Relationships between the posterior surface of the crystalline lens and instruments introduced into the vitreous cavity through pars plana incisions were evaluated in ten eyes from cadavers. Instruments were introduced 3.0 mm, 3.5 mm, and 4.0 mm posterior to the anterior part of the limbus. The distance between an instrument oriented toward the center of the vitreous cavity and the peripheral edge of the lens in that meridian was 1.6 mm when the sclerotomy was 3.0 mm from the limbus and 2.8 mm when the sclerotomy was 4.0 mm from the limbus. The arc length from the sclerotomy where the instrument was introduced to the most distal meridian of the ora serrata that could be reached without touching the lens ranged from 2.8 to 3.8 clock hours as the distance between the sclerotomy and the limbus increased from 3.0 mm to 4.0 mm. The distance between the ora serrata and the most peripherally accessible point on the retina in the meridian 180 degrees from the sclerotomy decreased from 6.0 mm to 3.1 mm as the distance between the limbus and the sclerotomy increased from 3.0 mm to 4.0 mm.