The sclera is perforated by many nerves and vessels passing through the posterior scleral foramen, the hole that is formed by the optic nerve. At the optic disc the outer two-thirds of the sclera continues with the dura mater (outer coat of the brain) via the dural sheath of the optic nerve. The inner third joins with some choroidal tissue to form a plate (lamina cribrosa) across the optic nerve with perforations through which the optic fibers (fasciculi) pass. The thickness of the sclera varies from 1 mm at the posterior pole to 0.3 mm just behind the rectus muscle insertions. The scleras blood vessels are mainly on the surface. Along with the vessels of the conjunctiva (which is a thin layer covering the sclera), those in the episclera render the inflamed eye bright red.In many vertebrates, the sclera is reinforced with plates of cartilage or bone, together forming a circular structure called the sclerotic ring. In primitive fish, this ring consists of four plates, but the number is lower in many living ray-finned fishes, and much higher in lobe-finned fishes, various reptiles, and birds. The ring has disappeared in many groups, including living amphibians, some reptiles and fish, and all mammals.The eyes of all non-human primates are dark with small, barely visible sclera. Histology
The collagen of the sclera is continuous with the cornea.
Usually the situation resolves itself, when the protrusion of content is returned to the abdominal cavity. Sometimes this needs to be done by a doctor at the ICU.The hernia content becoming trapped combined with severe pain, inability to perform bowel movement or pass gas, swelling, fever, nausea and/or discoloration over the area could be signs of a prolonged compromise in blood flow of the hernia content. If so, emergency surgery is often required, since prolonged compromise in blood flow otherwise threatens organ integrity.If hernias are symptomatic and disturb daily activity or have had episodes of threatening incarceration, preventive surgical treatment can be considered. The surgery is performed under anaesthesia, while the surgeon identifies the edges of the defect and bring them together permanently using either suture or mesh. Small umbilical hernias are often successfully repaired with suture, while larger hernias may require a suitable mesh, although some surgeons advocate mesh treatment for most hernias. The most common complications for both techniques are superficial wound infections and recurrence of the hernia and some people experience pain at the surgical site. See also
Fetal development
Umbilicoplasty
Paraumbilical hernia
Omphalocoele

References
External links

Overview at Cincinnati Childrens Hospital Medical Center
Overview at Penn State