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Sometimes the most useful and innovative ideas are the simplest. These "duh" ideas, as in "Duh, why didn't I think of that?" I find to be the most exciting and practical. How many times in a surgical session have we fought with a clear corneal incision that won't self seal, only to surrender to a 10-0 nylon suture that ensures a watertight incision? Wouldn't it be nice if there were a simple method of sealing the incision without having to resort to sutures or glue? Now, with a simple addition to the clear corneal incision, we can stromally hydrate the roof of the incision, in addition to the sides, and improve the ability of the clear corneal incision to seal on the table.
In this month's column, Michael Y. Wong, M.D., describes his ingenious
incision that allows for improved stromal hydration. Both the technique and explanation for how the method improves self sealability are intriguing. The alteration can be made at the start of the procedure or added when the surgeon realizes that the incision won't seal without some help. It's wonderful to be able to add this little trick to our surgical armamentarium, and as far as I'm concerned, there's nothing "wong" with having a few extra tricks.
Richard Hoffman, M.D.,
tools & techniques editor
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Figure 1. The surgeon begins by creating a stromal pocket that is 1.5-2 mm wide.
If using two stab incisions, he places them side by side so that the incision
resembles an upside down W. A side view shows the pocket to be just anterior
to and above the usual entry into the anterior chamber
Figure 2. At the conclusion of the case, the surgeon uses a 30-gauge cannula to hydrate the tip and edges of the supraincisional stromal pocket with balanced salt solution. The reformed anterior chamber pushes upward on the internal aspect of the corneal lip, while the stromal hydration pushes downward on the wound
Source (all): Michael Y. Wong, M.D.
Stromal hydration of a supraincisional pocket helps prevent bacterial
endophthalmitis
The increasing popularity of clear corneal incisions in cataract surgery has been accompanied by a worrisome suggestion that the incidence of bacterial endophthalmitis1 and toxic anterior segment syndrome are on the rise.2 This article describes a simple, quick, and inexpensive technique to tightly appose the lips of the incision, making for a more secure and prolonged seal.
Technique
Prior to creating the clear corneal incision, I make a supraincisional stromal pocket 0.5 mm anterior to the intended entrance. With a simple stab of a diamond or metal keratome, I create a 2 mm pocket that resembles an equilateral triangle, its base toward the limbus. The pocket's depth can be anywhere from one-third to two-thirds stromal thickness.
I hydrate the stroma through this pocket with balanced salt solution at the end of the case, thus creating a bulge that exerts an inward pressure on the external lip of the clear corneal incision. The internal lip is pressed outward by the IOP. The combined pressure makes for a tight apposition of both lips of the incision and thus prevents the egress or ingress of fluid through the wound for a period of 24 hours. By that time, the ciliary body is producing aqueous, and the endothelial pump has brought the lamellae of the stroma tightly together. The seal is firm enough to withstand fluctuations in IOP, whether high or low.
We can create two pockets instead of one if desired, and I have found that there is tremendous
latitude in the dimensions of the pocket(s) without impairing the effect (Figures 1 and 2). There are no significant complications of this technique. Formally described as stromal hydration of a supraincisional pocket, the technique is colloquially called the Wong incision or "Wong way."
Increased margin of safety
A perfectly constructed, square, or nearly square clear corneal incision created with a diamond knife is safe and secure.3,4 The outward forces of the IOP press up on the internal aspect of the corneal lip to provide a sufficient seal until the endothelial pump dries the internal channel of the incision. In practice, however, conditions are less than perfect. The incision's edges may not be as clean or long as desired, may be distorted by heat from the phaco tip, may be stretched by the IOL's insertion, or may be weakened by a limbal relaxing incision. The Wong incision can provide a margin of safety in these instances.
Effective seal through
vulnerable period of hypotony
The structural weakness of a standard clear corneal incision can be exposed in the post-op period when additional biomechanical stress occurs with blinking, rubbing of the eye, ocular movement, and hypotony from a relative shutdown of the ciliary body. In vitro, hypotony in a cadaveric eye results in an inflow of India ink placed on the ocular surface.5 In vivo, the release of aqueous through a clear corneal incision to manage a post-op pressure spike can result in temporary hypotony with a subsequent superficial inflow of fluorescein placed in the tear film.6 The resilience of the sclera causes the globe to expand from a relatively collapsed state in hypotony to produce a vacuum action. This situation may be one of the causes of toxic anterior segment
syndrome.
