How much blueberry should I eat to maintain my eyesight?

There's no specific daily amount of blueberries in grams that anyone actually recommends - that's just not how it works. Blueberries are good for your eyes because of anthocyanins, but they're not some magic cure that'll restore your vision if you keep them in your pocket. What matters way more is your overall diet - eating plenty of vegetables and fruits in different colors, plus protecting your eyes from strain. If your doctor gave you specific recommendations, it would've made sense to ask them right then about the amounts - it depends on your situation.