Variations in the cone packing density with eccentricity in emmetropes.

AIM: To describe the parafoveal cone arrangement in emmetropic subjects and its variations with eccentricity, meridians and change in axial length in Indian eyes. METHODS: We imaged 25 subjects using compact adaptive optics (AO) retinal camera prototype, the rtx1. Imaging was done at 1, 2, and 3° eccentricity from the fovea in four meridians: nasal, temporal, superior, and inferior. RESULTS: A statistically significant drop in the cone packing density was observed from 2 to 3° (2° eccentricity=25 350/mm(2) (5300/mm(2), 8400-34 800/mm(2)) 3° eccentricity=20 750/mm(2) (6000 mm(2), 9000-33 670/mm(2))) P<0.05. The spacing correspondingly increased with increase in distance from the fovea (2° eccentricity=6.9 µm (0.70 µm, 5.95-11.6 µm)) and 3°eccentricity=7.80 µm (1.00 µm, 6.5-13.5 µm) P<0.05. As the axial length increases, the cone density significantly decreases. Interocular variations were noted. CONCLUSION: With the advent of AO, visualization at the cellular level is now possible. Understanding the photoreceptor mosaic in the parafoveal space in terms of its density, spacing, and arrangement is crucial so as to detect early pathology and intervene appropriately. Newer therapeutic modalitites that are targeted at the cellular level like yellow micropulse laser, stem cells, gene therapy and so on may be better monitored in terms of safety and efficacy.

Biological and biomechanical responses to traditional epithelium-off and transepithelial riboflavin-UVA CXL techniques in rabbits.

PURPOSE: To compare the biological effects of riboflavin-ultraviolet A (UVA) corneal cross-linking (CXL) performed with a traditional epithelium-off method to several transepithelial methods in a rabbit model. Preliminary experiments on biomechanical rigidity were also performed. METHODS: Four treatment groups were included: (1) standard epithelium-off, (2) tetracaine transepithelial, (3) benzal-konium chloride-ethylenediaminetetraacetic acid (BKC-EDTA) transepithelial, and (4) femtosecond laser-assisted transepithelial riboflavin-UVA CXL. Six eyes from each treatment group and the untreated control group were analyzed at 24 hours and 2 months after treatment in wound healing studies. The TUNEL assay was performed to detect the extent of stromal cell death. Optical density was measured with a Scheimpflug analyzer. The corneal stiffening effect was quantitated in three eyes from each group using optical coherence elastography performed 2 months after treatments. RESULTS: Twenty-four hours after CXL, stromal cell death extended full corneal thickness with both standard epithelium-off CXL and femtosecond laser-assisted CXL, but only approximately one-third stromal depth after BKC-EDTA transepithelial CXL. Negligible stromal cell death was detected with tetracaine transepithelial CXL. Cell death results were statistically different between the BKC-EDTA transepithelial CXL and standard epithelium-off CXL groups (P < .0001). Significant corneal opacity differences were noted. Standard epithelium-off CXL had the greatest density and tetracaine transepithelial CXL had the least density compared to the control group after treatment. As measured with optical coherence elastography, a trend toward greater mean stiffening was observed with BKC-EDTA transepithelial CXL than with epithelium-off CXL, femtosecond laser-assisted CXL, or tetracaine transepithelial CXL, but the result did not reach statistical significance. All of the CXL treatment groups exhibited significantly smaller variance of stiffness compared to the control group. CONCLUSION: In the rabbit model, BKC-EDTA transepithelial CXL produced less stromal cell death and less risk of endothelial cell damage than standard epithelium-off CXL or femtosecond laser-assisted CXL. Additional study is needed to determine whether biomechanical stiffness is significantly different between the epithelium-off CXL and transepithelial CXL groups.

Novel pachymetric parameters based on corneal tomography for diagnosing keratoconus.

