Eye and ear histology

Special senses, such as vision, smell, hearing, and balance are senses that use specialized organs and sensory receptors in order to convey information about a person’s surroundings to the central nervous system.

This video will focus on the eyes, which are the sensory organs responsible for vision; and the inner ears, which are the sensory organs responsible for both hearing and balance.

The eyes are complex and highly developed photosensitive organs.

Each eye has three concentric layers or tunics that make up the outer portion of the eye.

The tough external fibrous layer is made up of both the sclera and transparent cornea.

The vascular layer consists of the pigmented iris, choroid, & ciliary bodies.

And the innermost sensory layer is formed by the retina.

The optic nerve transmits the signal from the retina to the cerebrum.

Even at low magnification, we can see that the inner portion of each eye is split into two main chambers by the lens: the aqueous chamber and vitreous chamber.

The aqueous chamber is filled with a clear fluid called aqueous humor, and the vitreous chamber contains a gelatinous and transparent connective tissue called the vitreous body.

Let’s first take a closer look at the outer fibrous layer or tunic.

The cornea covers the anterior 1/6th of the eye and can be further divided into five sub-layers.

Starting from the surface of the cornea is the corneal epithelium, then the bowman membrane, stroma, descemet’s membrane, and corneal endothelium along the inner surface.

The corneal epithelium is made of non-keratinized stratified squamous epithelium that stains darker than the remaining layers.

Bowman membrane is composed of collagen fibers and has a thickness between 7-12 µm.

When stained with hematoxylin and eosin it can be difficult to identify, but it has a more solid pink appearance when compared to the underlying stroma.

The stroma is the thickest layer of the cornea and is made of collagen fibers and fibroblasts that form a clear and avascular layer of connective tissue that bends or refracts incoming light to help the lens more easily focus light onto the retina.