ANATOMY & FUNCTIONS OF THE EYE

Eye globes sit in two bony sockets called the orbits of the skull. Within the orbit, the eye globe is embedded in orbital fat for protection. It is then enveloped in a membrane called the Tenon's capsule that keeps it separate from the orbital fat while also allowing it to move freely. The eye globes are moved in different directions by four rectus and two oblique muscles.

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Functions of the Eye

The eye itself is a highly complex organ. Here are some of the primary elements and their functions: 

  • Conjunctiva

  • Cornea

  • Iris

  • Lens

  • Macula

  • Optic Nerve

  • Pupil

  • Retina

  • Vitreous Humour

CONJUNCTIVA

This is the mucous membrane that lines the inner surface of the eyelids.

CORNEA

The transparent, domed portion of the eyeball that covers the iris and pupil. It acts like a window, letting light into the eye.

IRIS

The iris is a muscular diaphragm that is suspended in the front lens of the eye. It's deeply pigmented and designed to exclude light, except through the pupil.

MACULA 

Located behind the pupil, the lens focuses incoming light rays onto the retina.

OPTIC NERVE

This is the sensory nerve that carries electrical impulses from visual stimuli received by the retina. The end destination is the brain. 

PUPIL

Located in the iris, the pupil is designed to let light pass through to the lens of the eye.

RETINA

This is a layer of nervous tissue covering the back of the eyeball. Light hits the tissue and initiates an electrochemical reaction in which electrical impulses are transmitted to the brain.

VITREOUS HUMOUR

This is the gelatinous mass that occupies the space between the lens and the retina. It is composed of 99% water.

VISION

The eye is a complex optical system, very similar to a camera. Vision begins when light enters the eye through the cornea, a powerful focusing surface. Light then travels through clear aqueous fluid and passes through the pupil. As muscles in the iris relax or constrict, the pupil changes size to adjust the amount of light entering the eye. When light rays finally land on the retina - the part of the eye similar to film in a camera - they form an upside-down image. The retina converts the image into an electrical impulse that travels along the optic nerve to the brain, where it is interpreted as an upright image.

Vision is affected if the cornea becomes thickened and loses its transparency. Corneal thickening occurs as a result of swelling or fluid build-up in the cornea. This can occur after the eyes have been closed, or have had pressure applied to them for a period of time. Once the eyes have been opened, the air dehydrates the cornea reducing its thickness and therefore normal vision.

THE ANATOMY OF THE EYELID

The eyelid is a thin fold of skin that covers and protects the eye. It is extremely thin and includes a row of eyelashes along its margin.

The anatomy of an eyelid is more complex than most people perceive. Here are the key components:

  • Canthus (medial and lateral)

  • Cilia glands

  • Eyelashes (cilia)

  • Lacrimal puncta

  • Levator muscle

  • Meibomian glands

  • Orbicularis oculi muscle (palpebral or orbital)

  • Palpebral fissure

  • Upper eyelid crease

CANTHUS (MEDIAL AND LATERAL)

This is the point where the eyelids fuse together. The point nearest the nose is the medial canthus. The point nearest the ear is the lateral canthus.

CILLIS GLANDS

These are located near to where the eyelashes are connected to the eyelid margins. They are a type of sudoriferous gland.

EYELASHES (CILLIA)

The eyelashes are attached to the margins of the eyelids.

LACRIMAL PUNCTA

These are found on the eyelid margin, just before the medial canthus.

LEVATOR MUSCLE

This is responsible for opening the eye. It starts deep in the eye socket, extends over the top of the eye and then turns into a tendon.

MEIBOMIAM GLANDS

These secrete the lipid part of the tear film.

ORBICULARIS OCULI MUSCLE (PALPEBRAL OR ORBITAL)

This muscle closes the eye.

PALPEBRAL FISSURE

This is the empty space between the upper and lower eyelid margins when the eyelids are open.

UPPER EYELID CREASE

This is the indentation extending across the upper eyelid. It may be poorly formed or even absent in some instances.

EYELID FUNCTION

Eyelids are designed to cover and protect the eye. In conjunction with eyelashes, they protect it from dust, foreign bodies and perspiration. The eyelids are also responsible for spreading tears on the eye itself, to keep it moist and provide a protective covering.

THE ANATOMY OF THE EYELASHES

There are three types of hair that are found on the body:

VELLUS HAIRS

Soft, fine downy hairs found all over the body with the exception of the palms of the hands, soles of the feet, lips and eyelids. They are usually non-pigmented, depending on ethnicity.

