Module 21: Visual System
Learning Objectives:
By the end of this class, students will be able to:
- Describe the bones of the skull that make up the orbit.
- List and explain the function of the extrinsic muscles of the eye.
- Describe the anatomy of the eye, including the layers, and the function of all relevant structures.
- Describe vision receptors in the retina.
- Describe the blood supply to the retina.
- Explain the primary visual pathway and accessory pathways of the visual system.
- Describe the regions of the brain involved in vision.
Terms to Know
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Eye
*Covered only in lecture, not in this text |
Extrinsic Eye Muscles
Accessory Structures
Visual Pathways
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Accessory Structures of the Eye
This content will be covered in lecture.
The eyes are located within either orbit in the skull. The bony orbits surround the eyeballs, protecting them and anchoring the soft tissues of the eye. Several bones contribute to the orbit, including:
- Roof: Frontal bone
- Lateral wall: Zygomatic bone
- Floor: Maxillary bone and palatine bone
- Medial wall: Lacrimal bone and ethmoid bone
- Posterior wall: Sphenoid bone
The eyelids, with lashes at their leading edges, help to protect the eye from abrasions by blocking particles that may land on the surface of the eye. The space between the upper and lower eyelids is called the palpebral fissure. The medial and lateral angles are where the upper and lower eyelids meet on the medial and lateral aspects of the orbit. The eyelids are composed of very thin layers of skin and tissue. To ensure they maintain their shape as they move over the anterior surface of the eye, the eyelids each contain a layer of connective tissue called a tarsal plate. The orbicularis oculi muscle also inserts onto the tarsal plates. The eyelids also contain modified sebaceous glands, called tarsal glands, that lubricate the surface of the eye, prevent tear overflow, and prevent the eyelids from sticking together.
The inner surface of each lid is a thin membrane known as the palpebral conjunctiva. The conjunctiva extends over the white areas of the eye (the sclera), connecting the eyelids to the eyeball. The portion of the conjunctiva that covers the anterior eye is called the bulbar conjunctiva. Collectively, the conjunctiva is a transparent mucous membrane made of primarily stratified squamous epithelium.
Lacrimal Apparatus
Tears, or lacrimal fluid, are produced by the lacrimal gland, located in the superior lateral aspect of the orbit. See the lecture slides for the functions of lacrimal fluid and the detailed pathway that lacrimal fluid takes from production to draining into the nasolacrimal duct.
Muscles That Move the Eye
This content will be covered in lecture.
Movement of the eye within the orbit is accomplished by the contraction of six extraocular muscles that originate from the bones of the orbit and insert into the sclera, or white surface of the eye. Four of the muscles around the eye are named for their locations: the superior