I don't have any real evidence, but anecdotally I suspect that diet also has an effect on vision. Could be just a coincidence, but my vision declined as a child during a period when I was regularly stuffing myself with sweets, and know others with similar experience.
Is the diet in East Asian countries (Hong Kong, Taiwan, Singapore & South Korea) significantly worse than it was in the 1920s? As the article details, myopia is increasingly common in China as well. The Chinese suffered numerous famines between 1920 and 1960. I'm sure diet plays some role in eye health, but nutrition has likely improved in all of the countries they're discussing.
The value of a diet isn't just a single interval between "hungry" and "fed".