eLetters

633 e-Letters

  • Observations on data analysis on acanthamoeba keratitis

    Dear Editor
    We read the above paper with much interest and welcome the review and analysis of trends in acanthamoeba keratitis – a very important complication from contact lens wear. The paper discusses the incidence of acanthamoeba keratitis at Moorfields Eye Hospital, a large tertiary referral centre.
    We note an incidence of 18.5 cases per annum in 1997-1999, rising to a mean of 50.3 per annum in 2011-2016 and hence has been quite rightly quoted as almost a 3 fold increase in cases.
    We would however suggest some caution when using those figures to state that there is an epidemic at present.
    When one attempts to take into account the fluctuations in numbers of contact lens wearers with the United Kingdom per year and relate that to incidence of acanthamoeba keratitis one has a slightly modified view.1 There has been a steady increase in contact lens wear with figures from the ACLM estimating 4.2 million CL wearers in 2016. A figure has been created showing this relative incidence in a chart format.2
    The figure represents the number of cases diagnosed at Moorfields divided by the number of contact lens users (rising from 1.6 million in 1992 to 4.2 million in 2016). Therefore the mean number of cases when adjusted for CL wearers is 8.5 per year with a standard deviation of 5.8, with 11.8 in 2015 and 14 in 2016.
    Whilst there is still a significant rise in cases, compared to the mainly stable period of 1996-2010, the rates are still lower t...

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  • Optic nerve head analysis to rule out glaucoma

    Dear authors,

    We congratulate the authors for bringing out an ingenious theory regarding pathogenesis of cupping in glaucomatous (GC) and non-glaucomatous (NGC) eyes using this optical coherence tomography (OCT) model. (1) Differentiating a NGC from GC has been a point of discussion for decades and to finally have an objective parameter “anterior laminar depth (ALD)” which appears specific for glaucomatous cupping from this study is indeed beneficial. The authors have used a linear regression model to compare the GC and NGC eyes with healthy controls with adjustment of age, axial length and peripapillary choroidal thickness (PCT). However, it remains to be further studied, how the ALD is to be used for an individual patient, for eg., what cut-off of ALD above which a patient can be labelled as falling in the glaucomatous range. In this regard, we had a doubt regarding inclusion of PCT in ALD calculation. Since the authors have finally adjusted for PCT in the end, we wonder how the results will turn out if they would remove PCT from ALD measurement and compare the remainder measurement (ALD - PCT) between NGC and GC groups.
    Finally, we observed that in this sentence “No significant difference was found in visual field mean deviation (MD) <0.001).”, there is a typographical error and an inadequacy of explanation. No significant difference in visual field MD was indeed seen between NGC and GC groups (p should be >0.99 and not <0.001, as seen in Table...

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  • Re: Optical coherence tomography angiography identifies peripapillary microvascular dilation and focal non-perfusion in giant cell arteritis

    Dear Editor,
    We thank Dr. Balducci and her colleagues for their interest in our paper [1]. They raise several important points regarding optic nerve angiography, and we are thankful to have the opportunity to discuss these items further.
    In preparation of our manuscript, we felt that diffuse changes in the peripapillary capillary network were best appreciated at lower magnification. Balancing this objective in presentation with a sufficient resolution to appreciate the focal deficits we highlighted, the image sizes published represent what we felt was the best compromise. For those who feel that higher magnification images are needed, we have included in this letter Figure 1, which includes the same 6x6 mm OCT-A images in the acute phase for all cases in our study. Quantitation of OCT-A signal can be a powerful way to objectively assess regional as well as between eye and patient differences. We have recently performed a quantitative assessment of angiographic signal in non-arteritic anterior ischemic optic neuropathy using a different device, the Optovue Avanti (Fremont, CA) [1]. However, in the current study, the small number of affected eyes did not allow for meaningful statistical analysis of quantitative data. In addition, quantitative analyses can be misleading when confounding artifacts or segmentation errors are present as discussed below.
    Jia and colleagues [2] showed a strong non-linear correlation between RNFL thickness and radial peripapillary...

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  • Letter to the Editor - XFS Reply

    Dear Sir,

    We appreciate Dr. Taylor’s interest in our paper as well as drawing our attention to environmental factors that may influence XFS in Australian aboriginal people. Certainly, this is an area that deserves further investigation. Dr Taylor’s review article presents some interesting findings, particularly regarding the high incidence of XFS in Aboriginal individuals. (1)

    Consistent with recent literature, Dr. Taylor identified a ‘latitude effect’. Interestingly however, XFS was more commonly observed at lower latitudes, which contrasts other findings of high altitude exposure associated with XFS in an American population. (2)

    The recognition of solar radiation exposure as an environmental factor associated with XFS is plausible due to accumulating evidence that supports this relationship. (3) While providing some useful insights, this article justifies the lack of understanding and the need for further research on environmental factors.

