POSITION OF FILTRATION AREA UNDER EYELID
Our clinical experience has demonstrated the importance of avoiding an interpalpebral bleb or inferior bleb if at all possible. We recommend noting the position of the eyelid in relation to the limbus preoperatively and constructing the surgery and antimetabolite treatment to divert aqueous superiorly. Otherwise, the chance of discomfort for the patient and bleb-related complications such as dellen, a thin or leaking bleb, and blebitis/endophthalmitis—particularly if the bleb is interpalpebral or inferior—is much increased2 (Figure 1). If it is not possible to place the bleb under the upper eyelid, then other surgery should be considered.
Figure 1. This eye has a cystic interpalpebral bleb with secondary endophthalmitis.
CORNEAL TRACTION SUTURE/HEMOSTASIS
A corneal traction suture avoids a superior rectus hematoma, which will increase conjunctival scarring and contraction and achieve maximal traction. We use a 7–0 black silk suture on a semicircular needle. We also treat the conjunctiva preoperatively with a drop of apraclonidine 0.5% or adrenaline 0.01% to reduce bleeding.
THE RING OF STEEL AND ANTERIOR AQUEOUS FLOW
Background
In the past, we favored a limbus-based incision and adjunctive mitomycin C, because we were worried about postoperative leaks. Our laboratory research and clinical observation of cystic blebs, however, led us to hypothesize that cystic blebs had two things in common (Figure 2). The first was restricted posterior flow, which we called the ring of steel. The second was the anterior outflow of aqueous at the limbus (an anterior point of leakage is almost always visible during the exploration of a cystic bleb). In the laboratory, we found that the effects of treating a small area of conjunctiva with an antimetabolite were focal and long term.3,4 Our research also demonstrated that, despite halted growth, the cells at the edge of the treated area could still make scar tissue5,6 and encapsulate the area, thus resulting in thinning and a cystic bleb. Subsequent changes in our surgical technique in 1996 have dramatically reduced our incidence of cystic blebs, even 10 years after the alterations.1 We later confirmed our hypothesis experimentally.7
Figure 2. The ring of steel and anterior aqueous flow hypothesis.
Conjunctival Handling, Hydrodissection, and Large Pockets for the Antimetabolite
We converted to fornix-based conjunctival flaps. The ample exposure of the flap site that they provide allows us to treat a large area with an antimetabolite without requiring a posteriorly placed restricting scar, which is more often seen with limbus-based surgery. For surgeons who prefer a limbus-based flap, we recommend placing the incision as far back in the fornix as possible to avoid an incisional scar close to the sclerostomy, which would act as part of the ring of steel and result in a focal, cystic bleb. If the incision is placed far back, it is possible to achieve diffuse noncystic blebs even with the use of mitomycin and limbus-based surgery.
If the subconjunctival area is scarred, hydrodissection with balanced salt solution is very useful to delineate and free scarring. It avoids inadvertent buttonholes. We first dissect the conjunctiva backward on either side of the rectus tendon with a Westcott scissors to minimize bleeding and then dissect gently over but not into the area of the tendon. We make large, lateral pockets approximately 10 to 15 mm posterior to the limbus and about 5 mm wide to accommodate the antimetabolite-soaked sponges (Figure 3).
Figure 3. Large lateral pockets allow the treatment of a wide surface area.
Large Scleral Flap Designed to Divert Aqueous Posteriorly
We try to cut a large (4 X 3 mm) flap and leave the side cuts at the limbus incomplete (1 to 2 mm from the limbus). This configuration forces the aqueous backward over a wide area to produce a diffuse bleb. Any aqueous jet at the limbus increases the risk of an anterior, focal, cystic bleb.
Protection of the Conjunctival Edge
We use a special conjunctival T clamp (No. 2-686; Duckworth & Kent Ltd., Hertfordshire, England) Professor Khaw designed to hold back the conjunctiva and prevent its contact with the antimetabolite. The clamp maintains a pocket for the antifibrotic agent. Because our experiments have shown that the antimetabolite mainly affects the area it touches,3 protecting the conjunctival edge prevents leaking and dehiscence of the wound postoperatively.
Type of Subconjunctival Sponge
We prefer to use circular, medical-grade sponges made with polyvinyl alcohol rather than methylcellulose sponges, which may fragment. Cut in half and folded like IOLs, the sponges fit through the entrance to the pocket without touching the cut conjunctival edges or limbus (sponges are approximately 5 X 3 mm). We insert about six sponges (Figure 4).
Figure 4. A special clamp holds back the conjunctiva while the surgeon inserts folded, antimetabolite-soaked sponges into the pocket.
