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Vitreous Changes After Neodymium-YAG Laser Irradiation of the Posterior Lens Capsule or Mid-Vitreous: Reply
382
AMERICAN JOURNAL OF OPHTHALMOLOGY
What were the results of the third (T2c) group in Table 4? 5. The viscometry measurements in Table 3 indicate that only one monkey was studied by this method. The results in Table 4 are presented for only three rabbits and no primates. Was nuclear magnetic resonance performed on any primate eyes or any of the other rabbit eyes? Where are the data on the second monkey? Despite the overall excellent clinical experience with the neodymium-YAG laser to date, extending for a six-month follow-up, 2 this study raises interesting questions which we believe deserve careful consideration and investigation. We look forward to the answers to these questions and more complete studies in the future. ROGER F. S T E I N E R T ,
M.D.
CARMEN A. P U L I A F I T O ,
M.D.
Boston,
Massachusetts
REFERENCES 1. Taboada, J.: Interaction of short laser pulses with ocular tissues. In Trokel, S. L. (ed.): YAG Laser Ophthalmic Microsurgery. Norwalk, AppletonCentury-Crofts, 1983, pp. 15-38. 2. Keates, R. H. ; Steinert, R. F., Puliafito, C. A., and Maxwell, S. K.: Long-termfollow-upof Nd-YAG laser posterior capsulotomy. Am. Intra-Ocular Im plant Soc. ]. 10:164, 1984.
Reply EDITOR:
In reply to Drs. Steinert and Puliafito's comments regarding the produc tion of the shock wave as the desired principal mechanism for intraocular ap plication, I am unable to comment on the first reference they cite. However, I question this assertion because, in order to induce vaporization of the lens cap sule, one requires a power density of approximately 1 or 2 X 1012 W/cm 2 at the focal point (in this case the posterior lens capsule). In essence, one relies on the thermal effect of this power density. I certainly would not rely on the acous
SEPTEMBER, 1984
tic gradient generation to perform a capsulotomy. Furthermore, the refer ence cited in our article does not clearly state the foregoing concerning "shock waves." The paper cited in reference 4 of our article does not state that "the shock wave is the desired principal mechanism." In answer to the five additional points raised: 1. We are all aware that the rabbit eye is not the ideal model and thus that we must not extrapolate such experi ments directly to the human condition. We therefore used monkey eyes as well as rabbit eyes. Because the cost of pri mates is very high, the studies were performed on rabbits to provide a great er data base. The trends in both experi mental animals were similar. 2. The methods chosen (phakic vs aphakic or pseudophakic) are valid. Since the animals in this study were killed immediately after laser exposure, it would be surprising if "the release of liquid protein into the vitreous" could cause the vitreous changes. Further more, identical results were obtained in those animals that received mid-vitreous laser irradiation. (Their lenses were not affected at all.) 3. Tables 1 and 2 are clearly labeled to indicate that they present only con trol data. I see no reason for a statistical analysis on these data since they merely demonstrate the reproduceability of our methods and obviously do not require further analyses. These control studies were performed to evaluate the feasibil ity of utilizing the contralateral eye as the control for the eye exposed to the laser. The data in Tables 1 and 2 show an excellent correlation. Obviously, the data between different animals' eyes will differ much more compared with both eyes from one animal since the animals varied in age (that is, according to their weight); we should expect dif ferences in vitreous viscosity (with age).
VOL. 98, NO. 3
LETTERS TO THE JOURNAL
Once again, the studies were clearly de signed to monitor differences between both eyes of each experimental animal, rather than to compare the vitreous from one animal to another. The latter approach would markedly increase the variables and would certainly require statistical analyses. However, simply performing a statistical analysis irrespec tive of how and why the experiment was designed would be futile. 4. We presented three T2 values in Table 2 to demonstrate that there were at least two "bound water phases" in the vitreous (Tin and T2t>) and a T2C value of approximately 4 or 5 sec which repre sented free water (as noted on p. 473). There is a typographical error: the statement, "The T& values represent free water," is followed by a parentheti cal reference to Table 3; it should have read Table 2. These T2C values were omitted in Table 4 since they were, of course, unchanged and we believed that reporting free water T2 values once (Table 2) was sufficient. 5. It is true that the viscometry val ues for only one monkey were noted in Table 3. As noted in Material and Meth ods, we only used four monkeys and two were killed immediately. The re maining two were retained (along with half the rabbits) for our long-term stud ies. We only had data for one set of monkey eyes because the second set of eyes was accidentally placed in fixative before removal of the vitreous. How ever, we have recently killed all of our "long-term animals" and the vitreous data on both remaining monkeys and on the rabbits still show a similar effect, although the degree of viscosity and T2 changes are even greater than those noted in our article. These data togeth er with the histopathologic analyses on these eyes will be submitted for publi cation. SIDNEY LERMAN,
Atlanta,
M.D.
