It is a degenerative change – protrusion of the locally thinned sclera
Causes:
Thinning is caused by inflammation, poorly repaired perforated injury, high myopia or very high intraocular pressure. Through this thinned sclera, uvea shines darkly.
Treatment:
At the risk of perforation, the thinned spot is reinforced by implants (fascia; dead donor sclera).