Recent eLetters
Displaying 11-20 letters out of 402 published
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Authors' Response
Submit responseDear editor,
We would like to give a response to the letter of Dr. Anshuman Sinha concerning our article "23 Gauge versus 20 Gauge System for Pars Plana Vitrectomy: A Prospective Randomized Clinical Trial".
For analysis of postoperative pain we used a simplified verbal rating scale (ranging from 0, meaning no pain, to 3, meaning severe pain). The standardized verbal rating scale reaches from 0 (no pain) to 10 ("the worst pain possible"), which we think is too extensive for our patients and purpose. In literature verbal rating scales are described to be a valid, reliable and appropriate tool for determination of postoperative pain in clinical practice [1,2] Furthermore we believe that the assessment of postoperative pain is not likely to be biased if the assessor is not masked, because the perception of pain is a completely subjective parameter.
Regarding the sample size evaluation: The effect size was assumed to be 75% of the standard deviation and the power to be 80%. These assumptions were extrapolated from the observations of our previous study [3]. Unfortunately, this information had been dropped from a previous version of the manuscript for brevity.
It is well known that studies with single surgeons have better results than with multiple surgeons. On the other hand, it is recommended to choose a realistic situation to achieve more realistic results. Our surgeons were randomized and there was a general surgical protocol to be followed. This also is the reason why we used two different vitrectomy machines. Both of them work in a comparable way and the settings were preset and the same in both machines. We agree, that the lens status has an influence on the amount of vitreous removed and that an intraocular tamponade influences postoperative eye pressure. However, both factors were equally distributed in both surgical groups and therefore have no influence on the results. Concerning the way of suturing the 20 gauge wounds, this was done the same way in all patients using vicryl 7.0 sutures as described in the methods section.
A summary of nominal categorical data would have to be done by contingency tables and neither by mean nor by median and interquartile range. Since the data mentioned are not of nominal but ordinal nature, we assume that the author of this letter refers to ordinal data. We have to note that the summary presented in table 2 was done for the area under the curve (AUC) for the conjunctival injection and postoperative pain measured at days 0, 1, 2, 3, one week, one month and three months after surgery as indicated in figures 1 and 2. Although theses measurements are, strictly speaking, still of ordinal nature they have a large range of values (see table 2) and hence can be treated as metric variables. Moreover, it is common practice to summarize AUCs by mean and standard deviation. We also note that in a previous version of the paper we have given in addition to the mean and standard deviation also the median, first and third quartile. Unfortunately, these numbers as well as the information in the text that the AUCs are summarized have been omitted in the edited manuscript.
We furthermore agree that each complication represents a serious situation. However, from the data of our study we can not conclude that a clear indication for higher risk is given using 23 gauge vitrectomy. This question remains open and a larger prospective randomized study is needed to get a clear result of the safety of 23 gauge surgery. Since the data do not indicate a difference in the development of serious complications between the two treatment groups we made the cited careful assertion "seems to be a safe system".
Regarding the Consolidated Standards for Reporting Trials (CONSORT) statement [4], we certainly know and appreciate this publication and followed these recommendations. Moreover, our article represents the only prospective randomized study concerning this topic. We do appreciate your considerations, but we strongly believe that we have performed a well-designed study. Still, there are always things that can be improved.
References
1.Williamson A, Hoggart B. Pain: a review of three commonly used pain rating scales. J Clin Nurs. 2005 Aug;14(7):798-804.
2.Randall C. Cork, Ihab Isaac, Ahmad Elsharydah, Sarosh Saleemi, Frank Zavisca and Lori Alexander: A comparison of the verbal rating scale and the visual analog scale for pain assessment. The Internet Journal of Anesthesiology. 2004: Volume 8, Number1.
3.Kellner L, Wimpissinger B, Stolba U, Brannath W, Binder S. 25-gauge vs 20-gauge system for pars plana vitrectomy: a prospective randomised clinical trial. Br J Ophthalmol. 2007 Jul;91(7):945-8.
4.Moher D, Schulz KF, Altman DG. The CONSORT statement: revised recommendations for improving the quality of reports of parallel-group randomised trials. Lancet 2001;357:1191-4.
