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Biomedical subjects

J K Dart

Publications and source records attributed to J K Dart.

At least 19 recordsLinked to original sources
PubMed2001

Demonstration of biofilm in infectious crystalline keratopathy using ruthenium red and electron microscopy.

OBJECTIVE: Bacterial biofilm formation has been implicated in the pathogenesis of infectious crystalline keratopathy. Biofilm cannot be visualized by electron microscopy without the addition of a fixative that stabilizes the polysaccharide-rich bacterial extracellular matrix that surrounds the bacterial colonies in a biofilm. We used ruthenium red as a fixative to evaluate corneal biopsy specimens for the presence of bacterial biofilm in three cases of infectious crystalline keratopathy (ICK) and five cases of chronic microbial keratitis without crystalline changes. DESIGN: Case series with clinicopathologic correlation. PARTICIPANTS: Eight patients underwent corneal biopsy or therapeutic keratoplasty as part of their management for chronic unresponsive microbial keratitis. METHODS: The corneal specimens removed were trisected for microbiology, pathology, and transmission electron microscopy (TEM). The TEM specimens were fixed in 2.5% glutaraldehyde in 0.1 M sodium cacodylate buffer with 0.05% ruthenium red. MAIN OUTCOME MEASURES: Demonstration of bacterial biofilm with TEM. RESULTS: TEM demonstrated organisms with a surrounding extracellular matrix consistent with a bacterial biofilm in the three cases of ICK but not in the five other cases of chronic microbial keratitis. CONCLUSIONS: The presence of biofilm in ICK can be demonstrated with TEM with appropriate fixation techniques that stabilize the bacterial extracellular matrix. Biofilm stains intensely with periodic acid-Schiff because of the polysaccharide-rich extracellular matrix and weakly with Gram stain because of the high proportion of nonviable organisms. Biofilm formation occurs in ICK but probably not in chronic bacterial keratitis without crystalline changes. Secretion of an extracellular matrix by bacteria to form a biofilm is a response to a nutrient-deprived environment in which growth and replication is depressed. The extracellular matrix of the biofilm may mask bacterial antigens, explaining the relative lack of inflammatory response in these infections. It may also be one of the mechanisms explaining the resistance to in vivo antimicrobial therapy when in vitro sensitivities have been proven.

Aged↗
PubMed2001

Use of cyclosporin in the treatment of steroid resistant post-keratoplasty atopic sclerokeratitis.

AIMS: To demonstrate that oral cyclosporin is successful in the management of steroid refractory post-keratoplasty atopic sclerokeratitis (PKAS). METHODS: Series of three patients. RESULTS: The patients developed PKAS between 2 and 11 days after surgery. All cases failed to respond to oral prednisolone 60-80 mg daily for 10-30 days but resolved with the addition of systemic cyclosporin 5.0-7.5 mg/kg/day. There have been no relapses following withdrawal of therapy after 3-18 months. CONCLUSIONS: PKAS is an uncommon, but severe, complication of corneal graft surgery and often responds to oral prednisolone treatment. Oral cyclosporin results in rapid resolution of PKAS in steroid unresponsive cases.

Adult↗
PubMed2001

Autologous serum eyedrops for dry eyes and epithelial defects: clinical and in vitro toxicity studies.

