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Ocular integrity after refractive procedures: Author’s reply
Letters to the Editor Ocular
Integrity
after
Refractive
Procedures
Dear Editor: While I commend Peacock et al for their painstaking work in the study of rupture patterns of cadaver eyes having undergone various refractive procedures,’ I am concerned about the clinical applicability of the results generated, especially since they would most probably be used to disuade a patient from having incisional surgery in favor of a nonincisional technique. Although the authors acknowledge lack of wound healing in all procedures as a limitation of their study, this factor cannot be so easily dismissed, especially for RK. For example, Bryant et al* found no significant difference in tensile strength between cornea1 tissue from a patient with well-healed RK wounds 8 years after surgery and that of control untreated corneas. Thus, the conclusion that “RK eyes ruptured with significantly less energy than did normal eyes” may not have been true in the typical clinical situation of wellhealed incisions. Another possible shortcoming is inherent in the study device itself. While the authors recognized that the “considerable protection afforded to the globe by the orbit was not evaluated in the study,” indeed the circular depression in the wooden block used to hold the cadaver eyes, being a rigid surface, may have actually provided greater protection to the posterior globe than orbital fat, limiting or precluding ruptures in this region, which are obviously possible in traumatized virgin eyes in situ, thus interjecting an additional confounding factor. In fairness, some weakening of the cornea likely does occur after incisional surgery, although probably not as much as would be suggested by the study. In addition to the references cited by the authors on this issue, and contrasting with the Bryant study, Lee et al3 reported dehiscence of radial and arcuate cornea1 scars secondary to blunt trauma 91 months out (about 7 i/Z years). Yet, even if that is the case, reintroducing the possibility of a typically irreparable posterior traumatic rupture that might involve the retina and comparing that with a conceivably repairable anterior one, to the degree that they offer a potential “release valve” effect, incisional techniques might, under such circumstances, actually be more attractive than their nonincisional counterparts. CRAIG H. KLIGER, MD
Bakersjeld,
Culijornia
References
PeacockLW, Slade SG, Martiz J, et al. Ocular integrity after refractive procedures. Ophthalmology 1997;104: 1079-83. Bryant MR, Szerenyi K, SchmotzerH, McDonnell PJ. Corneal tensile strength in fully healed radial keratotomy wounds.Invest OphthalmolVis Sci 1994;35:3022-31. Lee BL, Manche EE, GlasgowBJ. Ruptureof radial and arcuatekeratotomy scarsby blunt trauma91 monthsafter incisionalkeratotomy. Am J Ophthalmol 1995;120:10810.
(The author of this correspondence declares that no ownership interest orjnancial corzflict of interest is believed to exist regarding the issue addressed in the letter.) Author’s reply Dear Editor: Dr. Kliger has correctly pointed out that wound healing is a significant factor in ocular integrity after incisional refractive surgery. With our study design it was, however, impossible to evaluate this effect which we described as a limitation of the study. We realize that this study may not be representative of the clinical situation of trauma in an eye with well-healed cornea1 incisions. As regards the study device, once again Dr. Kliger correctly points out that the eyes were placed into a circular depression within a wooden block before being subjected to trauma. Had we been able to use cadaver heads to more closely simulate the effects of the orbit, we may have had a more realistic evaluation of the reaction of the eye to trauma in situ. Dr. Kliger also introduces the interesting possibility of what he calls a “release valve” effect. The authors regard this possibility as a likely consequence following blunt trauma to eyes which have undergone incisional surgery. The question of whether this “release valve” protects the eye from posterior rupture has yet to be answered. LESTERW. PEACOCK, MD
Houston, Texus Dear Editor: I read with great interest the article entitled, “Ocular Integrity after Refractive Procedures” (Ophthalmology 1997; 104:1079-83) by Drs. Peacock et al. I would like to inquire of the authors whether or not the method of radial keratotomy done on the donor eye involved cutting the limbus or not cutting the limbus at the time of the procedure. There is much evidence that limbalsparing radial keratotomy preserves the strength of the globe much better than that involving the limbus. J. CHARLESCASEBEER,MD
Scottsdale, Arizona Author’s reply Dear Editor: Dr. Casebeer has inquired about the method of radial keratotomy performed on our donor eyes. As stated in the Materials and Methods section of the paper, we used a modified Lindstrom mini-RK nomogram and performed a limbal-sparing technique as described for this nomogram. Limbal-sparing techniques were preferred at the time of the study as a result of prior similar articles which revealed that limbal-sparing techniques preserve the integrity of the globe much better than those that involve the limbus. We apologize for any confusion on this point. LESTER W. PEACOCK, MD
