Spread of Epidemics and Rumours with Mobile Agents

We propose a simple model of infection that enables to study the coincidence time of two random walkers on an arbitrary graph. By studying the coincidence time of a susceptible and an infected individual both moving in the graph we obtain estimates of the infection probability. The main result of this paper is to pinpoint the impact of the network topology on the infection probability.

Exponential Random Graphs as Models of Overlay Networks

In this paper we give an analytic solution for graphs withnnodes andE=cnlognedges for which the probability of obtaining a given graphGisµn(G) = exp (-β∑i=1ndi2), wherediis the degree of nodei. We describe how this model appears in the context of load balancing in communication networks, namely peer-to-peer overlays. We then analyse the degree distribution of such graphs and show that the degrees are concentrated around their mean value. Finally, we derive asymptotic results for the number of edges crossing a graph cut and use these results (i) to compute the graph expansion and conductance, and (ii) to analyse the graph resilience to random failures.

[Post-traumatic inflammation with an intraocular foreign body]

BACKGROUND

To report on the diagnosis and management of a"firecracker" injury presenting with a post-traumatic intraocular inflammation.

CASE REPORT

A 10-year-old boy sustained a penetrating 16-mm cornea-sclera blast injury to his left eye with uveal prolapse and hemophthalmus and doubtful light perception. The cranial computed tomography revealed a metallic intraocular foreign body (IOFB), retinal detachment, and subretinal and subchoroidal hemorrhage. After primary wound closure and antibiotic treatment for 1 week, increasing cell infiltration and amaurosis developed, and a lensectomy, pars plana vitrectomy, and extraction of the 17x7x7-mm encapsulated IOFB via a scleral tunnel was indicated.

RESULTS

A vitreous specimen did not reveal microbial growth; however, plenty of polymorphonuclear cells, macrophages, and lymphocytes were observed. Spectroscopy of the IOFB showed copper, zinc, silicon, lead, and other metals. A diagnosis of noninfectious inflammation due to heavy metals, primarily copper (=chalcosis), was made. The postoperative course was unremarkable, the intraocular lens in place, fundus CDR 0.2, retina and macula attached, intraocular pressure 9 mmHg. Three weeks after surgery, the flash VEP showed absent potentials.

CONCLUSIONS

Large projectiles or parts should be removed from the eye immediately in order to prevent complications from toxic metallosis and early fibrotic reactions.

An effective integrated learning programme in the first year of the medical course

BACKGROUND

An integrated approach to teaching medical subjects is an effective educational strategy. Yet, this has not become popular in medical colleges in India. We describe an integrated learning programme to teach the gastrointestinal system in the first year of the medical course.

METHODS

The integrated learning programme was conducted for 3 years (2003-2005). It incorporated elements of problem-based learning, early clinical exposure, lectures and small group laboratory work. Student assessment was formative (for problem-based learning sessions) and summative (using problem-based learning and knowledge tests). Evaluation of the programme was based on feedback from the students and faculty members.

RESULTS

Ninety-six per cent of the students obtained more than 60% marks in the problem-based learning test. The mean (SD) score in the knowledge test was 62 (0.89)%. The majority of students received satisfactory and more than satisfactory grades for their performance in the problem-based learning sessions. The feedback from faculty members and students was positive, which highlighted benefits such as integrated learning of the basic sciences, their application to clinical cases and active student learning. The challenges encountered included the higher input required from faculty members. Most of the faculty members and students recommended that the integrated programme should be continued and extended to other parts of the curriculum.

CONCLUSION

An integrated learning programme is feasible within a conventional medical curriculum of an Indian medical college.

