rss

Recent eLetters

Displaying 1-9 letters out of 453 published

  1. Perceptual learning in visual acuity and contrast sensitivity: continuous improvement or discovery effect?

    In their paper "Repetitive tests of visual function improved visual acuity in young subjects" Otto and Michelson [1] assessed effects of practice on visual acuity, using the Freiburg Visual Acuity Test "FrACT" developed by one of us [2,3]. At first glance they seem to confirm our findings [4], which showed a marked increase of visual acuity after visual training, more than 0.1 logMAR. At closer inspection, discrepancies emerge: During the first 7 sessions, Otto and Michelson's found only a random variability. Then, suddenly, acuity improved in most subjects, and inter-subject variability decreased markedly. In contrast, we found a continuous improvement starting already during the first session (one session comprised 14 acuity test runs) [4]. When we provided feedback by displaying the correct orientation after the response, we found a marked additional step increase in performance already between the first and second session. (Otto and Michelson do not mention whether or not they employed feedback.) The shape of the time course has theoretical implications: A sudden increase of visual acuity like that reported by Otto and Michelson would suggest a "discovery effect" rather than a "fluency effect" [5].

    Otto and Michelson's data on contrast sensitivity are also challenging to understand, not only because the authors used the terms contrast threshold and contrast sensitivity interchangeably (the one is the reciprocal of the other). Looking at figure 1B and supplementary figure 2B, we suspect that the stated effect size of 45% (derived only from the last data point in the graph) can be attributed to random fluctuations, given the non-monotonous change of average contrast sensitivity over sessions. Otto and Michelson seem to share our reservation, since they write in the Discussion "the progress was not consistent enough to show a significant percentage development in one direction". Hopefully, this number 45% will not stick with readers, who could miss the fact that the p values where not derived from the same comparisons as the effect size.

    The reason why the learning curves of Otto and Michelson's subjects are different from those of Heinrich et al's subjects remains speculative. The methods appear to be similar. It is, however, unclear whether Otto and Michelson used feedback and whether or not they presented the optotypes separately or in rows. Furthermore, the participants underwent a practice scheme that included several different visual tasks, so it is difficult to attribute improvement of performance to any single task or combination of tasks. Clearly, future careful studies in this exciting field promise further insights and clinical applications.

    References

    1 Otto J, Michelson G. Repetitive tests of visual function improved visual acuity in young subjects. Br J Ophthalmol 2014;98:383-6. doi:10.1136/bjophthalmol-2013-304262

    2 Bach M. The Freiburg Visual Acuity Test - Automatic measurement of visual acuity. Optom Vis Sci 1996;73:49-53.

    3 Bach M. Homepage of the Freiburg Visual Acuity & Contrast Test ('FrACT'). 2009. http://michaelbach.de/fract.html

    4 Heinrich SP, Krueger K, Bach M. The dynamics of practice effects in an optotype acuity task. Graefes Arch Clin Exp Ophthalmol 2011;249:1319 -26. doi:10.1007/s00417-011-1675-z

    5 Kellman PJ, Garrigan P. Perceptual learning and human expertise. Phys Life Rev 2009;6:53-84. doi:10.1016/j.plrev.2008.12.001

    Conflict of Interest:

    None declared

    Read all letters published for this article

    Submit response
  2. Reproducibility of aberrometry-based intraoperative refraction during cataract surgery, Statistical issues

    We were interested to read the paper by Huelle JO and colleagues published in the May 2014 issue of BJO. The authors aimed to provide the first clinical data in determining the feasibility, quality and precision of intraoperative wavefront aberrometry (IWA)-based refraction in patients with cataract. Precision (reproducibility) and measurement quality was evaluated by the 'limits of agreement' approach, regression analysis, correlation analysis, Analysis of variance (ANOVA) and ORs for predicting measurement failure. Wavefront map (WFM) quality was objectivised and compared with the Pentacam Nuclear Staging analysis.1 They have reported high consistency across repeated measures were found for mean spherical equivalent (SE) differences in aphakia with -0.01D and pseudophakia with - 0.01D, but ranges were high (limits of agreement +0.69 D and -0.72 D; +1.53 D and -1.54 D, respectively). With increasing WFM quality, higher precision in measurements was observed.1 Why did the authors not use (agreement and not consistency) Intra class correlation coefficient (ICC) to assess the precision (reproducibility)? 2-4 Regarding inter-observer reliability or agreement, it is good to know that statistics cannot provide a simple substitute for clinical judgment. They also reported that IWA refraction in aphakia, for instance, appears to be reliable once stable and pressurised anterior chamber conditions are achieved. Such conclusion can be misleading due to inappropriate use and interpretation of statistical tests to evaluate relaibility.2-4

