Lens anatomical principles and their technical implications in cataract surgery. Part II: The lens nucleus.

Preservation of the intact ("true") capsular bag, with no tears to the periphery, is essential to assure permanent in-the-bag fixation of the intraocular lens. Removal of a large nucleus using the open-system planned extracapsular cataract extraction (ECCE) technique is often associated with tearing of the capsulectomy or serious complications such as zonular rupture, vitreous loss, unintended intracapsular cataract extraction, or posterior lens prolapse. A closed-system planned ECCE technique which allows a safe removal of the lens while maintaining the integrity of the capsular bag is presented. Hydrodissection of the lens nucleus to an epinucleus and a central hard nucleus allows hydroextraction of the small hard core while pushing the posterior capsule backward. The positive pressure in the anterior chamber, provided by the anterior chamber maintainer, keeps the position of the lens steady in its natural location, and minimizes the stress on the zonular apparatus during nucleus delivery. The remaining epinucleus can be either hydroexpressed or aspirated. Fracturing the central core, when possible, enables removal of the lens material through a small limbal incision. Viscoelastic material can be combined with a low-flow, anterior chamber maintainer in a closed-system and provides a useful surgical tool.