Aravind Roy

Positive δ13C excursion in carbonate and organic fractions from the Paleoproterozoic Aravalli Supergroup, Northwestern India

Abstract Carbon and oxygen isotopic investigations have been carried out on the Archean and Paleoproterozoic carbonate rocks of the Udaipur region in the Aravalli Mountain Belt, northwestern India. The study has led to the interesting finding of 13 C enrichment in the carbonate rocks of the Jhamarkotra Formation (δ 13 C carb up to 11.1‰ V-PDB) belonging to the ∼2200–1900 Ma Paleoproterozoic Aravalli Supergroup. Further, it is observed that the organic carbon from phosphorite bearing stromatolitic dolomites of the same formation are also enriched in 13 C (δ 13 C org up to −11.1‰). However, it must be emphasized that the 13 C enriched carbonates and the organic fractions are from different stratigraphic levels although in the same formation, the former being at a lower stratigraphic level. A critical analysis of the field geological, petrological as well as the isotopic data indicates that the observed δ 13 C excursion in the carbonate carbon is not due to local causes such as methanogenesis or evaporitic conditions. The shallow water environment of deposition of these carbonates as well as the immediately overlying formations rules out the stratified ocean model for the observed excursion. The model involving high sedimentation rates and organic carbon burial has been preferred to explain the δ 13 C excursion in the carbonates of the Jhamarkotra Formation. The 13 C enrichment in organic fraction occurred in localized regions of the Aravalli sedimentary basin, where high productivity was supported by phosphorous supply indicating that the diffusion-limited pathways of organic carbon fixation were operative in the Paleoproterozoic itself. The 13 C enriched carbonate rocks of the Jhamarkotra Formation serve as the Indian example for the Paleoproterozoic global δ 13 C excursion.

Endophthalmitis after cataract surgery: epidemiology, risk factors, and evidence on protection.

Purpose of review After publication of the results of the European Society of Cataract and Refractive Surgery (ESCRS) study, there is a lot of enthusiasm for using intracameral antibiotics for the prevention of postcataract endophthalmitis. However, despite level 1 evidence, the practice has not been adopted universally. The aim of this review is to present a summary of the articles published in the last 18 months on this topic. Recent findings The published literature highlights that the incidence rate of endophthalmitis declined after 2007. Simultaneously, there is a rising trend for using intracameral injection of antibiotics at the conclusion of cataract surgery. Although various drugs have been used for this purpose, nearly all provide comparable protection. Industry has started manufacturing formulations for commercial availability of intracameral injection. Innovations are also ongoing to use intraocular lens for drug delivery and developing other intraocular drug delivery devices. Summary Endophthalmitis prevention is at an interesting crossroad. Although there is hesitation the intracameral injection of antibiotics is increasingly being adopted by physicians, which is likely to grow further with commercial availability of formulations. However, it will be important to be cautious and report all adverse reactions associated with this practice.

Update on fungal keratitis.

Purpose of review The aim of this review article is to present an overview of some of the seminal work published in the last 18 months (July 2014 to December 2015). Recent findings The published literature highlights the need for the identification of fungal isolates to species and subspecies level using molecular methods. Molecular methods helped us identify some of the unknown fungi such as Pythium – fungi that causes keratitis unresponsive to conventional antifungal therapy. Although not popular fungal in-vitro susceptibility tests are showing better correlation between resistance and clinical outcomes. Several groups are trying to understand host responses controlling disease production as well as inflammation. On therapy front researchers are working to develop drug formulations and delivery systems that will provide superior pharmacokinetics and bioavailability. Collagen cross-linking and injections of antifungal agents into the corneal stroma and anterior chamber continue to be attractive to clinicians and more and more researchers are publishing their experiences. Summary It is an interesting time in the history of mycotic keratitis with a lot of positive developments. Molecular methods will help improved diagnosis and clinico-therapeutic correlation. Drug delivery devices with superior pharmacokinetics are on horizon.

Clinicomicrobiological characteristics and treatment outcome of sclerocorneal tunnel infection.

Purpose: To analyze the clinical presentation, microbiological evaluation, and management of post–cataract surgery sclerocorneal tunnel infection. Methods: This is a retrospective chart review of 11 patients with sclerocorneal tunnel infection after cataract surgery, managed between November 2006 and October 2009. The clinical characteristics and treatment outcomes were analyzed. Results: All patients presented within 1 to 10 weeks of primary surgery. The presenting visual acuity ranged from hand motions to 20/50. Ten of 11 patients had sclerocorneal involvement, and 4 patients had associated endophthalmitis. The causative organisms were fungus (n = 6), bacteria (n = 4), or both (n = 1). Deroofing of the tunnel and sclerocorneal patch graft was done in 4 patients. Intensive medication was administered to all patients. The final visual acuity ranged from light perception to 20/50 at a mean follow-up of 119 days (median, 66 days; range, 2–357 days). Five patients had ≥20/100 vision. The mean interval between presentation to resolution of infiltrate and formation of peripheral scarring was 20 days (median, 11 days; range, 2–66 days). Conclusions: Sclerocorneal tunnel infection must be microbiologically evaluated. Intensive medical management, wound revision and repair may lead to a favorable outcome.

