I read with interest the article by Hiti et al.[1] on the susceptibility of Acanthamoeba to a multipurpose disinfecting contact lens solution and two hydrogen peroxide systems. The association between acanthamoeba keratitis and contact lens wear is now firmly established. Thus, the use of contact lens disinfecting solutions effective at killing Acanthamoeba organisms is important in pr...
I read with interest the article by Hiti et al.[1] on the susceptibility of Acanthamoeba to a multipurpose disinfecting contact lens solution and two hydrogen peroxide systems. The association between acanthamoeba keratitis and contact lens wear is now firmly established. Thus, the use of contact lens disinfecting solutions effective at killing Acanthamoeba organisms is important in preventing corneal infections. I would like to make a few comments on this article.
The lack of standard methods for testing disinfecting solutions against Acanthamoeba represents a critical problem when sensitivity assays are set up.[2] The authors say that 1 ml of disinfectant per well was applied in 24-well plates, but the amount of acanthamoeba suspension distributed in each well is missing. PHMB (0.0005 %) was found to be ineffective against A.hatchetti and A. lenticulta cysts after 8 hours' exposure. This is not surprising. Indeed, at concentrations (0.5 to 15 µg/ml) used in commercial contact lens solutions, PHMB is almost ineffective against amoeba cysts.[3-6] PHMB concentrations ranging from 45 to 90 µg/ml are needed to kill 99.9 % of Acanthamoeba cysts in under 1 hour of exposure.[7]
The authors observed that a one-step 3 % H2O2 system with catalase was ineffective against Acanthamoeba cysts after 8 hours' exposure. Silvany et al.[4] reported similar results. Because the catalyst is present from the very beginning of the disinfection step, the H2O2 is neutralised long before any disinfection can occur. Therefore, adequate exposure time before neutralisation is crucial.
The authors also found that a two-step 0.6 % H2O2 system was effective against A. castellanii and A. hatchetti cysts after 8 hours' exposure. However, Zanetti et al.[6] observed that an equivalent dilution of 3 % H2O2 was ineffective against the cysts of a corneal isolate of A. castellanii after 9 hours' exposure. These variations in susceptibility may depend on inherent strain differences.[2] Therefore, unlike the authors, I would not recommend the two-step 0.6 % H2O2 system as a safe disinfectant against Acanthamoeba. From previous data,[6,8-9] I suggest that the following measures should result in less contact lens case and contact lens contamination, thereby possibly reducing the risk of microbial keratitis.
-Naturally: wash hands before handling contact lenses.
-Use "one day" disposable contact lenses. If other types are preferred:
(a)Use a two-step 3% H2O2 system and neutralize after 9 hours' exposure (overnight).
(b)Replace the contact lens case regularly (preferably fortnightly).
References
(1) Hiti K, Walochnik J, Haller-Schober EM, et al. Viability of Acanthamoeba after exposure to a multipurpose disinfecting contact lens solution and two hydrogen peroxide systems. Br J Ophthalmol 2002;86:144-6.
(2) Meisler MD, Rutherford I. Acanthamoeba and disinfection of soft contact lenses. Rev Infect Dis 1991;13:S410-2.
(3) Hugo ER, McLaughlin WR, Oh K, et al. Quantitative enumeration of Acanthamoeba for evaluation of cyst inactivation in contact lens care solutions. Invest Ophthalmol Vis Sci 1991;32:655-7.
(4) Silvany RE, Dougherty JM, McCulley JP. Effect of currently available contact lens disinfection systems on Acanthamoeba castellanii and Acanthamoeba polyphaga. Ophthalmology 1990;97:286-90.
(5) Silvany RE, Dougherty JM, McCulley JP. Effect of contact lens preservatives on Acanthamoeba. Ophthalmology 1991;98:854-7.
(6) Zanetti S, Fiori PL, Pinna A, et al. Susceptibility of Acanthamoeba castellanii to contact lens disinfecting solutions. Antimicrob Agents Chemother 1995;39:1596-8.
(7) Burger RM, Franco RJ, Drlica K. Killing Acanthamoebae with polyaminopropyl biguanide:quantitation and kinetics. Antimicrob Agents Chemother 1994;38:886-8.
(8) Grey TB, Cursons RTM, Sherwan JF, et al. Acanthamoeba, bacterial, and fungal contamination of contact lens storage cases. Br J Ophthalmol 1995;79:601-5.
(9) Pinna A, Sechi LA, Zanetti S, et al.Bacillus cereus keratitis associated with contact lens wear. Ophthalmology 2001;108:1830-4.
