• Ion movements into and out of the vitreous space after closed vitrectomy were the same as in open-sky vitrectomy in rabbits. Ion increase or decrease depended primarily on passive penetration, although active transport contributed to increases during the early phase in equilibration. Ions penetrated from the entire area of tissue in contact with the vitreous space; and the posterior wall, comprising the largest area of contact, was an important route. This feature was related to compromise of the blood-retinal barrier following vitrectomy.