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Reduction of Subepithelial Haze After Photorefractive Keratectomy by Cooling the Cornea
820
AMERICAN JOURNAL OF OPHTHALMOLOGY
References 1. Palmer, S. S.: Mitomycin as adjunct chemotherapy with trabeculectomy. Ophthalmology 98:317, 1991. 2. Skura. G. L., Beeson, C. c.. Higginbotham, E. J., Lichter, P. R., Musch, D. c.. Bergstrom, T. J., Klein, T. B., and Falck, F. Y., Jr.: Intraoperative mitomycin versus postoperative 5-fluorouracil in highrisk glaucoma filtering surgery. Ophthalmology 99:438,1992. 3. Stamper, R. L., McMenemy, M. G., and Lieberman, M. F.: Hypotonous maculopathy after trabeculectomy with subconjunctival 5-fluorouraciL Am. J. Ophthalmol. 114:544, 1992. 4. Kitazawa, Y., Kawase. K., Matsushita, H., and Minobe, M.: Trabeculectomy with mitomycin. A comparative study with fluorouracil. Arch. Ophthalmol. 109:1693,1991. 5. Melamed, S., Ashkenazi, I., Belcher, D. C.; and Blumenthal, M.: Donor scleral graft patching for persistent filtration bleb leak. Ophthalmic Surg. 22:164, 1991.
Reduction of Subepithelial Haze After Photorefractive Keratectomy by Cooling the Cornea Kazuo Tsubota, M.D., Ikuko Toda, M.D., and Seiji Itoh, M.D. Department of Ophthalmology, Tokyo Dental College (K. T., LT.); Department of Ophthalmology, Keio University School of Medicine (K.T., LT.); and the Itoh Hospital (S.I.). Inquiries to Kazuo Tsubota, M.D., Department of Ophthalmology, Tokyo Dental College, 11-13 Sugano 5 chome, lchikauia-shi, Chiba, Japan 272.
Excimer laser photorefractive keratectomy is a promising modality for the correction of myopia, particularly in patients with corrections of 6 diopters or less.' One problem with this technique, however, is the postoperative subepithelial corneal haze, which inevitably develops, especially in patients with severe myopia. Many surgeons now use corticosteroids and antirnetabolites to minimize this effect., We believe modification of the photorefractive keratectomy method itself may further reduce opacification. Although photorefractive keratectomy is believed to produce minimal thermal damage,
June, 1993
the local corneal temperature has increased to 53.3 c.2 We hypothesize that thermal damage can contribute to the haze formation. In our preliminary experiments using an infrared radiation thermometer, the corneal temperature increased to 40.0 C as the number of laser pulses increased. These increases may explain why photorefractive keratectomy for severe myopia, which requires longer laser exposures, is associated with more haze. In our patients, we cooled the cornea to minimize thermal damage during photorefractive keratectomy. We examined three women with severe myopia. The patients were aged 25, 30, and 36 years, respectively. Their uncorrected visual acuities, refractive errors, and corrected visual acuities were as follows: 20/400 -7.75 sph = 20/25,20/400 -6.75 sph = 20/25, and 20/800 -9.00 sph = 20/20, respectively. The first two patients had previously undergone ordinary photorefractive keratectomy. An excimer laser with an ablation diameter of 4.5 mm was used. The ocular surface was cooled by the continuous irrigation of BSS+ (4.0 C at room temperature of 22.0 C) for five minutes before the epithelial removal and by an additional three minutes of irrigation after the removal. The irrigation lowered the corneal temperature from 35.0 C to 17.0 C. The photorefractive keratectomies were then performed, by using a total of 238, 168, and 266 pulses, respectively. The temperature of the central cornea increased, but only to 25.0 C, as measured by the infrared thermometer. The ocular surface was irrigated for one minute after the keratectomy. An observation was that the excimer laser photo ablation zone, which is often visible during the procedure, was not detectable. Immediately after the procedure, the cornea was almost completely clear in all patients. Their uncorrected visual acuities, refractive errors, and corrected visual acuities were as follows: 20/60 + 1.50 sph = 20/40, 20/40 +0.75 sph = 20/30, and 20/400 +2.00 sph = 20/40, respectively. Four days postoperatively, the ablation area was covered by epithelium, without defects on fluorescein staining. Corneal sensitivity returned to normal at this time, with uncorrected visual acuity of 20/20 in two patients and corrected visual acuity of 20/20 in the other. The two patients who had undergone photorefractive keratectomies before had previously required one month for recovery of sensation and visual acuity. Those patients also reported less pain with our technique. There
821
Letters to The Journal
Vol. 115, No.6
Figure (Tsubota, Toda, and Itoh). Patient 1. Subepithelial corneal haze two months after excimer laser photorefractive keratectomy. Left, The appearance after the usual technique. Right, The appearance after cooling of the cornea. The opacity is less in the cooled cornea.