Dr Newsham's effort to inform parents of children with amblyopia about occlusion therapy is laudable but incomplete. Ethical considerations of informed consent require full disclosure of all aspect of the proposed treatment. In the current instance this compels inclusion of the following points:
1. Occlusion therapy has never been scientifically validated with a randomized, controlled study.
Dr Newsham's effort to inform parents of children with amblyopia about occlusion therapy is laudable but incomplete. Ethical considerations of informed consent require full disclosure of all aspect of the proposed treatment. In the current instance this compels inclusion of the following points:
1. Occlusion therapy has never been scientifically validated with a randomized, controlled study.
2. The dose / response relationship has never been defined. Flynn et al. stated that 'Success was not related to the duration of occlusion therapy, type of occlusion used'. [1] The variety of treatment protocols accentuate another dilemma 'owing to our paucity of knowledge on the dose-effect relation - a situation one finds hard to imagine for any
comparably established therapy outside ophthalmology. In other words we have no understanding of the dose-effect relation of occlusion in amblyopia therapy'. [2]
3.The application of 'greater levels of occlusion being prescribed for more severe amblyopia is
compromised by the observation 'that success was related to the depth of visual loss before treatment'.[4]
4. The benefits of treatment are likely to deteriorate following cessation of patching. [5]
5. Visual acuity normally improves as children become more mature, literate, and familiar with vision testing protocols. [6]
This is also true for amblyopic eyes. In amblyopic children between 3 and 7 years old without treatment visual acuity was
shown to consistently improve in each older age group. [7]
6. Both the occluded and the amblyopic eyes improve at the same rate during treatment. [8]
7. Success in amblyopia treatment is usually defined as improvement by a minimum of three lines. [9]Many of the successfully treated patients, by that criterion, will still not have normal vision at the end of presumably successful treatment. One quarter of treated patients with initial acuity better than 20/100 do not even achieve these limited goals. The comments about achieving normal vision may raise expectations that will not be achieved.
Moreover, it is not clear that performance on reading an eyechart is a complete indicator of visual function. Acuity
improvement with occlusion may not be accompanied by improved performance on the other tests - such as vernier acuity
or contrast sensitivity. [10]
8. Occlusion therapy does have potential adverse effects beyond disruption of family and social life [11] and interference with
education. [12]
9.Despite decades of occlusion therapy the prevalence of amblyopia in the adult population is similar to that of the school-age population. [13] Moreover, 'the prevalence of unilateral amblyopia was not found to be statistically different by age group'. [14] This suggests that long term benefits of conventional therapy are not demonstrated in demographic studies.
Patients and their families should be provided with comprehensive information concerning proposed treatments in order to make appropriate judgements. Physicians are obliged to make this information accurate and inclusive.
References
(1) Flynn JT, Schiffman J, Feuer W, Corona A The therapy of amblyopia: an analysis of the results of amblyopia therapy utilizing the pooled data of published studies. Trans Am Ophthalmol Soc 1998;96:431-50; discussion 450-3.
(2) Simonsz HJ, Polling JR, Voorn R, van Leeuwen J, Meester H, Romij C, Dijkstra BG. Electronic monitoring of treatment
compliance in patching for amblyopia. Strabismus 1999 Jun;7(2):113-23.
(3) Newsham D. A randomised controlled trial of written information: the effect on parental non-concordance with occlusion
therapy. Br J Ophthalmol 2002;86:787-91.
(4) Beardsell R, Clarke S, Hill M. Outcome of occlusion treatment for amblyopia. J Pediatr Ophthalmol Strabismus 1999
Jan-Feb;36(1):19-24.
(5) von Noorden GK, Attiah F Alternating penalization in the prevention of amblyopia recurrence. Am J Ophthalmol 1986 Oct 15;102(4):473-5.
(6) Robinson BE, Oladeji MM, Bobier WR. Visual acuity assessment in preschool children in Oxford County. ARVO 2000 Abstract # 4955.
(7) The Pediatric Eye Disease Investigator Group. The clinical profile of moderate amblyopia in children younger than 7 years. Arch Ophthalmol 2002;120:281-7. (Table 3 Baseline characteristics according to age at enrollment).
(8) Dorey SE, Adams GG, Lee JP, Sloper JJ. Intensive occlusion therapy for amblyopia. Br J Ophthalmol 2001 Mar;85(3):310-3.
(9) The Pediatric Eye Disease Investigator Group. A randomized trial of atropine vs patching for treatment of moderate amblyopia in children. Arch Ophthalmol 2002;120:268-78.
(10) Levi DM, Polat U, Hu YS. Improvement in Vernier acuity in adults with amblyopia. Practice makes better. Invest Ophthalmol Vis Sci 1997 Jul;38(8):1493-510.
(11) Snowdon SL, Stewart-Brown SL. Amblyopia and Disability: A Qualitative Study. Health Services Research
Unit: University of Oxford.
(12) Yang LL, Lambert SR. Reappraisal of occlusion therapy for severe structural abnormalities of the optic disc and macula. J Pediatr Ophthalmol Strabismus 1995 ;32(1):37-41.
(13) Buch H, Vinding T, La Cour M, Nielsen NV. The prevalence and causes of bilateral and unilateral blindness in an elderly urban Danish population. The Copenhagen City Eye Study. Acta Ophthalmol Scand 2001 Oct;79(5):441-9.
(14) Brown SA, Weih LM, Fu CL, Dimitrov P, Taylor HR, McCarty CA. Prevalence of amblyopia and associated refractive errors in an adult population in Victoria. Australia Ophthalmic Epidemiol 2000
Dec;7(4):249-58.