BACKGROUND/AIMS: Autologous serum drops have been reported to be beneficial in keratoconjunctivitis sicca (KCS) and persistent epithelial defects (PED). A clinical pilot study was carried out to examine these potential uses and in vitro toxicity testing on corneal epithelial cell cultures was performed to compare the effect of serum drops with unpreserved hypromellose (hydroxypropylmethylcellulose 0.3%). METHODS: Patients with KCS and PED, unresponsive to conventional treatment were recruited. Patients were examined before treatment, at 1 and 2 weeks after initiation, and then 2 weekly until treatment ceased. Symptoms were assessed at each visit. Clinical examination included Schirmer's test without anaesthesia, rose bengal staining, and fluorescein staining. Epithelial defects were measured with the slit beam. In the laboratory, cultured human corneal epithelial cells were exposed to serum drops and hypromellose, and their viability evaluated with fluorescent viability staining (Calcein AM ethidium homodimer) and an ATP assay. RESULTS: Autologous serum was used in 15 eyes of 13 patients with PED and 11 eyes of nine patients with KCS. In two patients serum drops were started after penetrating keratoplasty (PK). The PKs were performed for perforations secondary to PEDs. Of the 15 eyes with PED, nine healed at a mean of 29 days and six failed. The mean duration of PED before the use of serum drops was 48.2 days. Of the 11 eyes with KCS, six had improved subjective scores and fluorescein scores, and five had improved rose bengal scores after the use of serum drops. For the two patients who used serum eyedrops post-PK, there was a stable and intact epithelium at 1 week. Cessation of serum drops during the postoperative period led to deterioration in the subjective and objective scores in both patients. One developed a PED that responded to reinstitution of serum drops. The morphology and ATP levels of cultured epithelial cells exposed to serum were better maintained than those exposed to hypromellose. CONCLUSION: Autologous serum drops are useful for PED and KCS. This effect may be related to a number of active factors in serum including growth factors, fibronectin, vitamin A, and anti-proteases. In vitro toxicity testing demonstrated that serum drops have reduced toxicity compared with unpreserved hypromellose. Currently regulatory restrictions in the UK have prevented the establishment of a prospective randomised controlled trial examining the efficacy of autologous serum drops for the management of this group of ocular surface disorders.

Administration, Topical↗
PubMed2001

Persistence of acanthamoeba antigen following acanthamoeba keratitis.

AIM: To investigate the hypothesis that persistent corneal and scleral inflammation following acanthamoeba keratitis is not always caused by active amoebic infection but can be due to persisting acanthamoebic antigens METHODS: 24 lamellar corneal biopsy and penetrating keratoplasty specimens were obtained from 14 consecutive patients at various stages of their disease and divided for microscopy and culture. Histological sections were immunostained and screened for the presence of Acanthamoeba cysts by light microscopy. Cultures were carried out using partly homogenised tissues on non-nutrient agar seeded with E coli. Clinical data were obtained retrospectively from the case notes of these patients. RESULTS: Of the 24 specimens, 20 were obtained from eyes that were clinically inflamed at the time of surgery. Acanthamoeba cysts were present in 16 (80%) of these 20 specimens, while only five (25%) were culture positive. Acanthamoeba cysts were found to persist for up to 31 months after antiamoebic treatment. CONCLUSION: These findings support the hypothesis that Acanthamoeba cysts can remain in corneal tissue for an extended period of time following acanthamoeba keratitis and may cause persistent corneal and scleral inflammation in the absence of active amoebic infection. In view of these findings, prolonged intensive antiamoebic therapy may be inappropriate when the inflammation is due to retained antigen rather than to viable organisms

Acanthamoeba↗
PubMed2001

A simple corneal perfusion chamber for drug penetration and toxicity studies.

AIMS: Corneal perfusion chambers are important tools in the development and assessment of ophthalmic drugs. The aim of this study was to design and test a modified perfusion chamber suitable for topical application of drugs to isolated corneoscleral preparations, and which allowed continuous monitoring of endothelial cell function. METHODS: A polycarbonate and stainless steel perfusion chamber was designed to clamp corneas in a horizontal plane suitable for topical drug delivery. Endothelial cell function was assessed by ultrasonic pachymetry and specular microscopy during perfusion. Epithelial barrier function was assessed by penetration of fluorescein. Leakage was examined by measuring penetration of a large protein, IgG. Tissue architecture after perfusion was examined by conventional histology. RESULTS: Corneas maintained a functionally and morphologically intact endothelial monolayer during perfusion periods of up to 14 hours. The epithelial barrier function was well preserved. The tissue clamp sealed the preparation effectively against leakage of macromolecules. CONCLUSION: The new chamber device forms a reliable tool for in vitro drug penetration and toxicity studies in isolated perfused corneoscleral tissue.