    1. Taylor HR. Pseudoexfoliation, an environmental disease? Trans Ophthalmol Socs UK 1979; 99: 302- 307
    2. Stein JD, Pasquale LR, Talwar N, Kim DS, Reed DM, Nan B, Kang JH, Wiggs JL,Richards JE. Geographic and climatic factors associated with exfoliation syndrome. Arch Ophthalmol. 2011 Aug;129(8):1053-60.
    3. Jiwani AZ, Pasquale LR. Exfoliation Syndrome and Solar Exposure: New Epidemiological Insights Into the Pathophysiology of the Disease. International ophthalmology clinics. 2015;55(4):13.

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  • RE: Is combined cataract surgery associated with acute postoperative endophthalmitis? A nationwide study from 2005 to 2014

    Dear Editor,

    We read with interest the article written by Creuzot-Garcher and colleagues that was published in the June 2018 issue of your journal. 1 The authors retrospectively reviewed billings codes from a national database in France from January 2004 to December 2014 to examine acute postoperative endophthalmitis (POE) rates. They reported an incidence of acute POE in stand-alone phacoemulsification of 0.102% over this 11-year period. In contrast, combined surgery in which phacoemulsification was performed with another intraocular procedure had an overall higher incidence of 0.149%. The incidence of acute POE in combined phacoemulsification and glaucoma surgery, corneal surgery, and vitreoretinal surgery was found to be 0.089%, 0.142%, and 0.223% respectively.

    As Creuzot-Garcher and colleagues mention, many phakic patients who undergo either glaucoma surgery, corneal surgery, or vitreoretinal surgery, are elderly and likely will require cataract extraction at some point.1 In addition, it is well established that these surgeries promote cataract formation in phakic eyes, and therefore patients who do not undergo combination surgery will likely require stand-alone cataract surgery in the future.

    Hence, it would be instructive to compare the risk of acute POE in combined surgery with the total risk conferred by separately performing the two surgeries. We made the assumption that the chance of endophthalmitis in each surgery is independent. Using the...

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  • Letter to Editor

    We have read with great interest the e-letter from Karakucuk et al. published in BJO responding to our paper titled ‘Acute retinal toxicity associated with a mixture of perfluorooctane and perfluorohexyloctane: Failure of another indirect cytotoxicity analysis ’ and we appreciate their positive appreciation of our research work.
    We consider extraordinarily important that they have reported four more cases in their country, thus, supporting that acute toxicity cases were not a Spanish problem as has been stated by some retinologist at an European congress (Barcelona, September 2017).
    We believe that this letter should encourage other colleagues from other countries from all over the world to report cases that certainly exist, according to non-official information from several companies.
    We completely agree that the ISO (the International Organization for Standardization) guidelines to determine the in vitro cytotoxicity of intraocular medical devices should be immediately changed. These guidelines should adopt direct cytotoxicity methods to be performed with finished, sterilized, and ready for release products. The analytical method utilized should include cells or tissues close to those of the retina to guarantee specific sensitivity and should be scientifically validated.
    We support the suggestion of increasing chemical research, because some companies are promoting chemical tests, as a “safety guarantee”, whose scientific validity and their direct...

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  • Pseudotumor cerebri in Behçet’s disease

    We read with interest the masterly review of the neuro-ophthalmology of Behcet’s disease by Alghamdi et al (1). One small aspect we question. The authors state that in their patients with papilledema: “The diagnosis of CVT was documented in all patients by cerebral angiography and MRI showing partial or total lack of filling of at least one dural sinus and an elevated CSF opening pressure (>25 mm Hg) on lumbar puncture.” We have recently reported 8 BD patients with pseudotumor cerebri who did not have cerebral venous thrombosis (CVT) on MRI or MRV (2). Partial or total lack of filling of one venous sinus does not constitute the pathophysiological basis for intracranial hypertension; either the sagittal sinus must be occluded, or if only one transverse sinus is occluded then the other needs to be stenosed (3). It would be interesting to know what a review of their patient’s images by a neuro-radiologist would reveal.