Poon et al.[1] in their excellent article have reiterated the efficacy of autologous serum in the treatment of persistent epithelial defects (PEDs) of the cornea. We would like to invite the attention of the authors to certain aspects of the study.
The authors have considered a period of one week for labeling an epithelial defect to be persistent. However, most studies on a similar subject have tak...
Poon et al.[1] in their excellent article have reiterated the efficacy of autologous serum in the treatment of persistent epithelial defects (PEDs) of the cornea. We would like to invite the attention of the authors to certain aspects of the study.
The authors have considered a period of one week for labeling an epithelial defect to be persistent. However, most studies on a similar subject have taken the criterion to be two weeks.[2]
It is generally recommended that a 'wash out' period of a least two weeks be given with preservative free artificial tears3 and only those epithelial defects that remain either static or demonstrate an increase in size in this period be included in the study. The authors have not mentioned such a 'wash out' period being included in the protocol. When using autologous serum drops most investigators have not used any other therapeutic modality at the same time to enhance epithelialization apart from preservative free lubricants. The use of therapeutic contact lenses in five cases by the authors makes it difficult to evaluate the actual contribution of serum drops in the healing of the epithelial defect in these cases. Further, the use of serum drops in the immediate post operative period in two patients with poor ocular surface undergoing keratoplasty without waiting for the corneal epithelial defect to heal by itself cannot be extrapolated to making a comment on the beneficial effect of autologous serum. Also the rationale behind the use of 100 % serum when previous studies have proved the efficacy of a 20 % solution[2] is not clear. The 100 % concentration of serum can cause stickiness, which would be inconvenient to the patients and may reduce compliance. The use of the slit lamp micrometer by the authors for measuring the epithelial defects may not be accurate because of its inherent inter-observer and intra-observer variations. A better method would be measuring the area of the defect instead of the greatest dimensions by the use of digital photographs and area measuring software such as Image Pro PlusTM available from Media Cybernetics.
References
(1) Poon AC, Geerling G, Dart JKG, et al. Autologous Serum eye drops for dry eyes and epithelial defects: clinical and in vitro toxicity studies. Br J Ophthalmol 2001;85:1188-97.
(2) Tsubota K, Goto E, Shimmura S, et al. Treatment of persistent epithelial defect by autologous serum application. Ophthalmology 1999;106:1984-9.
(3) Gordon JF, Johnson P, Musch DC. Topical fibronectin ophthalmic solution in the treatment of persistent defects of the corneal epithelium. Am J Ophthalmol 1995;119:281-7.
Vajpayee and colleagues have criticised several aspects of our study and justified their views with unrepresentative quotations from the literature.
Choice of time period before an epithelial defect can be described as "persistent".
There is no accepted definition of persistent epithelial defect (PED) that includes a time period. We favour the definition given in one text"......
Vajpayee and colleagues have criticised several aspects of our study and justified their views with unrepresentative quotations from the literature.
Choice of time period before an epithelial defect can be described as "persistent".
There is no accepted definition of persistent epithelial defect (PED) that includes a time period. We favour the definition given in one text"... when the epithelium fails to regrow over a defect within the expected time course".[1] For the purpose of a study the time course must be specified. Vajpayee et al. Prefer 2 weeks [2] whereas in another recent paper 10 days was chosen with the proviso that the study treatment could start earlier if there was progression to perforation.[3] The penalty for patients at high risk of corneal melt, in the presence of a persistent defect, is substantial. In our study 2/13 patients had an epithelial defect for less than 2 weeks before inclusion in the study; Vajpayee et al. can ignore the data from these patients if they wish.
Wash-out period with preservative-free artificial tears
No "wash-out period" was used in this study, as we were trying to identify whether serum would have an additional effect on epithelial healing over preservative-free artificial tears and conventional therapy in patients with severe ocular surface disease. We were not trying to compare the efficacy of serum against preservative-free lubricants in healing PEDs. Conventional therapy was continued as serum alone could not fully address all the ocular surface problems, including aqueous tear deficiency and eyelid trauma, so that giving serum without continuing the other modalities may have caused harm to some of the patients. Other studies have adopted similar protocols with a PED defined as a defect that persisted "...despite conventional treatment such as artificial tears or extended wear contact lenses" with no wash out period [2] or that allowed a reduction in the 10 day wash out period if corneal ulceration progressed.[3] In a clinical study some ethical committees may not condone the treatment of persistent defects without non-preserved antibiotic prophylaxis against bacterial keratitis.
Keratoplasty patients being treated without waiting for the corneal epithelial defect to heal by itself
These patients had both failed previous grafts because of corneal perforation resulting from PEDs and one patient had recurrent epithelial breakdown, responding to the re-introduction of serum drops, after their initial withdrawal. We thought that, for some readers, this might be useful data to add to this descriptive study.
