Linfoma ocular primario vs celulitis orbitaria en tiempos de COVID-19 / Primary ocular lymphoma vs orbital cellulitis in times of COVID-19

Los tumores sólidos neoplásicos de tejido linfoide se caracterizan por proliferación acelerada de la porción linforreticular del sistema retículo endotelial, su incidencia mundial es de 4/100,000 prevalente en féminas entre 50-70 años, de etiología desconocida, asociado a helicobacter pylori, epstein barr y VIH. Clínicamente están presentes los síntomas B: fiebre, sudoraciones nocturnas, pérdida de peso, prurito y astenia. ausentes en el caso que nos ocupa de una paciente femenina de 46 años de edad que acudió a consulta de oftalmología por aumento de volumen a nivel de anejos de ojo izquierdo, proptosis indolora y disminución de la visión, con diagnóstico inicial de celulitis orbitaria tratada ambulatoriamente sin resolución. Se administró antibioticoterapia intravenosa sin mejoría clínica, se realizaron estudios complementarios de imagen radiológica, ultrasonido, resonancia magnética con evidencia de imagen tumoral de crecimiento antero lateral, desplazamiento de globo ocular, diámetro mayor de 57,3 mm, de características isointensas heterogéneas, secuencia T1 y flair, erosión de pared interna de orbita y la biopsia excisional informó linfoma primario de anexo ocular orbitario tipo no-Hodgkin. El abordaje acucioso con estudios complementarios para descartar neoplasias orbitarias en pacientes con celulitis orbitaria o dacriocistitis de evolución tórpida es necesario en todo momento, independiente de las condiciones atípicas de pandemia por COVID-19 que dificultan su manejo(AU)

Solid neoplastic tumors of lymphoid tissue are characterized by accelerated proliferation of the lymphoreticular portion of the reticulum endothelial system, their worldwide incidence is 4/100,000 prevalent in females between 50-70 years of age, of unknown etiology, associated with helicobacter pylori, epstein barr and HIV. Clinically, symptoms B are present: fever, night sweats, weight loss, itching and asthenia, absent in the present case of a 46-year-old female patient who came to the ophthalmology office due to increased volume at the level of the appendages. of the left eye, painless proptosis and decreased vision, with an initial diagnosis of orbital cellulitis treated outpatiently without resolution. Intravenous antibiotic therapy was administered without clinical improvement, complementary radiological imaging studies, ultrasound, magnetic resonance imaging were performed with evidence of an anterolateral growth tumor image, ocular globe displacement, diameter greater than 57.3 mm, heterogeneous isointense characteristics, T1 sequence and flair, erosion of the internal wall of the orbit and the excisional biopsy reported primary non-Hodgkin type orbital annex lymphoma. A careful approach with complementary studies to rule out orbital neoplasms in patients with orbital cellulitis or dacryocystitis of torpid evolution is necessary at all times, regardless of the atypical conditions of a COVID-19 pandemic that make its management difficult(AU)

Cuerpos extraños intracorneales retenidos / Retained intracorneal foreign bodies

Los cuerpos extraños constituyen la segunda forma más común de traumatismos corneales. Pueden localizarse superficiales o intracorneales. Se realiza presentación de caso de paciente con cuerpos extraños intracorneales retenidos de 34 años de evolución secundario a trauma por onda expansiva, con el objetivo de mostrar los hallazgos clínicos y resultados por pruebas diagnósticas como la microscopía confocal corneal, frente de onda corneal por topografía y microscopía especular. La presencia de cuerpos extraños intracorneales en este paciente provocó respuestas en el tejido corneal en dependencia de su composición, nivel de profundidad; evidentes a pesar de tiempo de retención. La presencia de estos induce niveles altos de aberraciones corneales que dependen del grado de afectación(AU)

Foreign bodies are the second most common form of corneal trauma. They can be superficial or intracorneal. A case of a patient was presented, with retained intracorneal foreign bodies of 34 years of secondary evolution due to blast wave trauma. The objective is to show the clinical findings and results of diagnostic tests such as corneal confocal microscopy, corneal wavefront topography and specular microscopy. The presence of intracorneal foreign bodies in this patient provoked responses in the corneal tissue depending on its composition, depth level; evident in spite of retention time. The presence of intracorneal foreign bodies induces high levels of corneal aberrations depending on the degree of involvement(AU)

La Oftalmología en tiempos de COVID-19 / Ophthalmology in the time of COVID-19

RESUMEN La historia de las pandemias y el hombre moderno han marcado un antes y un después en la medicina actual, como sucedió con la gripe española en el año 1918. La última registrada mundialmente es el Coronavirus, el cual -identificado como COVID-19 (por sus siglas en inglés), manifiesto por el agente viral SARS-CoV-2- desde su comienzo el 30 de diciembre del año 2019 guarda estrecha relación con la Oftalmología. El objetivo de esta investigación fue documentar la nueva evidencia científica relacionada con esta entidad y su manifestación ocular, mediante la revisión de la literatura comprendida del 1ro. de enero al 25 de abril del año 2020, con el uso de metabuscadores en inglés y en español. Dentro de los medios de transmisibilidad que han sido documentados, la sintomatología respiratoria es la más estudiada; sin embargo, existen manifestaciones oculares con la presencia del virus SARS-CoV-2 en la lagrima y en la conjuntiva de los pacientes infectados por COVID-19. El cuadro más característico se presenta con una conjuntivitis viral inespecífica. La tasa de mortalidad es un tema de especial relevancia. La estadística acumulada sugiere mayor letalidad y, por tanto, la necesidad de ejecutar medidas y acciones sociales para el control poblacional. La letalidad mundial en este momento es de 7,2 por ciento; en América Latina de 5,8 por ciento y en Cuba de 4,2 por ciento. El presente documento realiza un abordaje integral de la patología COVID-19 con respecto a las recomendaciones internacionales para el personal de Oftalmología y los centros oftalmológicos, así como acerca de los factores de riesgo, el cuadro clínico, los nuevos tratamientos y los reportes de estudios clínicos que se encuentran actualmente en fase de estudio(AU)