Houston, Texas 393
Integrity
after
Refractive
Procedures
Dear Editor: While I commend Peacock et al for their painstaking work in the study of rupture patterns of cadaver eyes having undergone various refractive procedures,’ I am concerned about the clinical applicability of the results generated, especially since they would most probably be used to disuade a patient from having incisional surgery in favor of a nonincisional technique. Although the authors acknowledge lack of wound healing in all procedures as a limitation of their study, this factor cannot be so easily dismissed, especially for RK. For example, Bryant et al* found no significant difference in tensile strength between cornea1 tissue from a patient with well-healed RK wounds 8 years after surgery and that of control untreated corneas. Thus, the conclusion that “RK eyes ruptured with significantly less energy than did normal eyes” may not have been true in the typical clinical situation of wellhealed incisions. Another possible shortcoming is inherent in the study device itself. While the authors recognized that the “considerable protection afforded to the globe by the orbit was not evaluated in the study,” indeed the circular depression in the wooden block used to hold the cadaver eyes, being a rigid surface, may have actually provided greater protection to the posterior globe than orbital fat, limiting or precluding ruptures in this region, which are obviously possible in traumatized virgin eyes in situ, thus interjecting an additional confounding factor. In fairness, some weakening of the cornea likely does occur after incisional surgery, although probably not as much as would be suggested by the study. In addition to the references cited by the authors on this issue, and contrasting with the Bryant study, Lee et al3 reported dehiscence of radial and arcuate cornea1 scars secondary to blunt trauma 91 months out (about 7 i/Z years). Yet, even if that is the case, reintroducing the possibility of a typically irreparable posterior traumatic rupture that might involve the retina and comparing that with a conceivably repairable anterior one, to the degree that they offer a potential “release valve” effect, incisional techniques might, under such circumstances, actually be more attractive than their nonincisional counterparts. CRAIG H. KLIGER, MD
Bakersjeld,
Culijornia
References
PeacockLW, Slade SG, Martiz J, et al. Ocular integrity after refractive procedures. Ophthalmology 1997;104: 1079-83. Bryant MR, Szerenyi K, SchmotzerH, McDonnell PJ. Corneal tensile strength in fully healed radial keratotomy wounds.Invest OphthalmolVis Sci 1994;35:3022-31. Lee BL, Manche EE, GlasgowBJ. Ruptureof radial and arcuatekeratotomy scarsby blunt trauma91 monthsafter incisionalkeratotomy. Am J Ophthalmol 1995;120:10810.
(The author of this correspondence declares that no ownership interest orjnancial corzflict of interest is believed to exist regarding the issue addressed in the letter.) Author’s reply Dear Editor: Dr. Kliger has correctly pointed out that wound healing is a significant factor in ocular integrity after incisional refractive surgery. With our study design it was, however, impossible to evaluate this effect which we described as a limitation of the study. We realize that this study may not be representative of the clinical situation of trauma in an eye with well-healed cornea1 incisions. As regards the study device, once again Dr. Kliger correctly points out that the eyes were placed into a circular depression within a wooden block before being subjected to trauma. Had we been able to use cadaver heads to more closely simulate the effects of the orbit, we may have had a more realistic evaluation of the reaction of the eye to trauma in situ. Dr. Kliger also introduces the interesting possibility of what he calls a “release valve” effect. The authors regard this possibility as a likely consequence following blunt trauma to eyes which have undergone incisional surgery. The question of whether this “release valve” protects the eye from posterior rupture has yet to be answered. LESTERW. PEACOCK, MD
Houston, Texus Dear Editor: I read with great interest the article entitled, “Ocular Integrity after Refractive Procedures” (Ophthalmology 1997; 104:1079-83) by Drs. Peacock et al. I would like to inquire of the authors whether or not the method of radial keratotomy done on the donor eye involved cutting the limbus or not cutting the limbus at the time of the procedure. There is much evidence that limbalsparing radial keratotomy preserves the strength of the globe much better than that involving the limbus. J. CHARLESCASEBEER,MD
Scottsdale, Arizona Author’s reply Dear Editor: Dr. Casebeer has inquired about the method of radial keratotomy performed on our donor eyes. As stated in the Materials and Methods section of the paper, we used a modified Lindstrom mini-RK nomogram and performed a limbal-sparing technique as described for this nomogram. Limbal-sparing techniques were preferred at the time of the study as a result of prior similar articles which revealed that limbal-sparing techniques preserve the integrity of the globe much better than those that involve the limbus. We apologize for any confusion on this point. LESTER W. PEACOCK, MD
Houston, Texas 393