Hi Philip, 

>(snip) 

> Cordain et al found that chronically high blood sugar is a 
> factor contributing to nearsightedness by causing excessive 
> growth in the vitreal chamber growth. Perhaps the Paleo 
> vision improvement occurs in part because of a reduction in 
> blood sugar spikes that reduces insulin level spikes, which 
> then somehow reverses some of the vitreal chamber growth. How 
> this reversal would occur I don't know. 
If memory serves, that work was done in infants and may not apply to adults.
Nonetheless, as you mention, uncontrolled blood sugar in diabetic patients
can lead to blindness. 

> (snip)

> Nutrients and antioxidants have also been reported to improve 
> vision or slow eye degeneration. The improved nutrition and 
> antioxidant levels of the Paleo diet and the improved 
> absorption of nutrients that result from it could result in 
> vision improvements.

I suspect that vitamin A status plays a huge part in improving night vision.

I experienced improved night vision status when I began a gluten-free diet
that was still very high in carbs. 

Best Wishes, 
Ron