2.3 Anatomy of the eyelash

Now that we have a firm grasp on the eyelid and a few of its more unique characteristics, lets progress to an in-depth examination of that which will be your canvas for many years to come: the eyelash.

Not just any strand of hair

Far from simply serving an aesthetic purpose, eyelashes perform a number of important functions as the first line of defence for the eye. In addition to keeping out small foreign objects like dust and insects, they also act to shield the eye from the elements: wind, rain and sunlight. Perhaps the most interesting function they perform, however, is to initiate what is known as the ‘protective response’.

Each eyelash is connected at its root to a hair plexus, which is a special group of nerve fibre endings that serve as an extremely sensitive receptor for touch sensation. In a similar fashion to the function of whiskers on a cat or a mouse, when an object touches an eyelash a signal is passed to the brain extremely quickly, warning of a foreign object in close proximity to the eye. In response, the brain reflexively signals the eyelids to close.

Eyelash properties

Similar to other hair on the body and scalp, eyelash hair is comprised of approximately 90 percent proteins (including keratin and melanin) and ten percent water, and receives nourishment from blood vessels within the hair root. However, as we touched on in the previous lesson, that is about where the similarities cease.

Eyelashes are much shorter and finer than scalp hair, with a length of approximately 4–14mm depending on factors such as location (on the eyelid margin), race and age. The upper eyelid houses approximately 80-150 individual lashes arranged in two to four rows. Upper eyelashes are more numerous and longer than lower lashes and curve upward. The lower eyelid will generally contain approximately 70-100 downward-curving lashes.

The lash itself is made up of three layers that fit into one another. These are:

  • the Medulla: innermost structure that consists of loose cells;
  • the Cortex: this makes up the major part of the fibre (90 percent of total weight) and provides the hair’s strength and stability. The pigmentation of the lash is the result of the melanin contained in the cortex; and
  • the Cuticle: the outermost protective layer which comprises of five to ten layers of non-pigmented flattened cells, arranged like tiles on a roof that overlap.

As also touched on in the previous lesson, all eyelashes are characterised by a tendency to grow in a curved shape. The degree of curvature is dependent on the asymmetric distribution of cells as the develop in the root of the lash. Studies on eyelash growth across various races have revealed curvature is most apparent in the African race, followed by Caucasian, and least in Asians.

Each eyelash extends approximately 2mm into the eyelid, and grows at a rate of approximately 0.15mm per day. Within the root of both upper and lower eyelash follicles exist two types of secretory glands that are critical for lash and eye health: the sebaceous glands of Zeis and the apocrine (sweat) glands of Moll. Secretions from these glands protect both the surface of the eyelid and the eye.