TERMINAL HAIRS

Thicker coarse hairs that are highly pigmented and designed to protect, as in the case of the eye lashes, which protect from the sun and from objects entering into the eye. They can also be found on the head, inside the nose, brows, under arms, legs and public region.

INTERMEDIATE HAIRS

These develop from vellus hairs during puberty and are deeply rooted, pigmented and coarse. They're the type of hair that's often removed from unwanted areas.

EYELASH HAIRS

Every eyelash hair consists of three main regions and three primary layers. The main regions are the root, shaft and tip:

ROOT - the part that grows in the follicle. It is the widest part of the eyelash.

SHAFT - the middle length of the eyelash. It is where the eyelash begins to taper.

TIP - the end of the eyelash, the point at which it is at its thinnest.

The three primary layers of the hair are the:

  • Cuticle

  • Cortex

  • Medulla

INTERMEDIATE HAIRS

This is the outer layer of the hair and is made of keratin. Under a microscope, it looks like a series of overlapping scales. Keratin is extremely hard and durable and its main function is to protect the inner layers of the hair. If the hair is over-processed, the cuticle will become damaged and the health of the hair is compromised.

THE CORTEX

This middle layer of the hair is made of large elongated cells containing melanin, giving the hair its colour. The cortex also contains moisture and therefore is reliant on the cuticle to maintain hydration levels in the hair.

THE MEDULLA

The inner layer is lade of cells that form a shaft up the middle of the hair. It serves no particular function and is often lacking in the fine vellus hairs.

EYELASH PLACEMENT

Each eyelid contains eyelashes and each is anchored into a root hair plexus. Unlike normal hairs, this gives eyelash hairs extra sensitivity, meaning they can cause the eye to reflexively snap closed if a foreign body reaches the eye. Eyelashes tend to graduate in length, being longest towards the centre of the eye and shorter towards the outer corners.

From a lash technician's perspective, it's important to note that the lashes on the upper lids and lower lid lashes tend to be thicker, longer, more numerous and curve in an upwards direction. The lashes on the lower lid, by contrast, are shorter and can have little or no curve.

EYELASH PLACEMENT

As a lash technician, a thorough understanding of the lash lifecycle is vital. All human hair, including eyelashes, follows three distinct phases:

  • Anagen

  • Catagen

  • Telogen

THE LASH LIFECYCLE

This is the 'active' growth phase of an eyelash. It takes 30-45 days (4-6 weeks) for each lash to reach its full length. This might seem like a long time for an eyelash, but in fact its extremely short compared to head hair, which can keep growing for a number of years. This is also why eyelashes do not grow as long as head hair - their anagen phase is too short for them to grow any longer.

At any one time. it's estimated that up to 40% of our eyelashes are in the anagen phase. When applying lashes, that means that 1 in 3 lashes on every eyelid are likely to still be growing in length.

CATAGEN PHASE

Also known as the 'transition' phase; while in the catagen phase the hair follicle shrinks. Although the hair itself stops growing at the end of the anagen phase due to it becoming detached from the dermal papilla, which is its source of nourishment, the shrinking of the hair follicle can cause the hair to be pushed upwards, giving the impression of growth. For eyelashes, this phase is thought to last 2-3 weeks and approximately 20% of hairs will be in the catagen stage.

TELOGEN PHASE

The hair is dormant during the telogen phase, which is why this is also known as the 'resting' phase. This phase can last up to 100 days. Although the hair itself is not changing during this period, the hair follicle is. Initially, the epidermal cells lining the follicle channel continue to grow and accumulate, anchoring the hair in place. Towards the end of the telogen phase, the follicle begins to grow again. This causes the anchor point in the follicle to soften, causing the hair to break free. It takes approximately two weeks after the hair is shed for the anagen growth phase to commence and for another hair to start growing. Approximately 40% of lashes will be found to be in the telogen phase.

TELOGEN PHASE

All three phases can occur at the same time, meaning that some eyelashes can be growing at the same time as others are ready to shed. Whilst approximately 40% of upper lashes are in the anagen phase at any one time, it's estimated that we all lose a few eyelashes every day. Identifying whether the lash is at the start or end of its life cycle is critical for understanding whether a lash extension should be applied to it. For example, if a technician applies extensions to lashes only in the telogen phase, then the client is likely to see increased lash extension loss.

This perception can also sometimes be exaggerated because the client will be very aware of their new lashes, so any lashes that have dropped out are far more visible because they've been extended. This can occasionally cause clients to think that the lashes have dropped out as a result of the treatment, when in fact they were simply at the end of their lifecycle. That's why we recommend explaining the lash lifecycle to clients during consultation.

Functions of the Eyelids

Function of Eyelashes