Читать книгу Essentials of Veterinary Ophthalmology - Kirk N. Gelatt - Страница 29

The orbital fascia consists of a thin, tough connective tissue lining that envelops all the structures within the orbit, including the bony fossa itself. This fascia consists of three anatomical components: the periorbita, Tenon's capsule or fascia bulbi, and the EOM fascial sheaths (Figure 1.7). Orbital surgery is usually confined within these fascial tissues or beneath it.

Figure 1.5 (a) Canine orbit. (b) Feline orbit. Bones of the orbit: frontal (F), lacrimal (L), maxilla (M), sphenoid (S), temporal (T), and zygomatic (Z). Orbital foramina: rostral alar (A), ethmoidal (E), optic (Op), and orbital fissure (Or).

Figure 1.6 Equine orbit. Bones of the orbit: frontal (F), lacrimal (L), sphenoid (S), temporal (T), and zygomatic (Z). Orbital foramina: rostral alar (A), ethmoidal (E), optic (Op), orbital fissure (Or), and supraorbital (So).

The periorbita is a conically shaped, fibrous membrane that lines the orbit and encloses the globe, EOMs, blood vessels, and nerves. The apex of the periorbita is located where the optic nerve exits the orbit and continuous with the dural sheath of the optic nerve. In the orbit, it is thin, attaches firmly to the orbital bones, and forms their periosteum. In the dog, the periorbita does not always fuse with the periosteum of the frontal and the sphenoid bones. In animals with an incomplete lateral orbital wall, the periorbita is thicker laterally next to the orbital ligament. Anteriorly, in the dorsolateral part of the orbit, the periorbita separates and surrounds the lacrimal gland. At the orbital rim, it divides into one part becoming continuous with the periosteum of the facial bones and the other, that is, the septum orbitale, merging with the eyelids and becoming continuous with the tarsal plates (the fibrous sheet in the eyelids). Within the periorbital tissue of carnivores (dogs and cats), smooth muscle has been observed along the lateral wall of the orbit, portions of the roof and floor of the orbit, and next to the periosteal lining of orbital bones, and contraction of the muscle has been produced by stimulation of the cervical sympathetic nerve trunk and results in forward movement of the globe.

Table 1.5 Foramina and associated nerves and blood vessels.

Foramen or fissure	Species	Associated nerves and vessels
Alar, rostral	Canine, equine, feline	Maxillary artery and nerve
Ethmoidal (one or more)	All species	Ethmoidal vessels and nerve
Orbital	Canine, equine, feline	Abducens, oculomotor, ophthalmic, and trochlear nerves
Orbitorotundum	Bovine	Cranial nerves III–IV, retinal and internal maxillary arteries
Optic	All species	Optic nerve, internal ophthalmic artery
Rotundum	Canine, equine, feline	Maxillary nerve
Supraorbital	Bovine, canine, equine (feline variable)	Supraorbital vessels and nerve
Caudal palatine	All species	Major palatine vessels and nerve
Maxillary	All species	Infraorbital vessels and nerve
Sphenopalatine	All species	Sphenopalatine vessels and pterygopalatine nerve

Figure 1.7 Divisions of orbital fascia: muscle fascia, periorbita, orbital septum, and Tenon's capsule.

Tenon's capsule (fascia bulbi) is connective tissue on the outer aspect of the sclera. Tenon's capsule is separated from the sclera by a narrow, cleft‐like space filled with loose connective tissue, Tenon's space. Tenon's capsule is attached to the sclera near the corneoscleral junction (i.e., limbus), and it becomes continuous with the fascia surrounding the EOMs. The fascial sheaths of the EOMs are dense, fibrous membranes loosely attached to the muscles with fine trabeculae of connective tissue. These sheaths are continuous with, or reflections of, Tenon's capsule, but they are not always considered part of it.