was no apparent corneal haze in any of the three patients (Figure). Our patients' epithelial, sensory, and visual recovery was quick, with less corneal haze." Although the number of patients was small, our preliminary findings suggest that extensive irrigation by cold BSS+ can reduce corneal haze. Extensive irrigation may have other beneficial effects, such as adjusting the pH, hydrating the corneal stroma, and flushing out the ablation products, but the principal mechanism of irrigation seems to be the reduction of ocular surface temperature. We believe this technique can greatly improve the surgical outcome of excimer laser photorefractive keratectomy.
References 1. Gartry, D. 5., Kerr Muir, M. G., and Marshall, J.: Excimer laser photorefractive keratectomy. 18month follow-up. Ophthalmology 99:1209, 1992. 2. Berns, M. W., Liaw, L. H., Oliva, A., Andrews, J. J., Rasmussen, R. E., and Kimel,S.: An acute light arid electron microscopic study of ultraviolet 193-nm excimer laser corneal incisions. Ophthalmology 95:1422, 1988. 3. Campos, M., Hertzog, L., Garbus, J. J., and McDonnell, P. J.: Corneal sensitivity after photore-
fractive keratectomy. Am. 1992.
J. OphthalmoI. 114:51,
Refractive Changes With Increasing Altitude After Radial Keratotomy Lawrence J. White, M.D., and COL. Thomas H. Mader,
M.e., U.S.A.
Eye and Skin Associates, P.c. (L.J.W.); and Madigan Army Medical Center (T.H.M.).
Inquiries to COL. Thomas H. Mader, M.e, U.S.A., Ophthalmology Service, Madigan Army Medical Center, Tacoma WA 98431.
Reports have described the postoperative stability of radial keratotomy, i.e but we documented postoperative refractive changes with altitude. We observed changes in refractive error in a patient who traveled from sea level to 10,000 ft one year after a radial keratotomy. Because skiers, hikers, and pilots commonly achieve an altitude of 10,000 ft or more, change in refractive error is a potentially important aspect of radial keratotomy.
AMERICAN JOURNAL OF OPHTHALMOLOGY
References 1. Palmer, S. S.: Mitomycin as adjunct chemotherapy with trabeculectomy. Ophthalmology 98:317, 1991. 2. Skura. G. L., Beeson, C. c.. Higginbotham, E. J., Lichter, P. R., Musch, D. c.. Bergstrom, T. J., Klein, T. B., and Falck, F. Y., Jr.: Intraoperative mitomycin versus postoperative 5-fluorouracil in highrisk glaucoma filtering surgery. Ophthalmology 99:438,1992. 3. Stamper, R. L., McMenemy, M. G., and Lieberman, M. F.: Hypotonous maculopathy after trabeculectomy with subconjunctival 5-fluorouraciL Am. J. Ophthalmol. 114:544, 1992. 4. Kitazawa, Y., Kawase. K., Matsushita, H., and Minobe, M.: Trabeculectomy with mitomycin. A comparative study with fluorouracil. Arch. Ophthalmol. 109:1693,1991. 5. Melamed, S., Ashkenazi, I., Belcher, D. C.; and Blumenthal, M.: Donor scleral graft patching for persistent filtration bleb leak. Ophthalmic Surg. 22:164, 1991.
Reduction of Subepithelial Haze After Photorefractive Keratectomy by Cooling the Cornea Kazuo Tsubota, M.D., Ikuko Toda, M.D., and Seiji Itoh, M.D. Department of Ophthalmology, Tokyo Dental College (K. T., LT.); Department of Ophthalmology, Keio University School of Medicine (K.T., LT.); and the Itoh Hospital (S.I.). Inquiries to Kazuo Tsubota, M.D., Department of Ophthalmology, Tokyo Dental College, 11-13 Sugano 5 chome, lchikauia-shi, Chiba, Japan 272.