PURPOSE: To describe pachymetric progression indices (PPI) of the Pentacam HR (Oculus Optikgeräte GmbH) and the concept of relational thickness, and to test their accuracy for differentiating keratoconic and normal corneas compared with single-point thickness values. METHODS: One hundred thirteen individual eyes randomly selected from 113 normal patients and 44 eyes of 44 patients with keratoconus were studied using the Pentacam HR by acquiring central corneal thickness (CCT), thinnest point (TP), position of the TP and PPI at minimal (PPI Min) and maximal (PPI Max) meridians, and the average (PPI Ave) of all meridians. Relational thickness parameters were calculated as the ratios of TP and CCT and PPI values. Mann-Whitney U test assessed differences in groups for each variable. Receiver operating characteristic (ROC) curves were calculated for all variables and pairwise comparisons were performed. RESULTS: Statistically significant differences were noted between normal and keratoconic eyes for all parameters (P<.001), except for horizontal position of TP (P=.79). The best parameters, named Ambrósio's Relational Thickness (ART), were ART-Ave (TP/PPI Ave) and ART-Max (TP/PPI Max) with areas under the ROC curves of 0.987 and 0.983, respectively. The best cutoffs were 424 µm and 339 µm for ART-Ave and ART-Max, respectively. Pachymetric progression indices and ART had a greater area under the curve than TP and CCT (P<.001); TP (0.955) had a greater area under the curve than CCT (0.909; P=.002). CONCLUSIONS: Tomographic-derived pachymetric parameters were better able to differentiate normal and keratoconic corneas than single-point pachymetric measurements. Further studies are needed to evaluate the role of tomography in identifying early forms of ectasia as well as ectasia risk among LASIK candidates.

Method for optical coherence elastography of the cornea.

The material properties of the cornea are important determinants of corneal shape and refractive power. Corneal ectatic diseases, such as keratoconus, are characterized by material property abnormalities, are associated with progressive thinning and distortion of the cornea, and represent a leading indication for corneal transplantation. We describe a corneal elastography technique based on optical coherence tomography (OCT) imaging, in which displacement of intracorneal optical features is tracked with a 2-D cross-correlation algorithm as a step toward nondestructive estimation of local and directional corneal material properties. Phantom experiments are performed to measure the effects of image noise and out-of-plane displacement on effectiveness of displacement tracking and demonstrated accuracy within the tolerance of a micromechanical translation stage. Tissue experiments demonstrate the ability to produce 2-D maps of heterogeneous intracorneal displacement with OCT. The ability of a nondestructive optical method to assess tissue under in situ mechanical conditions with physiologic-range stress levels provides a framework for in vivo quantification of 3-D corneal elastic and viscoelastic resistance, including analogs of shear deformation and Poisson's ratio that may be relevant in the early diagnosis of corneal ectatic disease.

Functional Disability and Associated Chronic Conditions among Geriatric Populations in a Rural Community of India.

BACKGROUND: Geriatric population and chronic diseases are increasing throughout the world especially in developing countries like India. Because of social change and urbanization, disability is also a problem in India. As the major reasons for geriatric disabilities are chronic diseases, a study was undertaken. OBJECTIVES: To find out the prevalence of different chronic diseases and disability among the geriatric population in a rural community of India and to determine the association between chronic diseases and disability of the geriatric population. METHOD: A cross-sectional, observational community based study was conducted in a rural area of West Bengal, India through house to house visit for Clinical examination, observation and interview with a predesigned pre-tested proforma RESULTS: Out of 495 study population, 80 (16.16%) were found to be functionally disabled as per ADL scale and more than half (56.2%) of them had 3 or more chronic conditions. 92.5% of study populations had one or more chronic conditions CONCLUSION: Association between different risk factors and disability was found with age, sex, anaemia, Chronic Obstructive Pulmonary Diseases(C.O.P.D), scabies, hypertrophy of prostate, ischaemic heart disease, osteoporosis, osteoarthritis and acid peptic disorder were the risk factors of disability. These data suggest the significant chronic conditions and risk factors associated with disability. Measures to reduce such chronic conditions and impairment would be the useful approach for the prevention of disability.

Concurrent assessment of epicardial coronary artery stenosis and microvascular dysfunction using diagnostic endpoints derived from fundamental fluid dynamics principles.

BACKGROUND: Simultaneously measured pressure and flow distal to coronary stenoses can be combined, in conjunction with anatomical measurements, to assess the status of both the epicardial and microvascular circulations. METHODS AND RESULTS: Assessments of coronary hemodynamics were performed using fundamental fluid dynamics principles. We hypothesized that the pressure-drop coefficient (CDPe; trans-stenotic pressure drop divided by the dynamic pressure in the distal vessel) correlates linearly with epicardial and microcirculatory resistances concurrently. In 14 pigs, simultaneous measurements of distal coronary arterial pressure and flow were performed using a dual sensor-tipped guidewire in the setting of both normal and disrupted microcirculation, with the presence of epicardial coronary lesions of lt; 50% area stenosis (AS) and > 50% AS. The CDPe progressively increased from lesions of < 50% AS to > 50% AS and had a higher resolving power (45 +/- 22 to 193 +/- 140 in normal microcirculation; 248 +/- 137 to 351 +/- 140 in disrupted microcirculation) as compared to fractional flow reserve (FFR) and coronary flow reserve (CFR). Strong multiple linear correlation was observed for CDPe with combined FFR and CFR (r = 0.72; p < 0.0001). Further, the ratio of maximum pressure drop coefficient evaluated at the site of stenosis and its theoretical limiting value of minimum cross-sectional area was also able to distinguish different combinations of coronary artery diseases. CONCLUSIONS: The CDPe can be readily obtained during routine pressure and flow measurements during cardiac catheterization. It is a promising clinical diagnostic parameter that can independently assess the severity of epicardial stenosis and microvascular impairment.