The rationale behind the use of 100 % serum when previous studies have proved the efficacy of a 20 % solution
The previous study Vajpayee et al. quote is, like ours and all the other studies on this subject, a descriptive study and no more proves that serum drops at 20 % work than does our own with 50% and 100%. Other studies, all uncontrolled, have used from 20% to 30% serum [2,4] for both persistent defect and dry eye. All these studies use empirical regimens for serum concentration and dosing frequency. Unlike Vajpayee et al., we have some patients (one reported in the study) who prefer 100 % serum to 50 %. Vajpayee et al. are probably also unaware of our study demonstrating that 100 % serum is less toxic that 50 % serum to cultured corneal epithelial cells;[5] this provides some laboratory data to support the use of 100 % serum. Lastly, the manufacture of 100 % serum requires less handling, reducing the risk of contamination.
The use of the slit lamp micrometer
Vajpayee et al. have missed the point that the treatment end point was closure of the defect, for which their proposed technique is inappropriate, rather than rate of closure, for which it would be ideal.
The deficiencies in our study are not the points that Vajpayee et al. have made but the fact that it was uncontrolled. The study was planned as a randomised controlled trial but could not be carried out as such for the reasons alluded to in the last paragraph. These regulatory problems are being overcome in the UK. We should all hope to see randomised treatment trials carried out in this area as well as the laboratory studies necessary to support the clinical application of serum.
John Dart
Alex Poon
References
(1) Macaluso DC, Feldman ST. Persistent epithelial defects and sterile ulceration. Pathogenesis of sterile corneal erosions and ulcerations. In Vol 1, Chapter 10; 204 of Krachmer J, Mannis M, Holland E, (Eds) Cornea; fundamentals of cornea and external disease. St Louis 1007: Mosby.
(2) Tsubota K, Goto E, Simmer S, Shimazaki J. Treatment of persistent epithelial defect by autologous serum application. Ophthalmology 1999;106:1984-9.
(3) Bonini S, Lambiase A, Rama P, Caprioglio G, Aloe L. Topical treatment with nerve growth factor for neurotrophic keratitis. Ophthalmology 2000;107:1347-51.
(4) Fox RI, Chan R, Michelson J, Belmont J, Michelson P. Beneficial effect of artificial tears made with autologous serum in patients with keratoconjunctivitis sicca. Arthritis Rheum 1984;29:577-83.
(5) Geerling G, Daniels JT, Dart JK, Cree IA, Khaw PT. Toxicity of natural tear substitutes in a fully defined culture model of human corneal epithelial cells. Investigative Ophthalmology & Visual Science 2001;42(5):948-56.
Thank you for the opportunity to reply to the letter from Dr Alpins concerning our recent article "Astigmatism and the analysis of its surgical correction".[1] Noel Alpins is a widely respected contributor to many international meetings, having written comprehensively on the use of astigmatism vector analysis. His software program ASSORT TM is widely used for the planning of refractive surgery a...
Thank you for the opportunity to reply to the letter from Dr Alpins concerning our recent article "Astigmatism and the analysis of its surgical correction".[1] Noel Alpins is a widely respected contributor to many international meetings, having written comprehensively on the use of astigmatism vector analysis. His software program ASSORT TM is widely used for the planning of refractive surgery and provides many derived indices (transformations) from the vector analysis of both refractive and topographic astigmatism. Although the derived indices are summary measures, we have argued that their usefulness for statistical analysis is limited. This is because the perception of astigmatism is a psycho-physical phenomenon altered by the orientation of the axis of astigmatism (the power meridians of the cornea and crystalline lens). Unfortunately the perceptual response means that the measurement of the axis of astigmatism (which is with an arbitrary 180° scale) is non-linear in outcome terms, as related to visual acuity outcome. Astigmatism obliquity is the least desirable outcome but this is separated into two on the scale by with-rule-astigmatism (WTR), which is generally the most desirable outcome. Oblique astigmatism also separates the two groups of against-the-rule astigmatism (ATR) from the WTR astigmatism. Developments of vector analysis so far have not resolved this issue of non-linearity of the axis of astigmatism compared with the visual outcome. Dr Alpins recognised the relative value of WTR astigmatism and described how to plan refractive corrections using this principle in his January 1997 article (Figure 10a, J Cataract Refract Surg 1997;23:65-75, reference 33 in our article). We suggested the "by-the-rule" transformation would help eliminate the problem of divided oblique and WTR astigmatism, but this makes the use of vector analysis difficult and does result in data compression.
I agree that my understanding of astigmatism is incomplete. With over 4000 responses to a search for astigmatism on PubMed, there is much to know and yet more still unknown. The references cited in the article were simply representative or illustrative of the arguments discussed in the article. By way of apology, the correct reference for the "surgical error" (originally given as 34) in Figure 7, equation 20, and the relevant text page 1131 should in fact be reference 70, Noel Alpins' first article on vector analysis. The surgical error is the arithmetic result of the preoperative vector combined with the surgically induced vector (SIA), less the target induced vector (TIA), which is analogous to neutralising a lens with another of the opposite sign (hence the reverse direction arrow). This produces two outcome measures, the difference in magnitude and axis. However, as our article's discussion on obliquely crossed cylinders described, misalignment due to rotation of the corrective cylinder produces not only an error in cylinder magnitude and axis, but also a spherical power error. Because of this interdependence all three should be analysed together, but this produces statistical difficulties. One way around this problem is to use an appropriate summary measure of the outcome instead.