    Siamak Sabour, MD, PhD1 Fariba Ghassemi, MD2 1 Shahid Beheshti University of Medical Sciences, Tehran, Iran 2 Farabi Hospital, Eye Research Centre, Tehran University of Medical Sciences, Tehran, Iran

    References:

    1- Huelle JO, Katz T, Druchkiv V, et al. First clinicial results on the feasibility, quality and reproducibility of aberrometry-based intraoperative refraction during cataract surgery. Br J Ophthalmol. 2014 May 30. pii: bjophthalmol-2013-304786. doi: 10.1136/bjophthalmol-2013- 304786. [Epub ahead of print]

    2- Epidemiology, biostatistics and preventive medicine, Jeckel, 1st edition, 2008

    3- Modern Epidemiology, K. Rothman, 3 rd edition, 2010 4- Epidemiology beyond the basics, Moyses Szklo and F. Javier Nieto, 2nd edition, 2007

    Conflict of Interest:

    None declared

    Read all letters published for this article

    Submit response
  3. FRACTURED OZURDEX IMPLANT DURING THE PROCEDURE

    In the recent article published in British Journal of Ophthalmology, Agrawal et al1

    reported two cases of desegmentation of Ozurdex implant in vitreous cavity. In this report, the authors comment that Allergan confirmed that fractured implants in the applicator have not been found to date during the quality control process. We recently reported2

    also two cases of implant fragmentation in response to a Roy et al3 . These authors reported a broken implant at the end of the injection. They postulate that the reason for breakage could be friction at the tip of the needle or some drug loading problem Our first case showed similar fundus image, dexamethasone implant fragments within vitreous cavity one month after injection In the second case, the implant broken after the ejection during an instructional wet-lab, outside surgical conditions. This event was recorded in a video that is available with our report. Therefore, this video proves that for a break to happen during the implantation is utterly feasible and .taking into account the comment of Allergan, reinforces that the friction at the tip of the needle during de ejection must be the reason for breakage. We agree with the authors that these patients with defragmented implants should be followed up carefully to monitor for unexpected complications, even more in patients with zonular dehiscence.

    REFERENCES: 1. Agrawal R, Fernandez-Sanz G, Bala S, et al. Desegmentation of Ozurdex implant in vitreous cavity: report of two cases. Br J Ophthalmol. 2014;98:961-3 2. Cabrerizo J, Garay-Aramburu G. Re: intravitreal dexamethasone implant fragmentation.Can J Ophthalmol. 2013;48:343. 3. Roy R,HegdeS. Split Ozurdex implant: a caution. Can JOphthalmol. 2013;48:e15-6

    Conflict of Interest:

    None declared

    Read all letters published for this article

    Submit response
  4. Is the term dry eye a misnomer?

    As an ophthalmologist for many years, I continue to find the diagnosis of dry eye difficult unless it is severe. I have spoken to colleagues who have the same experience. As detailed in this paper there are many things going on in the pathophysiology of which dryness may be one. Can I suggest it might be helpful to our understanding and approach to sore eyes, to be less dogmatic about attributing dryness as the reason for discomfort in these eyes. The discomfort may be caused by a host of factors which may or may not include dryness.

    Conflict of Interest:

    None declared

    Read all letters published for this article

    Submit response
  5. Significant design flaws bias the results in favour of aflibercept

    Dr Cho and colleagues present data on a very small cohort of patients with wet AMD that have switched treatment from either bevacizumab or ranibizumab to aflibercept. Of note, this subgroup comprised approximately 8% of the total number of patients switched to aflibercept.