Animals↗
PubMed2001

Extracapsular cataract extraction compared with small incision surgery by phacoemulsification: a randomised trial.

BACKGROUND: Cataract extraction constitutes the largest surgical workload in ophthalmic units throughout the world. Extracapsular cataract extraction (ECCE), through a large incision, with insertion of an intraocular lens has been the most widely used method from 1982 until recently. Technological advances have led to the increasing use of phacoemulsification (Phako) to emulsify and remove the lens The technique requires a smaller incision, but requires substantial capital investment in theatre equipment. In this randomised trial we assessed the clinical outcomes and carried out an economic evaluation of the two procedures. METHODS: In this two centre randomised trial, 232 patients with age related cataract received ECCE, and 244 received small incision surgery by Phako. The main comparative outcomes were visual acuity, refraction, and complication rates. Resource use was monitored in the two trial centres and in an independent comparator centre. Costs calculated included average cost per procedure, at each stage of follow up. RESULTS: Phako was found to be clinically superior. Surgical complications and capsule opacity within 1 year after surgery were significantly less frequent, and a higher proportion achieved an unaided visual acuity of 6/9 or better (<0.2 logMAR) in the Phako group. Postoperative astigmatism was more stable in Phako. The average cost of a cataract operation and postoperative care within the trial was similar for the two procedures. With the input of additional spectacles for corrected vision at 6 months after surgery, the average cost per procedure was pound359.89 for Phako and pound367.57 for ECCE. CONCLUSION: Phako is clinically superior to ECCE and is cost effective.

Aged↗
PubMed2001

Amniotic membrane grafts, "fresh" or frozen? A clinical and in vitro comparison.

BACKGROUND/AIMS: The use of "fresh" (hypothermically stored) and frozen amniotic membrane (AM) was compared in a patient with cicatricial pemphigoid with stem cell failure. The viability of both "fresh" and frozen AM epithelial cells was assessed after storage. METHODS: AM was stored at either +4 degrees C ("fresh") or at -80 degrees C (frozen). A "fresh" graft was applied to the cornea following superficial keratectomy. Subsequently, a further frozen graft was applied to the same eye. Viability of the stored AM epithelium was assessed by investigating membrane integrity and mitochondrial activity. RESULTS: In both cases the cornea re-epithelialised and visual acuity improved. Improvement, however, was not sustained. CONCLUSION: Although both procedures led to an improvement in visual acuity, "fresh" tissue performed no better than frozen in promoting re-epithelialisation. The authors suggest that logistical, safety, and cost considerations outweigh any benefits of using "fresh" as opposed to frozen graft material.

Amnion↗
PubMed2001

Toxicity of natural tear substitutes in a fully defined culture model of human corneal epithelial cells.

PURPOSE: Serum and saliva have recently been advocated as natural tear substitutes for intractable aqueous-deficient dry eyes, but the effects of these fluids on corneal epithelium have not been well characterized. A laboratory study was performed in a defined test model to compare the toxicity of natural and pharmaceutical tear substitutes and to identify potentially toxic factors in natural tear substitutes, such as amylase, hypotonicity, and variations in preparation. METHODS: Primary human corneal epithelial cells were cultured with defined keratinocyte serum-free medium. The cells were incubated with hypromellose (hydroxypropylmethylcellulose 0.3%) with and without benzalkonium chloride 0.01%, saliva with differing osmolalities, 100% serum, and 50% serum (1:1 vol/vol with chloramphenicol 0.5%) for varying times and concentrations. Toxicity was examined in four ways. Microvillous density was assessed with scanning electron microscopy. Cell membrane permeability and intracellular esterase activity were analyzed after staining with fluorescent calcein-AM/ethidium homodimer and cellular adenosine triphosphate (ATP) was quantified using a luciferin-luciferase-based assay. RESULTS: The toxicity ranking of the tear substitutes correlated in all assays. The ATP assay was the most sensitive, followed by ethidium cell permeability, and finally the esterase activity. Preserved hypromellose was more toxic than the unpreserved preparation. Among natural tear substitutes, natural saliva was most toxic. Isotonic saliva and 50% serum were of similar toxicity, and 100% serum was least toxic. Natural tear substitutes were-except for natural saliva-less toxic than unpreserved hypromellose. Hypotonicity, but not amylase, was the major toxic effect associated with saliva. The dilution of serum with chloramphenicol induced toxicity. CONCLUSIONS: This is the first toxicity study using human primary corneal epithelial cells cultured under fully defined conditions as an in vitro model. Cellular ATP is a sensitive parameter for quantifying toxicity. Isotonic saliva and serum offer greater therapeutic potential for severely aqueous-deficient dry eyes than do pharmaceutical tear substitutes.