The surgical error may be applied to treatments targeting non-zero goals despite not addressing changes in corneal shape. As an outcome measure of the surgical process it is equally applicable to the arithmetic result of the SIA with the TIA as it is with the SIA and the preoperative astigmatism vector. The transformation of the error between the SIA and the preoperative astigmatism vector into the "difference vector" (which is a mathematically precise and absolute measure of the surgical error) unfortunately does not address the problem of non-linearity (i.e. the relative value in terms of visual acuity outcome) so is not useful as a summary measure of the outcome. However the difference may be useful in understanding the effects of the surgery (i.e. as a process measure) and for deriving the "index of success".
Dr Alpins describes the SIA "torque" effect with reference to the preoperative axis of astigmatism (or the TIA) in his December 1997 article not cited in our Perspective article (J Cataract Rafract Surg 1997;23:1503-14). Torque needs to be distinguished from the effect of rotation of the corrective cylinder that is derived from the post-operative astigmatism value. Unfortunately, our discussion on the optical decomposition did not clearly state that the 45° polar value is derived from the postoperative result, thus correctly describes the rotation effect (as discussed with the obliquely crossed cylinder effects). We apologise for creating some confusion with the "torque" effect.
We agree that the healing response is connected to the surgical process, however healing is a very individual response. Vector analysis in terms of the SIA can only reflect the surgical process. Although a "vector" could be used to represent the measurement of the healing response at any point in time, it may not be representative of the healing responses at other times because the healing process is continuous. Furthermore an individual's response may not be well represented by the aggregate or mean vectorial response, which as discussed, is compounded by the non-linearity problem of the separation of the oblique and ATR astigmatism axis values (see reference 104 from our article).
In his early 1997 article (reference 33) Noel Alpins discusses surgical treatment planning combining the topographic astigmatism values with the refractive values to produce an optimal corneal curvature. Dr Alpins suggests that the surgical emphasis is best directed towards a WTR result when there is a disparity between the values requiring some residual astigmatism after surgery. Without recognising Javal's rule, Dr Alpins nonetheless has ascribed a better relative value to ATR astigmatism suggesting that optimal treatment planning be based on this psycho-physical phenomenon. As we stated "only using keratometric data for the planning of refractive surgery" would create a problem otherwise.
It is understandable that Dr Alpins feels that the concepts presented in our article are in conflict with some of his own, but these do not diminish the value of vector analysis as a process measure, particularly for individual cases. It is the use of vector analysis as an outcome measure relative to the visual acuity that was critically evaluated by our article.
Reference
(1) Morlet N, Minassian D, Dart J. Astigmatism and the analysis of its surgical correction. Brit J Ophthalmol 2001;85:1127-38.
We read with interest the paper by Gain et al. [1] which assessed two distinct
techniques to quantify corneal endothelial cell death in
donor corneas. A significantly higher rate of cell death
was observed with the TUNEL assay which labels
nuclei with fragmented DNA, compared to the trypan
blue exclusion method, which detects cells with
disrupted cell membranes. The authors conclude that...
We read with interest the paper by Gain et al. [1] which assessed two distinct
techniques to quantify corneal endothelial cell death in
donor corneas. A significantly higher rate of cell death
was observed with the TUNEL assay which labels
nuclei with fragmented DNA, compared to the trypan
blue exclusion method, which detects cells with
disrupted cell membranes. The authors conclude that
TUNEL analysis is more accurate than trypan blue
exclusion as a means of assessing the impact of
different corneal storage methods on endothelial
viability.
Our experience of using a number of cell death assays
to investigate fibroblast apoptosis together with the
findings of others [2,3] supports the notion that trypan
blue exclusion is not a good method for detecting
apoptosis in vitro. However, we would like to propose
that the sequential analysis of the same corneal tissue
in this study might account for some of the disparity
observed between the two methods. Following initial
incubation in trypan blue, buttons were subjected to
image analysis as well as cell density measurements
after further incubation in 0.9 % sodium chloride. After
this the buttons were fixed overnight in 10 %
formaldehyde in preparation for TUNEL. It is possible
that the higher rates of death observed by TUNEL
reflect the known toxicity of trypan blue, or are a
consequence of subsequent manipulation in image
analysis and cell density measurement. The low rates
of cell death observed by both techniques in non-stored
corneas do not negate this possibility, since healthier
corneas may be more resistant to the effects of trypan
blue and subsequent analysis. Randomisation of the
sequence of analysis between the techniques
compared would not have been possible, but the
authors could have divided the corneas before storage
or used paired eyes as separate matched specimens.
The authors argue that the disparity between
endothelial cell loss and observed cell death is greater
for trypan blue exclusion because loss of membrane
integrity occurs relatively late, giving a shorter
observational window in which to detect dying cells
than TUNEL analysis, which detects apoptosis earlier.
But the relatively high percentage of apoptotic cells
(12.7 %) observed by TUNEL analysis may be an
overestimate. Although the time span for apoptosis
varies greatly depending on the cell type and nature of
the apoptotic trigger, many estimates suggest that the
processes is completed in less than 24 hours.[4] If
12.7 % of cells undergo apoptosis at any given time it
can be predicted that complete endothelial cell death
would occur within 8 days. The actual loss observed
over the 22-day incubation period in this study was
however only around 14 %.
