Letters to the Editor
than group A. This increment in therapy had led to equalization of IOP with the only difference being therefore baseline IOP which therefore would reflect in mean IOP calculation between the 2 groups. So division into 2 groups in such a cohort would give very little details or differences as they may not actually belong to different groups at all after equalization of the risk factor by aggressive treatment. It is unclear why glaucoma change probability was used for assessing trend analysis while guided progression analysis give accurate values of change in visual field index and progression over time. It is unclear how disc hemorrhages were documented 3 to 4 months after detection in a retrospective study. Although disc hemorrhages were more frequent in group B, 14 of 49 eyes (28.6%) than group A, 14.3%, it is hard to understand why disc hemorrhage was risk factor for progression on the former when the rate of progression was similar. It may be possibly explained by aggressive treatment and precipitous IOP reduction in group B with resultant hemodynamic changes and disc hemorrhages.2,4 The wide confidence intervals for the hazard ratio (1.381 to 27.775) of disc hemorrhage as risk factor in group A with similar intervals in group B suggests that these results have to be accepted with caution. Despite these limitations, the clinical implications of such observations can be many-fold. One of the most important is that the baseline IOP (rather than mean IOP) may be the single most important determinant of progression irrespective of other risk factors. The other fact remains that the rate of progression equalizes by aggressive therapy even when baseline IOP is high which highlights the importance of IOP reduction in NTG cases.2 We may also be more cautious of systemic factors5 for eyes with lower baseline IOP and may warrant detailed systemic examination to rule out cardiovascular or systemic abnormalities in these eyes even after achieving target IOP with treatment. Aparna Rao, MD, DNB, FRCS Glaucoma Services, LV Prasad Eye Institute, Patia, Bhubaneswar, India
J Glaucoma
2.
3. 4.
5.
glaucoma patients. J Glaucoma. 2014; 24:553–560. Collaborative Normal-Tension Glaucoma Study Group. The effectiveness of intraocular pressure reduction in the treatment of normal-tension glaucoma. Am J Ophthalmol. 1998;126:498–505. Anderson DR, Drance SM, Schulzer M. Natural history of normal-tension glaucoma. Ophthalmology. 2001;108:247–253. Grieshaber MC, Terhorst T, Flammer J. The pathogenesis of optic disc splinter haemorrhages: a new hypothesis. Acta Ophthalmol Scand. 2006;84:62–68. Kaiser HJ, Flammer J. Systemic hypotension: a risk factor for glaucomatous damage? Ophthalmologica. 1991;203:105–108.
Change in Retinal Nerve Fiber Layer Thickness After Trabeculectomy To the Editor: It was with great interest that we read the article by Yamada et al1 evaluating the change in retinal nerve fiber layer thickness (RNFLT) after trabeculectomy.2 The authors observed changes in the inferotemporal and superotemporal quadrants, with MD being the only significant factor influencing such a change in the eyes with early glaucoma. Change in RNFLT after filtering surgery has been reported to be associated with rapid or more significant percentage change in intraocular pressure in earlier studies.3,4 However, this study provides conflicting results, showing a considerable change in the eyes with early damage, as indicated by better MD. But a careful relook into the results shows us the reason for these findings. The authors have included patients operated during 1997 to 1998, when complication rates of trabeculectomy were very high. With such a cohort dating back so many years, we could have expected more prospective changes in RNFLT with time or rather test-retest variability in these patients. A couple of patients would be expected to have cataract, which can influence repeatability of measurements because of changes induced by the cataractous