Sickle cell-haemoglobin E (HbSE) compound heterozygosity: a clinical and haematological study

The paucity of clinical reports in the world literature suggests that, as a disease entity, haemoglobin SE compound heterozygosity is of negligible importance. In view of the significant community prevalence of this haemoglobinopathy in the Sultanate of Oman where it is the second most prevalent sickling disorder, a hospital study of 12 SE compound heterozygotes from six unrelated Arab families was undertaken to determine their clinico-haematological features. Our findings were compared with those reviewed in the literature. Clinical and haematological evaluation was carried out by conventional methods including chromatographic haemoglobin analysis. At least 50% of those studied were asymptomatic throughout the study period but sickling-related complications occurred in the rest and included the acute chest syndrome (1/12), severe vaso-occlusive skeletal pain (2/12), frontal bossing (1/12) possibly indicative of significant chronic haemolysis and recurrent infections of the urinary tract (1/12). Steady-state haemoglobin levels fell within the reference range while MCV and MCH values were, as expected, reduced in most cases; nevertheless, concomitant inheritance of alpha-thalassaemia trait was also likely. Red cell morphology was striking by the absence or rarity of pseudo-sickled cells in the blood films of many patients during the steady state and in crises. Bearing in mind the prevalence of 0.05% of SE compound heterozygosity in Oman, the findings in this single study of the largest number of SE patients and their relatives confirm the predominantly asymptomatic nature of this sickling disorder in individuals in the community at large. HbF levels do not appear to explain the heterogeneous nature of this haemoglobinopathy. Correlation of the variable clinical and haematological features of SE cases with their alpha-globin gene status and beta-cluster haplotypes (linked to the beta(s)- and beta(e)-genes) merits a separate investigation, which is being currently organized.

Multiple simultaneous perineural infusions for postoperative analgesia in adolescents in an outpatient setting

We report a case series of five adolescents who were managed with dual simultaneous perineural infusions after orthopaedic surgery on an outpatient basis. Adolescents undergoing orthopaedic procedures involving more than one extremity or nerve distribution can be managed after operation with multiple catheters. Use of low concentrations of local anaesthetic infusions along with good patient and family education and close follow-up by a dedicated paediatric pain management team can make this feasible in an outpatient setting.

[Conceiving and implementing an ISO 9001:2000 quality management system: quality improvement and efficiency increase over 3 years at the Dept. of Ophthalmology, Sultan Qaboos University in Oman]

BACKGROUND

Oman is a developing country of the Middle East with a University Hospital in a national health system. Problems related to documentation, structure, and procedure prevailing in a multicultural environment result in a lack of productivity. The aim of this study was to test the feasibility of introducing a quality management system according to ISO 9001:2000 into a university department of ophthalmology with special reference to quality and efficiency data over 3 years.

MATERIALS AND METHODS

Standardized types of documentation (35 documents, 183 forms and formats, and 453 registers) under a formal roof (booklets for work instructions, quality management, procedures) were conceived in 2001 and implemented, and were evaluated by descriptive statistics over the years 2002-2005 with respect to quality and efficiency. In 2005, the departmental QMS was merged into the QMS of the whole hospital.

RESULTS

Establishment of "responsibility clusters" with structured surveillance tasks, procedural improvements, and continuous audits resulted in a significant quality improvement already during the implementation until ISO 9001:2000 certification in 2002, and over the following 3 years. The data were assessed by non-conformities documented monthly (total inpatients: -50%, outpatients: -20%, operating theater: -100%, teaching: -10%; p <0.05) and increased efficiency assessed by the most important performance indicators (before QMS vs a median of 3 years with QMS): major surgery: +459%, inpatient stay: -49.7%, occupancy rate: +63.9%, technical diagnostics: +292.9%, postgraduate teaching total: +740%, research output total: +330% (p <0.05).

CONCLUSIONS

It is feasible to introduce the quality management system according to ISO 9001:2000 into a developing country in the Middle East. It has an immediate effect on the increase of efficiency (measured by performance indicators) and quality in all systems providing the possibility for regional benchmarking.

Multiple locations on chromosome 3 are the targets of specific deletions in uveal melanoma

PURPOSE

Loss of chromosome 3 is a frequent event in uveal melanomas, which is associated with hepatic metastases and a poor prognosis. The entire copy of chromosome 3 is usually lost (monosomy 3); however, a small subset of tumours demonstrate partial deletions of chromosome 3. Analysis of these tumours may allow the identification of tumour suppressor genes (TSGs) that are the molecular target of monosomy 3. Therefore, the purpose of this investigation was to determine the location of these partial deletions of chromosome 3 in uveal melanomas.

