Enzymatic Zonulolysis in Cataract Surgery: a Review of 432 Cases.

SINCE the introduction of alpha-chymotrypsin (ACT) by Barraquer (1958a,b) as a zonulolytic agent to facilitate intracapsular cataract extraction, it has been widely used by surgeons in many countries. It is a proteolytic enzyme derived from the bovine pancreas, but its exact mechanism or mode of action is not clear.According to Barraquer it has specific action on the zonule and other structures are not affected, but according to Salmony (1959) its effect is not restricted specifically to the zonule, but it may also attack other structures such as the vitreous body which is developmentally similar to the zonule. Salmony investigated its proteolytic effect on tissues other than the zonular fibres through its ability to liberate amino acid from samples of aqueous, lens, and vitreous homogenates with which it was incubated. Bedrossian (1959), while experimenting on animals, came to the conclusion that the enzyme weakens the zonular fibres or its attachments but does not completely dissolve them. He thought that the healing of the corneal wound was not affected, but felt that the action of the enzyme might not be as selective as was claimed. Pieces of eye tissue submerged in a 1 in 5,000 solution of the enzyme for several hours were found to show no alteration even on microscopic histological examination (Barraquer, 1959), and the solution of the problem of the enzyme's mechanism of action may probably lie in the realm of biochemical and ultra-microscopic study. A preliminary study of human eyes and eyes of Rhesus monkeys by electron microscopy reveals that the anterior lens capsule has three distinct layers, the outermost of which is continuous with the zonular fibres (pericapsular membrane) and ceases to be apparent after contact with alpha-chymotrypsin. The zonule breaks down into clusters and fragments of relatively uniform length and arrangement, while the ciliary epithelium and internal limiting membrane remain unchanged. It is widely agreed that cataract extraction is facilitated by the use of this enzyme (Cogan, Symons, and Gibbs, 1959; Ainslie, 1959; Zorab, 1959). Paufique (1959), reviewing 200 cases, recommended it for cases in which unusual zonular resistance was expected; he further remarked that it should not be used for patients under the age of 10 years. Though Barraquer (1959) has used it in extracting congenital cataracts, his youngest patient being