Adenosine Triphosphate↗
PubMed2000

Management and outcome of cataract surgery in ocular cicatricial pemphigoid.

BACKGROUND: Patients with ocular cicatricial pemphigoid (OCP) lose vision due to corneal disease or cataract, which may be senile, drug induced or complex. The success of cataract surgery in these patients may be limited by an increased risk of surgical complications due to difficult access and visualisation, exacerbation of the cicatrising disease following surgery or later progression of the corneal disease. We report our experience on cataract surgery in OCP. METHODS: Cataract surgery was performed on 15 eyes of 13 patients. In the pre- and postoperative examinations the stage of the condition (according Foster's classification), the degree of conjunctival hyperaemia and the visual acuity (VA) were evaluated and topical and systemic medication recorded. All procedures used a corneal incision. The technique was intracapsular (ICCE) in 1, extracapsular (ECCE) in 4 and phacoemulsification in 10 eyes. In 13 of 15 cases an intraocular lens was implanted. The unoperated fellow eyes constituted a control group. Duration of postoperative follow-up was 35.8+/-39.1 months. RESULTS: 10 of 15 eyes had stage III disease or worse before surgery. Two eyes following ECCE showed early postoperative progression of the disease. Postoperative visual acuity improved in 14 eyes by 2 or more lines. Preoperatively 5 eyes met the criteria for blind registration, whereas postoperatively all eyes achieved a VA of at least 0.1. In 6 eyes the VA was sufficient to allow driving. However, by the 22nd postoperative month progressive cicatricial and ocular surface disease resulted in a regression of the achieved visual rehabilitation in 8 eyes. CONCLUSION: OCP does not prevent successful cataract surgery if appropriate techniques are used and precautions taken. Systemic perioperative immunosuppression is necessary in patients with active conjunctival inflammation. The use of small clear corneal incision surgery is recommended to reduce the risk of an acute exacerbation of conjunctival inflammation. Although visual rehabilitation may be only temporary due to progression of the conjunctival or corneal disease in OCP, cataract surgery can provide some benefit, in severely disabled patients, without precipitating an acute exacerbation of OCP.

Aged↗
PubMed2000

Anterior chamber flare after trabeculectomy and after phacoemulsification.

AIMS: To evaluate and compare prospectively the anterior chamber inflammatory response after phacoemulsification cataract surgery and after trabeculectomy with peripheral iridectomy. METHODS: Anterior chamber inflammation was measured using the Kowa FM-500 laser flare meter in 131 patients undergoing trabeculectomy and 148 patients undergoing phacoemulsification cataract extraction with intraocular lens implantation. Flare was measured before surgery and on each postoperative visit up to 12 months. RESULTS: Before surgery there was no significant difference in flare readings between the two groups. Following trabeculectomy flare returned to baseline levels 4 weeks after surgery, while following phacoemulsification cataract extraction it remained significantly higher at week 6 (p<0.006) and month 3 (p<0.05). CONCLUSIONS: Anterior chamber inflammation is more prolonged after cataract surgery than after trabeculectomy. This may have implications for the timing of trabeculectomy in relation to cataract surgery.

Aged↗
PubMed1998

Successful management of Aspergillus scleritis by medical and surgical treatment.

