Note to A Midsummer's Night Dream, 1.1.230-231: "And as he errs, doting on Hermia's eyes, / So I, admiring of his qualities"
And as he errs, doting on Hermia's eyes, / So I, admiring of his qualities: i.e., and as he wanders about in a daze of love, doting on Hermia's eyes, so do I, wondering at his attractive qualities. In her next lines Helena admits that Demetrius doesn't really deserve her devotion.