I am now aware of at least five people including myself who have reported
improvement in night vision or nearsightedness or both since going on a
Paleo diet (little or no grains, dairy or legumes). Not all Paleo dieters
report these improvements. Those with nearsightedness tend to report more
improvement, but I know at least one person who is not nearsighted and still
experienced vision improvements--especially with night vision. I used to
think that any reversal of myopia or night vision loss was impossible, but I
now see that it is possible. 

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. 

An eye doctor told a relative of mine who experienced amazing vision
improvement with the Paleo diet that diabetics have been known to experience
vision improvement when they get their blood sugar under control, and this
site--http://www.allaboutvision.com/conditions/diabetic-retinopathy-news.htm
--reports the following: "People with diabetes sometimes experience vision
loss when uncontrolled blood sugar damages blood vessels in the area of the
retina, leading to swelling and thickening of the macula where finely
detailed focusing occurs (macular edema)." Perhaps improving blood sugar
control reverses some of this thickening of the macula. Injecting a drug
into the eyes also reverses some of this thickening, but I'd rather get my
blood sugar under control. :-)

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.

Don Hogan wrote:
> I concur with Philip regarding eyesight improvement. Eyesight is one
> of my  easier methods of gauging the impact of the Paleo diet.
> When, and it 
> happens more frequently then I like, I eat nonPaleo, the 
> effects on my 
> eyesight occur within 12 hours.
> Don
>
> Philip wrote:
> ...I lost a lot more weight and
> much quicker
> > on the Paleo diet (not that I was trying to get as lean as
> I ended up)
> > and experienced other health improvements I did not get by more
> > conventional methods. As an example, my night vision and overall 
> > vision improved. I had been in need of a new, stronger prescription 
> > for my eyeglasses, but my vision improved enough that I no longer 
> > needed a stronger prescription and still don't years later.
> I just got
> > word today from a fellow Paleo dieter that her vision
> prescription has
> > improved twice in about a 3 year period since going Paleo (and her
> > night vision improved also). She now has to get lenses with
> a weaker
> > prescription. I know two other near-Paleo dieters who say
> their night
> > vision improved.

...

> > Cordain et al found that myopia is caused by chronic
> hyperinsulinaemia
> > (chronically high insulin levels in the bloodstream), so a
> reduction
> > in hyperinsulinaemia could account for the vision improvements that 
> > Paleo dieters such as myself have experienced.
> >
> > 	"...a previously unrecognized diet-related malady (chronic
> > hyperinsulinaemia) may play a key role in the pathogenesis of 
> > juvenile-onset myopia because of its interaction with hormonal 
> > regulation of vitreal chamber growth."
> >
> > Cordain L, Eaton SB, Brand Miller J, Lindeberg S, Jensen C. An 
> > evolutionary analysis of the etiology and pathogenesis of 
> > juvenile-onset myopia. Acta Ophthalmologica Scandinavica, 2002; 
> > 80:125-135. http://www.thepaleodiet.com/published_research/
> >
> > Hyperinsulinaemia could also have contributed to the flabby weight 
> > gain I experienced in my 30's, and could also explain why
> some studies
> > supposedly have found little or no weight loss for patients via 
> > exercise, as explained
> > here:
> >
> > "Carbohydrate Meals:
> > # Raise blood glucose levels.
> > # This in turn elevates levels of insulin on the blood
> > # That insulin takes excess energy (glucose) out of
> bloodstream. # And
> > that energy stored as fat. # THE RESULT is: weight gain!
> > # But insulin also inhibits use of energy from fat cells.
> > # THE RESULT IS: no weight loss [from exercise]!"
> >
> > Second Opinions: Diabetes Type 2, 
> > http://www.second-opinions.co.uk/diabetes-3.html
> >
> >   ...