What is the Ocular Orbit
The ocular orbit is an exocranial conical-pyramidal cavity, which contains and protects the eye.
Many bones of the skull (neurocranium) and of the facial massif (splancnocranium) articulate to form the orbital complex. This bony space therefore represents an anatomical crossroads into which blood vessels, nerve fibers, muscles, tear glands and other annexes converge, essential for the proper functioning of the organ of vision.
The pathologies of the orbit can be vascular, malformative, secondary to diseases of the thyroid (Graves' disease), infectious, traumatic, inflammatory or neoplastic.
Anatomy
Eyeballs and relations with the orbits
The eyes are two spherical formations with an average diameter of 24 mm (for instance, they are slightly smaller than a ping pong ball) and a weight of 8 g. Each bulb occupies the orbital cavity together with the extrinsic muscles of the eye, the lacrimal gland, the cranial nerves and the blood vessels also directed to the adjacent portions of the orbit and to the face. A fat pad (called the adipose body of the orbit) has filling and isolation functions.
Orbital cavities
The orbits are two cavity formations placed at the sides of the midline of the face, below the forehead, consisting of bones of the face and skull, in close correlation with each other.
From the morphological point of view, the orbit is comparable to a quadrangular pyramid, reversed backwards (with the apex back and the base forward), in which it is possible to distinguish:
- Base: represents the outer opening of the orbit. At its formation take part: frontal and sphenoid bone (upper margin); maxillary, palatine and zygomatic (lower margin); ethmoid, lacrimal and frontal bone (medial margin); zygomatic and sphenoid (lateral margin).
- Upper wall : constitutes the vault or roof of the orbit; it is bounded by the lower face of the frontal bone and the lower face of the small wing of the sphenoid.
- Lateral wall : it is formed by the orbital process of the zygomatic bone and by the anterior portion of the great wing of the sphenoid.
- Medial wall : is a sagittal bone plane formed by maxillary and lacrimal bone, lamina papyracea of the ethmoid and lateral face of the body of the sphenoid.
- Lower wall : it represents the floor of the orbit and borders with the upper face of the maxillary body, the upper face of the orbital process of the zygomatic bone and the orbital process of the palatine bone. Because of its thin thickness, the lower wall is the portion most frequently involved in orbital traumas.
- Apex: the posterior orbit of the orbit corresponds to the optical hole, crossed by veins, arteries and the optic nerve; this structure ensures communication between the eye and the middle cranial fossa.
Orifices and openings
The relationship between the bones of the orbital complex, although very narrow, is not absolute; the orbital walls have, in fact, holes and slits that connect this space with the adjacent structures. These openings cross, in particular, the posterior end of the orbital cavity, in correspondence of the apex (optical channel) or are located between the sphenoid and the maxillary bone (upper and lower orbital fissure).
Functions
The orbits perform a function of protection and containment of the ocular structures, as they surround each bulb. They also connect the eyeball to the rest of the body.
Illnesses
Orbital pathologies are generally inflammatory, traumatic, autoimmune or neoplastic. Infiltrative ophthalmopathy caused by Graves' disease is the most frequent cause of orbital disease. The fractures of the orbit represent, instead, about 40% of all the craniofacial traumas.
The most common symptoms determined by the involvement of the orbit in the various pathological processes are represented by pain in eye movements, alterations of the visual field, double vision and decreased vision. Orbital pathologies can also determine an alteration of the normal positioning of the eyeball in the orbit. We can thus observe: exophthalmos (bulbar protrusion), deviation (dislocation of the eye) and enophthalmos (hollowing).
In any case, an accurate eye examination is recommended and often, to confirm the diagnosis, investigations are required such as orbital ultrasound (studies the orbital content), computerized tomography (visualizes the orbital bone walls), nuclear magnetic resonance ( evaluate soft tissues more accurately) and biopsy suspicious lesions.
Inflammatory diseases
The phlogistic reactions involving the structures of the orbit are presented in extremely variable ways, in isolated form or as a condition diffused to several neighboring structures (extrinsic muscles, uvea, sclera, lacrimal glands etc.).
These include dacryadenitis (inflammation of the lacrimal gland), orbital cellulite and myositis of the orbit. In some cases, inflammations can result from underlying systemic diseases (infectious diseases, vasculitis or autoimmune conditions, such as Sjögren's syndrome, sarcoidosis and Wegener's granulomatosis).
The symptomatology includes the sudden onset of pain associated with bulbar movements, periorbital edema, erythema and swelling of the eyelids, proptosis, loss of visual acuity (if there is involvement of the optic nerve) and diplopia ( in case of involvement of extraocular muscles).
Treatment depends on the nature of the inflammatory reaction (non-specific, granulomatous or vasculitic) and may include the administration of non-steroidal anti-inflammatory drugs, oral corticosteroids, radiotherapy or immunomodulatory drugs. Recently, the use of monoclonal antibodies has also been introduced.