In contrast, the Wong incision remains watertight in the presence of hypotony, as evident upon hydrating the pocket at the end of a cataract operation without reforming the anterior chamber and exerting external pressure with a cellulose sponge. The IOP is low, and the incision does not leak. In the estimated 20% of patients who experience post-op hypotony,7 the eye would thus be protected from a superficial influx of fluid that might contain bacteria or other toxic substances.
More effective location
of stromal hydration
The stromal hydration of the sides and superior roof of the clear corneal incision can create the impression that the wound is watertight while the patient is on the operating table. This fluid, however, is often resorbed during the first few hours after surgery because it is relatively close to the endothelial pump. Further, my experience with LASIK surgery has shown that apposing stromal lamellae are more adherent when desiccated. Stromal hydration within the channel of the clear corneal incision works in opposition to this concept.
On the other hand, stromal
hydration in a separate and distinct stromal pocket that is external and anterior to the clear corneal incision typically lasts for 24-36 hours. The inward pressure remains beyond the time period of ciliary shutdown and hypotony. Further, because this supraincisional pocket of fluid is distal to the clear corneal incision with regard to the endothelium, the stromal lamellae within the channel of the clear corneal incision are desiccated and secure before the endothelium resorbs the supraincisional fluid.
Alternatives
Concern over a possible association between clear corneal incisions and the risk of endophthalmitis1 has prompted some surgeons to switch back to scleral tunnels. Relying on a thin layer of conjunctiva that often retracts with blinking, however, is an unreliable defense. Other surgeons suggest sealing the clear corneal incision with a fibrin adhesive, but doing so adds time, expense, and potential toxicity,8 and it may interfere with the desiccation of the stromal lamellae within the channel.
Uses
I prefer to hydrate a supraincisional pocket with every clear corneal incision for cataract surgery. Other surgeons use the technique only when the seal of the wound is tenuous at the end of a case. I also find that the technique is useful for a paracentesis of questionable competence, when the corneal structure is less rigid than usual (e.g., when the clear corneal incision is within a limbal relaxing incision or with a young patient), and in situations when anterior chamber stability is of the utmost importance during the early post-op period (e.g., after the insertion of a Crystalens [Bausch + Lomb, Rochester, N.Y.])
Conclusion
The Wong incision aids in sealing a clear corneal incision quickly, easily, and intuitively, and it entails no additional expense. Practically speaking, other than minor epithelial disruptions, this technique is complication-free. The best thing I can say about the Wong incision is that the worst thing that can happen is nothing.
References
1. Taban M, Behrens A, Newcomb RL, et al. Acute endophthalmitis following cataract surgery. Arch Ophthalmol. 2005;123:613-620.
2. Mamalis N, Edelhauser H, Dawson D, et al. Toxic anterior segment syndrome. J Cataract Refract Surg. 2006;32:324-333.
3. Ernest P, Kiessling LA, Lavery KT. Relative strength of cataract incisions in cadaver eyes. J Cataract Refract Surg. 1991;17:668-671.
4. Masket S, Belani S. Proper wound construction to prevent short-term ocular hypotony after clear corneal incision cataract surgery. J Cataract Refract Surg. 2007;33:383-386.
5. McDonnell PJ, Taban M, Sarayba M, et al. Dynamic morphology of clear corneal cataract incisions. Ophthalmology. 2003;110:2342-2348.
6. Chawdhary S, Anand A. Early post-phacoemulsification hypotony as a risk factor for intraocular contamination: in vivo model. J Cataract Refract Surg. 2006;32:609-613.
7. Shingleton B, Wadhwani R, O'Donoghue M, et al. Evaluation of intraocular pressure in the immediate period after phacoemulsification. J Cataract Refract Surg. 2001;27:524-527.
8. Realini T. Wound construction key to avoiding endophthalmitis. EyeWorld. 2007;
February:64-66.
Editors' note: Dr. Wong is clinical
instructor, Robert Wood Johnson
Medical School, New Brunswick, N.J., and medical director, Wills Eye Laser Vision, Princeton, N.J. He has no
financial interests related to this article.
Contact information
Wong: 609-921-9437,
mwong2020@hotmail.com |
