Estimation of the Central Corneal Power in Keratoconus: Theoretical and Clinical Assessment of the Error of the Keratometric Approach

Purpose: The aim of this study was to analyze theoretically the errors in the central corneal power calculation in eyes with keratoconus when a keratometric index (nk) is used and to clinically confirm the errors induced by this approach. Methods: Differences (DPc) between central corneal power estimation with the classical nk (Pk) and with the Gaussian equation (PGauss c ) in eyes with keratoconus were simulated and evaluated theoretically, considering the potential range of variation of the central radius of curvature of the anterior (r1c) and posterior (r2c) corneal surfaces. Further, these differences were also studied in a clinical sample including 44 keratoconic eyes (27 patients, age range: 14–73 years). The clinical agreement between Pk and PGauss c (true net power) obtained with a Scheimpflug photography–based topographer was evaluated in such eyes. Results: For nk = 1.3375, an overestimation was observed in most cases in the theoretical simulations, with DPc ranging from an underestimation of 20.1 diopters (D) (r1c = 7.9 mm and r2c = 8.2 mm) to an overestimation of 4.3 D (r1c = 4.7 mm and r2c = 3.1 mm). Clinically, Pk always overestimated the PGauss c given by the topography system in a range between 0.5 and 2.5 D (P , 0.01). The mean clinical DPc was 1.48 D, with limits of agreement of 0.71 and 2.25 D. A very strong statistically significant correlation was found between DPc and r2c (r = 20.93, P , 0.01). Conclusions: The use of a single value for nk for the calculation of corneal power is imprecise in keratoconus and can lead to significant clinical errors.

Immunohistochemical evidence of synaptic retraction, cytoarchitectural remodeling, and cell death in the inner retina of the rat model of Oygen-Induced Retinopathy (OIR)

Purpose. Postnatal exposure to hyperoxia destroys the plexiform layers of the neonatal rat retina, resulting in significant electroretinographic anomalies. The purpose of this study was to identify the mechanisms at the origin of this loss. Methods. Sprague-Dawley (SD) and Long Evans (LE) rats were exposed to hyperoxia from birth to postnatal day (P) 6 or P14 and from P6 to P14, after which rats were euthanatized at P6, P14, or P60. Results. At P60, synaptophysin staining confirmed the lack of functional synaptic terminals in SD (outer plexiform layer [OPL]) and LE (OPL and inner plexiform layer [IPL]) rats. Uneven staining of ON-bipolar cell terminals with mGluR6 suggests that their loss could play a role in OPL thinning. Protein kinase C(PKC)-α and recoverin (rod and cone ON-bipolar cells, respectively) showed a lack of dendritic terminals in the OPL with disorganized axonal projections in the IPL. Although photoreceptor nuclei appeared intact, a decrease in bassoon staining (synaptic ribbon terminals) suggests limited communication to the inner retina. Findings were significantly more pronounced in LE rats. An increase in TUNEL-positive cells was observed in LE (inner nuclear layer [INL] and outer nuclear layer [ONL]) and SD (INL) rats after P0 to P14 exposure (425.3%, 102.2%, and 146.3% greater than control, respectively [P < 0.05]). Conclusions. Results suggest that cell death and synaptic retraction are at the root of OPL thinning. Increased TUNEL-positive cells in the INL confirm that cells die, at least in part, because of apoptosis. These findings propose a previously undescribed mechanism of cell death and synaptic retraction that are likely at the origin of the functional consequences of hyperoxia.