Orbital pseudotumor
The orbital pseudotumor (also called idiopathic inflammation of the orbit) is an aspecific and idiopathic inflammation (it is not possible to identify a local or systemic cause). This process is characterized by the infiltration and proliferation of non-neoplastic cells in the mesenchymal tissues of the orbit. It is therefore a space-occupying lesion.
Typical symptoms of orbital pseudotumor include eye pain, redness and palpebral swelling, double vision, exophthalmos and reduced visual acuity.
In more serious cases, inflammation can cause progressive fibrosis that leads to the so-called "frozen orbit", a true fixation of the eyeball characterized by ophthalmoplegia, ptosis and marked visual changes.
Important! Pseudotumor can simulate the symptoms of a neoplasm of the orbit. For this reason, diagnostic tests must absolutely distinguish this pathology from the actual tumor forms.
Orbital cellulite
Orbital cellulitis is an infection of the orbital soft tissues, placed behind the orbital septum. The disease is caused by the extension of infectious processes by contiguity (nasal cavities, paranasal sinuses and dental elements), by the haematogenous diffusion of an infection originating in another site or by the direct entry of pathogenic agents following an orbital trauma which tears the orbital septum (eg animal bites, bruises or perforating lesions). The disease is characterized by an abrupt onset, with fever and a state of general malaise, associated with pain and reduced eye mobility, conjunctival hyperaemia and chemosis, reddening and palpebral and periorbital swelling, visual clouding and proptosis. In many cases, signs of primary infection may also be found (eg nasal discharge and nasal bleeding with sinusitis, periodontal pain and swelling with abscess etc.). The therapy must be timely and uses broad-spectrum antibiotics and, in the most serious cases, surgery.
Presectional cellulite
Preset and orbital cellulitis (postsettal) are two distinct pathologies that share some clinical symptoms.
Preset cellulite is an infection of the eyelid and surrounding skin, located prior to the orbital septum. This periorbital inflammation, in general, begins on the surface with respect to the orbital septum, after the spread of secondary infections to local traumas of the face or eyelids, insect or animal bites, conjunctivitis, calatio or sinusitis. Both are particularly common in children, but the presumption of cellulite is far more frequent than the orbital one.
Other inflammations of the orbit
- Dacrioadenite: inflammation of the lacrimal glands, acute or chronic. Dacryadenitis is common in children, following viral diseases such as measles and rubella. The chronic form is often associated with general diseases such as Sjogren's syndrome, sarcoidosis and Wegener's granulomatosis. Symptoms include fever, eyelid pain and swelling, and unilateral periorbital; a severe swelling can determine the dislocation of the eyeball downwards and inwards. The therapy includes the use of antibiotics, anti-inflammatories and, in the most serious cases, immunosuppressive drugs.
- Myositis of the orbit : non-specific inflammation of one or more extraocular muscles. It occurs at a young age, with eye pain accentuated by bulb movements and double vision. Often, it is associated with palpebral and periorbital edema, redness of the eye, ptosis and mild exophthalmos. The treatment involves the use of steroidal anti-inflammatories and, in the most serious cases, of immunosuppressive drugs.
- Toulouse-Hunt syndrome : idiopathic inflammation (ie of unknown origin) of the cavernous sinus, of the superior orbital fissure and of the orbital apex. It generally manifests with eye pain accentuated by eye movements, double vision and ipsilateral headache. Toulouse-Hunt syndrome may also cause mild exophthalmos and paralysis of the oculomotor nerves. The disorder typically presents with acute phases alternating with periods of remission. The therapy involves the use of steroidal anti-inflammatory drugs.
Orbital tumors
Orbital tumors can be primitive (that is, they originate from the tissues of the orbit) or derive from neoplastic processes affecting contiguous structures (eyeball, ocular appendages, paranasal sinuses and nasopharynx). Furthermore, the orbit may be affected by metastasis.
The symptoms are variable, but typically an expansive orbital process produces protrusion of the eyeball (exophthalmos), palpebral ptosis and double vision (diplopia). If the function of the optic nerve is impaired, a loss of vision can result.
Orbital fractures
A violent trauma can cause fracture of the bones of the facial massif. In many cases, this occurrence involves the involvement of several contiguous bone structures, such as the zygomatic-maxillary, naso-orbito-ethmoid complex and the frontal sinus.
Because of their anatomical location and bone thickness, therefore, the orbital cavities are often involved, especially at the level of their lower wall (orbit floor). In these fractures, various other structures may also be involved: the ocular musculature (rectus and inferior oblique muscle), the eyeball, the optic and infraorbital nerve, the artery and the ophthalmic vein.
The involvement of the orbital complex may be indicated by edema or periorbital ecchymosis, infraorbital nerve anesthesia, enophthalmos, diplopia and alterations of ocular motility. A lesion in the vicinity of the orbit always requires an eye examination, which includes at least the assessment of visual acuity, pupillary reactions and extraocular movements.
