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Iris and ciliary body anatomy
Anatomy & Optics
Key Points
- •The iris has 4 layers: anterior border layer (no true epithelium), stroma (with sphincter pupillae and vessels), dilator pupillae (myoepithelial from neuroectoderm), and posterior pigmented epithelium (2 layers); iris root is the thinnest part (iridodialysis site)
- •Sphincter pupillae: parasympathetic (CN III, M3 receptor, miosis, pilocarpine agonist); Dilator pupillae: sympathetic (SCG, alpha-1 receptor, mydriasis, phenylephrine agonist) - both muscles are uniquely derived from neuroectoderm
- •The ciliary body has pars plicata (anterior 2 mm, ~70 processes, aqueous production by NPE) and pars plana (posterior 4 mm, surgical entry zone at 4 mm from limbus in phakic eyes); ciliary muscle has longitudinal, radial, and circular fibres
- •Aqueous humour: produced at 2-3 uL/min by active secretion (80-90%, Na+/K+-ATPase + carbonic anhydrase in NPE); drains via trabecular pathway (90%) and uveoscleral pathway (10%, enhanced by prostaglandin analogues)
- •The blood-aqueous barrier is formed by tight junctions of NPE cells and iris vascular endothelium - breakdown → flare and cells (anterior uveitis); ciliary epithelium is unique apex-to-apex arrangement of PE and NPE (both neuroectodermal)
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13 more sections are included with the Clinical plan.
- Definition
- Epidemiology
- Aetiology and causes
- Pathogenesis
- Classification
- Clinical features