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Vision screening in children by Plusoptix Vision ScreenerTM compared with gold standard orthoptic as
Submit responseAmerican pediatricians, armed with a new reimbursement code for photoscreening young children (99174), are very interested in the validity of potential instruments. As such, we were interested in the recent report that compared Plusoptix photoscreener to orthoptic exam in early primary school children, reporting 100% specificity but relatively low sensitivity: “the sensitivity of the PVS to detect amblyopia-associated factors is 44%, with 95% CI from 28 to 62%. Even a sensitivity of 62% would be less than desirable for a standalone screening test”[1] We are concerned the methodology and terminology for “sensitivity” differs from what many pediatricians might expect. From Table 3, it appears the PlusOptix was able to detect most refractive errors but underestimated cycloplegic hyperopia and strabismus. We ask that the authors report their results by using pre-defined pediatric ophthalmology risk levels (ref 10) and clarify the limited number of their subject who actually completed the cycloplegic examination which others consider the gold standard[2]. Plusoptix allows users to pre-define age-based referral cut offs for various amblyopia risk factors. We wonder why the authors chose their PlusOptix cutoffs that differed from an attempt to calibrate the instrument in reference 21?[3] Furthermore we wonder if changing the cutoff for hyperopia may increase the accuracy of the device. It may be worthwhile to re-analyze this original cohort to see if the sensitivity would improve. It would also be worth noting how the gold standard orthoptic vision screening compares to a dilated cyclopleged examination by a pediatric ophthalmologist, as comparing the Plusoptix to a comprehensive ophthalmology examination may change the reliability. Orthoptists are ideally trained to provide an accurate pediatric vision screening on children, however in certain countries, such as the United States of America, with a population of approximately 305 million people and only approximately 300 orthoptists more efficient methods of pediatric vision screenings must be discovered and refined. In recent population studies the prevalence of childhood amblyopia, primarily comprised of refractive error and manifest esotropia, is about 2.5%[4]. If an acceptable screening technique has false positive rate less than 1/3, then the ideal referral rate should be about 4%, much closer to the PlusOptix compared to 12.5% for orthoptic screening. The author’s “gold standard” orthoptic screening has merit, but probably has low predictive value for amblyopia screening.
Robert W. Arnold, MD
Noelle Matta CO, CRC, COT, Orthoptist
Members of the Vision Screening Committee of AAPOSReferences
1. Dahlmann-Noor A, Vrotsou K, Kostakis V, et al. Vision screening in Children by Plusoptix Vision Screener compared with gold standard orthoptic assessment. Br J Ophthalmol 2008;92:e-pub.
2. Donahue S, Arnold R, Ruben JB. Preschool vision screening: What should we be detecting and how should we report it? Uniform guidelines for reporting results from studies of preschool vision screening. J AAPOS 2003;7:314-6.
3. Clausen MM, Arnold RW. Pediatric Eye/Vision Screening: Referral Criteria for the PediaVision PlusOptix S04 Photoscreener Compared to Visual Acuity & Digital Photoscreening: “Kindergarten Computer Photoscreening”. Binoc Vis and Strabismus Quart 2007;22:83-9.
4. MEPEDS. Prevalence of amblyopia and strabismus in African American and Hispanic children ages 6 to 72 months the multi-ethnic pediatric eye disease study. Ophthalmology 2008;115:1229-36 e1. -
Comments on 23-gauge versus 20-gauge system for pars plana vitrectomy
Submit responseDear editor,
We read with interest the paper by Wimpissinger et al comparing sutureless 23-gauge system to a standard 20-gauge system for pars plana vitrectomy, in a randomized clinical trial.[1] We aim to highlight a few issues in the design, methodology and analysis.
The authors have analysed postoperative pain and conjunctival injection as primary outcome measures. The effort by the assessor to elicit a response on the degree of pain is likely to be biased if he is not masked, as in this study. In assessment, the authors have used descriptive terms like no pain, mild, moderate and severe pain. The authors could have used other standardized methods described to measure pain such as numerical scores, faces scale, visual analogue scales and multidimensional instruments like various questionnaires. Literature in Ophthalmology has precedence of using a visual analogue scale for assessment of pain.[2]
The authors determined the sample size by statistical pre-study evaluation (by two group t-test with a 0.05 two-sided significance level). Since the authors have not provided data on effect size (delta), and power (1-beta), it is not clear how a sample size of 60 with 30 patients in each arm was arrived at.
The other confounding variable likely to be of significance are the issues like randomization of 4 surgeons (instead of preferably single surgeon), use of different machines for 20Ga and 23Ga surgeries, unspecified cut rates for 20Ga system (likely to influence time of vitrectomy), the lens status (likely to influence the extent of vitrectomy possible and aimed at), type of tamponade (likely to influence postoperative intraocular pressures) and suturing technique of conjunctiva (likely to influence subjective pain) after 20Ga surgery.
In analysis, nominal type of categorical data (as used for assessing postoperative pain and conjunctival injection) would have been better analysed in terms of median and interquartile range rather than taking their minimum, maximum and average values.
