Overview
This lecture explains how the eye accommodates to view near and distant objects, focusing on the roles of the lens, ciliary muscles, and suspensory ligaments.
Anatomy of the Eye Relevant to Accommodation
- The lens is elastic and convex, allowing it to change its shape.
- Suspensory ligaments attach around the edge of the lens, holding it in place.
- Ciliary muscles encircle the lens and control its shape via the suspensory ligaments.
- The ciliary muscle and suspensory ligaments work antagonistically: when one contracts, the other relaxes.
Accommodation for Near Vision (Objects < 6 meters)
- Ciliary muscles contract, decreasing their diameter.
- Suspensory ligaments slacken due to muscle contraction.
- The lens becomes more convex (bulges), increasing refraction of light.
- Increased refraction allows the eye to focus clearly on close objects.
- A clear image forms on the retina.
Accommodation for Distant Vision (Objects > 6 meters)
- Ciliary muscles relax, increasing their diameter.
- Suspensory ligaments contract and pull outward.
- The lens becomes flatter and thinner, decreasing its refractive power.
- Reduced refraction allows focused vision of distant objects.
- A clear image forms on the retina.
Comparison: Near vs. Distant Vision
- Near vision: ciliary muscles contracted, ligaments slackened, lens bulgy.
- Distant vision: ciliary muscles relaxed, ligaments pulled tight, lens flat.
- The antagonist relationship ensures proper focus adjustment for different distances.
Key Terms & Definitions
- Accommodation — The process by which the eye changes the shape of the lens to focus on near or distant objects.
- Lens — Elastic, convex structure that refracts/focuses light onto the retina.
- Suspensory Ligaments — Structures that connect the ciliary muscle to the lens and adjust its shape.
- Ciliary Muscle — Circular muscle around the lens that controls its thickness.
- Refraction — Bending of light to focus it onto the retina.
Action Items / Next Steps
- Study the diagrams on textbook pages 160-161.
- Write and practice a clear explanation of accommodation using memo and diagram as a guide.