REFERENCES 1. Lee J, Kong M, Kim J, et al. Comparison of visual field progression between relatively low and high intraocular pressure groups in normal tension
252 | www.glaucomajournal.com
Disclosure: The authors declare no conflict of interest. DOI: 10.1097/IJG.0000000000000184
Copyright
r
Volume 24, Number 3, March 2015
lens.5 These details have not been provided by the authors. The mean change in RNFLT was 6 to 10 mm, which is well within the normal testretest variability in a glaucoma patient.6,7 Hence, a statistical significance needs to be reviewed with care, taking into account that this may not reflect clinically significant change in the same parameter. In this study, MD showed a significant improvement after surgery in all patients. Yet, the test-retest variability of this parameter giving such a result has been ignored and the reason for such an improvement has not been discussed. The irrelevance of this result is reflected by minimal change in pattern SD. A careful look at the graph shows that many eyes had just an increase of 2 to 5 mm, whereas some eyes had more marked changes. This could have been correlated with percentage intraocular pressure reduction in the eyes with marked changes, which has, however, been overlooked. Interestingly, although changes were more in the temporal quadrant, MD was a significant independent factor influencing this change in the nasal quadrant. Such a discrepancy in results is not understandable and has not been discussed appropriately or explored. A change in RNFLT postsurgery has been attributed to the change in the reference plane or RNFL fibrosis, which increases the retardance or “thickness.”3,4 Such changes in retardance may also be caused by acceleration of cataractous changes postfiltering surgery.5 Therefore, this may not reflect actual clinical reversal of functions. This has been discussed and shown in several earlier studies.3,4,6 In summary, although the authors have come up with interesting yet conflicting results in this study, these have to be reevaluated keeping in mind the test-retest variability of measurements as well as causes of change in retardance postsurgery. Debananda Padhy, B.Optom, BSc Aparna Rao, MD, FRCS Glaucoma Service, LV Prasad Eye institute Patia, Bhubaneswar, India
REFERENCES 1. Yamada N, Tomita G, Yamamoto T, et al. Changes in the nerve fiber layer thickness following a reduction of intraocular pressure after trabeculectomy. J Glaucoma. 2000;9:371–375. 2. Tan JC, Hitchings RA. Reversal of disc cupping after intraocular pressure
2014 Wolters Kluwer Health, Inc. All rights reserved.
J Glaucoma
3. 4.
5.
6.
7.
Volume 24, Number 3, March 2015
reduction in topographic image series. J Glaucoma. 2004;13:351–355. Pederson JE, Herschler J. Reversal of glaucomatous cupping adults. Arch Ophthalmol. 1982;100:426–431. Irak I, Zangwill L, Garden V, et al. Change in optic disk topography after trabeculectomy. Am J Ophthalmol. 1996; 122:690–695. Sa´nchez-Cano A, Pablo LE, Larrosa JM, et al. The effect of phacoemulsification cataract surgery on polarimetry and tomography measurements for glaucoma diagnosis. J Glaucoma. 2010;19:468–474. Medeiros FA, Doshi R, Zangwill LM, et al. Long-term variability of GDx VCC retinal nerve fiber layer thickness measurements. J Glaucoma. 2007;16:277–281. Mai TA, Lemij HG. Longitudinal measurement variability of corneal birefringence and retinal nerve fiber layer thickness in scanning laser polarimetry with variable corneal compensation. Arch Ophthalmol. 2008;126:1359–1364.
