Diseases of the appendages of the eye - specialists and information

The appendages of the eye, which include the lacrimal gland, the tear ducts, the conjunctiva, the eyelids and the eye muscles, can be affected by various diseases and impairments. Below you will find further information and selected specialists for diseases of the appendages of the eye.

Appendages of the eye

The appendages of the eye refer to some body parts attached to the eye that supply, control and protect the eye.

• Lacrimal gland: Produces lacrimal fluid, which is conducted through a system of ducts and vessels and serves to supply and cleanse the eye
• Draining tear ducts: Tear fluid is absorbed on the inside of the eyelid via the superior and inferior lacrimal puncta, drained into the lacrimal sac via the superior and inferior lacrimal tubules such as the common lacrimal duct and into the nose via the nasolacrimal duct.
• Conjunctiva: Mucous membrane on the inside of the eyelids, which lies on the actual eyeball
• Eyelid: Consists of muscles, connective tissue and skin. It serves to protect the eye and distributes the tear fluid over the front surface of the eyeball with each blink with the help of the conjunctiva
• Eye muscles: Four straight and two oblique eye muscles move the eyeball in any direction

These appendages of the eye make up an extremely complex apparatus, the intricate interplay of which makes the astonishing performance of the eye possible.

The lacrimal apparatus of the eye

The lacrimal apparatus of the eye is responsible for the production of tear fluid as well as its transportation and drainage. The most important part of the lacrimal apparatus is the lacrimal gland. It produces the tear fluid and channels it to the surface of the eye. It also includes the lacrimal puncta, the lacrimal tubules and the lacrimal sac with the nasolacrimal duct, which drains the fluid to the nasal cavity.

Lacrimal gland (a) and lacrimal ducts: b = upper lacrimal punctum. c = upper lacrimal duct. d = lacrimal sac. e = lower lacrimal duct. f = lower lacrimal duct. g = nasolacrimal duct

The lacrimal gland as the central part of the lacrimal apparatus

The lacrimal gland (from the Latin glandula lacrimalis) is located in the upper outer part of the eye socket. It produces most of the lacrimal fluid (there are also many small glands in the lid margin and mucous membrane). The lacrimal gland releases its secretion via ducts to the conjunctiva and the surface of the eye. The secretion of this gland contains electrolytes and various protein compounds. The lacrimal fluid is guided into the vault of the conjunctival sac via 6-12 ducts and distributed over the cornea by blinking.

In this way, the lacrimal gland keeps the cornea moist and nourishes it. The glands release the secretion involuntarily. They are controlled by the autonomic nervous system and feedback mechanisms. Hormones are usually also involved.

Depending on the secretion, a general distinction is made between three different types of glands: mucous (viscous), serous (watery) or mixed (mucosal, seromucous) glands. The lacrimal gland of the appendage of the eye is a purely serous gland, which means that it only secretes watery secretions.

Impairment and disease of the lacrimal gland

Overproduction of the secretion can lead to eye watering. Causes of overproduction can be

• Mechanical irritation of the sensitive nerve endings of the eye, often the cornea: If the cornea registers a foreign body, the eye must be rinsed with tear fluid
• Healing of a disease of the cornea or conjunctiva
• Emotional stimuli (crying)
• Disturbance of tear drainage (no overproduction of the lacrimal gland)

It is also possible that too little tear fluid is produced: this is known as dry eye. Tear substitutes, which must be used regularly, often help here.

Inflammation of the lacrimal gland is relatively rare. The technical term for this is dacryoadenitis. Pressure pain occurs, the upper eyelid is swollen and reddened. The causes can vary greatly, but they are usually self-limiting, i.e. the inflammation resolves itself completely without treatment.

The conjunctiva of the eye

The conjunctiva is a transparent mucous membrane located on the inside of the eyelids and directly on the eyeball. It acts as a mobile equalizing layer that allows eye movement. It also serves as the boundary layer of the human immune system, i.e. this is where the recognition of and defense against pathogens and other intruders takes place.

The cavity enclosed by the conjunctiva of the eye is called the conjunctival sac. On the nasal side of the conjunctiva of the eye is a fold called the nictitating membrane or third eyelid. In humans, this fold of the conjunctiva of the eye is very small. In other mammals, it is so large that it can lie over the eye. Some vertebrates can slide the nictitating membrane over the entire eye like a transparent protective cover (reptiles, birds).

The function of the conjunctiva is to protect the eye. It sits like an outer covering over the eye and contributes to the tear film through small glands (accessory lacrimal glands).

Diseases of the conjunctiva of the eye

The conjunctiva of the eye is thin, pigment-free in Caucasians and well supplied with blood. The coloration of the conjunctiva of the eye can therefore be used to recognize many things.

Reddening of the conjunctiva indicates conjunctivitis. The cause may be irritation due to a foreign body in the eye and therefore the conjunctiva. However, a bacterial or viral infection as part of the so-called eye flu (keratoconjunctivitis epidemica) is also a possibility. Allergic conjunctivitis, better known as hay fever, is very common.

