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Pulse-Mode Mitomycin C Use in Pterygium Surgery
the temporal parafoveal area because the angle between the Henle fibers and light source becomes more perpendicular.1 Thus, the term outer nuclear layer thickness used in their report may be histologically inappropriate and may cause confusion in OCT interpretations. SUK HO BYEON YOUNG KWANG CHU
Seoul, Korea
fovea. It seems reasonable that outer nuclear layer thickness at the central fovea represents that of almost the photoreceptor layer. As reported, retinal histologic analysis of the primate has demonstrated a scant Henle fiber layer at the central fovea,1,3 which is confirmed by spectral-domain optical coherence tomography. We agree that the different intensity of the perifoveal Henle fiber layer in Figure 2 may be the result of the angle between measurement light and the object.4 HIDETAKA MATSUMOTO TAKU SATO SHOJI KISHI
REFERENCES
1. Matsumoto H, Sato T, Kishi S. Outer nuclear layer thickness at the fovea determines visual outcomes in resolved central serous chorioretinopathy. Am J Ophthalmol 2009;148:105– 110. 2. Yamada E. Some structural features of the fovea centralis in the human retina. Arch Ophthalmol 1969;82:151–159. 3. Gass JD. Müller cell cone, an overlooked part of the anatomy of the fovea centralis: hypotheses concerning its role in the pathogenesis of macular hole and foveomacular retinoschisis. Arch Ophthalmol 1999;117:821– 823. 4. Haouchine B, Massin P, Gaudric A. Foveal pseudocyst as the first step in macular hole formation: a prospective study by optical coherence tomography. Ophthalmology 2001;108:15–22.
REPLY WE THANK DRS BYEON AND CHU FOR THEIR INTEREST IN
our article. We appreciate their comment and insights and the issue they have raised. Their comment stimulated our interest about the microstructure of the fovea. A Müller cell is a large glial cell with a columnar structure. It is located between neural elements, which consist of photoreceptors, bipolar cells, and ganglion cells. Except for the fovea, Müller cell stands as perpendicular as a neural element. However, arrangement of the neural element is different in the fovea. Almost all layers of the retina are composed of densely packed cone cells in the foveal floor. The most proximal edge of the bipolar cell layer and ganglion cell layer are at the slope of the foveal pit and measure 350 m and 400 m diameter, respectively.1 Thus, Müller cells run obliquely along with the neural element in the foveal slope. We believe that a Müller cell cone reflects the obliquely arranged Müller cells in the fovea. It is known that the cytoplasm of Müller cells appears light in light microscopy as well as in electron microscopy. We agree that this obliquely arranged Müller cells play a critical role in the formation of macular hole or cystoid macular edema. In optical coherence tomography, even with ultra-high resolution, the outer nuclear layer is seen as a homogeneous layer with low reflectivity, which is no different at the foveal floor and in the perifoveal area.2 Although Müller cells are present in between the photoreceptor cells, an inverted cone-shaped zone is not observed at the VOL. 148, NO. 3
Maebashi, Japan
REFERENCES
1. Fine BS, Yanoff M. The retina. Ocular histology, second edition. Hagerstown, Maryland: Harper & Row, 1979:61–127. 2. Ko TH, Fujimoto JG, Schuman JS, et al. Comparison of ultra-high- and standard-resolution optical coherence tomography for imaging macular pathology. Ophthalmology 2005; 112:1922–1935. 3. Yamada E. Some structural features of the fovea centralis in the human retina. Arch Ophthalmol 1969;82:151–159. 4. Matsumoto H, Stao T, Kishi S. Outer nuclear layer thickness at the fovea determines visual outcomes in resolved central serous chorioretinopathy. Am J Ophthalmol 2009;148:105–110.
Pulse-Mode Mitomycin C Use in Pterygium Surgery EDITOR: WE READ WITH GREAT INTEREST THE ARTICLE ENTITLED
“Effect of Mitomycin C on Corneal Endothelium in Pterygium Surgery” by Bahar and associates.1 In this prospective, nonrandomized study, in the mitomycin C (MMC) group, a surgical sponge soaked with MMC 0.02% was placed on the exposed sclera for 2 minutes, with the conjunctival layer draped over the sponge. The authors reported that topical use of MMC 0.02% in pterygium surgery caused a decrease in the percentage of hexagonal corneal endothelium at 1 month. Toxic effects of MMC on corneal endothelium have been observed after photorefractive keratectomy,2 after trabeculectomy,3 and after pterygium surgery.4 In an animal study, penetration of MMC into the anterior chamber through deepihthelized cornea was directly proportional to both concentration and duration of exposure.5 We would like to discuss our technique of using MMC in pterygium surgery. To minimize the penetration of MMC into the anterior chamber, we apply a surgical sponge soaked with MMC 0.02% onto bare sclera for a total of 2 minutes, divided in 4 sessions. The length of each
CORRESPONDENCE
475
5. Song JS, Kim JH, Yang M, et al. Concentrations of mitomycin C in rabbit corneal tissue and aqueous humor after topical administration. Cornea 2006;25:S20 –S23.