Visual Electrodiagnosis in Glaucoma Screening: A Clinical Study To the Editor: We congratulate Tsaousis et al1 for the study titled “Visual electrodiagnosis in glaucoma screening: a clinical study.” The authors checked the role of steady-state pattern electroretinogram (PERG) and pattern visual evoked potentials (PVEP) in the early diagnosis of glaucoma. The method they used is excellent and results are interesting and encouraging for the early diagnosis and predicting glaucoma in clinical practice. The authors stated that glaucoma may be predicted/diagnosed with high sensitivity and specificity percentiles on the basis of the PERG and PVEP ratios of 1.07 and 1.57, respectively. However, they also stated that PERG and PVEP amplitudes for a single recording are not valuable. On the basis of these findings, we want to ask a question to the authors that they did not mention in the discussion of the article. Do they think that the findings above are related to the stimulation characteristics of the parvocellular and
Letters to the Editor
magnocellular retinal ganglion cells? If not, how can the findings be explained electrophysiologically? Another important finding in the study is the absence of correlation between PERG/PVEP ratios with glaucoma severity parameters (GDx VFI). As the authors stated, it is probably related to the low numbers of the patients and control subjects. We know that correlation P-values are strongly related to the numbers of the participants with respect to comparison analyses P-values (such as independent samples t test and ANOVA). We want to emphasize that we will assess the PERG/PVEP ratios in our clinics with high numbers of participants and use ratio values in the suspected glaucoma cases. Thanks to the authors again for the study that carries important message for glaucoma practitioners and ocular electrophysiologists. Fatih C. Gundogan, MD* Ahmet Tas, MDw Salih Altun, MD* *Department of Ophthalmology, GATA Medical School, Ankara wDepartment of Ophthalmology, Agrı Military Hospital, Agrı, Turkey
REFERENCE 1. Tsaousis KT, Plainis S, Parry NR, et al. Visual electrodiagnosis in glaucoma screening: a clinical study. J Glaucoma. 2013;22:427–431.
Reply to “Visual Electrodiagnosis in Glaucoma Screening: A Clinical Study” In Reply: We appreciate the interest shown by Gundogan and his colleagues in our study and welcome the pertinent comments on the early diagnosis of glaucoma in the clinical practice. The proposed methodology is based on preceding observations reporting a check-size–specific reduction in pattern electroretinogram (pERG) in ocular hypertension and early glaucoma.1,2
Disclosure: The authors declare no conflict of interest.
Disclosure: The authors declare no conflict of interest.
DOI: 10.1097/IJG.0000000000000183
DOI: 10.1097/IJG.0000000000000179
Copyright
r
2014 Wolters Kluwer Health, Inc. All rights reserved.
Since the amplitude of pERG, and especially of visual evoked potentials, “suffer” from a high interindividual variability, the “ratio” of responses to large and smaller check sizes is used to partly overcome this variability between subjects.2 Our results show that pERG and visual evoked potentials can form a sensitive indicator of ganglion cell function, only when a ratio of responses to 2 stimuli of different sizes is used. Research on early glaucoma diagnosis has been dominated for many years by the “magnocellular paradigm”, that is, the preferential damage to large nerve fibers. More recent studies, although, show that magnocellular damage in early glaucoma is only marginally greater—if at all—than parvocellular damage.2,3 This is in agreement with the well-known early blue deficits in glaucoma which are not compatible with a magnocellular mechanism.4 Whatever the case may be, further studies on the correlation between electrophysiological measures and examination techniques based on anatomic measurements such as GDx’s Nerve Fiber Index, optical coherence tomography, or Heidelberg retina tomograph need to be done. Konstantinos T. Tsaousis, MD, MSc*w Sotiris Plainis, MSc, PhD* Neil R.A. Parry, PhDz *Institute of Vision and Optics (IVO) School of Health Sciences, University of Crete, Heraklion wDepartment of Ophthalmology, Medical School, Aristotle University of Thessaloniki Thessaloniki, Greece zManchester Academic Health Science Centre, University of Manchester and Vision Science Centre, Manchester Royal Eye Hospital, Manchester, UK
REFERENCES 1. Bach M, Hiss P, Ro¨ver J. Check-size specific changes of pattern electroretinogram in patients with early open-angle glaucoma. Doc Ophthalmol. 1988;69: 315–322. 2. Bach M, Hoffmann M. Update on the pattern electroretinogram in glaucoma. Optom Vis Sci. 2008;85:386–395. 3. Johnson CA, Spry PGD, Cioffi GA, et al. Evaluation of a variety of visual function tests in ocular hypertension and early glaucoma patients. Invest Ophthalmol Vis Sci. 2000;41:S104. Abstract no 541. 4. Sample PA. Short-wavelength automated perimetry: it’s role in the clinic and for understanding ganglion cell function. Prog Retin Eye Res. 2000;19: 369–383.
