Explain accommodation for a near object
Follow ciliary contraction reduced ligament tension and a rounder lens.
Extended only (Supplement); Biology 0610, 2026–2028. Use the stated specimen features and evidence. Diagrams are schematic. Written practice is self-checked
Before you begin
- Recall receptors, electrical impulses, CNS organisation and the distinction between a stimulus and an effector response.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
What happens to ligament tension during near accommodation?
What you will learn
- Ciliary action changes ligament tension
- Lens shape changes refraction
Explain accommodation for a near object
| Feature | Meaning |
|---|---|
| Ciliary muscles | Contract |
| Suspensory ligaments | Reduced tension / slack |
| Lens | Rounder and thicker |
| Refraction | Stronger for near focusing |
Ciliary action changes ligament tension
Accommodation is adjustment of the lens to focus objects at different distances onto the retina. For a near object, the ciliary muscles contract. Their arrangement changes the pull transmitted through the suspensory ligaments: ligament tension is reduced and the ligaments become slack. Contraction of these muscles does not mean that the ligaments themselves actively contract.
With reduced tension, the elastic lens becomes thicker and more rounded, with more convex surfaces. This shape refracts light more strongly than the flatter lens used for a distant object. The chain links muscle state, ligament tension, lens shape and refraction, rather than leaving the explanation at the word accommodation.
Lens shape changes refraction
The lens does not become rounder by contracting like a muscle. Its elastic properties allow a shape change when the surrounding tension changes. Keep the locations distinct: the ciliary muscles act around the lens, the suspensory ligaments transmit tension, and the iris muscles alter pupil diameter. Calling all three an iris mechanism confuses focusing with aperture control.
Near-object focusing is not defined by bright or dim light. An object can be near in either lighting condition, so the required trigger in this account is object distance. The original model illustrates mechanical states and a qualitative change in refraction; it does not measure lens power, draw a clinical prescription or demonstrate that every learner can accommodate by the same amount.
Pause and explain
Which near-object chain is complete?
Worked example
Give the full near accommodation chain.
Show the worked solution
- Ciliary muscles contract and suspensory ligament tension decreases.
- The lens becomes thicker and rounder, refracting more strongly.
Answer Near: ciliary contract → ligaments slack → lens rounder/thicker → stronger refraction.
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Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
Explain accommodation for a near object using all four required links.
Give me a hint
Start with ciliary muscle contraction.
Compare my reasoning
- Contraction reduces ligament tension so the ligaments become slack.
- The lens becomes rounder and thicker and refracts more strongly.
Ciliary muscles contract; suspensory ligaments become slack; lens becomes thicker and rounder; refraction is stronger to focus a near object.
Look for these in your work
- Include muscles and tension
- Include shape and stronger refraction
Repair: near objects need taut ligaments and a flat lens after ciliary contraction.
Give me a hint
Follow what reduced surrounding tension allows an elastic lens to do.
Compare my reasoning
- Ciliary contraction reduces ligament tension.
- The lens becomes rounder and refracts more strongly.
Near accommodation uses slack ligaments and a rounder, thicker lens after ciliary contraction, giving stronger refraction.
Look for these in your work
- Correct ligament state
- Correct shape and refraction
An object moves nearer without a change in room brightness. Which adjustment is relevant to refocusing and why?
Give me a hint
Separate distance focusing from light entry.
Compare my reasoning
- Accommodation changes lens shape for object distance.
- Iris pupil control responds to light intensity.
Near accommodation is relevant: ciliary contraction reduces ligament tension so the lens becomes rounder and refracts more strongly; unchanged brightness does not define this distance adjustment.
Look for these in your work
- Trace the focusing chain
- Separate object distance and brightness
Common mistakes
- Saying contracting ciliary muscles tighten the ligaments in the near response.
- Calling the elastic lens a contracting muscle.
What can you explain now?
Which near-object chain is complete?
Compare with the explanation
Ciliary contract; ligaments slack; rounder lens; stronger refraction
The four linked states agree.
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Make it stick
Give the full near accommodation chain and distinguish it from pupil control.
If you needed the solution, close it and solve the problem again from a blank page. A correct answer is stronger when you can explain the reason for each step.