Applications of the polymerase chain reaction in clinical ophthalmology

The cereus matter of Bacillus endophthalmitis

Bacillus cereus (B. cereus) endophthalmitis is a devastating intraocular infection primarily associated with post-traumatic injuries. The majority of these infections result in substantial vision loss, if not loss of the eye itself, within 12-48 h. Multifactorial mechanisms that lead to the innate intraocular inflammatory response during this disease include the combination of robust bacterial replication, migration of the organism throughout the eye, and toxin production by the organism. Therefore, the window of therapeutic intervention in B. cereus endophthalmitis is quite narrow compared to that of other pathogens which cause this disease. Understanding the interaction of bacterial and host factors is critical in understanding the disease and formulating more rational therapeutics for salvaging vision. In this review, we will discuss clinical and research findings related to B. cereus endophthalmitis in terms of the organism's virulence and inflammogenic potential, and strategies for improving of current therapeutic regimens for this blinding disease.

Laboratory investigations in uveitis: current practice and future directions

Diagnosis and management of uveitis always remains a challenge to the treating ophthalmologists. Rapid diagnosis and timely initiation of appropriate, effective treatment in uveitis are the critical determinants that lead to good visual outcome and reduce the risk of ocular morbidity. In the last decade, significant progress has been made in molecular diagnostic modalities and in development of newer diagnostic tools, which included serological tests and imaging techniques. However, a tailored approach to laboratory investigations based on meticulous history and comprehensive ocular evaluation has been propounded as the gold standard for successful management of an uveitic entity. In this article, we review the laboratory diagnostic tests in uveitis as well as recent technological advances in laboratory science, which may be the future direction for diagnosis of uveitis.

Polymerase Chain Reaction and Goldmann-Witmer Coefficient Testing in the Diagnosis of Infectious Uveitis in HIV-Positive and HIV-Negative Patients in South Africa

PURPOSE

To use polymerase chain reaction (PCR) and Goldmann-Witmer coefficient (GWC) calculation to diagnose infectious uveitis.

METHODS

Prospective cross-sectional study.

RESULTS

Twenty-seven of 106 patients had positive PCR and/or GWC results on aqueous humor (AH) sampling and 15 of 27 (55.6%) were HIV-positive. Patients with non-anterior uveitis (NAU) were more likely to be HIV+ (p = 0.005). More than 1 possible pathogen was identified in 9 of 27 patients of whom 7 were HIV+. The final clinical diagnosis was discordant with AH findings in 9 of 27 cases. A positive EBV PCR result was associated with a discordant diagnosis (p = 0.001). All cases of herpetic anterior uveitis (42.9% HIV+) tested PCR-/GWC+ while all cases of herpetic NAU tested PCR+/GWC- (83.3% HIV+). All rubella virus cases were PCR+/GWC+.

CONCLUSION

PCR is useful to diagnose herpetic NAU in HIV+ patients while GWC is useful to diagnose herpetic anterior uveitis.

Comparison of methods for identifying causative bacterial microorganisms in presumed acute endophthalmitis: conventional culture, blood culture, and PCR

Background

Identification of bacterial pathogens in endophthalmitis is important to inform antibiotic selection and treatment decisions. Hemoculture bottles and polymerase chain reaction (PCR) analysis have been proposed to offer good detection sensitivity. This study compared the sensitivity and accuracy of a blood culture system, a PCR approach, and conventional culture methods for identification of causative bacteria in cases of acute endophthalmitis.

Methods

Twenty-nine patients with a diagnosis of presumed acute bacterial endophthalmitis who underwent vitreous specimen collection at King Chulalongkorn Memorial Hospital were enrolled in this study. Forty-one specimens were collected. Each specimen was divided into three parts, and each part was analyzed using one of three microbial identification techniques: conventional plate culture, blood culture, and polymerase chain reaction and sequencing. The results of the three methods were then compared.

Results

Bacteria were identified in 15 of the 41 specimens (36.5%). Five (12.2%) specimens were positive by conventional culture methods, 11 (26.8%) were positive by hemoculture, and 11 (26.8%) were positive by PCR. Cohen’s kappa analysis revealed p-values for conventional methods vs. hemoculture, conventional methods vs. PCR, and hemoculture vs. PCR of 0.057, 0.33, and 0.009, respectively. Higher detection rates of Enterococcus faecalis were observed for hemoculture and PCR than for conventional methods.

Conclusions

Blood culture bottles and PCR detection may facilitate bacterial identification in cases of presumed acute endophthalmitis. These techniques should be used in addition to conventional plate culture methods because they provide a greater degree of sensitivity than conventional plate culture alone for the detection of specific microorganisms such as E. faecalis.

Trial registration

Thai Clinical Trial Register No. TCTR20110000024.

Progressive outer retinal necrosis in an immunocompromised patient presenting with bilateral retrobulbar optic neuritis

Background: Progressive outer retinal necrosis (PORN) is a necrotizing chorioretinopathy caused by herpes simplex virus, varicella-zoster virus, or cytomegalovirus.

Objective: To describe the clinical morphology of PORN presenting with asymmetrical isolated bilateral retrobulbar optic neuropathy.

Method: The medical records of a 45-year-old human immunodeficiency virus infected patient presenting with bilateral visual loss at King Chulalongkorn Memorial Hospital were reviewed with respect for the privacy of patient.

Result: Gradual visual loss progressed to no light perception in the right eye and 20/200 in the left eye within 1 month. The patient was initially diagnosed with retrobulbar optic neuritis in both eyes. The investigations included MRI, vitreous tapping, lumbar puncture, and serological testing. MRI elicited enhancement around both optic nerves, which suggested optic neuritis. Thereafter, multifocal areas of retinal necrosis developed with rapid progression and additional cutaneous zoster lesions were established. These findings led to a diagnosis of PORN. The patient was promptly treated with intravenous ganciclovir, anti-retroviral therapy, and vitrectomy with endophotocoagulation and silicone injection. Unfortunately, his visual prognosis in the left eye was still poor

Conclusion: PORN was uncommonly present with bilateral isolated optic neuropathy before retinal lesions developed. Retrobulbar optic neuropathy from herpetic infection in immunocompromised patients should be considered despite a normal fundus at initial presentation. Early diagnosis and prompt intervention may preserve vision. This case demonstrates the importance of careful physical examination and follow up of retinal lesions.

Laboratory support in the diagnosis of uveitis

Intraocular inflammations are still a diagnostic challenge for ophthalmologists. It is often difficult to make a precise etiological diagnosis in certain situations. Recently, there have been several advances in the investigations of uveitis, which has helped the ophthalmologists a lot in the management of such clinical conditions. A tailored approach to laboratory diagnosis of uveitic cases should be directed by the history, patient's symptoms and signs, and clinical examination. This review summarizes various modalities of laboratory investigations and their role in the diagnosis of uveitis.

Vitreous analysis in the management of uveitis

A correct diagnosis of uveitis is often challenging, given the wide range of possible underlying conditions and the lack of typical phenotypes. Management decisions may be difficult in view of the risk of visual loss with either inappropriate or delayed therapy. Analysis of the vitreous may therefore be used to provide the clinician with valuable information. In this paper, we describe the main clinical situations in which vitreous sampling is indicated and provide some guidance to clinicians for tailoring their requests. These situations include suspected intraocular infection and suspected intraocular malignancy. We describe the principal tests carried out on vitreous samples, including cultures, polymerase chain reaction-based testing, and cytokine analysis. Limitations of the tests used are likely to become less as more advanced testing methods are introduced. The importance of selecting the appropriate investigations to support a clinical suspicion is emphasised, as is the interpretation of test results within a clinical context.