Ocular anatomy part 3 - Anatomy of the ciliary body

The ciliary body is a crucial structure within the eye, playing a significant role in the production of aqueous humor (the fluid in the eye) and in controlling the shape of the lens, which is essential for focusing. It is part of the uveal tract, which also includes the iris and the choroid.
###Anatomy of the Ciliary Body
The ciliary body is located between the iris (the colored part of the eye) and the choroid (the layer of blood vessels behind the retina). It is composed of several key components:
1. **Ciliary Muscle**:
- **Structure**: The ciliary muscle is a smooth muscle that is arranged in circular, longitudinal, and radial fibers.
- **Function**: It controls the shape of the lens through a process known as accommodation. When the ciliary muscle contracts, it releases tension on the zonular fibers (suspensory ligaments), allowing the lens to become more rounded, which is necessary for focusing on near objects. Relaxation of the ciliary muscle increases tension on the zonules, flattening the lens for distance vision.
2. **Ciliary Processes**:
- **Structure**: These are small, finger-like projections that extend from the ciliary body into the posterior chamber of the eye.
- **Function**: The ciliary processes are responsible for the production of aqueous humor, the fluid that fills the anterior chamber of the eye. The aqueous humor is produced by the epithelium covering the ciliary processes and plays a crucial role in maintaining intraocular pressure and nourishing the avascular structures of the eye, like the lens and cornea.
3. **Zonular Fibers (Suspensory Ligaments)**:
- **Structure**: These are fine, thread-like structures that connect the ciliary body to the lens.
- **Function**: The zonular fibers transmit the tension from the ciliary muscle to the lens, enabling the lens to change shape during accommodation.
4. Vascular Supply:
- **Structure**: The ciliary body is highly vascularized, receiving blood supply primarily from the ciliary arteries, which are branches of the ophthalmic artery.
- **Function**: The blood vessels within the ciliary body are involved in the production of aqueous humor and provide nourishment to the ciliary muscle and other structures.
5. **Pigmented and Non-Pigmented Epithelium**:
- **Structure**: The ciliary body is lined by two layers of epithelium: the pigmented epithelium (outer layer) and the non-pigmented epithelium (inner layer).
- **Function**: The non-pigmented epithelium is involved in the active secretion of aqueous humor. The pigmented epithelium plays a role in maintaining the blood-aqueous barrier.
Functions of the Ciliary Body
- **Accommodation**: The ciliary muscle allows the lens to adjust its shape for focusing on objects at different distances.
- **Aqueous Humor Production**: The ciliary processes produce aqueous humor, which maintains intraocular pressure and provides nutrients to the eye's avascular structures.
- **Maintenance of the Blood-Aqueous Barrier**: The ciliary epithelium helps regulate the exchange of substances between the blood and the aqueous humor, maintaining a stable environment within the eye.
Understanding the anatomy and function of the ciliary body is important for comprehending various eye conditions, such as glaucoma (where the drainage of aqueous humor is impaired) and presbyopia (age-related loss of accommodation).

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We discuss the functional anatomy of the lens in the next video