Anatomy of the eyelid
The eyelids are very important for the protection and healthy function of the eye. Before a clinical assessment is explained we briefly look at the normal anatomy of a lid.
The eyelid is composed of several layers as shown in the cross-sectional view in the image above.
- A - On the outside of the eyelid is skin which meets the palpebral (also known as the tarsal) conjunctiva (E) at the lid margin (B)
- B - The eyelashes are at the lid margin. They point forward, away from the eye.
- C - Underneath the skin is a layer of muscle called the orbicularis oculi. This is important for closing the eyelid.
A+C - These layers together are called called the “anterior lamella”.
- D - Behind the orbicularis oculi muscle is a layer of dense connective tissue called the tarsal plate. This gives the eyelid its shape and rigidity.
- E - The palpebral (or tarsal) conjunctiva lines the inner surface of the eyelid. It provides a moist smooth surface to rest against, and protect, the surface of the eye.
D, E - Together the tarsal plate and the palpebral (tarsal) conjunctiva form the “posterior lamella” of the eyelid
Changes to eyelid anatomy caused by trachoma
In trachoma the posterior lamella and lid margin become scarred and contract. This mostly affects the upper eyelid. The lid margin and eyelashes can be pulled and turn inwards so that they touch the eyeball. This is known as trachomatous trichiasis (TT). As the person blinks, their inturned eyelashes can rub against the cornea causing pain and eventually damaging the cornea, making it opaque and causing vision loss. This is known as corneal opacity (CO).
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