The following diseases occur far less frequently: If the conjunctiva of the eye is yellowish in color, jaundice (icterus) is suspected. If the conjunctiva of the eye is paler and whiter than normal, anemia (anaemia) must be considered.

The eyelid

The eyelids delimit the anterior eye socket with an upper and lower eyelid. The palpebral fissure between them allows the eye to see outwards.

The eyelid consists of skin, muscles, glands and connective tissue. As the lower and upper eyelids come together synchronously (blinking), the two eyelids can completely cover the eye and thus protect it from external influences such as foreign bodies, dirt or light. During sleep, the eyelids are closed.

A person blinks 10-20 times per minute. The permanent blinking of the eyelids always supplies the cornea and the front part of the sclera with sufficient tear fluid. This keeps the eye clean and prevents it from drying out.

The eyelids are connected to the edge of the eye socket by two ligaments and are covered with conjunctiva on the inside.

The eyelids play a significant role in a person's facial expression and facial expressions. Think of wide-open eyes when startled or frightened, of joy, tiredness and sadness.

Mammals have eyelashes on the edges of their eyelids, which are surrounded by several glands. The eyelashes protect the eyelids by keeping out dust and dirt. Some of the glands produce sebum for the eyelids, in this case called "eye butter". This secretion prevents tear fluid from overflowing over the eyelids. Sometimes such dried secretions are found on the inner eyelid in the morning. Other glands on the eyelid produce sweat.

Eyelids, here with pathological fat deposits

Diseases of the eyelids

A pathologically altered eyelid position means that the upper or lower eyelid edge is bent inwards or outwards. This leads to a misalignment of the eyelashes and associated irritation of the cornea.

The eyelid skin can be affected by fat deposits or pigment disorders. The eyelids are known to be susceptible to herpes infections and other inflammations. The sebaceous glands around the eyelids can also be affected by inflammation. This leads to a so-called "sty" or "chalazion" on the eyelids. Inflammation of the edge of the eyelids is often associated with conjunctivitis.

There are a number of movement disorders of the eyelids. Drooping of the eyelid (partially or completely) means that the eyelid cannot be opened normally. This so-called ptosis can have various causes. Muscle disorders or paralysis of the facial nerves can cause the eyelid to droop. A clear distinction must be made between drooping eyelids and drooping eyelids, which are caused solely by sagging skin. These drooping eyelids can be surgically removed by blepharoplasty.

Involuntary twitching of the eyelids can affect one or both eyelids and can last for hours or even days. However, the cause is usually harmless (irritation, fatigue, stress) and often disappears on its own.

A reduction in the frequency of eyelid blinking is known as Stellwag's sign. Increased blinking, on the other hand, leads to frequent blinking and is often caused by mechanical irritation or nervousness.

Tumors of the eyelid are also common. Although many are benign, prompt consultation with an ophthalmologist is strongly recommended.

The eye muscles

The different eye muscles are divided into inner and outer eye muscles according to their position and function.

• Outer eye muscles: Skeletal muscles that control the motor function of the eyeballs
• Inner eye muscles: control the function of the pupil and accommodation (from the Latin "to adapt"). Accommodation is important so that objects at any distance are sharply focused on the retina

Only the outer eye muscles are discussed below.

The outer muscles of the left eye

Humans have four straight and two oblique eye muscles. All but one of the eye muscles originate from the tip of the eye socket and run forward in a funnel shape, where they attach to the sclera of the eyeball. One of the oblique eye muscles originates at the bottom of the orbital wall. The outer eye muscles have a transversely striated musculature with two types of fibers and different nerve supply.

Thick muscle fibers (A-fibers, fibrillar structure) of the eye muscles with large end plates enable rapid eye movements. The eye muscles have a very different structure from other muscles. The outer eye muscles are the most active muscles in the entire human body. They are capable of performing up to three microcascades. A microcascade is a jerky movement of the eyes with an amplitude of 3-50 angular minutes (equivalent to one sixtieth of an angular degree).

The outer eye muscles work together as a unit with retaining ligaments and connective tissue structures. As a result, the outer eye muscles carry out all rotational movements of the eyes in every direction together. This guarantees that both eyes are parallel to each other and focus together on the object to be fixed.

The angle of vision of the eye when the body and head are in a still position is called the molecular field of vision. The field of vision is approx. 50° to the right and left.

As part of the eye muscles, the eyelid retractor ensures that the upper eyelid lifts when looking up and lowers accordingly when looking down. The inner eye muscles are controlled by the autonomic nervous system. They consist of smooth muscles. They control the size of the pupil and adjust the refractive power of the eye.

Disorders and diseases of the eye muscles

If the cranial nerves cannot supply the eye muscles properly, paralysis can occur. Functional disorders of the eye muscles are known as ophthalmoplegia. This results in restricted movement and the associated limitation of the molecular field of vision.

Further effects can be a squint or the occurrence of double vision. The cause of strabismus can also be that the complex interaction of the eye muscles is out of balance. This can have congenital or acquired causes.

Another reason for the loss of function of an eye muscle can be found in the inadequate transmission of stimuli from the nerves to the muscle fibers. Inflammation or damage to the connective tissue are also possible causes.