Ocular Anatomy & Physiology John C. Lloyd, MD Sunnybrook HSC December 2017 Financial Disclosure • Consultant to: – Abbott Medical Optics (AMO) – Alcon Eye = The “Globe” • Dimensions – average eye is about 23 mm in diameter – about the size of a quarter • Antero-posterior diameter – or “axial length” – Varies between 20 – 30 mm or more – Each mm results in a refractive change of ~ 3 D – Hyperopic eyes shorter, myopic longer – A highly myopic eye would be about the size of a “toonie” – Laser and ultrasonic measurements allow this to be measured accurately within 0.05 – 0.1 mm, allowing good refractive accuracy post cataract surgery Conjunctiva • Clear mucous membrane covering the sclera and reflected back onto the inner eyelids • Epithelial layer including mucous secreting goblet cells, and a vascular substantia propria containing lymphatics, plasma cells, macrophages, and mast cells • “Tenon’s capsule” is a thin fibrous layer between the conjunctiva and the sclera Conjunctiva • Innervated by trigeminal nerve (V1) • Bulbar conjunctiva on the globe, and palpebral conjunctiva on inside of lids, fornix the cul-de-sac where it reflects from the globe to the lids • Impossible for a contact lens to “get behind the eye”, though the superior fornix is deep and it can get lost up in there! • Upper lid requires “double-eversion” to see this area Conjunctiva 1. Limbus 2. Bulbar Conjunctiva 3. Fornix 4. Palpebral Conjunctiva 5. Punctum 6. Lid margin Lid Eversion Conjunctiva • Accessory lacrimal glands of Krause and Wolfring are in the stroma, and the mucous secreting goblet cells are in the epithelium • This is why conjunctival alkali burns, or Stevens- Johnson syndrome cause severe dry eye when the conjunctiva is damaged • The accessory lacrimal glands and goblet cells may function less well with aging, contributing to dry eye symptoms – including the paradox of the associated watery eye from “reflexive” tearing from the main lacrimal gland Cornea • Clear window allowing light to pass through, though composed of the same elements as sclera • Regular spacing and orientation of collagen fibrils permit clarity; disruption by injury or edema causes the cornea to become opaque & white • Convex, contributes about 2/3 of eye’s refractive power • 0.5 mm centrally, 1 mm peripherally