Human eye anatomy
Do you know anything about eye anatomy?
Here are a few snippets we learnt while making an anatomical 3D model of the eye with a few useful resources for additional reading.
There are over 2 million working parts in the human eye, it is one of the most complex organs in the body! So, there is a LOT to learn, especially considering it’s such a tiny organ at only 24mm in diameter. Therefore, the best way to learn about it is probably to break it down into snippets of information. This blog post takes a look at eye anatomy using interaction and visuals. It labels some of the parts and adds a brief description.
1. Lens
The lens is a transparent, curved structure which refracts light and focuses it on the retina to generate clear images. It changes shape to allow focus on things at different distances from the eye.
2. Iris
The visible, pigmented part of the eye is called the iris. It is the anterior part of the uvea, originating from the ciliary body. It surrounds a small aperture called the pupil, which changes in size due to the contraction and relaxation of the muscles of the iris. Different quantities of light to enter the eye as a result.
3. Cornea
The cornea is the outermost transparent layer in the visible part of the eye. It is continuous with the sclera. Refraction of light and focusing are its key responsibilities. It is sensitive is due to unmyelinated nerve endings which cause the involuntary reflex of closing the eyelid on touch. This prevents damage to the eye. This resource has further information on the cornea.
4. Sclera
The sclera is the tough, fibrous, outer layer of the eye, commonly known as the “white”. It forms the supporting wall of the eyeball which protects the interior components. It is covered by the conjunctiva which is a clear mucous membrane that helps lubricate the eye.
5. Retina
The retina lines the posterior portion of the eye, terminating in the ora serrata. It has photoreceptor cells which process light signals and uses the optic nerve to transmit these signals to the brain. The macula is located in the centre part of the retina and central to this is a depressed area called the fovea. This area is highly pigmented and is responsible for processing images in detail. Both this article and this article are useful resources on the retina.
6. Optic nerve
The optic nerve is a bundle of nerve cells that transmit sensory information from the retina to the brain. The optic disc is the point where the optic nerve joins the retina. There are no photosensitive cells in this area and so forms a natural blind spot. It is also responsible for the accommodation and light reflexes which cause the lens and the iris to change shape. The blood supply to the retina is provided by the central retinal artery and vein which travel through the optic nerve.
7. Choroid
The posterior portion of the uvea is called the Choroid. The uvea is the layer that falls between the sclera and the retina. It also comprises the ciliary body and the iris. The choroid is highly vascular and provides oxygen and nutrients to the retina. It is also responsible for temperature and pressure regulation.
8. Ciliary zonules
Ciliary zonules are the suspensory fibres which hold the lens in position. They anchor the lens to the ciliary body which contracts and relaxes to change the shape of the lens to alter focus. There are three types of zonules; zinn zonules stretch from the cilliary body to the lens, vitreous zonules join the vitreous body to the lens and the pars plana zonules attach the ciliary body at the edge of the retina (the pars plana) to the ciliary body. The images in this article clarify the positions and functions of the ciliary zonules.
9. Ciliary body
The part of the uvea between the choroid and the iris is the ciliary body. It includes ciliary muscles which contract and relax, loosening and tautening the ciliary zonules to change the shape of the lens. This is known as the accommodation reflex. It is also responsible for producing aqueous and vitreous humour. This is the clear fluid in the eye that both aids in providing nutrients to the surrounding tissues and maintains pressure in the eye. This resource has information on the ciliary body in addition to some striking photos of eye anatomy.
10. Ora Serrata
The ora serrata is the peripheral termination of the retina. It is serrated in shape and marks the junction from the ciliary body to the retina. The pars plana is the part of the ciliary body adjacent to the ora serrata. It is the attachment site of pars plana zonules, which contribute to shape changes in the lens.
