John Dart

Contact lenses and other risk factors in microbial keratitis

Microbial keratitis is a potentially binding disease that is rare in normal eyes unless associated with contact lens (CL) wear. To assess the risks of CL use, and other major causes, for keratitis, a case-control study of 91 cases of keratitis including 60 CL users was done. Relative risks (RR) and population attributable risk percentages (PAR%) for keratitis were estimated for different causes and for the different types of CL. The RR (95% confidence intervals) for CL wear was 80 (38-166) and for trauma cases 14 (6-32) compared with cases of keratitis without a predisposing condition. The PAR% for microbial keratitis attributed to CL wear was 65%. The RR for overnight wear soft lenses was 21 (7-60), for daily-wear soft lenses 3.6 (1-14), and for polymethylmethacrylate hard lenses 1.3 (0-9) compared with gas-permeable hard lenses. Continuous periods of CL wear for more than 6 days was associated with increased risk. CL wear is now the commonest cause, and has the highest risk, for new cases of microbial keratitis at Moorfields Eye Hospital. Soft CLs, especially extended-wear lenses, carry a significantly higher risk than do hard lenses for this disease.

Risk Factors for Microbial Keratitis with Contemporary Contact Lenses : A Case-Control Study

OBJECTIVE To assess the relative risks (RR) of microbial keratitis (MK) for contemporary contact lens (CL) types and wearing schedules. DESIGN A 2-year prospective case-control study begun in December 2003. PARTICIPANTS Cases were 367 CL wearers attending Moorfields Eye Hospital with proven or presumed MK. Controls were 1069 hospital controls, who were CL wearers with a disorder unrelated to CL wear, and 639 population-based controls who were CL wearers randomly selected from the Moorfields catchment area. Hospital patients completed a self-administered questionnaire; population-based controls were interviewed by telephone. TESTING Multivariate analysis was done both for all cases of MK, and for the moderate and severe MK subgroups alone. MAIN OUTCOME MEASURES The RR for developing MK, and vision loss, for all lens types compared with planned replacement soft lenses (the referent). RESULTS Compared with planned replacement soft lenses (the referent), the RR of MK was significantly increased with daily disposable (DD) CLs (RR, 1.56x [95% confidence interval (CI), 1.1-2.1]; P = 0.009) and differed between different brands of DD lens, was reduced for rigid lenses (RR, 0.16x [95% CI, 0.06-0.4]; P<0.001), and no different for silicone hydrogel or other types of soft lens. Although the risk of MK was higher overall among DD lens users, the risk of vision loss was less than for planned replacement soft CL users (P = 0.05); no DD lens users lost vision to the level of >or=20/40. The RR for overnight wear, for any lens type, was 5.4 times higher (95% CI, 3.3-10.9; P<0.001). Comparison of the DD soft CL types with planned replacement soft lenses (the referent), showed significant differences between brands for the risk of MK. CONCLUSIONS The risk of MK has not been reduced in users of DD and silicone hydrogel CLs. However, vision loss is less likely to occur in DD than in reusable soft CL users. Different brands of CL may be associated with significantly different risks of keratitis; understanding these differences should lead to the development of safer soft lenses. These findings suggest that lens/ocular surface interactions may be more important in the development of corneal infection than oxygen levels and CL case contamination.

Acanthamoeba keratitis: diagnosis and treatment update 2009.

PURPOSE To describe the current management of Acanthamoeba keratitis (AK). DESIGN A perspective based on the literature and author experience. RESULTS Early diagnosis and appropriate therapy are key to a good prognosis. A provisional diagnosis of AK can be made using the clinical features and confocal microscopy, although a definitive diagnosis requires culture, histology, or identification of Acanthamoeba deoxyribonucleic acid by polymerase chain reaction. Routine use of tissue diagnosis is recommended, particularly for patients unresponsive to treatment for AK. Topical biguanides are the only effective therapy for the resistant encysted form of the organism in vitro, if not always in vivo. None of the other drugs that have been used meet the requirements of consistent cysticidal activity and may have no therapeutic role. The use of topical steroids is controversial, but probably beneficial, for the management of severe corneal inflammatory complications that have not responded to topical biguanides alone. The scleritis associated with AK is rarely associated with extracorneal invasion and usually responds to systemic anti-inflammatory treatment combined with topical biguanides. Therapeutic keratoplasty retains a role for therapy of some severe complications of AK but not for initial treatment. With modern management, 90% of patients can expect to retain visual acuity of 6/12 or better and fewer than 2% become blind, although treatment may take 6 months or more. CONCLUSIONS Better understanding of the pathogenesis of the extracorneal complications, the availability of polymerase chain reaction for tissue diagnosis, and effective licensed topical anti-amoebics would substantially benefit patients with AK.