session is 30 seconds, with 1-minute intervals. During each interval, the sclera is irrigated with balanced salt solution. Because the penetration of MMC is directly proportional to exposure time, we decided to divide the total exposure time into 4 session. We named this technique pulse-mode MMC. We believe that our technique is safer for corneal endothelium than that of Bahar and associates.1 Further investigation is needed regarding the efficacy of pulsemode MMC in pterygium surgery. We want to raise awareness among our colleagues of pulse-mode MMC use in pterygium surgery.
REPLY WE THANK SAKARYA AND ASSOCIATES FOR THEIR COM-
ments regarding the pulse mode use of mitomycin C (MMC) in pterygium surgery. The authors state that to minimize the possible damage induced by the use of MMC, they apply a surgical sponge soaked with MMC 0.02% onto bare sclera for a total of 2 minutes divided into 4 sessions. The length of each session is 30 seconds with a 1-minute interval. In each interval, the sclera is irrigated with balanced salt solution. This is an interesting suggestion, but because the total application time and concentration of MMC are the same, there is no reason to assume that this technique is safer. A prospective, randomized clinical trial is needed to prove any benefit in the application method suggested by the authors. Because this is a new technique without proven data, we do not believe the authors can put this forward as being safer than what we studied and reported.
YASAR SAKARYA RABIA SAKARYA
Denizli, Turkey
REFERENCES
1. Bahar I, Kaiserman I, Lange AP, et al. The effect of mitomycin C on corneal endothelium in pterygium surgery. Am J Ophthalmol 2009;147:447– 452. 2. Morales AJ, Zadok D, Mora-Retana R, et al. Intraoperative mitomycin and corneal endothelium after photorefractive keratectomy. Am J Ophthalmol 2006;142:400 – 404. 3. Sihota R, Sharma T, Agarwal HC. Intraoperative mitomycin C and the corneal endothelium. Acta Ophthalmol Scand 1998;76:80 – 82. 4. Avisar R, Avisar I, Bahar I, Weinberger D. Effect of mitomycin C in pterygium surgery on corneal endothelium. Cornea 2008;27:559 –561.
476
AMERICAN JOURNAL
IRIT BAHAR IGOR KAISERMAN ALLAN R. SLOMOVIC
Toronto, Ontario, Canada
OF
OPHTHALMOLOGY
SEPTEMBER 2009
Seoul, Korea
fovea. It seems reasonable that outer nuclear layer thickness at the central fovea represents that of almost the photoreceptor layer. As reported, retinal histologic analysis of the primate has demonstrated a scant Henle fiber layer at the central fovea,1,3 which is confirmed by spectral-domain optical coherence tomography. We agree that the different intensity of the perifoveal Henle fiber layer in Figure 2 may be the result of the angle between measurement light and the object.4 HIDETAKA MATSUMOTO TAKU SATO SHOJI KISHI
REFERENCES
1. Matsumoto H, Sato T, Kishi S. Outer nuclear layer thickness at the fovea determines visual outcomes in resolved central serous chorioretinopathy. Am J Ophthalmol 2009;148:105– 110. 2. Yamada E. Some structural features of the fovea centralis in the human retina. Arch Ophthalmol 1969;82:151–159. 3. Gass JD. Müller cell cone, an overlooked part of the anatomy of the fovea centralis: hypotheses concerning its role in the pathogenesis of macular hole and foveomacular retinoschisis. Arch Ophthalmol 1999;117:821– 823. 4. Haouchine B, Massin P, Gaudric A. Foveal pseudocyst as the first step in macular hole formation: a prospective study by optical coherence tomography. Ophthalmology 2001;108:15–22.
