The sclera forms the largest portion of the thick fibrous outer ‘coat’ of the eye. It is continuous with the cornea anteriorly and posteriorly it joins the optic nerve. It consists of three layers:
1. The outermost episclera
2. The scleral stroma
3. The innermost lamina fusca
The sclera is primarily made up of irregular collagen fibres, making the sclera relatively opaque. Where the stroma has a large number of collagen fibres, it reflects light and this accounts for its white appearance.
Primary scleral disorders are uncommon in dogs and even rarer in cats and most pathologies are considered to originate from the cornea, only having a secondary impact on the limbus, sclera or episclera.