Effect of cataract surgery on the corneal endothelium: Modern phacoemulsification compared with extracapsular cataract surgery

PURPOSE To investigate whether modern phacoemulsification surgery results in more damage to the corneal endothelium than extracapsular cataract extraction (ECCE), and to examine which preoperative, operative, and postoperative factors influence the effect of cataract surgery on the endothelium. DESIGN Randomized controlled trial. PARTICIPANTS Five hundred patients 40 years or older were randomized into 2 groups (ECCE, 249; phacoemulsification, 251). METHODS Central corneal endothelial cell counts, coefficient of variation of cell size, and hexagonality were assessed before surgery and up to 1 year postoperatively. MAIN OUTCOME MEASURE Endothelial cell count. RESULTS Four hundred thirty-three patients completed the trial. The initial preoperative mean cell count for the entire sample was 2481 (standard error [SE]: 18.6), reduced at 1 year postoperatively to 2239 (SE: 23.5). An average 10% reduction in cell count was recorded by 1 year postoperatively. There was no such change in hexagonality or in the coefficient of variation. There was no significant difference in overall percentage cell loss between the 2 treatment groups. Factors associated with excessive cell loss (> or =15% by 1 year) were a hard cataract (odds ratio [OR]: 2.1, 95% confidence limits: 1.1-4.1; P = 0.036), age (OR: 1.04, P = 0.005), and capsule or vitreous loss at surgery (OR: 2.38, P = 0.106). Phacoemulsification carried a significantly higher risk (OR: 3.7, P = 0.045) of severe cell loss in the 45 patients with hard cataracts relative to ECCE (52.6% vs. 23.1%; chi-square test, P = 0.041), with both procedures achieving similar postoperative visual acuity outcomes. CONCLUSIONS No significant difference in overall corneal endothelial cell loss was found between these 2 operative techniques. The increased risk of severe cell loss with phacoemulsification in patients with hard cataracts suggests that phacoemulsification may not be the optimal procedure in these cases, and that ECCE should be preferred.

A review of 72 consecutive cases of Acanthamoeba keratitis, 1984–1992

A review of consecutive cases of Acanthamoeba keratitis presenting since 1984 was undertaken in order to assess prognostic factors, the success of culture procedures and the outcome of medical and surgical management, with reference to current clinical practice. Seventy-two consecutive cases (77 eyes) of Acanthamoeba keratitis have been managed. Sixty-four patients were contact lens wearers, 28 of these wearing disposable lenses. Superficial corneal involvement and perineural infiltrates were common in those diagnosed less than a month after first symptoms, designated ‘early’ presentation. Ring infiltrates and ulceration with stromal lysis characterised those presenting at 1-2 months (‘intermediate’) or after 2 months (‘late’); these groups also progressed more frequently to hypopyon, scleritis, glaucoma and cataract formation. Positive corneal cultures were obtained in 10 of 14 (71%) intermediate and 17 of 23 (74%) late cases; early cases underwent epithelial biopsy but formal trephine biopsy was not usually justified (1 of 35 cases) and only 19 of 35 (54%) were tissue-positive. Microbial co-isolates were obtained from 20 corneas. Thirty-four penetrating keratoplasties were performed in 23 eyes, 21 whilst inflamed and 13 when quiet. Of 13 failures in inflamed eyes, 9 were due to recurrence of Acanthamoeba infection. Medical cure is known to have been achieved in 64 of 73 (88%) eyes, 4 of the original 77 having been lost to follow-up abroad. Fifty-eight of 73 eyes (79%) achieved a final visual acuity of 6/12, and of the culture-positive cases, 32 of 46 (70%) achieved 6/12. Since 1984 an effective biguanide-propamidine treatment combination has been introduced, cases have been diagnosed increasingly early and consequently the time taken for medical cure has decreased. The prognosis of this potentially blinding keratitis has improved due to heightened clinical suspicion resulting in early diagnosis, a rigorous scheme of investigation and proven management strategies.

Acanthamoeba keratitis: multicentre survey in England 1992–6

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.

Corneal stem cells in review

The cornea provides the eye with protection and the refractive properties essential for visual acuity. The transparent epithelium is highly specialized with basal and stratified squamous cells that are renewed throughout life from a stem cell population. The stem cells are thought to reside at the corneal limbus and may be maintained by a variety of intrinsic and extrinsic factors such as the local environment, survival factors, and cytokines. A number of markers have been localized to the limbus in an attempt to identify stem cells; however, definite stem cell identification remains elusive. During homeostasis and following injury to the corneal epithelium, the limbal stem cells divide to produce daughter transient amplifying cells that proliferate, migrate, and differentiate to replace lost cells. However, this cannot occur if the stem cell population is depleted. Limbal stem cell deficiency then results in corneal re‐epithelialization by the neighboring conjunctiva, causing pain, poor vision, and even blindness. This review will focus on corneal epithelial stem cells in ocular surface repair and regeneration. The current knowledge of stem cell biology in the corneal epithelium, clinical consequences of stem cell deficiency, and therapeutic strategies aimed at reversing stem cell deficiency will be discussed.

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.

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 £359.89 for Phako and £367.57 for ECCE. CONCLUSION Phako is clinically superior to ECCE and is cost effective.

Clinical Features of Atopic Keratoconjunctivitis

The clinical spectrum of ocular disease in 37 patients with atopic keratoconjunctivitis (AKC) is described. Patients typically had a severe blepharoconjunctivitis. Associated corneal scarring, suppurative keratitis, or keratoconus were the major causes of visual loss. Serum and tear samples from these patients were analyzed to quantify total and specific IgE antibodies. The results were compared as a case control study with results from samples from 55 patients with other forms of atopic disease and 16 nonatopic volunteers. Although the mean values for total and specific IgEs in the serum of patients with atopic disease were markedly higher than the values from nonatopic controls (P less than 0.00002), a difference between the disease groups could not be demonstrated (P greater than 0.05). There were also differences between both the total IgE (P = 0.0002) and pollen-specific IgE (P = 0.015) in tears from patients with atopic disease and nonatopic controls, but not for house dust mite or cat dander-specific IgEs. These results suggest that clinical differences between groups of patients with chronic allergic external eye disease are not associated with specific patterns of IgE production.