Proinsulin slows retinal degeneration and vision loss in the P23H rat model of retinitis pigmentosa

Proinsulin has been characterized as a neuroprotective molecule. In this work we assess the therapeutic potential of proinsulin on photoreceptor degeneration, synaptic connectivity, and functional activity of the retina in the transgenic P23H rat, an animal model of autosomal dominant retinitis pigmentosa (RP). P23H homozygous rats received an intramuscular injection of an adeno-associated viral vector serotype 1 (AAV1) expressing human proinsulin (hPi+) or AAV1-null vector (hPi−) at P20. Levels of hPi in serum were determined by enzyme-linked immunosorbent assay (ELISA), and visual function was evaluated by electroretinographic (ERG) recording at P30, P60, P90, and P120. Preservation of retinal structure was assessed by immunohistochemistry at P120. Human proinsulin was detected in serum from rats injected with hPi+ at all times tested, with average hPi levels ranging from 1.1 nM (P30) to 1.4 nM (P120). ERG recordings showed an amelioration of vision loss in hPi+ animals. The scotopic b-waves were significantly higher in hPi+ animals than in control rats at P90 and P120. This attenuation of visual deterioration correlated with a delay in photoreceptor degeneration and the preservation of retinal cytoarchitecture. hPi+ animals had 48.7% more photoreceptors than control animals. Presynaptic and postsynaptic elements, as well as the synaptic contacts between photoreceptors and bipolar or horizontal cells, were preserved in hPi+ P23H rats. Furthermore, in hPi+ rat retinas the number of rod bipolar cell bodies was greater than in control rats. Our data demonstrate that hPi expression preserves cone and rod structure and function, together with their contacts with postsynaptic neurons, in the P23H rat. These data strongly support the further development of proinsulin-based therapy to counteract retinitis pigmentosa.

Constructing an Indigenous Model of the Self to Address Cultural and Mental Health Issues in the Canadian Subarctic

Since the last decades, academic research has paid much attention to the phenomenon of revitalizing indigenous cultures and, more precisely, the use of traditional indigenous healing methods both to deal with individuals' mental health problems and with broader cultural issues. The re-evaluation of traditional indigenous healing practices as a mode of psychotherapeutic treatment has been perhaps one of the most interesting sociocultural processes in the postmodern era. In this regard, incorporating indigenous forms of healing in a contemporary framework of indigenous mental health treatment should be interpreted not simply as an alternative therapeutic response to the clinical context of Western psychiatry, but also constitutes a political response on the part of ethno-cultural groups that have been stereotyped as socially inferior and culturally backward. As a result, a postmodern form of "traditional healing" developed with various forms of knowledge, rites and the social uses of medicinal plants, has been set in motion on many Canadian indigenous reserves over the last two decades.

MINLP Model for the Synthesis of Heat Exchanger Networks with Handling Pressure of Process Streams

This paper introduces a new mathematical model for the simultaneous synthesis of heat exchanger networks (HENs), wherein the handling pressure of process streams is used to enhance the heat integration. The proposed approach combines generalized disjunctive programming (GDP) and mixed-integer nonlinear programming (MINLP) formulation, in order to minimize the total annualized cost composed by operational and capital expenses. A multi-stage superstructure is developed for the HEN synthesis, assuming constant heat capacity flow rates and isothermal mixing, and allowing for streams splits. In this model, the pressure and temperature of streams must be treated as optimization variables, increasing further the complexity and difficulty to solve the problem. In addition, the model allows for coupling of compressors and turbines to save energy. A case study is performed to verify the accuracy of the proposed model. In this example, the optimal integration between the heat and work decreases the need for thermal utilities in the HEN design. As a result, the total annualized cost is also reduced due to the decrease in the operational expenses related to the heating and cooling of the streams.

A Computational Model of the Belief System Under the Scope of Social Communication

This paper presents an approach to the belief system based on a computational framework in three levels: first, the logic level with the definition of binary local rules, second, the arithmetic level with the definition of recursive functions and finally the behavioural level with the definition of a recursive construction pattern. Social communication is achieved when different beliefs are expressed, modified, propagated and shared through social nets. This approach is useful to mimic the belief system because the defined functions provide different ways to process the same incoming information as well as a means to propagate it. Our model also provides a means to cross different beliefs so, any incoming information can be processed many times by the same or different functions as it occurs is social nets.