We agree with the authors regarding the need for
accurate methods for determining endothelial cell
death. No individual assay per-se, is ideal for both
quantifying and determining the mode of cell death and
combinations of assays should give a clearer picture
of the impact of variations in corneal storage on
endothelial viability.
References
(1) Gain P, Thuret G, Chiquet C, Dumollard JM, Mosnier JF, Burillon C, Delbosc B, Hervé P, Campos L. Value of two mortality assessment techniques for organ cultured corneal endothelium: trypan blue versus TUNEL
technique. Br J Ophthalmol 2002;86:306-10.
(2) McCloskey, TW et al. Comparison of seven
quantitative assays to assess lymphocyte cell death
during HIV infection: measurement of induced
apoptosis in anti-Fas-treated Jurkat cells and
spontaneous apoptosis in peripheral blood
mononuclear cells from children infected with HIV.
AIDS Res Hum Retroviruses 1998;14(16):1413-22.
(3) Crowston, JG et al. Antimetabolite-induced
apoptosis in Tenon's capsule fibroblasts. Invest
Ophthalmol Vis Sci 1998;39(2):449-54.
(4) Kravtsov, VD, Daniel TO, Koury MJ.
Comparative analysis of different methodological
approaches to the in vitro study of drug-induced
apoptosis. Am J Pathol 1999;155(4):1327-39.
We have read with avid interest the article by Gupta et al. on the use of bovine pericardium as a wrapping material for hydroxyapatite orbital implants.[1] We are highly impressed by their results as none of the patients had implant extrusion. This is really commendable since implant extrusion rate has ranged from 9 % to 21 % in previous studies,[2] and it indicates meticulous technique and follow up....
We have read with avid interest the article by Gupta et al. on the use of bovine pericardium as a wrapping material for hydroxyapatite orbital implants.[1] We are highly impressed by their results as none of the patients had implant extrusion. This is really commendable since implant extrusion rate has ranged from 9 % to 21 % in previous studies,[2] and it indicates meticulous technique and follow up. We would like to clarify a few pertinent issues.
Although bovine pericardium is generally considered non-reactive, it has been reported to produce severe inflammatory reaction in cardiac use.[3] Another area of major concern with cardiovascular use of bovine pericardium has been development of calcification seen in both laboratory studies and cardiac patients.[4] It is still uncertain what impact such a calcification would have on an orbital implant and assessment of its effect would certainly require studies with a larger number of patients and longer follow up. However, it has been suggested that it may hamper its motility.[2] We suggest that the possibility of misinterpretation of imaging findings in cases of orbital recurrence of tumours should not be overlooked.
Another crucial area of concern is the risk of infection with xenografts, which cannot be totally eliminated even by highly stringent screening and processing procedures. We are referring to the group of bovine spongiform encephalopathies including Creutzfeld-Jakob disease (CJD) and its variant found in the United Kingdom (CJDv).
Therefore, the quest for a comparable synthetic wrapping material and better implants which do not require wrapping continues, and bovine pericardium should be considered, keeping in view its above mentioned shortcomings.
Mandeep S. Bajaj, MD
Neelam Pushker, MD
Dr Rajendra Prasad Centre for Ophthalmic Sciences
All India Institute of Medical Sciences
Ansari Nagar, New Delhi - 110 029
India
References
(1) Gupta M, Puri P, Rennie IG. Use of bovine pericardium as a wrapping material for hydroxyapatite orbital implants. Br J Ophthalmol 2002;86:288-9.
(2) Gayre GS, Debacker C, Lipham W, et al. Bovine pericardium as a wrapping for orbital implants. Ophthal Plast Reconstr Surg 2001;17:381-7.
(3) Skinner JR, Kim H, Toon RS, et al. Inflammatory epicardial reaction to processed bovine pericardium: case report. J Thorac Cardiovas Surg 1984;88: 789-91.
(4) Braile DM, Ardito RV, Greco OT, et al. IMC bovine pericardial valve: 11 years. J Card Surg 1991;6:580-8.
We read with great interest the article by Takei et al..[1] We
agree with the authors that axial length (AL) measurement in silicone
oil-filled eyes is a difficult situation. The need for accurate estimation
of AL has increased following advances in vitreoretinal surgical techniques
and improved visual results. We complement Takei and colleagues for an
excellent report on the matter. CT scanning for...
We read with great interest the article by Takei et al..[1] We
agree with the authors that axial length (AL) measurement in silicone
oil-filled eyes is a difficult situation. The need for accurate estimation
of AL has increased following advances in vitreoretinal surgical techniques
and improved visual results. We complement Takei and colleagues for an
excellent report on the matter. CT scanning for AL measurement is a novel
technique, but not without pitfalls.
