Issues in Wound Management

Introduction

The cataract incision serves as more than just the access point to the anterior segment. It affects corneal stability and overall ocular integrity. Wound construction is the critical determinant of this integrity, and two key elements of the wound involve size and architecture. Wound management after cataract surgery is required in cases of wound leakage, burns, or dehiscence.

This chapter reviews wound construction, mechanisms of wound healing, factors that can predispose to wound compromise, and the management of wound leakage, burns, and dehiscence.

Wound Construction

Cataract surgery has evolved from large incisions (>10 mm) to smaller incisions (1.8–3.0 mm), leading to more stable parameters during surgery, shorter healing time, and less surgically induced astigmatism with better visual outcomes. The two principal approaches to small cataract incisions are scleral tunnels (<3 mm) and clear corneal incisions (CCIs) (1.8–3.0 mm).

The traditional limbal or anterior scleral incision was designed for ready access to the anterior chamber and simple closure with radially oriented sutures. Two or three planes were incorporated into the incision, but the intrascleral (or intralimbal) portion was short (1 mm or less), and the site of entry into the anterior chamber was located near the iris root. In contrast, key elements of the self-sealing scleral tunnel incision include a long (>2 mm) intrascleral component and an anterior entry into the chamber. The latter creates an internal corneal valve that is closed by intraocular pressure (IOP).

Stimulated in part by advances in foldable lens implant design, the small incision (3.5 mm or less) has largely supplanted the traditional 6- to 7-mm scleral tunnel incision. Likewise, the scleral tunnel incision has largely been replaced by clear-corneal incisions except in special cases ( Table 48.1 ).

The clear corneal incision was first described by Fine in 1992 and has evolved over the past several decades, permitting incisions smaller than 2 mm, but its construction principles remain the same: create adequate tunnel length with an internal corneal valve to create a self-sealing wound.

• Several corneal incision constructions have been used: paracentesis incision, two-plane or grooved incision, hinged incision, and three-plane incision.

• Ernest et al. showed that clear-corneal incisions with an internal corneal valve demonstrated resistance to leakage comparable to similarly constructed scleral tunnel incisions.

• In an animal model, Ernest el al. evaluated the role of the site of external opening of the incision-on-incision healing and stability. They found that starting incisions in the vascular region (limbus) resulted in a fibroblastic response that enhanced incision stability and allowed rapid incision healing within 7 days postoperatively compared with the 60 days of healing time required for incisions started in the avascular region (cornea). Their findings were compelling, and more recent clinical studies have been performed, showing that wound location and architecture are the major factors for faster visual improvement ( Table 48.2 ).

  Table 48.2

  Clear Cornea Incision

  PROS	CONS
  Avoidance of the conjunctiva and sclera (virtually bloodless surgery); no suture-induced astigmatism	Poorer wound healing compared with limbal or scleral-tunnel incisions
  No suture-induced astigmatism)	Wound dehiscence after minimal trauma
  Minimal induced astigmatism (temporal incisions) or reduced postoperative astigmatism (steepest meridian)	Risk for cornea opacities (thermal burns)
  Easier access	Notable decrease in endothelial cell count compared with scleral-tunnel incisions
  Safer surgery
  Reduced operating time and fewer complications
  Faster visual recovery

After successful use in refractive surgery for laser in situ keratomileusis flap construction, the femtosecond laser was introduced in 2009 for use in cataract surgery. Although there appears to be promise in using femtosecond laser technology for wound construction in cataract surgery, the utility is still under consideration. Advantages include reproducibility of wound architecture, capsulorrhexis circularity with consistent optic overlap, less energy necessary for the nucleus fragmentation, and potential for smaller incisions. However, problematic endothelial gape and incision leakage have been reported in recent studies. The overall benefit of femtosecond laser assisted wound construction is still under evaluation.

Wound Healing

A scleral, limbal, or corneal incision creates a tissue gap that initiates a process of repair by tissue-addition. For scleral and limbal incisions, active wound healing begins within 48 hours of surgery; the initial phase is the ingrowth of episcleral vascular tissue. Over the next several weeks, this tissue fills the entire incision, creating a fibrovascular plug. Over the ensuing 2 years or more, remodeling occurs, resulting in reorientation of the wound healing collagen so that it becomes parallel to existing scleral collagen. Concurrently, vascularization and cellularity diminish.

• At 1 week postoperatively, wound strength is approximately 10% of that found in normal nonincised tissue.

• By 8 weeks postoperatively, this value is roughly 40%, and by 2 years postoperatively, the wound has regained approximately 75% to 80% of its original strength.

  Therefore, although the wound is most vulnerable to dehiscence early in the postoperative period, depending on its size and construction, the cataract incision retains a permanent susceptibility to traumatic dehiscence.

• Corneal incisions heal by ingrowth of keratocytes, which initially are oriented parallel to the incision and therefore, perpendicular to lamellae of the cornea stroma. These keratocytes then undergo fibroblastic transformation and, over months, reorient themselves to become parallel to the corneal lamellae. Compared with scleral and limbal wound healing, the wound-healing process of the corneal incision is much slower and ultimately produces a weaker incision, as attested by the relative fragility of corneal graft wounds.

• The clinical impact of this slower healing for cataract corneal wounds depends in large part on incision size and construction. For standard 2.2- to 2.7-mm corneal tunnel incisions, the small incision size and wound construction appear to largely or even fully compensate for the deficiencies in the corneal wound-healing process. However, the slower healing of corneal incisions can predispose to problems with dehiscence in poorly constructed small incisions and in incisions longer than ~3 mm.

• In addition, it is probable (but unproven to date) that there is greater against-the-wound astigmatic shift with corneal incisions compared with limbal or scleral wounds of the same size, but this appears to pertain primarily to superior clear corneal incisions and perhaps to temporal clear corneal incisions >3.0 mm. Data suggest that a 2.4 clear corneal incision induces a mean astigmatic shift of less than 0.1 to 0.2 D.

Compromise of Wound Integrity

One of the biggest concerns of any procedure is postoperative infection and endophthalmitis, which can be caused by a compromised incision.