www.glaucomajournal.com |
253
than group A. This increment in therapy had led to equalization of IOP with the only difference being therefore baseline IOP which therefore would reflect in mean IOP calculation between the 2 groups. So division into 2 groups in such a cohort would give very little details or differences as they may not actually belong to different groups at all after equalization of the risk factor by aggressive treatment. It is unclear why glaucoma change probability was used for assessing trend analysis while guided progression analysis give accurate values of change in visual field index and progression over time. It is unclear how disc hemorrhages were documented 3 to 4 months after detection in a retrospective study. Although disc hemorrhages were more frequent in group B, 14 of 49 eyes (28.6%) than group A, 14.3%, it is hard to understand why disc hemorrhage was risk factor for progression on the former when the rate of progression was similar. It may be possibly explained by aggressive treatment and precipitous IOP reduction in group B with resultant hemodynamic changes and disc hemorrhages.2,4 The wide confidence intervals for the hazard ratio (1.381 to 27.775) of disc hemorrhage as risk factor in group A with similar intervals in group B suggests that these results have to be accepted with caution. Despite these limitations, the clinical implications of such observations can be many-fold. One of the most important is that the baseline IOP (rather than mean IOP) may be the single most important determinant of progression irrespective of other risk factors. The other fact remains that the rate of progression equalizes by aggressive therapy even when baseline IOP is high which highlights the importance of IOP reduction in NTG cases.2 We may also be more cautious of systemic factors5 for eyes with lower baseline IOP and may warrant detailed systemic examination to rule out cardiovascular or systemic abnormalities in these eyes even after achieving target IOP with treatment. Aparna Rao, MD, DNB, FRCS Glaucoma Services, LV Prasad Eye Institute, Patia, Bhubaneswar, India
J Glaucoma
2.
3. 4.
5.
glaucoma patients. J Glaucoma. 2014; 24:553–560. Collaborative Normal-Tension Glaucoma Study Group. The effectiveness of intraocular pressure reduction in the treatment of normal-tension glaucoma. Am J Ophthalmol. 1998;126:498–505. Anderson DR, Drance SM, Schulzer M. Natural history of normal-tension glaucoma. Ophthalmology. 2001;108:247–253. Grieshaber MC, Terhorst T, Flammer J. The pathogenesis of optic disc splinter haemorrhages: a new hypothesis. Acta Ophthalmol Scand. 2006;84:62–68. Kaiser HJ, Flammer J. Systemic hypotension: a risk factor for glaucomatous damage? Ophthalmologica. 1991;203:105–108.
Change in Retinal Nerve Fiber Layer Thickness After Trabeculectomy To the Editor: It was with great interest that we read the article by Yamada et al1 evaluating the change in retinal nerve fiber layer thickness (RNFLT) after trabeculectomy.2 The authors observed changes in the inferotemporal and superotemporal quadrants, with MD being the only significant factor influencing such a change in the eyes with early glaucoma. Change in RNFLT after filtering surgery has been reported to be associated with rapid or more significant percentage change in intraocular pressure in earlier studies.3,4 However, this study provides conflicting results, showing a considerable change in the eyes with early damage, as indicated by better MD. But a careful relook into the results shows us the reason for these findings. The authors have included patients operated during 1997 to 1998, when complication rates of trabeculectomy were very high. With such a cohort dating back so many years, we could have expected more prospective changes in RNFLT with time or rather test-retest variability in these patients. A couple of patients would be expected to have cataract, which can influence repeatability of measurements because of changes induced by the cataractous
