- Email: [email protected]
Panretinal Photocoagulation for Proliferative Diabetic Retinopathy
Now, we are fully convinced that injured eyes with NLP vision can be saved and can achieve light perception or better vision by vitreoretinal surgery.
hypoxia and associated neovascularization, as the authors reported.1 With the introduction of PASCAL, many physicians started using lighter lesions that naturally occur with shorter pulse durations, which produce less inner retinal damage and reduces scarring.4 Because lighter lesions have smaller diameters, they therefore require a larger number of spots to coagulate the same total area.3 We would like to bring to the authors’ attention several publications regarding clinical experience with the PASCAL method in the treatment of proliferative diabetic retinopathy,5,6 in which an increased number of spots was applied. The authors point out: “As pulse durations are decreased below 50 ms, the mechanism of cellular injury transitions from thermal energy at higher pulse durations to mechanical rupture because of transient vapor formed adjacent to melanosomes.5” In the cited paper (by Schuele and associates), which aims at destruction of retinal pigmented epithelium cells by forming microbubbles around melanosomes while sparing photoreceptors, the critical pulse duration at which the mechanism of tissue damage changes from thermal coagulation to vaporization is 50 microseconds. In PASCAL photocoagulation, pulses are much longer (in tens of milliseconds); therefore, heat diffuses into the retina. Therefore, not only the retinal pigment epithelium, but also the photoreceptors and the inner retina are affected. The extent of heat diffusion and the undesirable effect of vaporization in retinal photocoagulation are discussed in multiple publications, such as by Jain and associates.2 We thank the authors for highlighting the importance of laser parameters in the management of diabetic retinopathy and suggest that in any treatment—pharmaceutical and laser alike— dosimetry requires careful attention.
KANG FENG YUN TAO HU ZHI ZHONG MA
Beijing, People’s Republic of China CONFLICT OF INTEREST DISCLOSURES: SEE THE ORIGINAL article1 for any disclosures of the authors.
REFERENCES
1. Feng K, Hu Y, Ma Z. Prognostic indicators for no light perception after open-globe injury: eye injury vitrectomy study. Am J Ophthalmol 2011;152(4):654 – 662. 2. Feng K, Shen L, Pang X, et al. Case-control study of risk factors for no light perception after open-globe injury: Eye Injury Vitrectomy Study. Retina 2011;31(10):1988 –1996.
Panretinal Photocoagulation for Proliferative Diabetic Retinopathy EDITOR: THE AUTHORS ARE TO BE COMMENDED FOR THEIR AT-
tempt to look systematically at the outcomes of pan retinal photocoagulation as a function of laser parameters.1 Authors found that their neovascularization recurrence rates after pan retinal photocoagulation with 20-ms laser pulses were higher than those occurring with 200-ms laser pulses when the same number of lesions and the same beam diameter was applied. We would like to comment on this issue and on mechanisms of shorter-pulse retinal photocoagulation with the PASCAL method. According to Diabetic Retinopathy Study (DRS) and Early Treatment Diabetic Retinopathy Study (ETDRS) recommendations, lesions are to be applied either as a mild scatter, with 1-lesion diameter spacing, or as a full scatter, with lesions spaced by half a diameter. DRS/ETDRS studies were conducted with pulses of 100 to 200 ms in duration. Lesions produced by shorter pulses are smaller than similar-grade lesions produced by longer pulses.2,3 Therefore, if the spacing between the lesions is to be maintained as one (or half) diameter of the lesion, the grid density and the total number of lesions delivered to the same area should increase by the reciprocal of the square of the lesion diameter. This increase simply reflects a requirement to coagulate the same total area of the retina, based on the assumption of a correlation between the size of the coagulated area and reduction in retinal hypoxia or ischemia. Coagulating a smaller area and destroying a lower number of photoreceptors by using an equivalent number of smaller burns, one would be expected to reduce the benefit of decreasing the retinal 780
AMERICAN JOURNAL
DANIEL PALANKER
Palo Alto and Stanford, California MARK S. BLUMENKRANZ
Palo Alto, California
CONFLICT OF INTEREST DISCLOSURES: ALL AUTHORS have completed and submitted the ICMJE Form for Disclosure of Potential Conflicts of Interest. Both authors and their institution receive royalties from and have patents with Topcon Medical Laser Systems. Dr Palanker is a paid consultant, and Dr Blumenkranz is an unpaid consultant to Topcon Medical Laser Systems.
