Explain accommodation for a distant object
Follow ciliary relaxation increased ligament tension and a flatter 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
Which lens shape is used for distant accommodation?
What you will learn
- Relaxation allows increased ligament tension
- A flatter lens refracts less strongly
Explain accommodation for a distant object
| Feature | Meaning |
|---|---|
| Ciliary muscles | Relax |
| Suspensory ligaments | Increased tension / taut |
| Lens | Thinner and flatter |
| Refraction | Less strong than near state |
Relaxation allows increased ligament tension
For a distant object, the ciliary muscles relax. Suspensory ligaments become taut as the surrounding arrangement increases the pull on the lens. This is the reverse of the reduced tension associated with ciliary contraction in near accommodation. State the ligament tension explicitly; a description of muscle relaxation alone does not explain the resulting lens shape.
The increased ligament tension pulls the elastic lens into a thinner, flatter shape. It still refracts light, but less strongly than the rounder lens in the near state. Less strongly is a comparison between lens shapes, not a claim that a distant-viewing lens becomes transparent to light without any refraction.
A flatter lens refracts less strongly
The lens focuses light onto the retina through this adjustment within the wider optical system. The cornea also refracts entering light and is not replaced by the lens explanation. Accommodation describes the changeable lens mechanism, while recognising the cornea avoids the mistaken assertion that every part of refraction occurs in the lens alone.
Use distance as the input and follow the causal chain through ciliary muscles, suspensory ligaments, shape and refraction. Brightness is not a sufficient cue for choosing the distant chain: a distant object can be viewed in bright or dim surroundings. The model compares two qualitative focusing states rather than establishing an individual eye diagnosis or an exact focal distance.
Pause and explain
Which distant chain preserves all required states?
Worked example
Give the full distant accommodation chain.
Show the worked solution
- Ciliary muscles relax and suspensory ligaments become taut.
- The lens becomes thinner and flatter and refracts less strongly.
Answer Distant: ciliary relax → ligaments taut → lens flatter/thinner → weaker 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 distant accommodation using all four links.
Give me a hint
Start with ciliary relaxation.
Compare my reasoning
- Relaxation allows taut suspensory ligaments.
- They pull the lens thinner and flatter, giving weaker refraction.
Ciliary muscles relax; suspensory ligaments become taut; lens becomes thinner and flatter; refraction is less strong for distant focusing.
Look for these in your work
- Include relaxed muscle and taut ligaments
- Link flat shape with weaker refraction
Compare lens shape and ligament tension in near and distant viewing.
Give me a hint
Use opposing states.
Compare my reasoning
- Near: slack ligaments and rounder lens.
- Distant: taut ligaments and flatter lens.
Near viewing uses slack ligaments and a rounder, thicker lens; distant viewing uses taut ligaments and a flatter, thinner lens.
Look for these in your work
- Give both tension states
- Give both lens shapes
A learner says the distant lens does not refract any light. Correct this using the stated comparison.
Give me a hint
Weaker is relative to the rounder lens.
Compare my reasoning
- The flatter lens still refracts.
- It refracts less strongly than the near-state lens.
The distant-state lens still refracts light, but less strongly than the rounder near-state lens; the cornea also contributes refraction.
Look for these in your work
- Retain lens refraction
- Use the relative comparison
Common mistakes
- Reversing distant ligament tension.
- Interpreting weaker refraction as no refraction.
What can you explain now?
Which distant chain preserves all required states?
Compare with the explanation
Ciliary relax; ligaments taut; flatter lens; weaker refraction
It links muscle, tension, shape and refraction.
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Make it stick
Contrast the complete distant and near accommodation chains.
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.