We had studied AL in 28 eyes pre and post-silicon oil removal (viscosity
1000 centistoke) using A-scan ultrasonography in the sitting position and
found that the ratio between actual AL and AL measured in silicon oil-filled
eyes varied widely, from 0.64 to 0.92. This is in contrast to the study by
Murray et al.[2] who showed minimal variability and could derive a
mathematical constant of 0.71 to calculate AL in silicon oil-filled eyes to
get the actual AL.
We did find that the AL in the fellow eye compared well with the post SO
removal AL. Although the best method of biometry in silicon oil-filled eyes
still eludes us, we feel that AL measurement prior to the vitreo-retinal
procedure may be the best option (using combined A and B scan
ultrasonography). Failing that, AL in the fellow eye may give a fair
estimate. However the claims of CT scan for accurate determination of AL
needs further evaluation and refining considering its lack of easy
availability, high cost and irradiation exposure.
References
(1) Takei K, Sekine Y, Okamoto F and Hommura S. Measurement of axial
length of eyes with incomplete filling of silicone oil in the vitreous
cavity using X-ray computed tomography. Br J Ophthalmol 2002;86:47-50.
(2) Murray DC, Potamitis T, Good P, Kirkby GR, Benson MT. Biometry of
the silicone oil-filled eye. Eye 1999 Jun;13; 319-24.
I read with great interest the excellent perspective by Plsková et al1 in which they raise the issue of transient corneal opacification following corneal transplantation in the mouse model and argue that it might be due to a sufficient number of endothelia[l] cells regaining function.
What the authors describe for the mouse model, also occurs in the rat model. In fact most researchers in the rat model pr...
I read with great interest the excellent perspective by Plsková et al1 in which they raise the issue of transient corneal opacification following corneal transplantation in the mouse model and argue that it might be due to a sufficient number of endothelia[l] cells regaining function.
What the authors describe for the mouse model, also occurs in the rat model. In fact most researchers in the rat model probably have this experience, but for some reason do not think it is very important and/or choose to ignore it. Apart from the article by Williams et al[2], there is - as far as I know - only one other author who has explicitly mentioned this transient opacification. In his paper, Herbort[3] wrote "The grafts began clearing 4 weeks after surgery … and vessels in the graft diminished from 6 weeks post-surgery." and "It has to be noted that after acute rejection most corneas regain some clarity by 7-8 weeks." Transient corneal opacification also occurs in the rat model I used[4] (AO rats (strain RT1u) served as recipients of corneas from PVG rats (strain RT1c) and corneas were sutured with a single running suture). Allogeneic transplanted corneas showed no initial opacification immediately postoperative; neither did the syngeneic controls. All allogeneic corneas "rejected" (or more precisely showed total
opacification) around day 11-13 and those corneas, when followed long enough, all cleared. Opacification remained higher than 2 (meaning an increased corneal haze, but some anterior chamber structures still visible) at days 17-21 and became lower than 2 (slight haze) around days 21-32.
It would be exciting to know if the hypothesis put forward by Plsková et al1 would also apply to the rat model and to find out if this 'clearing' of the opacification also occurs in other rat strains than the ones mentioned.
Plsková et al have brought up a very important topic where a lot of uncertainty still exists, which warrants further research.
REFERENCES
(1) Plsková J, Kuffová L, Holán V, Filipec M, Forrester JV. Evaluation of corneal graft rejection in a mouse model. Br J Ophthalmol 2002;86:108-113.
(2) Williams KA, Coster DJ. Penetrating corneal transplantation in the inbred rat; a new model. Invest Ophthalmol Vis Sci 1985;26:23-30.
(3) Herbort CP, Matsubara M, Nishi M, Mochizuki M. Penetrating keratoplasty in the rat: a model for the study of immunosuppressive treatment of graft rejection. Jpn J Ophthalmol 1989;33:212-220.
(4) Claerhout I, Beele H, Verstraete A, Van den Broecke C, Kestelyn P. The effect of duration and timing of systemic cyclosporine therapy on corneal allograft survival in the rat model. Graefe's Arch Clin Exp Ophthalmol 2001;239:152-157.
Dr Ilse Claerhout
Department of Ophthalmology
Ghent University Hospital
De Pintelaan 185
9000 Gent
Belgium
Ilse.claerhout@rug.ac.be
We thank Dr. Panda for her comments on our recent paper entitled
"Treatment of fungal keratitis by penetrating keratoplasty". Dr. Panda
noted correctly that treatment modalities differ on different types of
keratitis. About 20% of the cases in our study were mixed infections, that
is, fungal infection combined with bacterial or herpes simplex virus
infection. However, the focus of our study was to s...
We thank Dr. Panda for her comments on our recent paper entitled
"Treatment of fungal keratitis by penetrating keratoplasty". Dr. Panda
noted correctly that treatment modalities differ on different types of
keratitis. About 20% of the cases in our study were mixed infections, that
is, fungal infection combined with bacterial or herpes simplex virus
infection. However, the focus of our study was to study the treatment of
severe fungal keratitis cases that could not be controlled by antifungal
medication. KOH wet mount was prepared for all the infected eyes. Though
calcoflour white and acridine orange stain have become popular in the
world, it is difficult to get them in China now. In addition, we do not
feel that KOH wet mount preparation can be substituted by normal saline
smear method, because KOH can dissolve the impurities in the smear so that
the fungal filaments could be seen more clearly through the microscope.