    1: Alghamdi A, Bodaghi B, Comarmond C, Desbois AC, Domont F, Wechsler B, Depaz R, Le Hoang P, Cacoub P, Touitou V, Saadoun D. Neuro-ophthalmological manifestations of Behçet's disease. Br J Ophthalmol. 2018 Apr 26. pii: bjophthalmol-2017-311334. doi: 10.1136/bjophthalmol-2017-311334.
    2: Akdal G, Yaman A, Men S, Çelebisoy N, Toydemir HE, Bajin MS, Akman-Demir G. Pseudotumor cerebri syndrome without cerebral venous sinus thrombosis in Behçet's disease. J Neurol Sci. 2017;383:99-100.
    3: Halmagyi GM, Ahmed RM, Johnston IH. The Pseudo...

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  • Letter to Editor

    Dear Editor:

    We read the article ‘Acute retinal toxicity associated with a mixture of perfluorooctane and perfluorohexyloctane: Failure of another indirect cytotoxicity analysis ’ by Coco et al. with great interest.[1] In this study, the authors reported on ocular toxicity due to perfluorooctane (PFO). They advised that the protocols used to determine the cytotoxicity of intraocular medical devices (which have been approved by the Organisation for the Standardisation of International Standards based on indirect methods) should be revised to ensure safety. We congratulate Coco et al.1 for their report because we believe that it has the potential to be a significant contribut or to the literature on this topic.

    As is commonly known, PFO is saturated with PFO liquids, which have highly stable carbon-fluorine bonds that consequently make them inert. PFO has highly specific gravity, low viscosity, optical clarity immiscibility in water and interface tension towards water. It is regularly used in vitreoretinal surgery for complex retinal detachment repair because it displaces subretinal fluid and blood anteriorly, unfolds the retina in giant retinal tear cases and provides counter traction and retinal stabilisation during membrane peeling in eyes with proliferative vitreoretinopathy.[2,3] These properties make PFO useful for intraocular surgery. However, some limitations exist regarding PFO use as a long- term tamponade such as amaurosis, a lack of light perce...

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  • Confounders to be addressed

    I read with great interest the article by Bae and collegues.1 In their retrospective study, the authors concluded that the presence of atypical epiretinal tissue (AET) in a full-thickness macular hole (FTMH) was related to poorer anatomical success and less visual recovery after surgery.
    I agree with the authors on the association of their OCT findings with the visual prognosis. I also agree with them that it is important to identify a good indicator of visual prognosis based on OCT findings. However, there are many confounders to be addressed in this study. For example, preoperative MH size with OCT has been known as a prognostic factor for postoperative visual outcome and anatomical success rate of MH surgery.2,3 A previous study also demonstrated that ERM prevalence increased with severity and size of the FTMH.4 In addition, preoperative visual acuity or preoperative photoreceptor integrity also seems to correlate with visual prognosis.
    Thus, their results should be supported by appropriate statistical analysis, that is, multivariate regression analyses. I hope that the authors will comment on the results of multivariate regression analyses to identify the most significant factor to predict visual prognosis after MH surgery.

    References
    1. Bae K, Lee SM, Kang SW, et al. Atypical epiretinal tissue in full-thickness macular holes: pathogenic and prognostic significance. Br J Ophthalmol. 2018 (in press)
    2. Ullrich S, Haritoglou C, Gass...

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  • Re: Optical coherence tomography angiography identifies peripapillary microvascular dilation and focal non-perfusion in giant cell arteritis

    Dear Editor,
    We read with interest the paper by Gaier et al.1 The collection of 5 eyes affected by acute A-AION and analyzed with OCT-A is remarkable, due to the rare disease presentation. The main finding of the paper was that during the acute phase of A-AION, diffusely dilated superficial peripapillary capillaries were detectable on OCT-A. Interestingly, peripapillary capillary dilatation was also noted in the fellow eye. Unfortunately, the figures presented by the authors are too small to allow the reader to qualitatively appreciate the capillaries dilatation. More detailed images and a quantitative vessels analysis would have helped to document the microvascular changes.
    They hypothesized that the capillary dilatation may represent a form of luxury perfusion in the setting of short ciliary arterial compromise or a centrally mediated autoregolatory mechanisms in the setting of reduced perfusion of the optic nerve. These hypotheses are interesting, but it is important to differentiate the RNFL thickness increase from the capillary dilatation, as peripapillary capillary plexus density and RNFL thickness are highly correlated and fit well with a nonlinear stacked-layer model.2
    Moreover, the authors stated that OCT-A laminar analysis did not highlight the choroidal/choriocapillaris perfusion defects seen on FA. However, a recent study3 showed a tight correspondence between the choroidal perfusion defects visible on FA (and even better on indocyanine green...

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