METHODS

Microsatellite analysis and restriction fragment-length polymorphism analysis were performed on 52 primary uveal melanomas using 19 markers located on both arms of chromosome 3. Cytogenetic analysis and fluorescence in situ hybridisation were performed, where possible, to confirm molecular findings.

RESULTS

Of 52 tumours studied, five tumours (10%) demonstrated LOH at one or more informative markers, but retention of heterozygosity was observed at other loci on chromosome 3, consistent with the presence of structural abnormalities to chromosome 3. Consistent with previous findings, the pattern of LOH in these tumours indicates the presence of deletions around 3p25-26 and on 3q, and that a new target region at 3p11-14 is preferentially deleted.

CONCLUSIONS

These results indicate the presence of several tumour suppressor loci on chromosome 3 and support the notion that the high rate of monosomy 3 in uveal melanoma is driven by disruption of several TSGs located on both arms of chromosome 3.

Escobar variant with pursed mouth, creased tongue, ophthalmologic features, and scoliosis in 6 children from Oman

We report on six Omani children from two consanguineous families, with a multiple congenital anomaly syndrome defined by arthrogryposis multiplex congenita, typical facial appearance, ophthalmologic anomalies, atrophic calf muscles, and interdigital, neck and axillar pterygia. In addition, the patients present unique features as a furrowed tongue and enlarged corneal nerves, undescribed previously in association with other distal arhtrogryposis syndromes (DA). The patients can be classified as multiple pterygium syndrome (Escobar syndrome) but display overlapping features with Freeman-Sheldon syndrome and arthrogryposis with ophthalmologic abnormalities. We excluded two known arthrogryposis loci on chromosome 9p13 (TPM2) and 11p15 (TNNI2, TNNT3). We conclude that our patients display a subtype of multiple pterygium syndrome with overlapping features to other DAs.

En bloc excision of intraocular epithelial cystic downgrowth using syngeneic auricular cartilage

AIM

To describe the surgical management of epithelial cystic downgrowth by en bloc excision and use of syngeneic auricular cartilage in two children.

STUDY DESIGN

Retrospective interventional case series.

METHOD

The charts of two patients treated for epithelial cystic downgrowth with en bloc excision and auricular cartilage transplant were reviewed. Details of ocular history, preoperative and postoperative visual acuity, intraocular pressure, ocular examination findings, surgical procedure and subsequent management were noted.

RESULTS

Two children aged 4 and 6 years, with epithelial cysts who underwent en bloc excision were identified. The cysts had developed following penetrating eye injury. Surgery involved en bloc resection of the cyst and associated tissue, and replacement of the excised corneoscleral tissue with syngeneic auricular cartilage. One patient additionally required synechiolysis, discission of a secondary cataract and anterior vitrectomy. In both cases, the epithelial tissue was successfully removed and the auricular cartilage transplant was well-apposed. Visual acuity remained at the preoperative level in the first patient due to amblyopia; in the second patient visual acuity improved to 6/7.5 with mild astigmatic correction.

CONCLUSION

En bloc excision provides the most definitive surgical treatment of cystic epithelial downgrowth. Auricular cartilage may be used for sclerokeratoplasty when donor cornea or sclera is unavailable.

Retinopathy of prematurity in VLBW and extreme LBW babies

OBJECTIVE

This is a hospital-based, prospective clinical study to determine the incidence, risk factors, and outcome of extreme low birth weight and very low birth weight pre-term babies with retinopathy of prematurity (ROP) at the Sultan Qaboos University Hospital, Oman.

METHODS

All babies with a birth weight =/< 1500 g and gestational age =/< 32 weeks admitted in the Neonatal Unit, were screened for ROP between 4 to 6 weeks of age and staged according to the international classification and were followed up until complete vascularization of the retina. Fifty nine babies formed the study group.

RESULTS

The overall incidence of ROP was 25.4% (15 out of 59), of which 6 babies had severe ROP and underwent cryotherapy/laser. All babies with ROP had a birth weight < 1250 g and were born before 31 weeks of gestation.

CONCLUSION

ROP is a multifactorial disease, the immature retina of the pre-term baby being the primary factor. Incidence and severity was inversely proportional to birth weight and gestational age. Multiple logistic regression analysis showed that sepsis and total parenteral nutrition to be highly significant risk factors. Repeated blood transfusions, hypotension and congenital heart disease with left to right shunt were seen to be considerably associated with the development of ROP. A decrease in overall incidence and severity of ROP was observed in this study.

