Eyelids fold due to the interaction between skin, muscle, and connective tissue. The skin and muscle between the eyebrow and the eyelid crease create the eyelid skin fold. The eyelid crease itself is formed by attachments between the skin and the muscle that orbits the eye, specifically the levator palpebrae superioris muscle, which is responsible for lifting the upper eyelid. This connection causes the skin to fold inwards when the eye opens.
Here's a breakdown:
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The Levator Palpebrae Superioris Muscle: This muscle is the primary elevator of the upper eyelid. When it contracts, it pulls the eyelid upwards.
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Connective Tissue Attachments: Fibrous connections extend from the levator aponeurosis (a tendon-like sheet of the levator palpebrae superioris) through the orbital septum to the dermis of the eyelid skin. These connections are what cause the skin to fold inwards as the muscle lifts the eyelid. This creates the characteristic eyelid crease.
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Skin Elasticity: The elasticity of the eyelid skin also plays a role. As we age, the skin loses some of its elasticity, which can affect how the eyelid folds, sometimes leading to a deeper or more pronounced fold.
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Fat Pads: The presence and position of fat pads around the eye can also influence the appearance of the eyelid fold.
The absence of a strong connection between the levator aponeurosis and the dermis can result in a single or absent eyelid crease, common in some ethnicities. Furthermore, the development of multiple folds, sometimes referred to as a "triple eyelid," occurs when the primary eyelid fold divides into two or more folds. This can happen due to aging, changes in skin elasticity, or other factors.