The authors have concluded that "The 23 gauge system seems to be a safe system suitable for a broad spectrum of vitreoretinal diseases". We disagree with this conclusion as the data provided shows that 3 (10%, 95% CI -0.74 to 20.74%) patients developed serious complications, 2 of whom required re-surgery.[1]
An international group developed the Consolidated Standards for Reporting Trials (CONSORT) statement in an attempt to improve documented suboptimal reporting of RCTs.[3] In an attempt to further improve the reporting of RCTs, the same international group published the revised CONSORT statement in 2001 which outlined a checklist of 22 items.[4]
References
1. B Wimpissinger, L Kellner, W Brannath, K Krepler, U Stolba, C Mihalics and S Binder. 23-gauge versus 20-gauge system for pars plana vitrectomy: a prospective randomised clinical trial. Br J Ophthalmol 2008; 92; 1483-1487.
2. Mathew MR, Williams A, Esakowitz L, Webb LA, Murray SB, Bennett HG. Patient comfort during clear corneal phacoemulsification with sub- Tenon's local anesthesia. J Cataract Refract Surg 2003 ; 29(6): 1132-6.
3. Begg C, Cho M, Eastwood S, et al. Improving the quality of reporting of randomized controlled trials. The CONSORT statement. JAMA 1996;276:637-9.
4. Moher D, Schulz KF, Altman DG. The CONSORT statement: revised recommendations for improving the quality of reports of parallel-group randomised trials. Lancet 2001;357:1191-4.
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Fast Macular Thickness Versus Radial Lines protocol?
Submit responseI read with interest the recent study by Yi et al.
A very minor point... were the Stratus OCT images obtained using the "Radial Lines" protocol or the "Fast Macular Thickness" protocol? From Figure 1, I suspect that the higher resolution Radial Lines protocol was used (and not Fast Macular Thickness as described in the manuscript).
In any event, I commend the authors for a worthwhile addition to the literature.
Pearse Keane
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Spontaneous visual improvement in dominant optic atrophy
Submit responseDear Editor:
I read with interest the article by Dr. Cohn, et al regarding the natural history of autosomal dominant optic atrophy (DOA). The authors describe an average of 10-year follow up for 69 patients with genetically confirmed DOA. In their study, 6 (9%) patients enjoyed improvement in visual acuity by 2 or more lines.
I found this surprising, and I wonder if the authors could provide further information regarding this group. Is it the opinion of the authors that these patients actually improved or that this may represent testing artifact or bias? Were they significantly younger than the rest of the cohort? Was their follow up significantly shorter? By how much did the acuities improve among this group? Was their baseline acuity more likely to come from outside records?
Sincerely,
Michael S Lee, MD
Minneapolis, MN -
Authors Response
Submit responseAuthor’s Response re letter by Nathan M Radcliffe
Dear Editor,
We are very interested to read Prof Radcliffe’s data showing a variable IOP rise in different subjects tested with the same goggle design. Their results, like ours,[1] suggest that individual anatomic or physiologic factors are important in determining the IOP rise. Currently, these factors are unknown with significant certainty, however some of our results identified that subjects with reduced orbital area were more prone to IOP elevation. These results were not confirmed by subsequent measurement and analysis of a separate cohort.[1] However, it is our impression that subjects with a flatter orbital profile, without a prominent orbital brow and with more soft tissue in the anterior orbit are at greater risk of IOP rise.
We also provide a service to our patients whereby we can test their IOP response to wearing goggles. We use either a standard set with holes drilled or their own and drill holes through to enable applanation tonometry whilst they wear them in the clinic. We agree fully with Prof Radcliffe that this is a useful service for glaucoma patients and suspects.
Yours Sincerely
W H MorganFor W H Morgan, T S Cunneen, C Balaratnasingam and D-Y Yu
Reference
1. Morgan WH, Cunneen TS, Balaratnasingam C, Yu DY. Wearing swimming goggles can elevate intraocular pressure. British Journal of Ophthalmology 2008;92:1218-21.
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Swimming goggles and elevated intraocular pressure
Submit responseWe would like to congratulate Drs Morgan and colleagues on their recent paper “Wearing swimming goggles can elevate intraocular pressure.” We performed a similar study and presented our data at the Association for Research in Vision and Ophthalmology in 2007. Our findings demonstrated that in healthy participants, IOP measurements taken during goggle wear were significantly higher at both one and five minutes, with an average increase of 12.5% or +1.5 mmHg. A small subset of eyes (10%) in our study had an increase in IOP greater than 5 mmHg at both one and five minutes of goggle wear. We applaud the use of a predictive model in evaluating which goggles may be associated with IOP elevation. In our study, utilizing a single goggle design (Speedo), the IOP did not increase significantly in 40% of subjects but increased over 5mmHg in others. In light of this variability we have retained our prototype study goggle in order to measure the goggle-induced IOP effect in our glaucoma patients who wish to swim. Regularly testing these patients in the office allows us to better inform our patients of the potential risks of goggle wear during swimming.