    Any retrospective review is likely to be heavily biased by the anticipated 'treatment benefit' of a new therapy particularly if, as in this case, the readers of retinal optical coherence tomography (OCT) scans have the ability to manually correct and alter data that were originally generated by semi-automated methods. In this study, the magnitude of change observed in central foveal thickness was of marginal clinical relevance (7.8% reduction from Baseline) after 1 injection and was further attenuated by 6 months; these results suggest that the retinal OCT scan reader was an important source of bias. This view is further supported by the observation that visual acuity, which may be less liable to investigator related bias, remained unchanged throughout.

    Retrospective reviews are of scientific value when conducted in a rigourous and independent manner. Selective reporting of data from this study inevitably undermines any clinical conclusions regarding the relevance of switching patients from anti-VEGF therapies to aflibercept.

    Conflict of Interest:

    I have consulted for a number of pharmaceutical companies including Novartis, the MAH of ranibizumab in the EU.

    Read all letters published for this article

    Submit response
  6. The long-term psychosocial impact of correction surgery for adults with strabismus

    We read with interest Jackson and Morris's response to our letter.

    The author's indicated that it was not possible to conduct a repeated measures ANOVA using SPSS. However, SPSS provides several ways to analyze repeated measures ANOVA through the general linear model command. There are several excellent texts that illustrate how to conduct an ANOVA using a repeated measures design in the SPSS environment.

    Second, they posed a question about whether it was reasonable to assume that the data collected 18 months post surgically was specifically related to data collected previously. To answer, yes, any time several measurements are collected over time on the same subject, the data points within each subject are related. Therefore the use of statistical procedures that account for this clustering must be used. The fact that the study was exploratory in nature does not preclude the application of basic statistical principles. On the other hand, the authors correctly noted that they had also analyzed the data using a 2x3 design. This approach is reasonable. Unfortunately, the actual p-values were not provided for the readers in the original article or in their response to our editorial.

    Conflict of Interest:

    None declared

    Read all letters published for this article

    Submit response
  7. Re:Non-inferiority or superiority?

    We would like to thank Dr. Geitzenauer for his comments and concerns regarding our study.

    As he has pointed out, in a non-inferiority study there is potential for bias which may narrow down the difference in efficacy. Therefore, conducting a superiority study simultaneously would be difficult, unless sufficient quality is ensured during study planning, conduct as well as data analysis.

    However, our study in question was a well-controlled study, with a reasonable non-inferiority margin specified in advance, and conducted in accordance with applicable Guidelines. Therefore we believe our study method is acceptable.

    The study plan was sufficiently evaluated as a double-masked comparison study, and the study itself was conducted according to the study protocol and in compliance with GCP (Good Clinical Practice). Further, non-inferiority and superiority were verified for different endpoints, Fluorescein staining score and Rose Bengal staining score, respectively, and the methods were specified beforehand in the protocol. In consideration of multiplicity, significance level was maintained by adopting a closed testing method, by which superiority would be verified only if inferiority has already been verified.

    EU regulatory authorities have also accepted the simultaneous data analysis for non-inferiority and superiority if it is a well-controlled study, using previously specified analytical methods 1).

    Therefore, we believe that the verification methods used in our study are acceptable.

    1) Committee For Proprietary Medicinal Products (CPMP) , Point to consider on switching between superiority and non-inferiority, EMEA 2000; July.

    Conflict of Interest:

    None declared

    Read all letters published for this article

    Submit response
  8. Non-inferiority or superiority?