REFERENCES 1. Lee J, Kong M, Kim J, et al. Comparison of visual field progression between relatively low and high intraocular pressure groups in normal tension
252 | www.glaucomajournal.com
Disclosure: The authors declare no conflict of interest. DOI: 10.1097/IJG.0000000000000184
Copyright
r
Volume 24, Number 3, March 2015
lens.5 These details have not been provided by the authors. The mean change in RNFLT was 6 to 10 mm, which is well within the normal testretest variability in a glaucoma patient.6,7 Hence, a statistical significance needs to be reviewed with care, taking into account that this may not reflect clinically significant change in the same parameter. In this study, MD showed a significant improvement after surgery in all patients. Yet, the test-retest variability of this parameter giving such a result has been ignored and the reason for such an improvement has not been discussed. The irrelevance of this result is reflected by minimal change in pattern SD. A careful look at the graph shows that many eyes had just an increase of 2 to 5 mm, whereas some eyes had more marked changes. This could have been correlated with percentage intraocular pressure reduction in the eyes with marked changes, which has, however, been overlooked. Interestingly, although changes were more in the temporal quadrant, MD was a significant independent factor influencing this change in the nasal quadrant. Such a discrepancy in results is not understandable and has not been discussed appropriately or explored. A change in RNFLT postsurgery has been attributed to the change in the reference plane or RNFL fibrosis, which increases the retardance or “thickness.”3,4 Such changes in retardance may also be caused by acceleration of cataractous changes postfiltering surgery.5 Therefore, this may not reflect actual clinical reversal of functions. This has been discussed and shown in several earlier studies.3,4,6 In summary, although the authors have come up with interesting yet conflicting results in this study, these have to be reevaluated keeping in mind the test-retest variability of measurements as well as causes of change in retardance postsurgery. Debananda Padhy, B.Optom, BSc Aparna Rao, MD, FRCS Glaucoma Service, LV Prasad Eye institute Patia, Bhubaneswar, India
REFERENCES 1. Yamada N, Tomita G, Yamamoto T, et al. Changes in the nerve fiber layer thickness following a reduction of intraocular pressure after trabeculectomy. J Glaucoma. 2000;9:371–375. 2. Tan JC, Hitchings RA. Reversal of disc cupping after intraocular pressure
2014 Wolters Kluwer Health, Inc. All rights reserved.
J Glaucoma
3. 4.
5.
6.
7.
Volume 24, Number 3, March 2015
reduction in topographic image series. J Glaucoma. 2004;13:351–355. Pederson JE, Herschler J. Reversal of glaucomatous cupping adults. Arch Ophthalmol. 1982;100:426–431. Irak I, Zangwill L, Garden V, et al. Change in optic disk topography after trabeculectomy. Am J Ophthalmol. 1996; 122:690–695. Sa´nchez-Cano A, Pablo LE, Larrosa JM, et al. The effect of phacoemulsification cataract surgery on polarimetry and tomography measurements for glaucoma diagnosis. J Glaucoma. 2010;19:468–474. Medeiros FA, Doshi R, Zangwill LM, et al. Long-term variability of GDx VCC retinal nerve fiber layer thickness measurements. J Glaucoma. 2007;16:277–281. Mai TA, Lemij HG. Longitudinal measurement variability of corneal birefringence and retinal nerve fiber layer thickness in scanning laser polarimetry with variable corneal compensation. Arch Ophthalmol. 2008;126:1359–1364.
