The anatomy of the eyes, eyelids and eye sockets

Orbita (eye socket)

The eye socket is a bony structure that houses the eye. The bottom consists of several bones, including the cheekbone (os zygomaticum) and the upper jaw (maxilla). The eye socket then has a lateral wall formed by the cheekbone (os zygomaticum) and sphenoid bone (os sphenoidale), a medial wall consisting of the ethmoid bone (os ethmoidale), lacrimal bone (os lacrimale) and the upper jaw (maxilla) and an upper wall formed through the frontal bone (os frontale) and the sphenoid bone (os sphenoidale).

Bulbus oculi (eyeball)

The bulbus oculi, the eyeball, has an axis length of approximately 24 millimeters and is located in the orbita, the eye socket. The eyeball contains several structures that contribute to the function of the eye. The eyeball consists of three layers. From the outside in, these are the tunica fibrosa, tunica vasculosa and tunica interna.

• Cornea is the transparent, spherical front part of the eye that transmits light and helps the eye focus.
• Sclera (hard sclera) The sclera is the white outer layer of the eye. This connective tissue layer provides protection and strength. The sclera merges into the cornea at the front of the eye.
• Anterior chamber The anterior chamber is a space filled with aqueous humor between the cornea and the iris.
• Iris The colored part of the eye is the iris. It regulates the size of the pupil and thus the amount of light entering the eye.
• Pupil The black part of the eye, in the center of the iris, ensures that light travels to the lens.
• Lens The lens is a transparent structure behind the iris that further bends light and focuses it on the retina.
• Retina (retina) The retina consists of rods and cones.
  • Rods: sensitive to light and dark. Help with night vision and peripheral vision.
  • Cones: sensitive to color and details. Help with color vision and central vision.
• Fovea Contain the highest concentration of cones, essential for clear vision.
• Macula (yellow spot) This is the central part of the retina responsible for sharp and detailed vision.
• Papilla (blind spot) The optic nerves converge at the blind spot and leave the eyeball.
• Uvea The uvea is located between the sclera and the retina. The uvea contains cells that produce pigment, melanocytes.
• Choroid (choroid) This vascular layer lies between the sclera and the retina and provides nutrition and oxygen to the eye.
• Ciliary body (radiating body) The ciliary body is the thickening that is just before the transition from the choroid to the iris.
• Vitreous humor This is a transparent gelatin substance that fills the largest space within the eye and gives shape to the eye.

Innervation (optic nerves and muscles)

The eye contains several nerves that are essential for the functions of vision, eye movements and reflexes. The major nerves involved in the eye are:

• Optic Nerve (Nervus Opticus): Responsible for transporting visual information from the retina to the brain. The optic nerve begins at the retina, passes through the eye socket and partially crosses at the optic chiasm before reaching the visual cortex in the brain.
• Eye movement nerves These nerves control the muscles that control the movements of the eye:
  • Oculomotor nerve (III): Controls four of the six extrinsic eye muscles (the superior, medial, and inferior rectus muscles, and the inferior oblique muscle), and the muscle that lifts the upper eyelid (levator palpebrae superioris). It also innervates the muscles that control pupil size and lens shape for accommodation. The Oculomotor Nerve runs from the brain stem through the eye socket to the eye muscles.
  • Trochlear nerve (IV): Innervates the superior oblique muscle, which rotates the eye downward and inward. The Trochlear Nerve runs from the brainstem through the eye socket to the superior oblique muscle.
  • Abducens nerve (VI): Innervates the lateral rectus muscle, which moves the eye outward. The Abducens nerve runs from the brainstem through the eye socket to the lateral rectus muscle.
  • Trigeminal nerve (V): Provides sensation to the face and has a branch (ophthalmic nerve) that supplies sensation to the front of the eye, eyelids and conjunctiva. The ophthalmic nerve, a branch of the trigeminal nerve, divides into several branches that run through the eye socket and provide sensory information to the eye and the environment.
  • Facial Nerve (VII): Innervates the orbicularis oculi muscle, which is involved in closing the eyelids. The Facial Nerve runs from the brain stem through the face and supplies the facial muscles with nerve signals.
• Sympathetic and parasympathetic fibers:
  • Sympathetic Fibers: Regulate pupil dilation and eyelids.
  • Parasympathetic fibers: Control pupillary constriction and accommodation via the oculomotor nerve.

These nerves work together with muscles to coordinate the movements of the eye. Eye movements are controlled by six extra ocular muscles:

• Rectus superior: lifts the eye upwards.
• Inferior rectus: turns the eye downwards.
• Rectus medialis: moves the eye towards the nose.
• Rectus lateralis: moves the eye towards the temple.
• Superior oblique: moves the eye downward and outward.
• Inferior oblique: moves the eye up and out.