    Dear editors,

    Takamura et al. report in a recent edition of the BJO about a "multi- center, randomised, double-masked, parallel study" which leads to both a non-inferiority and a superiority claim of the ophthalmic solution being tested (diquafosol ophthalmic solution).(Reference 1) From a methodological standpoint, the conclusions reached by the authors are not in agreement with current accepted standards in the field of randomised controlled trials. It is methodologically unacceptable to draw conclusions about superiority and non-inferiority at the same time using the same set of data. Already at the design stage a decision has to be made whether a non-inferiority or a superiority trial is to be conducted. Hence, claiming both non- inferiority and superiority at the end of such a trial, as tempting as it may be, violates fundamentals of clinical trials methodology. Non-inferiority trials have specific characteristics which make emphasis on rigorous methods even more important than in superiority trials.(Reference 2) In a superiority trial, the objective is to detect a difference, whereas in a non-inferiority trial, the objective is to fail to detect a difference. These different objectives, among others, have important implications with regard to the analysis and conclusion of a trial. It is flawed to analyse and present data mixing up both approaches. Recommendations for improving the quality of reporting of parallel-group randomised trials, noninferiority and equivalence trials are published and freely accessible on the internet. (References 3 and 4) Adoption of the CONSORT statement in the editorial policy is likely to be beneficial to the high standards of the BJO and would certainly be welcomed by this reader.

    Wolfgang Geitzenauer MD MSc FEBO

    1 Takamura E, Tsubota K, Watanabe H, Ohashi Y. A randomised, double- masked comparison study of diquafosol versus sodium hyaluronate ophthalmic solutions in dry eye patients. BJO; 96(10):1310-5.

    2 Fleming TR. Current issues in non-inferiority trials. Stat Med; 27(3):317-32.

    3 Schulz KF, Altman DG, Moher D; CONSORT Group. CONSORT 2010 statement: updated guidelines for reporting parallel group randomised trials. BMJ;340:c332.

    4 Piaggio G, Elbourne DR, Pocock SJ, Evans SJ, Altman DG; CONSORT Group. Reporting of noninferiority and equivalence randomized trials: extension of the CONSORT 2010 statement. JAMA. 2012; 308(24):2594-604.

    Conflict of Interest:

    None declared

    Read all letters published for this article

    Submit response
  9. Risk of cataract for patients with diabetes mellitus

    I read the paper entitled "Risk of selected eye diseases in people admitted to hospital for hypertension or diabetes mellitus: record linkage studies" with interest. It elucidated that diabetes mellitus has a risk of several ocular diseases with significance using two big epidemiological data. However, I have two queries on their outcome by selecting the association between cataract and diabetes mellitus.

    First, Goldacre et al. described rate ratios concerning several eye diseases caused by hypertension or diabetes mellitus. For example, risk of cataract in diabetes was high presenting rate ratio (95% confidence interval) of 2.95 (2.75 to 3.16) and 2.30 (2.24 to 2.35) in their two epidemiological datasets (1). Although sex, age, year of admission and patients' area of residence was adjusted by matching procedure, their outcome is a hospital-based case control study with no specification on the type of cataract. Mukesh et al. conducted a follow-up study, and diabetes mellitus and having taken calcium channel blockers for longer than 5 years were independent risk factors for posterior subcapsular cataract (2), presenting hazard ratio (95% confidence interval) of 2.9 (1.7-5.1) and 2.9 (1.2-6.9), respectively. In addition, hazard ratio (95% confidence interval) of age by one year increase for posterior subcapsular cataract was 1.09 (1.07-1.1) (2). Effect of confounding variables on the association between cataract and diabetes mellitus are more understandable in cohort study compared with case-control study as mentioned above.

    Second, Goldacre et al. described the study limitation for the lack of information on the clinical state of diabetes mellitus including treatment (1). The information on the clinical state of diabetes mellitus is useful in combination with diabetic retinopathy.

    The hospital-based case control study has a merit of satisfactory statistical power, and further study on the association between cataract and diabetes mellitus should be conducted including the above mentioned information.

    References

    1. Goldacre MJ, Wotton CJ, Keenan TD. Risk of selected eye diseases in people admitted to hospital for hypertension or diabetes mellitus: record linkage studies. Br J Ophthalmol 2012;96:872-6.

    2. Mukesh BN, Le A, Dimitrov PN, et al. Development of cataract and associated risk factors: the Visual Impairment Project. Arch Ophthalmol 2006;124:79-85.

    Conflict of Interest:

    None declared

    Read all letters published for this article

    Submit response

Register for free content


Free sample
This recent issue is free to all users to allow everyone the opportunity to see the full scope and typical content of BJO.
View free sample issue >>

Don't forget to sign up for content alerts so you keep up to date with all the articles as they are published.