We gave systemic antifungal medication to all the patients, but just
orally for 2 to 3 weeks for the purpose of preventing recurrent fungal
infection after PKP. We agree that fluconazole is only effective on a few
genera of fungi. However, usually it takes at least 3 days to identify the
infected fungi through fungal culture, so we used fluconazole combined
with natamycin or amphotericin B before the fungi were identified.
Furthermore, it is quite necessary to go on using antifungal medication
topically during and after surgery in case the infected tissue has not
been removed in its entirety. Topical antifungal medication is inevitably
epitheliotoxic, which may be endurable comparing with the recurrence of
fungal infection.
Dr. Panda is interested in the characteristic feature of fungi. We
reported it in another recent publication regarding fungal keratitis. [1]
In our study, the patients we performed PKP on were those with fungal
infection that could not be controlled by antifungal medication. We had
observed that more complications would occur after PKP in patients with
fungal keratitis than those with keratococus. However, the result of this
study was exciting, because we attached great importance to the prevention
of complications after surgery. A series of scientific articles written in
Chinese by us regarding this point has been published in the medical
journals in China, and we are preparing manuscripts submitted to journals
published in English in order to introduce them to international
colleagues.
A point of concern was raised about large graft. The optical result
is related to the size of graft, that is, patients with large grafts can
obtain better visual acuity than those with small ones. As long as the
infected tissue has been thoroughly removed, the only thing we need to do
after surgery is to prevent immunorejection.
Amniotic membrane transplantation has been performed at our hospital
for some recalcitrant corneal ulcers, and satisfactory effects were
achieved. Also, we have tried this therapy in a few cases of fungal
keratitis in which the infection just reached the superficial corneal
stroma and was completely removed, but did not get good postoperative
visual acuity. Therefore, at present, only LKP was chosen for the
treatment of fungal infection at the superficial or middle stroma at our
hospital.
Lixin Xie, MD
Shandong Eye Institute & Hospital
Qingdao 266071, P. R. China
References
(1) Xie L, Shi W, Liu Z, Li S. Lamellar keratoplasty for the treatment of
fungal keratitis. Cornea 2002;21:33-7
Dear Editor
I read with interest the article by Hiti et al.[1] on the susceptibility of Acanthamoeba to a multipurpose disinfecting contact lens solution and two hydrogen peroxide systems. The association between acanthamoeba keratitis and contact lens wear is now firmly established. Thus, the use of contact lens disinfecting solutions effective at killing Acanthamoeba organisms is important in pr...
Dear Editor
Dr Newsham's effort to inform parents of children with amblyopia about occlusion therapy is laudable but incomplete. Ethical considerations of informed consent require full disclosure of all aspect of the proposed treatment. In the current instance this compels inclusion of the following points:
1. Occlusion therapy has never been scientifically validated with a randomized, controlled study.
...Dear Editor
Poon et al.[1] in their excellent article have reiterated the efficacy of autologous serum in the treatment of persistent epithelial defects (PEDs) of the cornea. We would like to invite the attention of the authors to certain aspects of the study. The authors have considered a period of one week for labeling an epithelial defect to be persistent. However, most studies on a similar subject have tak...
Dear Editor
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Choice of time period before an epithelial defect can be described as "persistent".
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Dear Editor
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Dear Editor
We read with interest the paper by Gain et al. [1] which assessed two distinct techniques to quantify corneal endothelial cell death in donor corneas. A significantly higher rate of cell death was observed with the TUNEL assay which labels nuclei with fragmented DNA, compared to the trypan blue exclusion method, which detects cells with disrupted cell membranes. The authors conclude that...
Dear Editor
We have read with avid interest the article by Gupta et al. on the use of bovine pericardium as a wrapping material for hydroxyapatite orbital implants.[1] We are highly impressed by their results as none of the patients had implant extrusion. This is really commendable since implant extrusion rate has ranged from 9 % to 21 % in previous studies,[2] and it indicates meticulous technique and follow up....
Dear Editor
We read with great interest the article by Takei et al..[1] We agree with the authors that axial length (AL) measurement in silicone oil-filled eyes is a difficult situation. The need for accurate estimation of AL has increased following advances in vitreoretinal surgical techniques and improved visual results. We complement Takei and colleagues for an excellent report on the matter. CT scanning for...
I read with great interest the excellent perspective by Plsková et al1 in which they raise the issue of transient corneal opacification following corneal transplantation in the mouse model and argue that it might be due to a sufficient number of endothelia[l] cells regaining function.
What the authors describe for the mouse model, also occurs in the rat model. In fact most researchers in the rat model pr...
Dear Editor,
We thank Dr. Panda for her comments on our recent paper entitled "Treatment of fungal keratitis by penetrating keratoplasty". Dr. Panda noted correctly that treatment modalities differ on different types of keratitis. About 20% of the cases in our study were mixed infections, that is, fungal infection combined with bacterial or herpes simplex virus infection. However, the focus of our study was to s...
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