46,XY,der(3)t(1;3)(q23;p22): double aneuploidy at a new breakpoint

A 12-month-old Omani boy is described with double aneuploidy involving chromosomes 1 and 3. In this case the aberration involved segment (q23;p22) which has not been reported previously.

Low frequency of bacteraemia during eye surgery obviates the need for endocarditis prophylaxis

PURPOSE

To determine the incidence of bacteraemia following eye surgery, and thereby evaluate the need for antibiotic cover during such procedures, in patients who are at risk for bacterial endocarditis.

METHODS

This prospective study involved 50 consecutive patients undergoing extraocular surgery at the Sultan Qaboos University Hospital, Muscat, Oman. Local preparation of the surgical site in all patients included pre-operative instillation of 0.3% gentamicin and 3% povidone-iodine eye drops. Two eye swabs (one from the conjunctival sac and another from the eyelid margin) and two venous blood samples (one taken just before the procedure and the second 10 min into it) were collected and cultured for aerobic and anaerobic bacteria. Surgery-related bacteraemia was defined as a negative pre-operative blood culture followed by a positive intraoperative blood culture of the same bacterium identified in the positive eye swab.

RESULTS

Only two patients (4%) demonstrated surgery-related bacteraemia: one caused by Staphylococcus epidermidis (following entropion correction) and the other by Haemophilus influenzae (following dacryocystorhinostomy). Four other patients had positive conjunctival swabs without bacteraemia, the causative organisms being Haemophilus influenzae in two, and Staphyloccus aureus and Klebsiella pneumoniae in one each.

CONCLUSION

Ophthalmic surgery is not associated with significant bacteraemia, and therefore does not mandate routine antibiotic cover in patients at risk for bacterial endocarditis. Stringent pre-operative preparation of the surgical site may suffice to minimise bacteraemia; however, this requires further study.

Vigabatrin associated retinal dysfunction in children with epilepsy

BACKGROUND

Recent reports have established that eye changes occur in patients treated with vigabatrin.

AIM

To identify the eye changes associated with vigabatrin, based on a prospective study of children treated for seizures.

METHODS

Twenty nine children on vigabatrin (mainly as add on therapy) were followed up for 6.5 years. Ophthalmic examination was performed before starting treatment and then six monthly in the outpatient clinic.

RESULTS

Twenty one children fulfilled the inclusion criteria. Most had epileptic syndromes with infantile spasms-namely West syndrome, Lennox-Gastaut syndrome, and partial seizures. Vigabatrin dose was 25-114 mg/kg/day (mean 55.8); duration of therapy was 6-85 months (mean 35.7). Four children (19%) developed eye changes (retinal pigmentation, hypopigmented retinal spots, vascular sheathing, and optic atrophy). Visual evoked potentials were abnormal in 16 children. Electroretinography and electro-oculography, which could have picked up eye changes in early stages, were not performed, as this facility was not available.

CONCLUSIONS

Vigabatrin causes eye damage. Most children with epileptic syndromes on vigabatrin cannot complain of their eye problems, hence 3-6 monthly ophthalmic follow up is strongly advised, along with regular electroretinography, electro-oculography, and visual evoked potentials if possible.

Orbital involvement in sickle cell disease: a report of five cases and review literature

PURPOSE

To present five cases of orbital infarction in sickle cell disease and review relevant literature.

METHOD

We reviewed the hospital records of 5 patients with sickle cell disease who developed a periorbital swelling during a vaso-occlusive crisis and were managed at our hospital between April 1992 and June 2000.

RESULTS

The 5 patients (4 with homozygous sickle cell disease and 1 with sickle cell-beta-thalassaemia disease) were aged 6-15 years with a history of multiple admissions for vaso-occlusive crises. The periorbital swelling spread to the orbit in 4 cases and resulted in proptosis (2 cases), restriction of ocular motility and visual impairment. In all 4 cases, computed tomography and/or magnetic resonance imaging of the orbits showed a mass adjacent to the orbital wall. In 2 cases the mass was identified as a haematoma. Orbital wall infarction was demonstrated in 3 cases by bone/bone marrow scintigraphy. Epidural haematomas were detected by computed tomography in one case. All patients received intravenous fluids, analgesics, broad spectrum antibiotics and steroids, as well as simple or exchange transfusion, and responded well to medical management.

