Monocular Accommodative Reflex?

[Xalatan]

Hi how are you? I am new to the forum. My question is whether someone with only one functional eye can still have an accommodative reflex?

 

Presumably the brain needs depth perception to tell whether an object is moving from far to near - so without stereoscopic vision provided by two eyes, can monocular vision still accommodate?

 

I'm thinking yes because depth perception is not completely lost with monocular vision - it's just not as precise as if one had two eyes. But then this raises the question of whether accommodative reflex is partially impaired when someone closes one eye?

 

Thank you!

 

 

[Function]

Here's what I think, based on what I know from functional neuroanatomy and neurophysiology

 

I think, indeed, the accommodation reflex will be preserved. So the ciliary muscle will contract (together with the sphincter pupillae muscle), being innervated by the general visceral efferent fibres in the third cranial nerve, originating the Edinger-Westphal nucleus. This, I think, is in turn connected to vestibular nuclei, which are ipsilaterally innervated by the fastigial nucleus in the cerebellum. This, in turn, receives input from the contralateral pontine nuclei, connected directly to the middle superior temporal area and indirectly to the middle temporal area (projecting into the middle superior temporal area), forming essential area's on the magnocellular pathway (important visual area's being namely V5 and V3), important for the perception and tracking of moving objects located in the contralateral visual field.

 

So, in short, if your left eye spots something that is coming closer, it will trigger pathways on the contralateral occipital and temporal lobes (decussation via optic chiasm), in turn triggering pathways on, again, the ipsilateral side of the left eye (decussation of pontine nuclei to cerebellum), initiating accommodation.

 

Just try it yourself: close your one eye and bring your finger back and forth: you'll see that it's as sharp as with both your eyes open.

I think, but this might be wishful thinking, that indeed it takes me a bit longer to accommodate than with both eyes open.

 

There is also a phenomenon called perceptual steadfastness, namely: you don't care if an object is black on white, or white on black, you recognize it. You don't care if an object is 2 cm away from your eye or standing 2 metres away from you, in the first case you won't think that it's suddenly a hundred times bigger. And so on.

Edited January 1, 2016 by Function