Excimer laser photorefractive keratectomy is a promising modality for the correction of myopia, particularly in patients with corrections of 6 diopters or less.' One problem with this technique, however, is the postoperative subepithelial corneal haze, which inevitably develops, especially in patients with severe myopia. Many surgeons now use corticosteroids and antirnetabolites to minimize this effect., We believe modification of the photorefractive keratectomy method itself may further reduce opacification. Although photorefractive keratectomy is believed to produce minimal thermal damage,
June, 1993
the local corneal temperature has increased to 53.3 c.2 We hypothesize that thermal damage can contribute to the haze formation. In our preliminary experiments using an infrared radiation thermometer, the corneal temperature increased to 40.0 C as the number of laser pulses increased. These increases may explain why photorefractive keratectomy for severe myopia, which requires longer laser exposures, is associated with more haze. In our patients, we cooled the cornea to minimize thermal damage during photorefractive keratectomy. We examined three women with severe myopia. The patients were aged 25, 30, and 36 years, respectively. Their uncorrected visual acuities, refractive errors, and corrected visual acuities were as follows: 20/400 -7.75 sph = 20/25,20/400 -6.75 sph = 20/25, and 20/800 -9.00 sph = 20/20, respectively. The first two patients had previously undergone ordinary photorefractive keratectomy. An excimer laser with an ablation diameter of 4.5 mm was used. The ocular surface was cooled by the continuous irrigation of BSS+ (4.0 C at room temperature of 22.0 C) for five minutes before the epithelial removal and by an additional three minutes of irrigation after the removal. The irrigation lowered the corneal temperature from 35.0 C to 17.0 C. The photorefractive keratectomies were then performed, by using a total of 238, 168, and 266 pulses, respectively. The temperature of the central cornea increased, but only to 25.0 C, as measured by the infrared thermometer. The ocular surface was irrigated for one minute after the keratectomy. An observation was that the excimer laser photo ablation zone, which is often visible during the procedure, was not detectable. Immediately after the procedure, the cornea was almost completely clear in all patients. Their uncorrected visual acuities, refractive errors, and corrected visual acuities were as follows: 20/60 + 1.50 sph = 20/40, 20/40 +0.75 sph = 20/30, and 20/400 +2.00 sph = 20/40, respectively. Four days postoperatively, the ablation area was covered by epithelium, without defects on fluorescein staining. Corneal sensitivity returned to normal at this time, with uncorrected visual acuity of 20/20 in two patients and corrected visual acuity of 20/20 in the other. The two patients who had undergone photorefractive keratectomies before had previously required one month for recovery of sensation and visual acuity. Those patients also reported less pain with our technique. There
821
Letters to The Journal
Vol. 115, No.6
Figure (Tsubota, Toda, and Itoh). Patient 1. Subepithelial corneal haze two months after excimer laser photorefractive keratectomy. Left, The appearance after the usual technique. Right, The appearance after cooling of the cornea. The opacity is less in the cooled cornea.
was no apparent corneal haze in any of the three patients (Figure). Our patients' epithelial, sensory, and visual recovery was quick, with less corneal haze." Although the number of patients was small, our preliminary findings suggest that extensive irrigation by cold BSS+ can reduce corneal haze. Extensive irrigation may have other beneficial effects, such as adjusting the pH, hydrating the corneal stroma, and flushing out the ablation products, but the principal mechanism of irrigation seems to be the reduction of ocular surface temperature. We believe this technique can greatly improve the surgical outcome of excimer laser photorefractive keratectomy.
References 1. Gartry, D. 5., Kerr Muir, M. G., and Marshall, J.: Excimer laser photorefractive keratectomy. 18month follow-up. Ophthalmology 99:1209, 1992. 2. Berns, M. W., Liaw, L. H., Oliva, A., Andrews, J. J., Rasmussen, R. E., and Kimel,S.: An acute light arid electron microscopic study of ultraviolet 193-nm excimer laser corneal incisions. Ophthalmology 95:1422, 1988. 3. Campos, M., Hertzog, L., Garbus, J. J., and McDonnell, P. J.: Corneal sensitivity after photore-
fractive keratectomy. Am. 1992.
J. OphthalmoI. 114:51,
Refractive Changes With Increasing Altitude After Radial Keratotomy Lawrence J. White, M.D., and COL. Thomas H. Mader,
M.e., U.S.A.
Eye and Skin Associates, P.c. (L.J.W.); and Madigan Army Medical Center (T.H.M.).
Inquiries to COL. Thomas H. Mader, M.e, U.S.A., Ophthalmology Service, Madigan Army Medical Center, Tacoma WA 98431.
Reports have described the postoperative stability of radial keratotomy, i.e but we documented postoperative refractive changes with altitude. We observed changes in refractive error in a patient who traveled from sea level to 10,000 ft one year after a radial keratotomy. Because skiers, hikers, and pilots commonly achieve an altitude of 10,000 ft or more, change in refractive error is a potentially important aspect of radial keratotomy.