Rajbir Singh

On allocation of spares at component level versus system level

Design engineers are well aware that a system where active spare allocation is made at the component level has a lifetime stochastically larger than the corresponding system where active spare allocation is made at the system level. In view of the importance of hazard rate ordering in reliability and survival analysis, Boland and El-Neweihi (1995) recently investigated this principle in hazard rate ordering and demonstrated that it does not hold in general. They showed that for a 2-out-of-n system with independent and identical components and spares, active spare allocation at the component level is superior to active spare allocation at the system level. They conjectured that such a principle holds in general for a k-out-of-n system when components and spares are independent and identical. We prove that for a k-out-of-n system where components and spares have independent and identical life distributions active spare allocation at the component level is superior to active spare allocation at the system level in likelihood ratio ordering. This is stronger than hazard rate ordering, thus establishing the conjecture of Boland and El-Neweihi (1995). ACTIVE SPARE ALLOCATION; HAZARD RATE ORDERING; ORDER STATISTICS; LIKELIHOOD RATIO ORDERING AMS 1991 SUBJECT CLASSIFICATION: PRIMARY 62N05 SECONDARY 90B25

Deranged Metabolic Profile and Identification of Biomarkers in the Vitreous Humour of Patients with Proliferative Diabetic Retinopathy

BACKGROUNDnSystemic biochemical disarray has been implicated in the pathogenesis and progression of diabetes and its complications. However, the modifications in the metabolic state of the retina and its microenvironment in response to the systemic metabolic malfunction has not been documented.nnnOBJECTIVEnThe objective of the present study was to document the various biomarkers that may be involved in the pathogenesis and progression of Proliferative Diabetic Retinopathy (PDR).nnnMETHODnThe vitreous humour and plasma samples from 38 PDR, 7 Proliferative Vitreo Retinopathy (PVR) and 17 control patients undergoing pars plana vitrectomy were analysed for sixteen different biomarkers. Whole genome Single Nucleotide Polymorphism (SNP) microarray was performed on ten PDR patients peripheral blood samples.nnnRESULTSnThe vitreous humour glucose, creatinine, micro protein, phosphorus and lactate dehydrogenase were found significantly increased in the PDR patients compared to controls. The plasma urea, creatinine and micro protein were also significantly increased. The plasma phosphorus of PDR patients on oral hypoglycemic therapy was found significantly decreased compared with PDR patients on insulin therapy and controls. SNPs previously associated with glucose (5), lactate dehydrogenase (2) and creatinine (2) levels were identified to be polymorphic homozygous (minor allele) in ≥ 60% patients in this study, suggesting enhanced susceptibility.nnnCONCLUSIONnThe metabolic overactivity of the retinal microenvironment appears to play a vital role in the pathogenesis of PDR. The significantly elevated biomarkers may have diagnostic, prognostic and therapeutic significance. These findings shed light on the biochemical disarray in the vitreous humour of PDR patients that could have significant management implications.

Adult onset coats disease in a 56-year-old male: An atypical presentation

Coats disease is a congenital retinal vascular disease, which is seen commonly in childhood and remits and exacerbates throughout life. However, it is not rare for coats disease to present in adulthood for the first time. This has been referred to as adult onset coats disease. We do hereby present a rare case of adult onset coats disease in a 56-year-old male patient who presented with visual acuity of 20/200 in the left eye. Fundus findings typical of coats disease included telangiectasis, macular exudation and edema. Fluorescein angiography revealed peripheral capillary nonperfusion areas and telangiectasis. Optical coherence tomography showed cystoid macular edema. After the treatment with intravitreal injection of bevacizumab (1.25 mg in 0.05 ml) and sectoral panretinal photocoagulation to the area of capillary nonperfusion the macular edema was reduced by 100 microns, which translated to a visual acuity of 20/80, proving the point that the prognosis in these cases is not as grave as in classical coats disease.

Submacular Parasite Masquerading as Posterior Pole Granuloma

Parasites enter the eye through hematogenous spread. The interaction with host immune system may result in its destruction but not without collateral damage to the vital retinal structures. Currently, the accepted treatment for ocular parasitosis is surgical removal or direct laser photocoagulation. A 24-year-old Indian woman presented with abrupt painless loss of vision to 5/300. A large yellow-white lesion centered at macula was observed with associated retinal and subretinal hemorrhage and neurosensory retinal detachment. A parasite was seen protruding at the center of the lesion. Fluorescein angiography demonstrated disc leakage and vessel wall staining. Ultrasonography demonstrated a highly reflective subretinal lesion with aftershadowing. Serological test was positive for anti-cysticercus (IgM) antibody. Treatment with prednisolone and albendazole resulted in resolution of the lesion within 2 months with improvement of visual acuity to 20/400. A noncystic form of subretinal cysticercosis is likely with suggestive B-scan ultrasonography and serological investigations.

Endocapsular hematoma: a rare form of ocular hemorrhage after thrombolysis with streptokinase

Context: Endocapsular hematoma has previously been described as a cataract surgery complication more commonly observed in eyes receiving a combined cataract and glaucoma surgery. However, it can also be a rare form of ocular bleed following thrombolysis with streptokinase. Case Report: A 65-year-old diabetic male presented to us with complain of sudden painless diminution of vision in his left eye, which he developed while he was being thrombolysed with streptokinase administered intravenously for an episode of acute myocardial infarct. On examination, left eye was pseudophakic with collection of blood in the capsular bag (Endocapsular hematoma). Conclusion: Endocapsular hematoma can be a rare form of ocular bleeding complicated by thrombolysis. Reporting this case becomes more relevant in the present era with increasing number of patients suffering from ischemic heart disease and likely to undergo thrombolysis.

Testing uniform stochastic ordering for survival functions

Let and be the survival functions of lifetimes of two units under study. F is said to be uniformly stochastically smaller than G, denoted by F <+G, if (x)/& (x) is a nondecreasing function, In this paper, we construct some tests for testing the null hypothesis H0:F=G against Ha : F <+ G and F ≠ G,where G is a known cdf, A test based on the estimator of Rojo and Samaniego ( 1993 ) turns out to be the Kolmogorov-Smirnov test Dn +, indicating suitability of Dn +, for testing H0 against Ha, Power comparisons of these tests and that of Kochar(i984) have been made for some specific H0 and Ha, The above testing procedures have been applied to a data set of observed lifetimes of Kevlar H epoxy pressure vessels.