REFERENCES
1. Chappelow AV, Tan K, Waheed NK, Kaiser PK. Panretinal photocoagulation for proliferative diabetic retinopathy: pattern scan laser vs argon laser. Am J Ophthalmol 2012;153(1): 137–142. 2. Jain A, Blumenkranz MS, Paulus Y, et al. Effect of pulse duration on size and character of the lesion in retinal photocoagulation. Arch Ophthalmol 2008;126(1):78 – 85. 3. Palanker D, Lavinsky D, Blumenkranz MS, Marcellino G. The impact of pulse duration and burn grade on size of retinal OF
OPHTHALMOLOGY
APRIL
2012
photocoagulation lesion: implications for pattern density. Retina 2011;31(8):1664 –1669. 4. Paulus YM, Jain A, Gariano RF, et al. Healing of retinal photocoagulation lesions. Invest Ophthalmol Vis Sci 2008; 49(12):5540 –5545. 5. Muraly P, Limbad P, Srinivasan K, Ramasamy K. Single session of Pascal versus multiple sessions of conventional laser for panretinal photocoagulation in proliferative diabetic retinopathy: a comparative study. Retina 2011;31(7):1359 –1365. 6. Nagpal M, Marlecha S, Nagpal K. Comparison of laser photocoagulation for diabetic retinopathy using 532-nm standard laser versus multispot pattern scan laser. Retina 2010;30(3):452– 458.
dard laser versus multispot pattern scan laser. Retina 2010;30(3):452– 458. 3. Muraly P, Limbad P, Srinivasan K, Ramasamy K. Single session of Pascal versus multiple sessions of conventional laser for panretinal photocoagulation in proliferative diabetic retinopathy: a comparative study. Retina 2011;31(7): 1359 –1365.
Choice of Analytic Approach for EyeSpecific Outcomes: One Eye or Two? EDITOR: KARAKOSTA AND ASSOCIATES HIGHLIGHT THE IMPOR-
REPLY WE THANK PALANKER AND BLUMENKRANZ FOR HIGH-
lighting the importance of dosimetry when comparing efficacy of various laser methods. Furthermore, we appreciate their appropriate correction of our article1 indicating 50 microseconds, not 50 ms, as the laser-induced retinal damage threshold for transition from thermal denaturation to thermomechanical damage. Since our article submission, 2 reports have offered evidence of improved pattern scan laser outcomes (versus those reported in the present study) with parameters that better approximate the burn area produced by Early Treatment Diabetic Retinopathy standard laser.2,3 As such, we echo the urging of Palanker and Blumenkranz to be vigilant about carefully considering laser parameters in treatment planning. As we noted in our discussion, when using the PASCAL system for panretinal photocoagulation, physicians need to be cognizant of the need for settings different than those used previously with the argon laser. Anecdotally, our diabetic patients currently enjoy favorable outcomes after relatively brief and pain-free PASCAL treatment sessions using adjusted parameters. AIMEE V. CHAPPELOW KEVIN TAN PETER K. KAISER
Cleveland, Ohio NADIA K. WAHEED
Boston, Massachusetts CONFLICT OF INTEREST DISCLOSURES: SEE THE ORIGINAL article1 for any disclosures of the authors.
REFERENCES
1. Chappelow AV, Tan K, Waheed NK, Kaiser PK. Panretinal photocoagulation for proliferative diabetic retinopathy: pattern scan laser vs argon laser. Am J Ophthalmol 2012;153(1): 137–142. 2. Nagpal M, Marlecha S, Nagpal K. Comparison of laser photocoagulation for diabetic retinopathy using 532-nm stan-
VOL. 153, NO. 4
tance of taking into account interocular correlation when both eyes of the same subject are included in statistical calculations.1 We would like to add that such an adjustment also could be important when dealing with summed data that can contain multiple contributions from individual eyes. When assessing characteristics of lesions of interest (tumors, nevi, retinal breaks, corneal opacities, etc.) within the eye, where one eye may contain multiple such lesions, each lesion should not necessarily be treated as an independent entity, given that it may well be the case that lesion characteristics within the same eye could be correlated. The degree of correlation will differ for different parameters. Epidemiologic studies of choroidal nevi, for example, have yielded proportions of nevi with various characteristics, without explicitly adjusting for intraocular correlation in all cases.2,3 Given the low proportion of eyes with multiple nevi, such a correlation may not be expected to affect the overall comparisons significantly, although the quantification of such correlations may be interesting in understanding pathogenesis. Studies of patterns of retinal detachments similarly often have counted the total number of retinal breaks over a cohort and then quantified the proportion in each quadrant, neglecting the likelihood that multiple breaks within the same eye may not be independent with respect to location, size, and so forth.4,5 The dynamics of vitreous detachment in a particular eye may be such that multiple breaks result in the same quadrant; simply to total the number of breaks in a single quadrant in a number of eyes would mean this becomes a confounding factor. A better method, when seeking to answer whether retinal breaks are more likely to be, for example, inferonasal in one population compared with another, may be to quantify the proportion of eyes with presence (or absence) of an inferonasal break in each population (rather than simply comparing the number of inferonasal breaks in total), and then to consider numbers of breaks separately. Thus, some consideration of within-eye correlation not only may affect the validity of calculated P values and thus the presumed statistical significance of clinical
