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Monitoring a Leaking Bleb
LETTERS
Because of the difficulties with the handheld mask, the technique had been abandoned for the "mask in the rail" by the time we completed our small sample of patients. We realized that no one would actually be doing this technique as described; however, we thought it might be interesting to others to get a general idea of what was involved and the results we experienced. Currently, we have switched to the Apogee (Apex Plus) Summit technology and are treating our astigmatic patients with the mask-in-the-rail technique. Although we have had this machine for only 1 month, our results to date have been good and we will be using the Alpins method of analyzing vectors to write a paper that should give a more meaningful analysis of the performance of the PMMA disc and astigmatism. We hope to have a reasonable representation of what this method of treating astigmatism can do by the 1997 ASCRS meeting.-Patricia K. Teal, MD
Progressive hyperopia is not from permanent weakening of the cornea by the radial incisions. There is no evidence that RK causes permanent weakening of the cornea. The operation works by increasing the tissue volume peripherally where the incisions have been made. With a fixed base and internal pressure, this causes an increase in the curvature of the peripheral cornea. This has to be equalized and is done by a consequent flattening of the central cornea. Radial keratotomy has an excellent short- and longterm safety record. The overcorrections and micro perforations experienced by the authors, while experienced by all refractive surgeons, can be minimized. Having made these observations, we should welcome comparative studies such as this. WILLIAM J. JORY, FRCS(C), FRCQPHTH
Preventing Overcorrection and Microperforations with RK
I
wish to comment on the radial keratotomy (RK) aspects of the paper about the efficacy and safety of photorefrac1 tive keratotomy and RK for bilateral myopia. The authors state that they targeted for emmetropia. Naturally, patients want the best possible distance vision but will find initial or progressive hyperopia much more troublesome than a small degree of undercorrection. Microperforations, although experienced by all of us, should be minimized and regarded as a complication. fu the authors state, microperforations can lead to overcorrection and hyperopia. They state that five of their six overcorrections were associated with microperforations, which also increase endothelial cell loss and the remote risk ofendophthalmitis. They should be minimized by careful blade calibration and accurate pachymetry. My personal incidence of such complications has decreased from 3.0% in my first 1000 cases to less than 0.50% after 8000 cases. There is never an excuse for invading the optical dear zone. Not only can this lead to overcorrection; it can also interfere with best visual acuity. It can be avoided by using single-edge diamond knives accurately calibrated with more modern microscopes rather than by gauge block. The recent introduction of diamond blades completely edged on one side and double-edged only on the very tip of the other side, which is otherwise blunt, will avoid such intrusions while maximizing correction by achieving correct depth at the optical zone margin.
London, England Reference 1. EI-Maghraby A, Salah T, Polit F, et al. Efficacy and safety of excimer laser photorefractive keratectomy and radial keratotomy for bilateral myopia. J Cataract Refract Surg 1996; 22:
51-58
Monitoring a Leaking Bleb
I
read with great interest the consultation section on the leaking bleb. 1 While most contributors favored a conservative approach, no one suggested a way of monitoring the leak. A simple method that I have been using for many years to monitor the leak and assess the efficacy of the treatment is to instill a single drop of topical anesthetic and place the tip of a standard fluorescein strip at the lower margin of the bleb for 15 seconds while holding the upper lid to prevent blinking. The degree of discoloration on the strip is noted. This treatment is repeated in exactly the same way at regular intervals, as the discoloration is proportional to the amount of fluid leak. If within 2 weeks of commencing the treatment the strip marking has not diminished, an alternative method of treatment should be considered. FAIZ TAPPOUNI, MD, FRCQPHTH
London, England Reference 1. Masket S, ed. Consultation section. J Cataract Refract Surg
1996; 22:397-402
J CATARACT REFRACT SURG-VOL 22, SEPTEMBER 1996
873
Because of the difficulties with the handheld mask, the technique had been abandoned for the "mask in the rail" by the time we completed our small sample of patients. We realized that no one would actually be doing this technique as described; however, we thought it might be interesting to others to get a general idea of what was involved and the results we experienced. Currently, we have switched to the Apogee (Apex Plus) Summit technology and are treating our astigmatic patients with the mask-in-the-rail technique. Although we have had this machine for only 1 month, our results to date have been good and we will be using the Alpins method of analyzing vectors to write a paper that should give a more meaningful analysis of the performance of the PMMA disc and astigmatism. We hope to have a reasonable representation of what this method of treating astigmatism can do by the 1997 ASCRS meeting.-Patricia K. Teal, MD
Progressive hyperopia is not from permanent weakening of the cornea by the radial incisions. There is no evidence that RK causes permanent weakening of the cornea. The operation works by increasing the tissue volume peripherally where the incisions have been made. With a fixed base and internal pressure, this causes an increase in the curvature of the peripheral cornea. This has to be equalized and is done by a consequent flattening of the central cornea. Radial keratotomy has an excellent short- and longterm safety record. The overcorrections and micro perforations experienced by the authors, while experienced by all refractive surgeons, can be minimized. Having made these observations, we should welcome comparative studies such as this. WILLIAM J. JORY, FRCS(C), FRCQPHTH
Preventing Overcorrection and Microperforations with RK
I
wish to comment on the radial keratotomy (RK) aspects of the paper about the efficacy and safety of photorefrac1 tive keratotomy and RK for bilateral myopia. The authors state that they targeted for emmetropia. Naturally, patients want the best possible distance vision but will find initial or progressive hyperopia much more troublesome than a small degree of undercorrection. Microperforations, although experienced by all of us, should be minimized and regarded as a complication. fu the authors state, microperforations can lead to overcorrection and hyperopia. They state that five of their six overcorrections were associated with microperforations, which also increase endothelial cell loss and the remote risk ofendophthalmitis. They should be minimized by careful blade calibration and accurate pachymetry. My personal incidence of such complications has decreased from 3.0% in my first 1000 cases to less than 0.50% after 8000 cases. There is never an excuse for invading the optical dear zone. Not only can this lead to overcorrection; it can also interfere with best visual acuity. It can be avoided by using single-edge diamond knives accurately calibrated with more modern microscopes rather than by gauge block. The recent introduction of diamond blades completely edged on one side and double-edged only on the very tip of the other side, which is otherwise blunt, will avoid such intrusions while maximizing correction by achieving correct depth at the optical zone margin.
London, England Reference 1. EI-Maghraby A, Salah T, Polit F, et al. Efficacy and safety of excimer laser photorefractive keratectomy and radial keratotomy for bilateral myopia. J Cataract Refract Surg 1996; 22:
51-58
Monitoring a Leaking Bleb
I
read with great interest the consultation section on the leaking bleb. 1 While most contributors favored a conservative approach, no one suggested a way of monitoring the leak. A simple method that I have been using for many years to monitor the leak and assess the efficacy of the treatment is to instill a single drop of topical anesthetic and place the tip of a standard fluorescein strip at the lower margin of the bleb for 15 seconds while holding the upper lid to prevent blinking. The degree of discoloration on the strip is noted. This treatment is repeated in exactly the same way at regular intervals, as the discoloration is proportional to the amount of fluid leak. If within 2 weeks of commencing the treatment the strip marking has not diminished, an alternative method of treatment should be considered. FAIZ TAPPOUNI, MD, FRCQPHTH
London, England Reference 1. Masket S, ed. Consultation section. J Cataract Refract Surg
1996; 22:397-402
J CATARACT REFRACT SURG-VOL 22, SEPTEMBER 1996
873