Crystalline Lens

👁️ What Is the Crystalline Lens?

The lens is a biconvex, transparent structure located behind the iris and pupil and in front of the vitreous body. It’s suspended by the zonular fibers (suspensory ligaments) that connect it to the ciliary body.




📚 Anatomical Features of the Crystalline Lens:

1. Lens Capsule

  • Outermost layer: thin, transparent, elastic membrane

  • Acellular, basement membrane-like structure

  • Thicker anteriorly (where epithelial cells are located)

  • Site for zonular fiber attachment

2. Anterior Lens Epithelium

  • A single layer of cuboidal cells located only on the anterior surface

  • Responsible for:

    • Metabolism of the lens

    • Producing lens fibers throughout life

3. Lens Fibers

  • Long, thin, transparent cells with no nuclei (in mature fibers)

  • Arranged in concentric layers like an onion

  • Originating from the equator, they elongate and interdigitate toward the center

4. Nucleus and Cortex

  • Cortex: Peripheral region of newer lens fibers

  • Nucleus: Central older part; composed of embryonic, fetal, and adult nuclei

  • With aging, the nucleus becomes denser (leading to presbyopia and nuclear sclerosis)

🌟 Lens Zones:

  1. Capsule

  2. Epithelium (anterior only)

  3. Cortex

  4. Nucleus

🔌 Attachments:

  • Held in place by zonular fibers (aka suspensory ligaments of the lens)

  • Zonules arise from the non-pigmented ciliary epithelium and attach to the lens capsule around the equator

🎯 Functions of the Lens:

  • Focuses light onto the retina (especially fine-tuning near vision)

  • Changes shape via accommodation:

    • Ciliary muscle contracts → zonular tension decreases → lens thickens (near vision)

    • Ciliary muscle relaxes → zonular tension increases → lens flattens (distance vision)

  • Maintains transparency and minimizes light scatter

🧾 Clinical Relevance:

  • Cataract: Opacification of the lens; most common cause of blindness globally

  • Presbyopia: Age-related loss of accommodation due to decreased lens elasticity

  • Lens dislocation (ectopia lentis):

    • Seen in Marfan syndrome, homocystinuria

  • Posterior capsular opacification (PCO): Common complication after cataract surgery

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