BACKGROUND: Inflammatory scleral disease is frequently associated with autoimmune disorders and only occasionally caused directly by an infective agent. Fungal infections primarily involving the sclera are rare, and the outcome is generally poor. Here we report three patients with post-operative Aspergillus scleritis who were successfully managed by medical therapy and surgical intervention. PATIENTS: Scleral infection with Aspergillus sp. was diagnosed 6 and 5 months after cataract extraction in a 76-year-old diabetic and an 82-year-old woman respectively, and in a 54-year-old man 3 months after trabeculectomy. Swabs and/or scrapings had not been conclusive and the diagnosis of Aspergillus infection was established in all cases only after scleral biopsy. RESULTS: The infection was eliminated in all cases. This was achieved in one eye by treatment with systemic and topical amphotericin B. The two patients with fungal scleritis after cataract extraction required in addition to the medical therapy (oral itraconazole, topical econazole and amphotericin B) scleral excisions and patch grafts to control infection. CONCLUSION: Fungal scleritis may remain undiagnosed for months. A scleral biopsy may be necessary to establish this diagnosis. Prolonged systemic antifungal therapy alone may not eradicate fungal infection. Surgical excision improves the outcome of fungal scleritis.

Aged↗
PubMed1998

Bacterial biofilm on contact lenses and lens storage cases in wearers with microbial keratitis.

Bacterial biofilm formation on contact lenses (CLs), and CL storage cases may be a risk factor for CL-associated corneal infection and may explain the persistence of organisms in CL storage cases. This study evaluated biofilm formation on, and microbial contamination of, CLs and CL storage cases from patients with microbial keratitis. Contact lenses and CL storage cases from 20 wearers with microbial keratitis were sampled microbiologically and visualized using scanning electron microscopy (SEM). Culture results from the cornea were also noted. Bacterial biofilm was present more frequently (P < 0.05) on CL storage case surfaces (17/20) compared with CL surfaces (11/20) and biofilm density was significantly greater on case surfaces (P < 0.05). There was no association between poor compliance and microbial contamination of the CL storage case, nor between poor compliance and biofilm formation or density on the CL or CL storage case. Biofilm formation occurred equally frequently with hydrogen peroxide and chlorine release care systems. Microbial keratitis in CL wearers is frequently associated with bacterial biofilm in the CL storage case. Despite the use of current CL disinfection systems, the CL storage case is a favourable environment for proliferation of certain organisms. Biofilm on CLs may prolong the retention time of organisms at the ocular surface and increase their potential pathogenicity.

Biofilms↗
PubMed1998

Disposable contact lens use as a risk factor for microbial keratitis.

AIMS: A case-control study was performed to evaluate soft contact lens (SCL) wear modality as a risk factor for microbial keratitis. METHODS: Contact lens wearers presenting as new patients to Moorfields Eye Hospital accident and emergency department during a 12 month period completed a self administered questionnaire detailing demographic data and contact lens use habits. Cases were patients with a clinical diagnosis of SCL related microbial keratitis. Controls were SCL users attending with disorders unrelated to contact lens wear. Odds ratios (estimates of relative risks) and 95% confidence limits (CL) were calculated through multivariable logistic regression analysis. RESULTS: There were 89 cases and 566 controls. A substantially increased risk with 1-4 weekly disposable SCL compared with non-disposable SCL was identified among both daily wear (DW) (odds ratio = 3.51, 95% CL 1.60-7.66, p = 0.002) and extended wear (odds ratio 4.76, 95% CL 1.52-14.87, p = 0.007) users after adjustment for demographic, lens use and hygiene variables. Other significant factors among DW users were "occasional" overnight use, use of chlorine based (as opposed to other chemical) systems in combination with poor storage case hygiene, and irregular disinfection. CONCLUSION: Properties of some disposable SCL may be partly responsible for these excess risks. It is also possible, however, that this finding is largely a reflection of widespread complacency among patients and practitioners with respect to disposable SCL fitting and use.

Adolescent↗
PubMed1998

Acanthamoeba keratitis: multicentre survey in England 1992-6. National Acanthamoeba Keratitis Study Group.

