MedBucket

Sclera is a part of the outer layer of the eye. Its external side is free because of the eye movements. Sclera is surrounded by a membrane called capsula bulbi. Sclera’s external surface is full of various gaps. The biggest and the most important one is a gap through which the optic nerves go, and the central retinal artery and vein along with them. An interesting thing about this gap is that sclera doesn’t stop because of the nerves going through — it sends it parts through the nerves and forms an area called area cribrosa. From a clinical aspect, that place is a locus minoris resistentiae (pervious for various defects) because that’s where the sclera gets excavated most often if the intraocular pressure increases. It can stay intact in case of  normal intraocular pressure levels.

Apart from that main gap, there are various other gaps called emissaria sclerae posteriores and emissaria sclerae anteriores. Through the former ones pass the arteriae iridis, arteriae choroideae and the ciliary nerve. Through the latter ones pass the ramuli ciliares.
Around the equator, there are also emissaria sclerae equatorialia through which four venae choroideae majores pass.

Sclera’s internal side is also free, and it has various smaller gaps. This side is somewhat darkish in color, but that is not because it contains its own pigment. The color (pigment) comes from the middle layer of the eye. That is called the lamina fusca sclerae.

Sclera’s tissue, towards the front side of the eye, gets transformed and becomes cornea. The opening of sclera is called rima cornealis, which contains two lips (labium anterius and posterius). In the tissue of sclera, near the rima cornealis, there is a so-called vein space called sinus venosus sclerae. Sometimes this space gets divided into numerous canals, and then it’s called the plexus venosus. A thin layer of sclera tissue which is located inside the sinus venosus sclerae is called lig. pectinatum anguli iridocornealis.

Sclera is made out of bundles of binder fibrils which go and cross each other in all directions. Sclera is on the front side covered with conjunctiva. It doesn’t have many blood vessels — all it has comes from arteriae ciliares posteriores breves and arteriae ciliares posteriores longae. The innervation comes from the ciliary nerves.