Accommodation

👁 The Eye – Focusing & Vision Defects (Triple only)

Accommodation = the eye changing lens shape to focus on near or distant objects.

• Lens focusing works with:

  • Ciliary muscles (circular muscles around lens).

  • Suspensory ligaments (fibres attaching lens to ciliary muscles).

• Ciliary muscles contract → suspensory ligaments loosen → lens thicker → refracts more strongly (for near objects).

• Ciliary muscles relax → suspensory ligaments tighten → lens thinner → refracts less strongly (for distant objects).

🔹 Focusing on Distant objects

• Only small refraction needed.

• Ciliary muscles relax.

• Suspensory ligaments tighten.

• Lens pulled thin.

• Light refracted slightly → focuses on retina.

🔹 Focusing on Near objects

• Large refraction needed.

• Ciliary muscles contract.

• Suspensory ligaments loosen.

• Lens becomes thicker.

• Light refracted strongly → focuses on retina.

Vision Defects

Long-sight (Hyperopia)

• Can see distant objects, struggle with near objects.

• Causes:

  • Eyeball too short → light focuses behind retina.

  • Lens too weak / less elastic (age-related) → cannot thicken enough.

• Correction:

  • Convex (converging) lenses → refract light rays inwards before entering eye.

Short-sight (Myopia)

• Can see near objects, struggle with distant objects.

• Causes:

  • Eyeball too long → light focuses in front of retina.

  • Lens too thick → refracts too strongly.

• Correction:

  • Concave (diverging) lenses → spread light out slightly before entering eye.

Other Treatments

• Contact lenses (hard or soft) – sit on eyeball, same effect as glasses.

• Laser eye surgery – reshapes cornea to change refraction.

• Artificial lens replacement – replacing natural lens with plastic lens.

✅ Exam tip:

• Be able to draw and explain ray diagrams for both hyperopia and myopia.

• Remember: Convex → converging → hyperopia; Concave → diverging → myopia.