The scleral cartilage is a type of cartilage that develops within the sclera, the dense, fibrous outer layer of the vertebrate eye. It is found in many vertebrate groups, including birds, most other reptiles, teleost fishes, and cartilaginous fishes, but is absent in placental mammals and has been secondarily lost in groups like snakes.

The primary function of scleral cartilage is to provide structural rigidity to the eyeball. This helps maintain the eye's shape, supports the attachment of extraocular muscles, and in some species, aids in visual accommodation.

The term "scleral cartilage" has historically been used inconsistently in scientific literature, leading to confusion about the homology and evolution of different skeletal elements within the vertebrate eye. For example, the term has been used to describe any cartilage in the sclera, regardless of its developmental origin or evolutionary relationship to elements in other species. To address this ambiguity, biologist Tamara A. Franz-Odendaal proposed a revised terminology in 2025.

The scleral cartilage sensu stricto is widely distributed:

Evolutionarily, the cartilaginous sclera is a derived condition from an ancestral, purely fibrous scleral capsule, and have likely been gained and lost many times.

The scleral cartilage makes the eyeball more rigid, which serves several purposes:

It develops from the periocular mesenchyme, which is rather plastic. The mesenchyme may switch between a fibrous and a cartilaginous state, as seen in myopic chickens and in the different morphologies of sighted versus blind cavefish. Even in humans, whose sclera is entirely fibrous, cartilage nodules can occasionally form.

The fate of the cartilage varies. In birds and most reptiles, it remains as a permanent cartilage throughout life. In many teleost species, however, it serves as a replacement cartilage that is partially or fully replaced by bone through endochondral ossification to form scleral ossicles.