Area of Subconjunctival Treatment
The principle is to apply the antimetabolite to as large an area as possible, including under the scleral flap. Increasing the surface area treated results in a much more diffuse, noncystic area clinically. A large area prevents the development of the ring of steel, which restricts flow and leads to the development of a raised, cystic, avascular bleb.
Our changes in the area of treatment as well as the construction of conjunctival and scleral flaps have led to a dramatic difference in the bleb's appearance and decreased the incidence of short- and long-term complications (Figures 5 and 6). These alterations have reduced cystic areas within the bleb from 90% to 29%. Our rate of blebitis and endophthalmitis during a period of 3 to 5 years was 20% for older limbus-based techniques with a smaller treatment area versus zero for the same period with our current technique.1 In the US, Paul Palmberg, MD, has also reported a reduction in the rate of complications (6.0% to 0.5%) in low-risk populations (oral communication, May 2006).
Figure 5. Several technical changes have improved the conjunctiva's appearance and led to safer surgery.
Figure 6. This patient's blebs have dramatically different appearances. His left eye was treated before and his right eye after the authors changed their surgical technique.
Conjunctival Closure
For a fornix-based flap, the options for closing the conjunctiva are one or two sutures placed at either end of the relieving incision or a more thorough approach of interrupted mattress sutures or a continuous suture with or without corneal grooves. To achieve an extremely watertight closure, we make a series of corneal grooves (corneal/conjunctival grooved closure) through which all of the closing sutures pass (Figure 7). We bury the knots in the cornea so that they do not cause patients discomfort. The sutures enter via the corneal groove, are configured for a purse string, exit via the corneal groove, and are tied in the groove. This process is repeated without a purse string for the central sutures. For us, the technique has virtually eliminated central conjunctival retraction, leaks, and suture-related discomfort.
Figure 7. Corneal conjunctival closure is watertight, and there is no need to remove the sutures.
CONCLUSION
Simple changes in surgical technique related to the conjunctiva can dramatically reduce both short-term (eg, leakage) and long-term (eg, endophthalmitis) complications related to the bleb area.
The authors would like to acknowledge support for their research from the Medical Research Council (G9330070), the Guide Dogs for the Blind, the Wellcome Trust, the International Glaucoma Association, Fight for Sight, the Singapore National Medical Research Council, Moorfields Trustees, the Alcon Institute Prize, the Haymans Trust, Ron and Liora Moskovitz, and the Michael and Ilse Katz foundation. Videos and other handouts are available on the Internet at http://www.ucl.ac.uk/ioo/research/khawlibrary.htm.
Peng T. Khaw, PhD, FRCS, FRCOphth, FRCP, FRCPath, FIBiol, FMedSci, is Professor of Glaucoma and Ocular Healing and Consultant Ophthalmic Surgeon, Glaucoma Unit and ORB (Ocular Repair and Regeneration Biology), Institute of Ophthalmology and Moorfields Eye Hospital, London. He designed all of the systems and instruments mentioned herein but stated that he holds no financial interest in them or their manufacturer. Professor Khaw may be reached at p.khaw@ucl.ac.uk.
Usman Sarodia, FRCOphth, is a glaucoma fellow at Moorfields Eye Hospital in London. He acknowledged no financial interest in the products or companies mentioned herein.
1. Wells AP, Cordeiro MF, Bunce C, Khaw PT. Cystic bleb formation and related complications in limbus versus fornix based conjunctival flaps in paediatric and young adult trabeculectomy with mitomycin C. Ophthalmology. 2003;110:2192-2197.
2. Greenfield DS, Suner IJ, Miller MP, et al. Endophthalmitis after filtering surgery with mitomycin. Arch Ophthalmol. 1996;114:943-949.
3. Khaw PT, Doyle JW, Sherwood MB, et al. Prolonged localized tissue effects from 5-minute exposures to fluorouracil and mitomycin C. Arch Ophthalmol. 1993;111:263-267.
4. Khaw PT, Sherwood MB, MacKay SL, et al. Five-minute treatments with fluorouracil, floxuridine, and mitomycin have long-term effects on human Tenon's capsule fibroblasts. Arch Ophthalmol. 1992;110:1150-1154.
5. Occleston NL, Daniels JT, Tarnuzzer RW, et al. Single exposures to antiproliferatives: long-term effects on ocular fibroblast wound-healing behavior. Invest Ophthalmol Vis Sci. 1997;38:1998-2007.
6. Daniels JT, Occleston NL, Crowston JG, Khaw PT. Effects of antimetabolite induced cellular growth arrest on fibroblast-fibroblast interactions. Exp Eye Res. 1999;69:117-127.
7. Cordeiro MF, Constable PH, Alexander RA, et al. Effect of varying the mitomycin-C treatment area in glaucoma filtration surgery in the rabbit. Invest Ophthalmol Vis Sci. 1997;38:1639-1646.