REPLY WE THANK DRS BYEON AND CHU FOR THEIR INTEREST IN
our article. We appreciate their comment and insights and the issue they have raised. Their comment stimulated our interest about the microstructure of the fovea. A Müller cell is a large glial cell with a columnar structure. It is located between neural elements, which consist of photoreceptors, bipolar cells, and ganglion cells. Except for the fovea, Müller cell stands as perpendicular as a neural element. However, arrangement of the neural element is different in the fovea. Almost all layers of the retina are composed of densely packed cone cells in the foveal floor. The most proximal edge of the bipolar cell layer and ganglion cell layer are at the slope of the foveal pit and measure 350 m and 400 m diameter, respectively.1 Thus, Müller cells run obliquely along with the neural element in the foveal slope. We believe that a Müller cell cone reflects the obliquely arranged Müller cells in the fovea. It is known that the cytoplasm of Müller cells appears light in light microscopy as well as in electron microscopy. We agree that this obliquely arranged Müller cells play a critical role in the formation of macular hole or cystoid macular edema. In optical coherence tomography, even with ultra-high resolution, the outer nuclear layer is seen as a homogeneous layer with low reflectivity, which is no different at the foveal floor and in the perifoveal area.2 Although Müller cells are present in between the photoreceptor cells, an inverted cone-shaped zone is not observed at the VOL. 148, NO. 3
Maebashi, Japan
REFERENCES
1. Fine BS, Yanoff M. The retina. Ocular histology, second edition. Hagerstown, Maryland: Harper & Row, 1979:61–127. 2. Ko TH, Fujimoto JG, Schuman JS, et al. Comparison of ultra-high- and standard-resolution optical coherence tomography for imaging macular pathology. Ophthalmology 2005; 112:1922–1935. 3. Yamada E. Some structural features of the fovea centralis in the human retina. Arch Ophthalmol 1969;82:151–159. 4. Matsumoto H, Stao T, Kishi S. Outer nuclear layer thickness at the fovea determines visual outcomes in resolved central serous chorioretinopathy. Am J Ophthalmol 2009;148:105–110.
Pulse-Mode Mitomycin C Use in Pterygium Surgery EDITOR: WE READ WITH GREAT INTEREST THE ARTICLE ENTITLED
“Effect of Mitomycin C on Corneal Endothelium in Pterygium Surgery” by Bahar and associates.1 In this prospective, nonrandomized study, in the mitomycin C (MMC) group, a surgical sponge soaked with MMC 0.02% was placed on the exposed sclera for 2 minutes, with the conjunctival layer draped over the sponge. The authors reported that topical use of MMC 0.02% in pterygium surgery caused a decrease in the percentage of hexagonal corneal endothelium at 1 month. Toxic effects of MMC on corneal endothelium have been observed after photorefractive keratectomy,2 after trabeculectomy,3 and after pterygium surgery.4 In an animal study, penetration of MMC into the anterior chamber through deepihthelized cornea was directly proportional to both concentration and duration of exposure.5 We would like to discuss our technique of using MMC in pterygium surgery. To minimize the penetration of MMC into the anterior chamber, we apply a surgical sponge soaked with MMC 0.02% onto bare sclera for a total of 2 minutes, divided in 4 sessions. The length of each
CORRESPONDENCE
475
5. Song JS, Kim JH, Yang M, et al. Concentrations of mitomycin C in rabbit corneal tissue and aqueous humor after topical administration. Cornea 2006;25:S20 –S23.
session is 30 seconds, with 1-minute intervals. During each interval, the sclera is irrigated with balanced salt solution. Because the penetration of MMC is directly proportional to exposure time, we decided to divide the total exposure time into 4 session. We named this technique pulse-mode MMC. We believe that our technique is safer for corneal endothelium than that of Bahar and associates.1 Further investigation is needed regarding the efficacy of pulsemode MMC in pterygium surgery. We want to raise awareness among our colleagues of pulse-mode MMC use in pterygium surgery.
REPLY WE THANK SAKARYA AND ASSOCIATES FOR THEIR COM-
ments regarding the pulse mode use of mitomycin C (MMC) in pterygium surgery. The authors state that to minimize the possible damage induced by the use of MMC, they apply a surgical sponge soaked with MMC 0.02% onto bare sclera for a total of 2 minutes divided into 4 sessions. The length of each session is 30 seconds with a 1-minute interval. In each interval, the sclera is irrigated with balanced salt solution. This is an interesting suggestion, but because the total application time and concentration of MMC are the same, there is no reason to assume that this technique is safer. A prospective, randomized clinical trial is needed to prove any benefit in the application method suggested by the authors. Because this is a new technique without proven data, we do not believe the authors can put this forward as being safer than what we studied and reported.
YASAR SAKARYA RABIA SAKARYA
Denizli, Turkey
REFERENCES
1. Bahar I, Kaiserman I, Lange AP, et al. The effect of mitomycin C on corneal endothelium in pterygium surgery. Am J Ophthalmol 2009;147:447– 452. 2. Morales AJ, Zadok D, Mora-Retana R, et al. Intraoperative mitomycin and corneal endothelium after photorefractive keratectomy. Am J Ophthalmol 2006;142:400 – 404. 3. Sihota R, Sharma T, Agarwal HC. Intraoperative mitomycin C and the corneal endothelium. Acta Ophthalmol Scand 1998;76:80 – 82. 4. Avisar R, Avisar I, Bahar I, Weinberger D. Effect of mitomycin C in pterygium surgery on corneal endothelium. Cornea 2008;27:559 –561.
476
AMERICAN JOURNAL
IRIT BAHAR IGOR KAISERMAN ALLAN R. SLOMOVIC
Toronto, Ontario, Canada
OF
OPHTHALMOLOGY
SEPTEMBER 2009