Visual Electrodiagnosis in Glaucoma Screening: A Clinical Study To the Editor: We congratulate Tsaousis et al1 for the study titled “Visual electrodiagnosis in glaucoma screening: a clinical study.” The authors checked the role of steady-state pattern electroretinogram (PERG) and pattern visual evoked potentials (PVEP) in the early diagnosis of glaucoma. The method they used is excellent and results are interesting and encouraging for the early diagnosis and predicting glaucoma in clinical practice. The authors stated that glaucoma may be predicted/diagnosed with high sensitivity and specificity percentiles on the basis of the PERG and PVEP ratios of 1.07 and 1.57, respectively. However, they also stated that PERG and PVEP amplitudes for a single recording are not valuable. On the basis of these findings, we want to ask a question to the authors that they did not mention in the discussion of the article. Do they think that the findings above are related to the stimulation characteristics of the parvocellular and
Letters to the Editor
magnocellular retinal ganglion cells? If not, how can the findings be explained electrophysiologically? Another important finding in the study is the absence of correlation between PERG/PVEP ratios with glaucoma severity parameters (GDx VFI). As the authors stated, it is probably related to the low numbers of the patients and control subjects. We know that correlation P-values are strongly related to the numbers of the participants with respect to comparison analyses P-values (such as independent samples t test and ANOVA). We want to emphasize that we will assess the PERG/PVEP ratios in our clinics with high numbers of participants and use ratio values in the suspected glaucoma cases. Thanks to the authors again for the study that carries important message for glaucoma practitioners and ocular electrophysiologists. Fatih C. Gundogan, MD* Ahmet Tas, MDw Salih Altun, MD* *Department of Ophthalmology, GATA Medical School, Ankara wDepartment of Ophthalmology, Agrı Military Hospital, Agrı, Turkey
REFERENCE 1. Tsaousis KT, Plainis S, Parry NR, et al. Visual electrodiagnosis in glaucoma screening: a clinical study. J Glaucoma. 2013;22:427–431.
Reply to “Visual Electrodiagnosis in Glaucoma Screening: A Clinical Study” In Reply: We appreciate the interest shown by Gundogan and his colleagues in our study and welcome the pertinent comments on the early diagnosis of glaucoma in the clinical practice. The proposed methodology is based on preceding observations reporting a check-size–specific reduction in pattern electroretinogram (pERG) in ocular hypertension and early glaucoma.1,2
Disclosure: The authors declare no conflict of interest.
Disclosure: The authors declare no conflict of interest.
DOI: 10.1097/IJG.0000000000000183
DOI: 10.1097/IJG.0000000000000179
Copyright
r
2014 Wolters Kluwer Health, Inc. All rights reserved.
Since the amplitude of pERG, and especially of visual evoked potentials, “suffer” from a high interindividual variability, the “ratio” of responses to large and smaller check sizes is used to partly overcome this variability between subjects.2 Our results show that pERG and visual evoked potentials can form a sensitive indicator of ganglion cell function, only when a ratio of responses to 2 stimuli of different sizes is used. Research on early glaucoma diagnosis has been dominated for many years by the “magnocellular paradigm”, that is, the preferential damage to large nerve fibers. More recent studies, although, show that magnocellular damage in early glaucoma is only marginally greater—if at all—than parvocellular damage.2,3 This is in agreement with the well-known early blue deficits in glaucoma which are not compatible with a magnocellular mechanism.4 Whatever the case may be, further studies on the correlation between electrophysiological measures and examination techniques based on anatomic measurements such as GDx’s Nerve Fiber Index, optical coherence tomography, or Heidelberg retina tomograph need to be done. Konstantinos T. Tsaousis, MD, MSc*w Sotiris Plainis, MSc, PhD* Neil R.A. Parry, PhDz *Institute of Vision and Optics (IVO) School of Health Sciences, University of Crete, Heraklion wDepartment of Ophthalmology, Medical School, Aristotle University of Thessaloniki Thessaloniki, Greece zManchester Academic Health Science Centre, University of Manchester and Vision Science Centre, Manchester Royal Eye Hospital, Manchester, UK
REFERENCES 1. Bach M, Hiss P, Ro¨ver J. Check-size specific changes of pattern electroretinogram in patients with early open-angle glaucoma. Doc Ophthalmol. 1988;69: 315–322. 2. Bach M, Hoffmann M. Update on the pattern electroretinogram in glaucoma. Optom Vis Sci. 2008;85:386–395. 3. Johnson CA, Spry PGD, Cioffi GA, et al. Evaluation of a variety of visual function tests in ocular hypertension and early glaucoma patients. Invest Ophthalmol Vis Sci. 2000;41:S104. Abstract no 541. 4. Sample PA. Short-wavelength automated perimetry: it’s role in the clinic and for understanding ganglion cell function. Prog Retin Eye Res. 2000;19: 369–383.
www.glaucomajournal.com |
253
