Eye Anatomy

Eye anatomy can be pretty intimidating when seeing it for the first time. However, when we break it down into varying sections, we can start learning this anatomy bit-by-bit and working out what the different parts of the eye do.

Human Eye Anatomy

Fig. 1 - Overview of eye anatomy

The human eye is slightly different anatomically compared to other animals and primates. The most significant difference between human eye anatomy and the anatomy of other animals is that our eyes have three distinct colours. We have our:

• sclera - the white area on our eyeball
• iris - the part of your eye that determines your eye colour
• pupil - the black part in the centre

Eyeball Anatomy

The anatomy of the eyeball can be divided into the external eye anatomy and internal eye anatomy. We will detail the anatomy of these two different sections in the 'external eye anatomy' and the 'internal eye anatomy' sections.

The anatomy of the eye follows the function of the eye; when we understand the function of the eye, we can understand its anatomy. The eye's primary role is as a sensory organ. It sends information to the brain so that we can interact with our environment. For this reason, the eye needs to have photoreceptors. These are the cone cells and rod cells found in the retina, which are broken down by light so that a message can be transmitted to the brain. Now that we understand the role of these photoreceptors, we can understand why the different aspects help to focus and refract light onto the retina (where the photoreceptors are found).

The eye also plays an important immune function. The conjunctiva and sclera protect the eye but also help to produce tears and mucus. These tears contain an enzyme called lysozyme, which helps to break down pathogens such as viruses and bacteria.

We can break down each part of the eye into whether it plays a role in maintaining the eyeball's shape, protecting the body from microbes, or whether it helps in refracting light and sending the message to the brain.

External Eye Anatomy

The external eye refers to the parts of the eye that are visible outside the body. You can see these parts of the eye when looking at someone's eye. We will break down each of the features of the eye and describe their function.

There are many functions carried out by the external eye, including refraction. This is important as it allows our eye to ensure that light hits the correct part of the inner eye (the retina) to send clear messages to the brain via the optic nerve.

Table 1. The structures of the external eye

Accommodation

Accommodation is vital as it helps us to adjust our focus to objects at different distances.

To achieve this, two components of the eye are required. These are the ciliary muscle and the suspensory ligaments of the eye. The ciliary muscle is a circular ring of muscle that surrounds the lens; suspensory ligaments attach the lens and ciliary muscle.

The ciliary muscles and suspensory ligaments work in an antagonistic way. This means that when one contracts, the other relaxes. When our ciliary muscles contract, the suspensory ligaments slacken (relax) and vice versa. Let's have a look at what happens when the ciliary muscles relax and contract;

• When the ciliary muscle relaxes, it becomes wider. This causes the suspensory ligaments to tighten, which pulls the lens thinner. The ciliary muscle relaxes, and suspensory ligaments become taught when we focus on a distant object.

• When the ciliary muscle contracts, it becomes smaller. This causes the suspensory ligaments to slacken, which causes the lens to return to a thicker shape. This sequence of events happens when we focus on a nearby object.

Fig. 2 - Pupil dilation and constriction

Internal Eye Anatomy

We can split the aspects of the internal eye into different categories depending on their function. The aqueous and vitreous humour plays a role in maintaining the eyeball's shape. The retina, lens, and optic nerve are essential in vision, as they help refract light and send a message to your brain.

Fig. 3 - Refraction of light to the retina

Table 2. Structures of the internal eye

Eye Anatomy Diagram

Now that we have discussed the internal eye anatomy and the external eye anatomy, make sure you can label these different areas of the eye on a blank diagram.

Fig. 4 - Overview of eye anatomy