Fat pads

Fat in the eyelids are natural fat pads located in both the upper and lower eyelids. These fat pads have a protective function and provide support to the eyes. However, for a variety of reasons, these fat pads can become more visible and cause cosmetic problems.

• Aging As we age, the skin and muscles around the eyes lose their elasticity and strength. This can cause the fat normally supported by these structures to protrude, causing the eyelids to appear swollen or swollen.
• Genetics Hereditary factors play an important role in the formation of fat pads in the eyelids. Some people are naturally more prone to accumulating fat in this area.
• Fluid retention Fluid retention, often caused by factors such as lack of sleep, high salt content in the diet, allergies or hormonal changes, can lead to swollen eyelids.
• Lifestyle An unhealthy lifestyle such as excessive alcohol consumption, smoking, stress and insufficient sleep can contribute to the formation of swollen eyelids.

For cosmetic or functional reasons, you may choose to surgically remove fat from the eyelids. This is also called blepharoplasty.

• Cosmetic reasons for blepharoplasty:
  • Excess fat causes a puffy or puffy appearance of the upper and/or lower eyelids.
  • Drooping eyelids that give a tired or older-looking look.
  • Bags under the eyes that do not appear to be resolved with other treatments.
• Functional reasons for blepharoplasty:
  • Excess skin and fat that limits vision by hanging over the eyelashes.
  • Eye irritation from excess skin rubbing against the eyelids.
  • Difficulty wearing glasses or contact lenses due to excess fat and skin.

Superior/inferior palpebra (eyelids)

The eyelids are thin folds of skin that protect the eye from dirt and light and help keep the surface of the eye moist. The anatomy of the eyelids can be divided into several layers and components:

• Skin The skin of the eyelids is the thinnest on the entire body and contains no subcutaneous fat. The eyelid is a thin, elastic skin.
• Subcutaneous tissue There is a thin layer of connective tissue under the skin. This layer connects the skin to the underlying muscles.
• Muscles The eyelids are mainly moved by the Musculus Orbicularis Oculi and the Musculus Levator Palpebrae Superioris.
  • Musculus Orbicularis Oculi: This muscle is responsible for closing the eyelids. It plays a crucial role in blinking, which is essential for spreading tears across the surface of the eye and removing small particles and dust. The orbicularis oculi muscle consists of three parts:
    1. Pars Palpebralis: produces soft blinking.
    2. Pars Orbitalis: ensures strong closing of the eyelids, such as in bright light or when protecting the eye.
    3. Pars Lacrimalis: Helps pump tears into the lacrimal duct system.
  • Musculus Levator Palpebrae Superioris This muscle is responsible for lifting the upper eyelid, which is essential for opening the eye.
  • Musculus Tarsalis Superior (Müller’s Muscle) This is a smooth muscle that contributes to opening the eye. It plays a role in maintaining eyelid position during wakefulness. Dysfunction of this muscle can lead to ptosis (drooping eyelid).
• Tarsal plate This is a firm but flexible structure that shapes the eyelid.
• Conjunctiva The conjunctiva is a thin, transparent mucous membrane layer that covers the inner surface of the eyelids and extends to the surface of the eye. This layer helps protect and moisturize the eye.
• Glands
  • Meibomian Glands: The Meibomian glands lie in the tarsal plate that produce oil to keep the tears stable and prevent dehydration.
  • Sebaceous glands (Zeiss glands): drain further into the hair follicles of the eyelashes.
  • Sweat glands (Moll’s glands): drain further into the hair follicles of the eyelashes or directly on the skin surface
  • Eyelashes: The eyelashes run along the edge of the eyelid and protect the eye from dirt and small particles.

Glandulae lacrimales (lacrimal glands)

The lacrimal glands (glandulae lacrimales) are an important part of the lacrimal system and play a crucial role in the production of tears. The lacrimal glands are located in the upper outer corners of the eye sockets, just above the eyeballs. Each lacrimal gland is about the size of an almond and consists of two parts: a larger orbital (eye socket) lobe and a smaller palpebral (eyelid) lobe. The main function of the lacrimal glands is the production of tears. Tears are essential for the ocular surface, supplying nutrients and oxygen to the outer layers of the eye, and removing dirt and microorganisms. The composition of tears consists of:

• An oily (lipid) layer.
• An aqueous (aqueous) layer.
• A mucus-like (mucin) layer.

The production of tears is regulated by both the autonomic nervous system and reflex mechanisms.

• Basal tear production occurs continuously to keep the eye moist.
• Reflex tears are produced in response to eye irritation such as dust, smoke, or strong emotions (crying).

The entire system of eyes, eyelids and eye sockets work together to receive, process and protect visual information. This is crucial for vision.