CONCLUSIONS

Infarction of orbital bones during vaso-occlusive crises in sickle cell disease presents acutely with a rapidly progressive periorbital swelling. Haematomas frequently complicate the condition and, along with the inflammatory swelling, may lead to orbital compression syndrome. The condition is therefore sight-threatening, and necessitates prompt diagnosis and appropriate management for resolution without adverse sequelae. Imaging techniques are invaluable in the evaluation of patients. The majority of cases resolve with conservative treatment that includes steps to combat the vaso-occlusive crisis and use of systemic steroids under antibiotic cover.

Scleral suspension pars-plana lensectomy for ectopia lentis followed by suture fixation of intraocular lens

PURPOSE

To describe a simple technique of scleral suspension-pars plana lensectomy (SS-PPL) in acquired and congenital ectopia lentis and scleral fixation of intraocular lens (IOL).

MATERIALS AND METHODS

Twenty eyes of 16 patients (12 unilateral and 4 bilateral cases of "essential familial lens subluxation") aged 10-40 years (mean 25 years) underwent SS-PPL with implantation of scleral fixated IOL. Indications for surgery were best-corrected visual acuity < 6/18, bisection of pupil by the lens, and lens-induced glaucoma. Prerequisites for SS-PPL were, visibility of part of the lens in the pupillary area and soft lens.

RESULTS

Postoperative visual acuity ranged from 6/6 - 6/36. Lens tilt in 3 cases(15%) and small decentration in 2 cases(10%) were seen; however these did not seriously compromise the visual result. Scant vitreous bleeding on the first postoperative day was seen in 3 cases (15%).

CONCLUSION

The advantages of the scleral suspension of subluxated lens prior to lensectomy include stabilization; it allows proper viewing of the lens, avoids injury to the iris and ciliary body during lensectomy and reduces the possibility of dislocation of the lens.

Hydrodissection of conjunctival flap during trabeculectomy in eyes with conjunctival scarring caused by trachoma

BACKGROUND AND OBJECTIVE

Conjunctival scarring caused by trachoma represents a substantial challenge even to the most experienced cataract/glaucoma surgeon. We describe a simple technique of hydrodissection of conjunctival flap during combined trabeculectomy and phacoemulsification in eyes with conjunctival scarring caused by trachoma, and discuss its impact on surgical outcome.

PATIENTS AND METHODS

A prospective study was conducted in 10 Omani patients, aged 48 to 83 who underwent combined trabeculectomy and phacoemulsification with intraocular lens (IOL) implantation. The conjunctival flap was prepared after hydrodissection using a mixture of 1 mL of balanced salt solution (BSS) and 1 mL of lignocaine 2% with 1:200,000 adrenaline. Outcome measures that were evaluated were visual function, intraocular pressure (IOP) and bleb characteristics. Patients were followed-up postoperatively for a minimum period of 6 months.

RESULTS

The mean age of patients was 60.4 years (48-83) and a functioning bleb after 6 months was seen in 8 (80%) cases. IOP < 20 mm of Hg (applanation tonometry) without antiglaucoma medications was found in 8 cases; 1 case required one antiglaucoma medication and 1 case required more than one antiglaucoma medication for control of IOP. The latter was reoperated for control of IOP. Nonprogression of visual field was found in 8 (80%) cases.

CONCLUSION

Preparation of conjunctival flap by hydrodissection was found to be a simple modification of the conventional technique during combined trabeculectomy and phacoemulsification in trachomatous eyes. It reduced conjunctival dissection, use of cautery and possibility of button-holing of the conjunctiva during dissection in scarred eyes. The minimal tissue dissection involved in this procedure reduced wound healing and thereby increased chances of a functioning bleb, control of IOP and nonprogression of visual field compared to combined surgery employing a conventional method (nonhydrodissection method) of conjunctival flap dissection.