Our eyes are probably the most important vital structures we have in our body. They discovered on the surface by a thin layer of skin and soft tissue called the eyelids. The eyelids serve multiple purposes including protecting the eyeball from injury, controlling the amount of light that enters the eye and also constantly lubricating the eyeball with tears secreted by the lacrimal gland during blinking. All these functions together help maintain the structural integrity of the eyeball and protect them from external influences.
From an anatomical point of view, the eyelid consists primarily of skin, underlying soft tissue also called a subcutaneous tissue and a thin layer of muscle called the orbicularis oculi. Under this muscle are other issues that divide the area into different planes. These are called septum and include the fibrous orbital septum and tarsi. In addition to this, in order for the eyelids to open are lid retractors that help assist blinking. Finally, there also exists a small amount of fat tissue as well. The eyeball is covered by a thin layer of tissue called the conjunctiva.
The description above only offers a superficial overview of the anatomy of the eyelid. If one were to look at the eyelid in a more detailed manner, a sagittal section taken across the eyelid will offer a clear view of the various structures that form it. Of course, it must be borne in mind that the structures that are visualised depend on the plane at which the sections are taken.
As mentioned above, the tissues can be divided into planes by structures called the septum. The orbital septum differentiates the orbital tissue from the lid. Behind the septum are a number of different other structures, a knowledge of which is essential if surgery is to be performed. In particular, it is essential to identify the anterior and posterior lamellae. In essence, the anterior lamella consists of the skin and the orbicularis oculi muscle while the posterior lamella consists of the conjunctiva and the tarsus.
Let’s take a look at the structures of the eyelid in a bit more detail.
|Muscle||Innervation||Primary function||Secondary function||Tertiary function|
|Levator palpebrae superioris||Oculomotor nerve||Elevation of the superior (upper) eyelid|
|Superior rectus||Oculomotor nerve||Elevation||Intorsion||Adduction|
|Inferior rectus||Oculomotor nerve||Depression||Extorsion||Adduction|
|Lateral rectus||Abducens nerve||Abduction|
|Medial rectus||Oculomotor nerve||Adduction|
|Superior oblique||Trochlear nerve||Intorsion||Depression||Adduction|
|Inferior oblique||Oculomotor nerve||Extorsion||Elevation||Adduction|