includes the ciliary muscle that alters the shape of the lens to focus light.
The iris is the colored part of the eye, controlling pupil size and light entry, made up of circular and radial muscles.

Circular and Radial Muscles of the Iris

The circular muscle, composed of smooth muscle fibers, constricts the pupil and is innervated by the parasympathetic system.
The radial muscle, made of modified contractile epithelial cells, dilates the pupil and is innervated by the sympathetic nervous system.

Blood Supply to the Eye

Blood supply follows a pathway from the common carotid artery to the internal carotid, then to the ophthalmic artery, supplying the vascular and nervous tunics.

Nervous Tunic

The nervous tunic contains the retina, which provides a direct view of blood vessels, aiding in diagnosing conditions like hypertension and diabetes.
The retina's two parts include the pigmented epithelium, which absorbs light, and the neural part containing photoreceptors (rods and cones).

Structure of the Retina

The retina is about the size of a postage stamp, primarily located in the posterior part of the eye.
The macula lutea, a small yellow spot, is crucial for central vision, while the fovea centralis provides the highest visual acuity.

Photoreceptors

Rods (120 million) are located mainly in the periphery and are sensitive to low light, aiding night vision.
Cones (6 million) are primarily in the fovea and are responsible for color vision and high visual acuity, requiring brighter light to function.

Lens Structure and Function

The lens is biconvex, avascular, and composed of crystallins arranged in layers, allowing it to focus light onto the retina.
Cataracts result from protein buildup in the lens, reducing transparency and flexibility with age.

Eye Cavities

The eye interior is divided into anterior and posterior cavities filled with aqueous humor and vitreous humor, respectively.
Aqueous humor is continuously produced and drained, with its imbalance leading to conditions like glaucoma, characterized by increased pressure and potential retinal damage.

Visual Pathways and Disorders

The optic nerve, formed by ganglion cell axons in the retina, transmits visual information to the brain, where two optic tracts represent visual fields.
Disorders such as astigmatism (irregular lens/cornea curvature), strabismus (misalignment of eyes), and pituitary tumors (causing tunnel vision) can affect vision quality.

Neural Convergence

Neural convergence occurs mainly in rods, where multiple rods connect to a single bipolar cell, enhancing sensitivity in low light. Cones have a one-to-one connection, providing detailed color vision.

Description

Explore the essential components of the eye, including the fibrous, vascular, and nervous tunics, as well as the lens and visual fields. This quiz will help you understand the structure and functions of the eye through detailed flashcards. Perfect for students studying anatomy and physiology.