Continuous circular capsulorhexis (CCC) can create an ideal opening in the anterior capsule of the lens that is resistant to tearing during cataract surgery. However, in eyes with a mature cataract and a white lens cortex, CCC is often difficult to perform because of poor visibility of the anterior lens capsule. First described by Klöti in 1984 and then by Gassmann and coauthors in 1988,1 radiofrequency diathermy is an alternative method to other capsulorhexis techniques, with some advantages. It is simple to perform in intumescent or hypermature cataract cases without an obvious red reflex,2 in the infantile capsule that is highly elastic and difficult to tear, and in small pupil cases, when CCC is dangerous to perform. Furthermore, the thermal effect of the radio frequency diathermy neither causes greater postoperative disturbance of the blood-aqueous barrier nor induces a higher risk of postoperative inflammation in the anterior chamber.3 However, the mechanical quality and capsular elasticity of the diathermy capsulotomy edge have been reported to be less than that of the CCC edge.4"6 Compared with CCC, radio frequency diathermy capsulorhexis has a higher rate of radial tears in the anterior lens capsule with a resultant higher incidence of malpositioning of the intraocular lens.3 We present 2 cases of accidental corneal burn as a rare complication of radiofrequency diathermy in clear cornea cataract surgery. To our knowledge, this is the first report of this rare complication.
A 76-year-old man underwent phacoemulsification using a clear corneal temporal approach in his right eye. The wound through which the capsulotomy using radiofrequency diathermy was performed was 2.6 mm wide. However, no opening of the capsule, except a small air bubble, was noted. Meanwhile, the area of the corneal tunnel that contacted the shoulder of the diathermy tip became opaque and shrank. A small defect of the anterior corneal lip was found. After the corneal defect was tightly closed by two 100 nylon stitches, the anterior chamber was still relatively shallow. To protect the corneal endothelium from thermal and mechanical damages during phacoemulsification in a shallow anterior chamber, the surgical method was shifted to a superior approach extracapsular cataract extraction (ECCE) through a can-open capsulotomy. On the first postoperative day, best-corrected visual acuity (BCVA) was 6/20 with a shallow anterior chamber and iris incarceration into the corneal defect. The Seidel test was negative. Patching of the right eye was prolonged until the anterior chamber returned to normal depth on the next day. At 2 months, BCVA improved to 6/10 with a minimal irregular astigmatism (Figure 1).
Figure 1. (Case 1) Mild pupil peaking and iris incarcerations into defect of the corneal tunnel were present 2 months after Note that phacoemulsification was shifted to extracapsular cataract extraction because of poor maintenance of the anterior chamber depth.
The following week, a 65-year-old woman underwent phacoemulsification using a clear corneal temporal approach in her left eye. Again, the diathermy tip did not work and only a small bubble appeared in the anterior lens capsule. Though we stopped the energy as soon as possible, the anterior lip of the corneal tunnel became opaque and shrank immediately. We found the shoulder of the diathermy tip that contacted the corneal tunnel had turned black. After the small defect on the anterior corneal lip was closed with one 10-0 nylon stitch, the anterior chamber depth was maintained within normal limits. For the entry of the phacoemulsification probe, the surgeon enlarged the corneal incision from the side of the previous wound. Phacoemulsification was then performed after a canopen capsulotomy. A shallow anterior chamber and iris incarceration into the corneal defect were also noted on the first postoperative day. After prolonged patching for one more day and close follow up, BCVA improved to 616.7 at 6 weeks after the operation (Figure 2).
Figure 2. (Case 2) Mild pupil peaking and iris incarcerations into the defect of the corneal tunnel were present 6 weeks after the surgery.
The Klöti Bipolar Unit Diathermy consists of a foot paddle-controlled main machine, a handpiece, and a capsulotomy tip. The lens capsule is coagulated and cut by the platinum-iridium alloy tip heated to approximately 1600C by a modulated high frequency current of 500 kHz. The Klöti Bipolar Unit Diathermy power output is 8 watts maximum. The electrical resistance of the tip end must be high to produce such a high temperature during normal function. The possible cause of the corneal burns we experienced may have been an accidental short circuit. The diathermy tip had been disinfected in an autoclave and the metal in the tip may have become fused to create a short circuit of low electrical resistance. According to the formula of energy production, E=V2IK, energy (E) increases dramatically when electrical resistance (R) decreases suddenly. Therefore, a large amount of energy was produced in the corneal tunnel instead of in the lens capsule. The heat conductivity of corneal tissue is slow and inefficient, so most of the energy produced locally is turned into the heat for the vaporization of any water in the cornea. That is why the burned corneas in our patients became opaque and shrank. The focal corneal tissue decreased in thickness and lost its normal elasticity because the water component was vaporized. It was said when human corneal collagen is heated to 55°C to 65°C, the collagen fibers shrink to one third their original length.7 In reviewing the surgical procedure, the corneal burns might have been avoided. Before performing the capsulotomy, we should have checked the function of radio frequency diathermy tip. Early detection of a failed capsulotomy caused by a spoiled diathermy tip is very important. Be aware of any early opaque change in the corneal tunnel and stop the energy via the foot paddle as soon as possible. This may minimize the severity of the corneal burn.
Although recently many capsular-staining techniques have been developed to facilitate performance of the circular continuous capsulorrhexis in cases with poor red reflex and traumatic cataract.8,9 further study is needed to prove the long-term safety of intraocular indocyanine green or trypan blue. Currendy, radiofrequency diathermy is still accepted as a relatively safe and simple procedure in cataract surgery. Nonetheless, we should emphasize great caution in the use of any equipment with the capacity to produce high temperatures, especially when used intraocularly.
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