Course Content
Deepen your understanding of ocular anatomy as you delve further into the complex structures and functions of the eye. This lesson covers the eye's main parts and regions while developing your understanding of the principles of refraction and accommodation. You will also learn about the six extraocular muscles and gain valuable insight into how the eye moves.
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Overview of the Visual System

Chapter 1 of 5

The eye is often referred to as a window to the soul. While this is a statement about our emotions, in reality, the eye is an extension of the central nervous system that converts light signals into electrical signals for brain processing.

The Eye Has 3 Main Layers

The Outer Layer: The Sclera

The sclera is a white, tough tissue that is the outer coating of the eyeball visible as “the white” of the eye. The sclera is protective, and also functions as the insertion point for the extra-ocular muscles that control eye movement.

The Middle Layer: The Choroid

The middle layer, the choroid, or uveal tract consists of the iris, the ciliary body and the choroid. The iris controls the amount of light entering the eye through the pupil, and is noticeable due to its variety of colors. The ciliary body controls the focusing ability of the eye, and it also produces the aqueous fluid in the front chambers of the eye. The choroid is full of vessels, and provides nourishment for the other structures.

The Inner Layer: The Retina

The retina is the most internal layer of the eye. It is composed of ten distinct layers, including specialized light-sensitive neurons: rods and cones. Cones are located centrally in the macular region, with the highest concentration found in the fovea (the center of the macula). Cones are responsible for color perception and details. Therefore, when we discuss visual acuity, we also discuss cone function. Rods, which are more concentrated in the periphery of the retina, are responsible for low-light vision and movement detection. Eventually, all of the electrical signals created by these photoreceptors travel through a series of interconnecting neurons to finally reach the optic nerve. That bundle of nerve fibers is the beginning of the visual pathway, where the visual signal travels from the eye to the occipital (more posterior) part of the brain, where the sense of vision comes to life.

The Crystalline Lens Is the Central Part of the Eye

The crystalline lens, or simply lens, is transparent, biconvex, and can change its shape inorder to adjust the focusing of the eye – a process known as accommodation.

The Inside of the Eye Is Divided Into 3 Different Regions

The eye is divided into different anatomical landmarks or regions. The anterior segment consists of the anterior and posterior chambers. Past the lens is the vitreous body. The back of the eye is referred to as the posterior segment.


The sclera is the most external layer to the globe. It is a white, thick tissue that is responsible for maintaining the shape of the eye and offering some protection thanks to its mechanical properties. The sclera has very little vascularization (blood vessel supply) and innervation (nerve supply). It serves as an insertion point for the extra ocular muscles. Did you know? The


The cornea is a continuity of the sclera but with a different arrangement of the tissue that provides its exceptional clarity. The cornea itself is composed of five layers. The most anterior layer is known as the corneal epithelium and the most posterior corneal layer is known as the corneal endothelium. Its main role is to pump water out of the cornea so it can maintain its transparency.


The choroid is a highly vascular layer. Its primary function is to provide nutrition to the retina. Histologically the choroid extends anteriorly into the uveal tract. While they may look anatomically different, the iris, the ciliary body, and processes are essentially an extension of choroidal tissue with different functions.

Ciliary Body

Immediately past the iris, posteriorly, is the ciliary body which helps control the focusing system of the eye or accommodation. The ciliary processes are responsible for producing the aqueous humor which fills the anterior and posterior chambers of the eye.


The iris, aside from giving the eye its color, is a ring shape tissue that controls the size of its adjustable opening: the pupil. The iris contains muscles: In low light conditions, the pupil dilates to allow more light to enter the eye, creating a rod response on the retina. Conversely, in high-light situations, the pupil constricts to limit the amount of light that enters the eye. This protects the eye by preventing glare, photophobia, and saturation of the photoreceptors.


The pupil is an opening that allows light to enter the eye. The size of the pupil is controlled by the muscles in the Iris.

Optic Nerve

The optic nerve is the nerve that carries messages from the retina to the brain. Made up of more than 1 million nerve fibers that convert visual messages to electrical signals, damage to the optic nerve can cause vision loss.


The macula is a small area that is roughly in the center of the retina. It is responsible for our central vision. It has the highest concentration of cones, providing the clearest vision for details, including fine vision and color vision.


The retina is made up of photosensitive cells, rods, and cones. All of these parts have a fundamental role to play. The photosensitive cells turn the light hitting the retina into electrical signals which travel from the retina through the optic nerve to the brain.

Ora Serrata

The ora serrata is the peripheral termination of the retina and lies approximately 5 mm anterior to the equator of the eye. Its name derives from the scalloped pattern of bays and dentate processes; the retina extends further anteriorly on the medial side of the eye. The ora serrata is the serrated junction between the retina and the ciliary body. This junction marks the transition from the simple non- of the retina to equator of the eye. Its name derives from the scalloped pattern of bays and dentate processes; the retina extends further anteriorly on the medial side of the eye. The ora serrata is the serrated junction between the retina and the ciliary body. This junction marks the transition from the simple non- photosensitive area of the retina to the complex, multi-layered photosensitive region.

Crystalline Lens

The crystalline lens is flexible and accommodates changes in vision from near to far by altering its shape as needed. This is called the “Power of Accommodation.” Accommodation refers to the ability of the lens to shift between focusing on near to far objects with little interference. This ability relies on the flexibility of the crystalline lens, which makes it easier to change focal distances. As we age, the crystalline lens loses its flexibility, resulting in a condition called presbyopia.

Vitreous Humor

Behind the crystalline lens, we can find the vitreous humor. It is a type of transparent jelly that provides structure to the eye and support the retina.

Posterior Chamber

The posterior chamber is a narrow space behind the peripheral part of the iris, in front of the suspensory ligament of the lens and ciliary processes. It is an important structure involved in production and circulation of aqueous humor. Aqueous humor produced by the epithelium of the ciliary body is secreted into the posterior chamber, from which it flows through the pupil to enter the anterior chamber.

Anterior Chamber

The anterior chamber is the space inside the eye between the iris and the cornea. The chamber is filled with a transparent water-like fluid similar to plasma called aqueous humor. Although similar to plasma, aqueous humor contains low protein concentrations. The aqueous humor fluid is produced by the ciliary processes and drained by various structures located at the junction found between the cornea and the iris, called the iridocorneal angle. The fluid fills both the anterior and posterior chambers of the eye and provides oxygen and nutrients to both the lens and the cornea.