Georgia
383
Clinical and Pathologic Description of 17 Cases of Corneal Intraepithelial Neoplasia EDITOR:
In the article, "Clinical and patholog ic description of 17 cases of corneal in traepithelial neoplasia" (Am. J. Ophthalmol. 97:547, May 1984), by G. O. Waring III, A. M. Roth, and M. B. Ekins, I agree with the statement that tissue should be placed flat on a suppor tive surface. However, I disagree that a fine cellulose sponge should be used. The sponge will expand when placed into the fixative and the tissue will tear or become distorted. I suggest using sterile filter paper as the "supportive surface." M O R T O N E. S M I T H ,
St. Louis,
M.D.
Missouri
Reply EDITOR:
We agree with Dr. Smith's observa tion that placing tissue on a fine cellu lose sponge is not an optimal way to place it in fixative. Sterile filter paper or unsterile paper, such as that which en closes disposable goods, will support the tissue better. G E O R G E O. W A R I N G III,
Atlanta,
ALAN M. R O T H ,
Davis,
M.D.
California
MARILYN B. E K I N S ,
Atlanta,
M.D.
Georgia
M.D.
Georgia
Therapeutic Efifects of Short-Term Plasma Exchange in Endogenous Uveitis EDITOR:
In their article, "Therapeutic effects of short-term plasma exchange in endog enous uveitis" (Am. J. Ophthalmol. 97:565, May 1984), A. J. S. Wizemann and V. Wizemann presented an innova tive approach in the treatment of endog enous uveitis. However, certain points require clarification before their conclu-
AMERICAN JOURNAL OF OPHTHALMOLOGY
What were the results of the third (T2c) group in Table 4? 5. The viscometry measurements in Table 3 indicate that only one monkey was studied by this method. The results in Table 4 are presented for only three rabbits and no primates. Was nuclear magnetic resonance performed on any primate eyes or any of the other rabbit eyes? Where are the data on the second monkey? Despite the overall excellent clinical experience with the neodymium-YAG laser to date, extending for a six-month follow-up, 2 this study raises interesting questions which we believe deserve careful consideration and investigation. We look forward to the answers to these questions and more complete studies in the future. ROGER F. S T E I N E R T ,
M.D.
CARMEN A. P U L I A F I T O ,
M.D.
Boston,
Massachusetts
REFERENCES 1. Taboada, J.: Interaction of short laser pulses with ocular tissues. In Trokel, S. L. (ed.): YAG Laser Ophthalmic Microsurgery. Norwalk, AppletonCentury-Crofts, 1983, pp. 15-38. 2. Keates, R. H. ; Steinert, R. F., Puliafito, C. A., and Maxwell, S. K.: Long-termfollow-upof Nd-YAG laser posterior capsulotomy. Am. Intra-Ocular Im plant Soc. ]. 10:164, 1984.
