1

One to shorten the lense for near focus, one to lengthen it for far focus?

Or is there a single "ciliary" muscle that is either engaged or not?

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    I'm voting to close this question as off-topic because I believe this is a better fit in Biology.SE – Chris Rogers Apr 23 '18 at 23:28
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The eye is formed by three layers. From the outside to the inside, you have:

  1. The fibrous layer: formed by the cornea and the sclera.
  2. The vascular layer: formed (from posterior to anterior) by the choroid, ciliar body and iris.
  3. The neural layer: formed by the retina.

Another important "element" is the lens, which changes the focal distance of the eye.

Focusing on the second layer, the ciliar body is "attatched" to the lens by small extentions called ciliary processes. These have ciliary muscules that upon stimulation, they contract and create a respective response on the lens. Basically there is an adjustment of the lens in order to create a clear image of what you see from a close distance.

Here's some additional information if you'd like to read more about the eye in general.

Edit: After reading DoctorWhom's comment, I'd like to add two links that might help. Oculomotor Nerve - Accommodation reflex (Jean-Pierre Barral, Alain Croibier 2009) Complementary information

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    This is great but doesn't include information on whether there are muscles that act to oppose the ciliary body, which is the root of the OP's question Which I believe does not exist, but don't have a clear reference to demonstrate that it works only by relaxation. – DoctorWhom Apr 25 '18 at 1:12
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Iris has dilator and constrictor pupillae While cilliary musckes act by contraction and relaxation not antagonism

  • Welcome to Health.SE :-) Due to the nature and requirements of this site, can you please provide some links to articles which can back up this answer? I would recommend going through the Health.SE tour and tips on how to write good questions and good answers, both of which tend to get more upvotes. Unreferenced claims can lead to answers being deleted. – Chris Rogers Apr 24 '18 at 12:46
  • Also, can you provide more detail? For example: What and where are the cilliary muscles? – Chris Rogers Apr 24 '18 at 12:50

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