LONDON — The model in the latest Victoria Beckham eyewear advertising campaign looks young and waiflike, her twiglike limbs in a silken tunic and cotton-candy pink slacks, her face as full of sharp angles as the square-frame tortoiseshell spectacles perched on her nose.

The glossy image of the Lithuanian model Giedre Dukauskaite, published by Ms. Beckham on social media last week as she unveiled designs from her spring and summer 2018 eyewear range, has drawn a fierce public response. It is not the first time the fashion designer has been accused of promoting an unhealthy body image while advertising her luxury products, and is just the latest campaign to fan the perennial debate around when thin is too thin.

In a recent study the research and advocacy group Model Alliance conducted in conjunction with Harvard and Northeastern University, the results of which were published in the International Journal of Eating Disorders, 81 percent of the models surveyed reported a body mass index of less than 18.5, which the World Health Organization considers underweight.