This idiom can be said by a person who orders more food than they are able to finish eating. (The food looked so good, that they ordered, or took, too much.)
我的眼睛比胃還大！（我點太多菜了！）
台語有一種說法：「肚子飽了，眼睛（目啁）還未飽！」意義相近，通常是在吃飽了的時候講的，表示菜餚很好，雖然快吃撐了，還想再來一口。