AIM: To investigate the frequency, outcomes, and risk factors for acanthamoeba keratitis (AK) in England during the past 4 years. METHODS: An ophthalmologist in 12 of the 14 regional health authorities (RHAs) coordinated identification of patients in their region presenting with AK between 1 October 1992 and 30 September 1996. Clinical and postal patient questionnaire data were analysed. RESULTS: 243 patients (259 eyes) with an AK diagnosis were identified, equating to an annualised incidence of 0.14 per 100,000 individuals. UK resident patients for each year numbered 50, 71, 73, and 32 respectively. Among patients with sufficient data 170/237 (72%) were diagnosed early (within 30 days of presentation), 197/218 (90%) were treated with polyhexamethyl biguanide and/or chlorhexidine, and 40/243 (16%) underwent surgery. Visual acuities of 6/12 or better were achieved by 222/259 (86%) eyes, including 84 eyes of patients under review or lost to follow up. Non-contact lens (CL) wearers were associated with delayed diagnosis, increased need for surgery and a poorer visual outcome (only 10/18 eyes, 56%, achieved 6/12 acuity). 225/243 (93%) patients were CL wearers, and 205/243 (84%) were soft CL (SCL) users. Among SCL user respondents, previously identified risk factors--swimming with CL (47/138, 34%), non-sterile CL rinsing (11/138, 8%), omitted disinfection (85/138, 62%), and chlorine release disinfection (65/138, 47%)--were identified for 125/138 (91%) patients. CONCLUSIONS: Earlier diagnosis and more effective medical therapy have improved the prognosis for most AK patients. The study demonstrates the highly preventable nature of the disease: 91% of the SCL wearers could have avoided the disease by refraining from inadvisable practices, and a marked fall in frequency was seen after intensive media attention to AK, possibly in conjunction with increasing penetrance of new CL products. Since the frequency of AK appears to be largely determined by the ever changing trends in CL use, continued monitoring is indicated.

Acanthamoeba Keratitis↗
PubMed1998

Polymerase chain reaction analysis of corneal epithelial and tear samples in the diagnosis of Acanthamoeba keratitis.

PURPOSE: Acanthamoeba is an uncommon cause of corneal infection in which the best visual outcome follows prompt diagnosis and a long course of appropriate antimicrobial therapy. Because conventional detection techniques for Acanthamoeba have certain limitations, we investigated the ability of the polymerase chain reaction (PCR) to confirm the clinical diagnosis of Acanthamoeba keratitis, with the ultimate aim of achieving early diagnosis. METHODS: Using two different pairs of primers, PCR was performed on representative cultured Acanthamoeba isolates to confirm the assay's ability to amplify Acanthamoeba DNA from a wide range of acanthamoebae. Subsequently, corneal epithelial samples from 19 patients and tear samples from 12 patients with Acanthamoeba keratitis were analyzed by PCR for the presence of Acanthamoeba DNA. RESULTS: Acanthamoeba DNA was amplified by PCR from 16 (84%) of 19 corneal epithelial samples, whereas Acanthamoeba was cultured from 10 samples (53%), all of which were PCR positive. Tear samples from 8 (66%) of 12 patients were positive on PCR testing, and one tear sample was PCR positive, whereas the corresponding epithelial biopsy had yielded a negative PCR result. Samples from culture-positive patients were positive on PCR testing more frequently than those from culture-negative patients (10/10 culture-positive corneal epithelial and 5/7 [71%] culture-positive initial tear samples versus 6/9 [66%] culture-negative corneal epithelial and 2/5 [40%] culture-negative tear samples). All control epithelial (n = 15) and tear (n = 15) samples yielded negative results. CONCLUSIONS: PCR was a more sensitive diagnostic test than a culture for Acanthamoeba keratitis, and the use of two different primers achieved better sensitivity than a single set. A PCR of a tear sample also may be a useful complementary test and, in combination with PCR of epithelial samples, would prove particularly helpful in confirming the clinical diagnosis in culture-negative cases.

Acanthamoeba↗