Collagen cross-linking for microbial keratitis

Collagen cross-linking is gaining popularity not only for arresting the progression of keratoconus but also other indications including management of corneal infections. In this review article, we analyzed the published literature to understand the level of evidence for its use in corneal ulcer. Photoactivated riboflavin and ultraviolet A light are known to possess antimicrobial properties. The treatment also induces formation of inter- and intra-fibrillar bonds, thereby making the corneal collagen resistant to the action of proteases arresting stromal melt. Both properties are well documented in in vitro experiments. The antimicrobial action is seen against bacteria, fungi, and parasites. The animal experiments have documented its efficacy against bacterial and fungal keratitis models. The literature on its application in human corneal infection is highly variable and comprises case reports, case series, and comparative nonrandomized and randomized trials. The treatment has been used as primary treatment, adjunctive treatment along with antibiotics, as the first line of treatment as well as for failed medical treatment cases. Even the cases included are of variable severity caused by a variety of microorganisms including culture-negative cases. Furthermore, the treatment protocols are also variable. While most reports show beneficial effects for bacterial corneal ulcer cases, especially those with superficial infiltrate, the effect has been mixed for fungal and parasitic keratitis. In view of these characteristics, we infer that the level of evidence for its use in corneal ulcer is at most weak. We need well-characterized, high-quality, clinical trials of sufficient power to assess its true value.

Mixed Nocardia cyriacigeorgica and Staphylococcus aureus Infection in the Periocular Skin and Orbit in an Immunocompetent Adult

A 32-year-old non-alcoholic, immunocompetent male with history of prior trauma presented with pain and protrusion of the left eye of 8 months’ duration. A firm nontender mass could be palpated in the superomedial orbit and the periocular skin had multiple discharging nodules. Computed tomography of the orbit showed an ill-defined lesion in the left orbit with preseptal soft tissue thickening, lacrimal gland infiltration and a moth eaten appearance of the left orbital roof. Tissue sampling from discharging cutaneous sinuses grew confluent colonies of Staphylococcus aureus and Nocardia cyriacigeorgica (16S rRNA gene sequencing; GQ376180). Histopathological examination showed mixed inflammatory infiltrates and eosinophilic granules showing Splendore-Hoeppli phenomenon. Despite an early response to treatment with intravenous amikacin, reactivation of left orbital inflammation led to eventual loss of vision. A prolonged treatment course with intravenous amikacin and oral trimethoprim-sulfamethoxazole over a period of 1 year showed clinical resolution with periocular scarring, hypoglobus, and sensory exotropia.

Penetrating sclerokeratoplasty in massive recurrent invasive squamous cell carcinoma.

A 35-year-old man presented with a recurrent temporal conjunctival mass (25 × 12 mm) involving about 6 clock hours of the limbus in the left eye. The mass encroached onto the temporal half of the cornea and showed surface keratin, intrinsic vasculature, and large feeder vessels. There was deep stromal infiltration. There were no cells in the anterior chamber. Ultrasound biomicroscopy confirmed infiltration of deep corneal stroma without intraocular extension. Surgery involved excision of the conjunctival component with a 4-mm margin, lamellar sclerectomy, and a penetrating sclerokeratoplasty with 3 mm of healthy corneal margin. Cryotherapy (double freeze-thaw) was done to the conjunctival margins. Histopathology showed it to be invasive squamous cell carcinoma. A thin layer of deep corneal stroma and all conjunctival margins were uninvolved. Twelve months after treatment, there was no recurrence, and the left eye recorded a visual acuity allowing finger counting at a 1-meter distance.

20G silicone rod as monocanalicular stent in repair of canalicular lacerations: Experience from a tertiary eye care centre

To evaluate the outcome of 20G silicone rod as monocanalicular stent in canalicular lacerations. Retrospective case series involving patients between July 2006 and June 2010. Fourteen canalicular repairs in 12 consecutive patients were done in the study period. Eleven were male and mean age was 30.5 years. A single canaliculus was involved in 10 patients and associated injury to the globe was noted in 3 patients. The median lag time between injury and repair was 3 (range 1-9) days. The mean duration of stenting was 6.9 (SD 3.2) weeks. Spontaneous extrusion of monocanalicular stent occurred in 3 patients. Patency on syringing was noted in 10 (70%) canaliculi over a median follow up of 7 (range 2-17) months. 20G silicone rod may be used as an effective and economical alternative in canalicular lacration repairs.

Update on Antimicrobial Resistance and Ocular Isolates

The phenomenon of “Antimicrobial Resistance (AMR)” is as old as the era of antibiotics. However, currently, it is posing a serious challenge in the management of various infectious diseases including ocular infections. Realizing the seriousness of the problem, the World Health Organization and other health agencies have adopted several programs to contain the menace. The surveillance of AMR is an essential part of the action plan and has contributed significant knowledge in this field. In the last decade, three nationwide surveillance studies from United States addressed AMR among ocular isolates. These studies indicate that AMR in ocular infections shows trends similar to systemic infections. Realizing the value of surveillance studies, there is a need to conduct similar studies in other parts of the world because AMR trends demonstrate regional variations. Further, there is enough evidence to suggest that prolonged and recurrent use of topical antibiotics in ophthalmology can result in colonization of the ocular surface by resistant organisms.

Post Operative Care in Manual Small Incision Cataract Surgery

Manual Small Incision Cataract Surgery (MSICS) is a variant of extracapsular cataract surgery (ECCE), the important differences being construction of a self-sealing scleral tunnel wound, capsulorhexis, in-toto prolapse of nucleus through capsulorhexis into anterior chamber, and delivering it out of the eye in a closed chamber state. The surgical steps require considerable manual dexterity. Like any other surgical procedure, MSICS is also associated with complications and some of these are unique to this surgical procedure. A good understanding of these complications and management will go a long way in ensuring vision restoration in these patients. In this chapter we will be discussing medical therapy including pre-, peri-, and postoperative care of patients undergoing MSICS as well as complications and their management.