Reply EDITOR:
In reply to Drs. Steinert and Puliafito's comments regarding the produc tion of the shock wave as the desired principal mechanism for intraocular ap plication, I am unable to comment on the first reference they cite. However, I question this assertion because, in order to induce vaporization of the lens cap sule, one requires a power density of approximately 1 or 2 X 1012 W/cm 2 at the focal point (in this case the posterior lens capsule). In essence, one relies on the thermal effect of this power density. I certainly would not rely on the acous
SEPTEMBER, 1984
tic gradient generation to perform a capsulotomy. Furthermore, the refer ence cited in our article does not clearly state the foregoing concerning "shock waves." The paper cited in reference 4 of our article does not state that "the shock wave is the desired principal mechanism." In answer to the five additional points raised: 1. We are all aware that the rabbit eye is not the ideal model and thus that we must not extrapolate such experi ments directly to the human condition. We therefore used monkey eyes as well as rabbit eyes. Because the cost of pri mates is very high, the studies were performed on rabbits to provide a great er data base. The trends in both experi mental animals were similar. 2. The methods chosen (phakic vs aphakic or pseudophakic) are valid. Since the animals in this study were killed immediately after laser exposure, it would be surprising if "the release of liquid protein into the vitreous" could cause the vitreous changes. Further more, identical results were obtained in those animals that received mid-vitreous laser irradiation. (Their lenses were not affected at all.) 3. Tables 1 and 2 are clearly labeled to indicate that they present only con trol data. I see no reason for a statistical analysis on these data since they merely demonstrate the reproduceability of our methods and obviously do not require further analyses. These control studies were performed to evaluate the feasibil ity of utilizing the contralateral eye as the control for the eye exposed to the laser. The data in Tables 1 and 2 show an excellent correlation. Obviously, the data between different animals' eyes will differ much more compared with both eyes from one animal since the animals varied in age (that is, according to their weight); we should expect dif ferences in vitreous viscosity (with age).
VOL. 98, NO. 3
LETTERS TO THE JOURNAL
Once again, the studies were clearly de signed to monitor differences between both eyes of each experimental animal, rather than to compare the vitreous from one animal to another. The latter approach would markedly increase the variables and would certainly require statistical analyses. However, simply performing a statistical analysis irrespec tive of how and why the experiment was designed would be futile. 4. We presented three T2 values in Table 2 to demonstrate that there were at least two "bound water phases" in the vitreous (Tin and T2t>) and a T2C value of approximately 4 or 5 sec which repre sented free water (as noted on p. 473). There is a typographical error: the statement, "The T& values represent free water," is followed by a parentheti cal reference to Table 3; it should have read Table 2. These T2C values were omitted in Table 4 since they were, of course, unchanged and we believed that reporting free water T2 values once (Table 2) was sufficient. 5. It is true that the viscometry val ues for only one monkey were noted in Table 3. As noted in Material and Meth ods, we only used four monkeys and two were killed immediately. The re maining two were retained (along with half the rabbits) for our long-term stud ies. We only had data for one set of monkey eyes because the second set of eyes was accidentally placed in fixative before removal of the vitreous. How ever, we have recently killed all of our "long-term animals" and the vitreous data on both remaining monkeys and on the rabbits still show a similar effect, although the degree of viscosity and T2 changes are even greater than those noted in our article. These data togeth er with the histopathologic analyses on these eyes will be submitted for publi cation. SIDNEY LERMAN,
Atlanta,
M.D.
Georgia
383
Clinical and Pathologic Description of 17 Cases of Corneal Intraepithelial Neoplasia EDITOR:
In the article, "Clinical and patholog ic description of 17 cases of corneal in traepithelial neoplasia" (Am. J. Ophthalmol. 97:547, May 1984), by G. O. Waring III, A. M. Roth, and M. B. Ekins, I agree with the statement that tissue should be placed flat on a suppor tive surface. However, I disagree that a fine cellulose sponge should be used. The sponge will expand when placed into the fixative and the tissue will tear or become distorted. I suggest using sterile filter paper as the "supportive surface." M O R T O N E. S M I T H ,
St. Louis,
M.D.
Missouri
Reply EDITOR:
We agree with Dr. Smith's observa tion that placing tissue on a fine cellu lose sponge is not an optimal way to place it in fixative. Sterile filter paper or unsterile paper, such as that which en closes disposable goods, will support the tissue better. G E O R G E O. W A R I N G III,
Atlanta,
ALAN M. R O T H ,
Davis,
M.D.
California
MARILYN B. E K I N S ,
Atlanta,
M.D.
Georgia
M.D.
Georgia
Therapeutic Efifects of Short-Term Plasma Exchange in Endogenous Uveitis EDITOR:
In their article, "Therapeutic effects of short-term plasma exchange in endog enous uveitis" (Am. J. Ophthalmol. 97:565, May 1984), A. J. S. Wizemann and V. Wizemann presented an innova tive approach in the treatment of endog enous uveitis. However, certain points require clarification before their conclu-