Suture Needles

6 Suture Needles

The diversity of tissues and surgical maneuvers encountered in ophthalmic surgery makes the choice of needle an important one. Fortunately there is an exceptionally wide range of needles to choose from, and the thought process used to select the one best suited for a particular purpose begins with an understanding of the fundamental properties inherent to each. To begin with, all commonly used ophthalmic needles are made from stainless steel, and each needle is divided into three major parts: the point or tip, the body, and the swage ( Fig. 6.1).

The tip is extremely sharp, and is designed to penetrate into or cut through tissue. The needle is gripped on the body, which transmits force to the tip. The body determines the length and curve of the needle, and its resistance to bending. The swage holds the suture thread, and is typically created by laser drilling an opening into the end of the body, into which the thread is placed and physically secured by crimping.

There are several different tip designs for use in ophthalmic surgery, the most basic of which are tapered, conventional cutting, reverse cutting, and spatulated ( Fig. 6.2). Unlike the other tips, the taper point does not cut the tissue, but rather pierces and separates it as the body of the needle passes. The reverse-cutting tip, on the other hand, has three cutting edges (i.e., each side and the outer curve), making it ideally suited for cutting through dense fibrous soft tissues. Conventional cutting tips, with cutting edges on both sides as well as the inner curve are also available, but less commonly utilized. Their major disadvantage relative to the reverse cutting tip is that they place a cut in the tissue on the side of the pass that will experience the stress of the wound closure the most. This is a potentially less stable situation compared to that created by the reverse cutting tip, where the inner surface of the needle tract is left intact. The spatulated tip has cutting edges on the sides only, and its flattened body is designed to maintain a constant depth in the cornea or sclera, where the connective tissue is uniquely organized into a lamellar architecture, and full-thickness passes are to be avoided. Although tapered and reverse-cutting tips are utilized widely across many surgical specialties, spatulated needles are designed specifically for ophthalmic use. The spatulated needle tip comes in a few different design modifications.

The body of the ophthalmic needle is curved, and does not have cutting edges, but passes easily through the opening in the tissue made by the sharp tip. The shape of the body may be low trapezoidal (spatulated), triangular (reverse cutting), or semi-rounded (taper). A needle’s resistance to bending and deformation increases with the thickness, or diameter, of the body. It also varies with the shape of the body and the composition of the metal alloy. For example, the triangular geometry of the reverse-cutting needle imparts greater resistance to bending compared to the flattened body of spatulated needles, or the semi-rounded body of taper needles. The overall size of the needle is described in terms of several dimensions ( Fig. 6.3) that include thickness or diameter, linear and chord length, radius of curvature, and arc ( Fig. 6.4).