1. What is the crystalline lens of the eye?
A transparent, avascular, biconvex structure that refracts light and changes shape during accommodation.
2. Where is the lens located within the eyeball?
Immediately posterior to the iris and pupil and anterior to the vitreous body.
3. What are the two surfaces of the crystalline lens?
The anterior and posterior convex surfaces, with the posterior surface normally more strongly curved.
4. What is the equator of the lens?
The circumferential peripheral margin where the anterior and posterior lens surfaces meet.
5. What are the three principal structural components of the lens?
The lens capsule, lens epithelium, and lens fibers.
6. What is the lens capsule?
A thick, transparent, elastic basement membrane that completely surrounds the lens.
7. Which collagen type is the principal structural component of the lens capsule?
Type IV collagen.
8. Where is the lens epithelium located?
Immediately beneath the anterior lens capsule, extending toward the equator.
9. What type of epithelium forms the anterior lens epithelium?
Simple cuboidal epithelium.
10. Where are new lens fibers generated throughout life?
From proliferating epithelial cells in the germinative zone near the lens equator.
11. What happens to the nuclei and organelles of lens fiber cells during maturation?
They are degraded, creating an organelle-free zone that helps maintain transparency.
12. What are crystallins?
Highly concentrated structural proteins in lens fibers that contribute to transparency and refractive properties.
13. How are the lens cortex and nucleus anatomically distinguished?
The cortex contains younger peripheral lens fibers, while the nucleus contains older central fibers.
14. What are the lens sutures?
Lines where the ends of elongating lens fibers meet at the anterior and posterior poles.
15. What are the suspensory ligaments of the lens called?
Zonular fibers, collectively forming the ciliary zonule.
16. What is the primary structural protein of the lens zonular fibers?
Fibrillin, particularly fibrillin-1, organized into extracellular microfibrils.
17. Where do the zonular fibers attach to support the lens?
They extend from the ciliary region to the lens capsule near its equator.
18. What is accommodation of the eye?
Adjustment of lens curvature to focus objects at different distances onto the retina.
19. What happens to the lens during accommodation for near vision?
It becomes thicker and more convex, increasing its refractive power.
20. How does contraction of the ciliary muscle affect zonular tension?
It reduces tension on the zonular fibers, allowing the elastic lens to become more rounded.
21. What happens to the lens during distant vision?
Increased zonular tension flattens the lens and decreases its refractive power.
22. Which cranial nerve provides the parasympathetic pathway controlling lens accommodation?
The oculomotor nerve (cranial nerve III), through its parasympathetic fibers to the ciliary muscle.
23. Which structure provides most metabolic nutrients to the adult lens?
The aqueous humor, through diffusion and transport across the lens capsule and epithelium.
24. Does the adult crystalline lens contain blood vessels or nerves?
No. The mature lens is avascular and lacks direct innervation.
25. From which embryonic structure does the crystalline lens develop?
The lens placode, a thickening of surface ectoderm induced by the developing optic vesicle.
26. What embryonic structure gives rise to the lens after the lens placode invaginates?
The lens vesicle, which separates from the surface ectoderm.
27. What is the hyaloid artery's relationship to the developing lens?
It contributes to the fetal vascular system that nourishes the developing lens before regressing.
28. What is a cataract?
An opacity of the crystalline lens that interferes with the transmission of light.
29. What is presbyopia?
Age-related loss of accommodative ability, primarily due to increasing stiffness of the crystalline lens.
30. What is ectopia lentis?
Displacement of the crystalline lens from its normal position, often associated with zonular weakness or disruption.
