: Is there an antagonistic pair of muscles in the eye? 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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The eye is formed by three layers. From the outside to the inside, you have:

The fibrous layer: formed by the cornea and the sclera.
The vascular layer: formed (from posterior to anterior) by the choroid, ciliar body and iris.
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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Iris has dilator and constrictor pupillae
While cilliary musckes act by contraction and relaxation not antagonism