CORRESPONDENCE
781
hypoxia and associated neovascularization, as the authors reported.1 With the introduction of PASCAL, many physicians started using lighter lesions that naturally occur with shorter pulse durations, which produce less inner retinal damage and reduces scarring.4 Because lighter lesions have smaller diameters, they therefore require a larger number of spots to coagulate the same total area.3 We would like to bring to the authors’ attention several publications regarding clinical experience with the PASCAL method in the treatment of proliferative diabetic retinopathy,5,6 in which an increased number of spots was applied. The authors point out: “As pulse durations are decreased below 50 ms, the mechanism of cellular injury transitions from thermal energy at higher pulse durations to mechanical rupture because of transient vapor formed adjacent to melanosomes.5” In the cited paper (by Schuele and associates), which aims at destruction of retinal pigmented epithelium cells by forming microbubbles around melanosomes while sparing photoreceptors, the critical pulse duration at which the mechanism of tissue damage changes from thermal coagulation to vaporization is 50 microseconds. In PASCAL photocoagulation, pulses are much longer (in tens of milliseconds); therefore, heat diffuses into the retina. Therefore, not only the retinal pigment epithelium, but also the photoreceptors and the inner retina are affected. The extent of heat diffusion and the undesirable effect of vaporization in retinal photocoagulation are discussed in multiple publications, such as by Jain and associates.2 We thank the authors for highlighting the importance of laser parameters in the management of diabetic retinopathy and suggest that in any treatment—pharmaceutical and laser alike— dosimetry requires careful attention.
KANG FENG YUN TAO HU ZHI ZHONG MA
Beijing, People’s Republic of China CONFLICT OF INTEREST DISCLOSURES: SEE THE ORIGINAL article1 for any disclosures of the authors.
REFERENCES
1. Feng K, Hu Y, Ma Z. Prognostic indicators for no light perception after open-globe injury: eye injury vitrectomy study. Am J Ophthalmol 2011;152(4):654 – 662. 2. Feng K, Shen L, Pang X, et al. Case-control study of risk factors for no light perception after open-globe injury: Eye Injury Vitrectomy Study. Retina 2011;31(10):1988 –1996.
Panretinal Photocoagulation for Proliferative Diabetic Retinopathy EDITOR: THE AUTHORS ARE TO BE COMMENDED FOR THEIR AT-
tempt to look systematically at the outcomes of pan retinal photocoagulation as a function of laser parameters.1 Authors found that their neovascularization recurrence rates after pan retinal photocoagulation with 20-ms laser pulses were higher than those occurring with 200-ms laser pulses when the same number of lesions and the same beam diameter was applied. We would like to comment on this issue and on mechanisms of shorter-pulse retinal photocoagulation with the PASCAL method. According to Diabetic Retinopathy Study (DRS) and Early Treatment Diabetic Retinopathy Study (ETDRS) recommendations, lesions are to be applied either as a mild scatter, with 1-lesion diameter spacing, or as a full scatter, with lesions spaced by half a diameter. DRS/ETDRS studies were conducted with pulses of 100 to 200 ms in duration. Lesions produced by shorter pulses are smaller than similar-grade lesions produced by longer pulses.2,3 Therefore, if the spacing between the lesions is to be maintained as one (or half) diameter of the lesion, the grid density and the total number of lesions delivered to the same area should increase by the reciprocal of the square of the lesion diameter. This increase simply reflects a requirement to coagulate the same total area of the retina, based on the assumption of a correlation between the size of the coagulated area and reduction in retinal hypoxia or ischemia. Coagulating a smaller area and destroying a lower number of photoreceptors by using an equivalent number of smaller burns, one would be expected to reduce the benefit of decreasing the retinal 780
AMERICAN JOURNAL
DANIEL PALANKER
Palo Alto and Stanford, California MARK S. BLUMENKRANZ
Palo Alto, California
CONFLICT OF INTEREST DISCLOSURES: ALL AUTHORS have completed and submitted the ICMJE Form for Disclosure of Potential Conflicts of Interest. Both authors and their institution receive royalties from and have patents with Topcon Medical Laser Systems. Dr Palanker is a paid consultant, and Dr Blumenkranz is an unpaid consultant to Topcon Medical Laser Systems.
