1. What is the sclera?
The dense, opaque, fibrous connective tissue forming the posterior five-sixths of the eyeball's outer coat.
2. What are the primary functions of the sclera?
To maintain eyeball shape, protect intraocular structures, and provide attachment for extraocular muscles.
3. What is the anatomical junction between the sclera and cornea?
The corneoscleral limbus.
4. What are the three principal layers of the sclera from superficial to deep?
Episclera, scleral stroma (substantia propria), and lamina fusca.
5. What is the episclera?
A thin, vascular connective tissue layer covering the external surface of the sclera.
6. What is the substantia propria of the sclera?
The thick middle layer composed mainly of dense, irregularly arranged collagen bundles and fibroblasts.
7. What is the lamina fusca?
The innermost scleral layer containing collagen fibers, elastic fibers, and pigmented melanocytes.
8. Which collagen type predominates in the scleral stroma?
Type I collagen.
9. Why is the sclera opaque while the cornea is transparent?
Its collagen bundles have irregular arrangements, variable diameters, and less uniform spacing.
10. Which cells primarily synthesize and maintain the scleral extracellular matrix?
Scleral fibroblasts.
11. Where is the sclera generally thickest?
Near the posterior pole around the optic nerve, where it reaches approximately 1 mm in thickness.
12. Where is the sclera generally thinnest?
Immediately posterior to the rectus muscle insertions, where it may measure approximately 0.3 mm.
13. What is the relationship between the sclera and the choroid?
The choroid lies immediately internal to the sclera, separated from it by the suprachoroidal space.
14. What is Tenon's capsule?
A fibroelastic fascial sheath surrounding the eyeball externally, separated from the sclera by the episcleral space.
15. What is the episcleral space?
A potential space containing loose connective tissue between the sclera and Tenon's capsule.
16. Which extraocular muscles attach directly to the sclera?
The four rectus muscles and the superior and inferior oblique muscles.
17. What is the spiral of Tillaux?
The spiral arrangement of rectus muscle insertions at progressively increasing distances from the corneal limbus.
18. Which rectus muscle inserts closest to the corneoscleral limbus?
The medial rectus muscle.
19. What is the lamina cribrosa of the sclera?
A perforated collagenous structure at the posterior scleral opening through which optic nerve axons pass.
20. What structures pass through the posterior scleral opening?
Optic nerve fibers and the central retinal artery and vein.
21. What are the scleral emissary canals?
Channels through the sclera that transmit ciliary nerves and blood vessels, including vortex veins.
22. What is the primary vascular supply of the sclera?
Branches of the anterior and posterior ciliary arteries, particularly through episcleral and adjacent choroidal vessels.
23. Why is the scleral stroma considered relatively avascular?
It contains very few intrinsic blood vessels and receives much of its nutrition by diffusion from adjacent vascular tissues.
24. Which nerve division provides sensory innervation to most of the sclera?
The ophthalmic division of the trigeminal nerve (cranial nerve V1), primarily through the ciliary nerves.
25. What is the scleral spur?
An inward projection of scleral tissue near the iridocorneal angle that anchors the trabecular meshwork and ciliary muscle.
26. What is the relationship between the sclera and Schlemm's canal?
Schlemm's canal lies within the corneoscleral tissue near the limbus and receives aqueous humor from the trabecular meshwork.
27. What is scleritis?
Inflammation of the sclera, typically producing deep ocular pain and potentially threatening ocular integrity.
28. How does episcleritis anatomically differ from scleritis?
Episcleritis primarily involves superficial episcleral tissue, while scleritis involves the deeper scleral stroma.
29. What is a scleral staphyloma?
An abnormal outward bulging of weakened or thinned scleral tissue, often with underlying uveal tissue.
30. Why can the sclera appear bluish in certain connective tissue disorders?
Scleral thinning or altered collagen structure allows the underlying pigmented uveal tissue to become more visible.