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Authors' Reply
Submit responseDear Editor
We thank Dr. Alm for his interest and comment on our paper entitled “Practical recommendations for measuring rates of visual field change in glaucoma.” We agree that the standard error of slope estimates is dependent on the number of examinations and duration of follow-up. However, these two parameters are not interchangeable. As pointed out correctly by Dr. Alm, the same number of examinations over a longer time period will lead to a better slope estimation and therefore greater power simply because the amount of net change is larger. Hence the difference in follow-up of 3 (27 compared to 24 months) months in his example yields an additional change of -0.5 dB in Mean Deviation and therefore the number of examinations derived to obtain equivalent power is not surprising.
The goal of our first recommendation of 6 examinations in the first two years was not to determine whether the slope of visual field decay is statistically significant or not. It was to identify patients who we feel are progressing rapidly. In these patients we do not feel that prolonging the follow-up is an adequate substitute for more frequent examinations. Even if equivalent statistical power is obtained with this approach, prolonging the follow-up comes with the very significant cost of more visual field loss.
Our paper was meant to be an initial guideline for clinicians on what rates of visual field change could be detected (with varying degrees of power) with a given frequency of examinations. We would like to emphasise that there is a large distinction between detection of progression and determining the rate of visual field change. Therefore the proposed guidelines are not necessarily designed to detect progression. We welcome the comments of Dr. Alm and others that encourage us to factor in aspects such as the time-separation between tests and measures besides Mean Deviation which consider the location of visual field defects.
Sincerely,
BC Chauhan, DF Garway-Heath, FJ Goñi, L Rossetti, B Bengtsson, AC Viswanathan and A Heijl
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PASCAL FLUENCE
Submit responseThere are many pertinent and interesting observations in your article. As one of the first few users of PASCAL in India, we have now a large data-base of patients in a short span of time. Critical to understanding PASCAL is the fluence. Contrary to what we always thought, retinal hemorrhages and acoustic damage are not seen at 10 ms pulses if the fluence is within limits. I wish that PASCAL was also programmed to fix the fluence level at the beginning of each procedure (titrated for each eye) so that inadvertently fluence does not shoot up when the spot size is changed. PASCAL has really taken out the sting from PRP.
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Multifocal-ERG in ARMD after intravitreal use of bevacizumab
Submit responseDear Editor,
In the article entitled 'Electrophysiological effects of intravitreal Avastin (bevacizumab) in the treatment of exudative age-related macular degeneration (ARMD)' by Karanjia et al (Br J Ophthalmol 2008), the authors examine the sensitivity of multifocal-electroretinogram (mfERG) at measuring changes in retinal electrical activity in response to Avastin treatment for ARMD. In this interesting paper the authors study the changes of P1 response amplitude and support that this is the first study to demonstrate a statistically significant change in retinal electrical activity post-bevacizumab in patients with ARMD. I would like to draw attention to the authors of this article that in our prospective study 'Intravitreal use of bevacizumab (Avastin) for choroidal neovascularization due to ARMD: a preliminary mfERG and OCT study' by Moschos MM et al (Doc Ophthalmol 2007; 114:37-44) really for the first time we evaluated the macular function before and after intravitreal use of Avastin. In our paper based on the study of 18 eyes, 1 month after treatment the retinal response density of mfERG really shows an improvement but 3 months after treatment no difference was found between baseline and 3 months.
Our results show that there are anatomical correlates to support the concept of disease amelioration 1 month after treatment. This is mainly the decrease of macular thickness as measured by OCT in an extremely significant degree (p<0.001) the first month after treatment. On the contrary the mean visual acuity improved only by 0.03 the first month after treatment and by 0.02 three months after treatment. On the contrary the mfERG improvement did not follow the decrease of macular thickness and is significant only the first month after treatment. These findings show that the increase of visual acuity, as also the improvement of electrical responses of the macular area is disproportional to the decrease of macular thickness. This may be explained by the fact that macular edema is only a parameter that may affect visual acuity and electrophysiological responses in the beginning of the disease. Atrophy of the retina, particularly of the photoreceptors, atrophy of the pigment epithelium and scarring are all unmeasured variables, which influence vision [1, 2].
References
1. Moschos M, Brouzas D, Apostolopoulos M, et al. Intravitreal use of bevacizumab (Avastin) for choroidal neovascularization due to ARMD: a preliminary multifocal-ERG and OCT study. Doc Ophtalmol 2007;114:137-144.
2. Moschos M, Panayotidis D, Theodossiadis G, et al. Assessment of macular function by electroretinography in age-related macular degeneration before and after photodynamic therapy. J Fr Ophtalmologie 2004;27:1001-1006.
Marilita M Moschos, MD, PhD Department of Ophthalmology, University of Athens, Athens, Greece
Correspondence and reprints: Moschos M. Marilita MD, PhD 144, Kountouriotou Str 185 35 Piraeus Greece Tel : ++30 6944887319 Fax: ++30 210 4122139 E-mail: moschosmarilita@yahoo.fr
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