REFERENCES
1. Chappelow AV, Tan K, Waheed NK, Kaiser PK. Panretinal photocoagulation for proliferative diabetic retinopathy: pattern scan laser vs argon laser. Am J Ophthalmol 2012;153(1): 137–142. 2. Jain A, Blumenkranz MS, Paulus Y, et al. Effect of pulse duration on size and character of the lesion in retinal photocoagulation. Arch Ophthalmol 2008;126(1):78 – 85. 3. Palanker D, Lavinsky D, Blumenkranz MS, Marcellino G. The impact of pulse duration and burn grade on size of retinal OF
OPHTHALMOLOGY
APRIL
2012
photocoagulation lesion: implications for pattern density. Retina 2011;31(8):1664 –1669. 4. Paulus YM, Jain A, Gariano RF, et al. Healing of retinal photocoagulation lesions. Invest Ophthalmol Vis Sci 2008; 49(12):5540 –5545. 5. Muraly P, Limbad P, Srinivasan K, Ramasamy K. Single session of Pascal versus multiple sessions of conventional laser for panretinal photocoagulation in proliferative diabetic retinopathy: a comparative study. Retina 2011;31(7):1359 –1365. 6. Nagpal M, Marlecha S, Nagpal K. Comparison of laser photocoagulation for diabetic retinopathy using 532-nm standard laser versus multispot pattern scan laser. Retina 2010;30(3):452– 458.
dard laser versus multispot pattern scan laser. Retina 2010;30(3):452– 458. 3. Muraly P, Limbad P, Srinivasan K, Ramasamy K. Single session of Pascal versus multiple sessions of conventional laser for panretinal photocoagulation in proliferative diabetic retinopathy: a comparative study. Retina 2011;31(7): 1359 –1365.
Choice of Analytic Approach for EyeSpecific Outcomes: One Eye or Two? EDITOR: KARAKOSTA AND ASSOCIATES HIGHLIGHT THE IMPOR-
REPLY WE THANK PALANKER AND BLUMENKRANZ FOR HIGH-
lighting the importance of dosimetry when comparing efficacy of various laser methods. Furthermore, we appreciate their appropriate correction of our article1 indicating 50 microseconds, not 50 ms, as the laser-induced retinal damage threshold for transition from thermal denaturation to thermomechanical damage. Since our article submission, 2 reports have offered evidence of improved pattern scan laser outcomes (versus those reported in the present study) with parameters that better approximate the burn area produced by Early Treatment Diabetic Retinopathy standard laser.2,3 As such, we echo the urging of Palanker and Blumenkranz to be vigilant about carefully considering laser parameters in treatment planning. As we noted in our discussion, when using the PASCAL system for panretinal photocoagulation, physicians need to be cognizant of the need for settings different than those used previously with the argon laser. Anecdotally, our diabetic patients currently enjoy favorable outcomes after relatively brief and pain-free PASCAL treatment sessions using adjusted parameters. AIMEE V. CHAPPELOW KEVIN TAN PETER K. KAISER
Cleveland, Ohio NADIA K. WAHEED
Boston, Massachusetts CONFLICT OF INTEREST DISCLOSURES: SEE THE ORIGINAL article1 for any disclosures of the authors.
REFERENCES
1. Chappelow AV, Tan K, Waheed NK, Kaiser PK. Panretinal photocoagulation for proliferative diabetic retinopathy: pattern scan laser vs argon laser. Am J Ophthalmol 2012;153(1): 137–142. 2. Nagpal M, Marlecha S, Nagpal K. Comparison of laser photocoagulation for diabetic retinopathy using 532-nm stan-
VOL. 153, NO. 4
tance of taking into account interocular correlation when both eyes of the same subject are included in statistical calculations.1 We would like to add that such an adjustment also could be important when dealing with summed data that can contain multiple contributions from individual eyes. When assessing characteristics of lesions of interest (tumors, nevi, retinal breaks, corneal opacities, etc.) within the eye, where one eye may contain multiple such lesions, each lesion should not necessarily be treated as an independent entity, given that it may well be the case that lesion characteristics within the same eye could be correlated. The degree of correlation will differ for different parameters. Epidemiologic studies of choroidal nevi, for example, have yielded proportions of nevi with various characteristics, without explicitly adjusting for intraocular correlation in all cases.2,3 Given the low proportion of eyes with multiple nevi, such a correlation may not be expected to affect the overall comparisons significantly, although the quantification of such correlations may be interesting in understanding pathogenesis. Studies of patterns of retinal detachments similarly often have counted the total number of retinal breaks over a cohort and then quantified the proportion in each quadrant, neglecting the likelihood that multiple breaks within the same eye may not be independent with respect to location, size, and so forth.4,5 The dynamics of vitreous detachment in a particular eye may be such that multiple breaks result in the same quadrant; simply to total the number of breaks in a single quadrant in a number of eyes would mean this becomes a confounding factor. A better method, when seeking to answer whether retinal breaks are more likely to be, for example, inferonasal in one population compared with another, may be to quantify the proportion of eyes with presence (or absence) of an inferonasal break in each population (rather than simply comparing the number of inferonasal breaks in total), and then to consider numbers of breaks separately. Thus, some consideration of within-eye correlation not only may affect the validity of calculated P values and thus the presumed statistical significance of clinical
CORRESPONDENCE
781