Measurement of hemodynamic and anatomic parameters in a swine arteriovenous fistula model.

PURPOSE: Although arteriovenous fistulae (AVFs) are currently the preferred mode of permanent hemodialysis access they do have significant problems due to initial non-maturation and a later venous stenosis. These problems appear to have been exacerbated following a push to increase AVF prevalence in the US. The reasons for both AVF non-maturation and the later venous stenoses are unclear but are thought to be related to abnormal hemodynamic wall shear stress (WSS) profiles. This technical note aims to describe the successful development of measurement techniques that can be used to establish a complete hemodynamic profile in a pig model with two different configurations of AVF. METHODS AND RESULTS: The curved and straight AVF configurations were created in an in vivo pig model. Flow and pressure in the AVFs were measured using the perivascular flow probes and Doppler flow wires while the pressure was recorded using a pressure transducer. The anatomical configuration was obtained using two different approaches: a) combination of intravascular ultrasound (IVUS) and angiograms, (b) 64 slice CT angiography. 3D models were reconstructed using image processing and computer modeling techniques. Numerical calculations were then performed by applying the measured flow and pressure data into the configurations to obtain the hemodynamic WSS profiles. CONCLUSION: The described methodologies will allow the calculation and optimization of WSS profiles in animal models. This information could then be translated to the clinical setting where it would have a positive impact on improving the early maturation rates of AVFs as well as reducing the late venous stenoses.

In vitro measurement and calculation of drag force on iliac limb stentgraft in a compliant arterial wall model.

Interventional treatment of aortic aneurysms using endovascular stentgrafting is a minimally invasive technique. Following device implantation, transient drag forces act on the stentgraft. When the drag force exceeds the fixation force, complications like stentgraft migration, endoleaks and stentgraft failure occur. In such a scenario the device becomes unstable, causing concern over the long-term durability of endovascular repairs. The objective of this study is: (1) to measure the drag force on iliac limb stentgraft, having a distal diameter that is half the size of the proximal end, in an in vitro experiment; (2) to calculate the drag force using blood flow-compliant arterial wall interaction model and compare it with the measured values on the stentgraft for the in vitro experiment; (3) to calculate drag force on the stentgraft using physiological flow conditions. Experimental data for a stentgraft within a silicon tubing, representing a compliant artery, shows a peak drag force of 2.79 N whereas the calculation predicts a peak drag force of 2.57 N; thus a percentage difference of 7.8% is observed. When physiological flow and pressure pulse are used for the blood flow-compliant arterial wall computations, a peak drag force of 0.59 N is obtained for the same stentgraft that was used in the experiment. The outer cavity between the distal end of the iliac limb stentgraft and the arterial wall reduces the drag force. These forces can be used as design guideline for determining the fixation force needed for the stentgraft under physiological pulsatile flow.

A pilot survey on hand washing among some communities of West Bengal.

A cross-sectional observational study was carried out between April to May 2006 by interview method and observation technique with the objective to know the knowledge regarding hand washing in the community and it was done in the slum and nonslum urban areas and also one rural area. The result shows that in urban slum area 98% washed their hands with soap after defecation; Only 36%, 16% and 2% washed their hands with soap before meal, before serving food and before cooking respectively. However, it was observed that 69% used soap and water for hand washing after cleaning the child's faeces. In rural area 71% used soap and water after defecation while 26% used mud or ash. Only 13%, 1%, 1% and 5% used soap and water before meal, before serving food, before cooking and after cleaning the child's faeces. 82.35% of respondents in non slum area and 89% of respondents in rural area considered that diarrhoea and dysentery could be prevented by hand washing while they did not give importance to hand washing in prevention of diarrhoea over other methods like cleanliness, boiling and purification of water. ARI was much higher (25.72%) in rural area followed by slum area (13.77%) and non-slum area (3.87%). Out of 30 observations among 302 interview made on hand-washing only first step i.e. palm washing (transient rubbing the palm with soap) was followed by all the participants observed. Time taken for such hand-washing was only around five seconds (ideal 15-30 seconds) in urban slum and rural areas while in non slum area it varied between 7-10 seconds on an average. No one followed any other steps of hand-washing, recommended by IFH.