ABSTRACT The history of pandemics and modern man have marked a before and after in current medicine, as was the case with the Spanish flu in 1918. The last pandemic recorded worldwide is coronavirus, identified as COVID-19, caused by the viral agent SARS-CoV-2. From its onset on 30 December 2019 this disease has had a close connection to ophthalmology. The purpose of the study was to document the new scientific evidence about this condition and its ocular manifestation through a literature review covering the period extending from 1 January to 25 April 2020, using search terms in English and Spanish. Respiratory symptoms are among the transmission routes most commonly dealt with. However, some ocular manifestations are characterized by the presence of the SARS-CoV-2 virus in tears and in the conjunctiva of patients infected with COVID-19. The most typical manifestation is nonspecific viral conjunctivitis. Mortality rate is a topic of special relevance. The statistics accumulated suggest greater fatality and thus the need to implement social measures and actions aimed at population control. The current fatality rate is 7.2 percent worldwide, 5.8 percent in Latin America and 4.2 percent in Cuba. The present paper provides a comprehensive analysis of COVID-19 based on international recommendations for ophthalmology personnel and facilities, as well as the risk factors, clinical status, new treatments and reports about ongoing clinical studies(AU)

Novel approximation of misalignment fading modeled by Beckmann distribution on free-space optical links.

A novel accurate and useful approximation of the well-known Beckmann distribution is presented here, which is used to model generalized pointing errors in the context of free-space optical (FSO) communication systems. We derive an approximate closed-form probability density function (PDF) for the composite gamma-gamma (GG) atmospheric turbulence with the pointing error model using the proposed approximation of the Beckmann distribution, which is valid for most practical terrestrial FSO links. This approximation takes into account the effect of the beam width, different jitters for the elevation and the horizontal displacement and the simultaneous effect of nonzero boresight errors for each axis at the receiver plane. Additionally, the proposed approximation allows us to delimit two different FSO scenarios. The first of them is when atmospheric turbulence is the dominant effect in relation to generalized pointing errors, and the second one when generalized pointing error is the dominant effect in relation to atmospheric turbulence. The second FSO scenario has not been studied in-depth by the research community. Moreover, the accuracy of the method is measured both visually and quantitatively using curve-fitting metrics. Simulation results are further included to confirm the analytical results.

Impact of nonzero boresight pointing error on ergodic capacity of MIMO FSO communication systems.

A thorough investigation of the impact of nonzero boresight pointing errors on the ergodic capacity of multiple-input/multiple-output (MIMO) free-space optical (FSO) systems with equal gain combining (EGC) reception under different turbulence models, which are modeled as statistically independent, but not necessarily identically distributed (i.n.i.d.) is addressed in this paper. Novel closed-form asymptotic expressions at high signal-to-noise ratio (SNR) for the ergodic capacity of MIMO FSO systems are derived when different geometric arrangements of the receive apertures at the receiver are considered in order to reduce the effect of nonzero inherent boresight displacement, which is inevitably present when more than one receive aperture is considered. As a result, the asymptotic ergodic capacity of MIMO FSO systems is evaluated over log-normal (LN), gamma-gamma (GG) and exponentiated Weibull (EW) atmospheric turbulence in order to study different turbulence conditions, different sizes of receive apertures as well as different aperture averaging conditions. It is concluded that the use of single-input/multiple-output (SIMO) and MIMO techniques can significantly increase the ergodic capacity respect to the direct path link when the inherent boresight displacement takes small values, i.e. when the spacing among receive apertures is not too big. The effect of nonzero additional boresight errors, which is due to the thermal expansion of the building, is evaluated in multiple-input/single-output (MISO) and single-input/single-output (SISO) FSO systems. Simulation results are further included to confirm the analytical results.

Novel space-time trellis codes for free-space optical communications using transmit laser selection.

In this paper, the deployment of novel space-time trellis codes (STTCs) with transmit laser selection (TLS) for free-space optical (FSO) communication systems using intensity modulation and direct detection (IM/DD) over atmospheric turbulence and misalignment fading channels is presented. Combining TLS and STTC with rate 1 bit/(s · Hz), a new code design criterion based on the use of the largest order statistics is here proposed for multiple-input/single-output (MISO) FSO systems in order to improve the diversity order gain by properly chosing the transmit lasers out of the available L lasers. Based on a pairwise error probability (PEP) analysis, closed-form asymptotic bit error-rate (BER) expressions in the range from low to high signal-to-noise ratio (SNR) are derived when the irradiance of the transmitted optical beam is susceptible to moderate-to-strong turbulence conditions, following a gamma-gamma (GG) distribution, and pointing error effects, following a misalignment fading model where the effect of beam width, detector size and jitter variance is considered. Obtained results show diversity orders of 2L and 3L when simple two-state and four-state STTCs are considered, respectively. Simulation results are further demonstrated to confirm the analytical results.

Ergodic capacity analysis for DF strategies in cooperative FSO systems.

This paper focuses on the ergodic capacity analysis in the context of cooperative free-space optical (FSO) systems when the line of sight is available. Novel asymptotic closed-form expressions for the ergodic capacity corresponding to two different decode-and-forward (DF) strategies are obtained for a cooperative FSO communication system. Here, the atmospheric turbulence is modeled by a gamma-gamma distribution of parameters α and ß which allows to study a wide range of turbulence conditions (moderate-to-strong) as well as the effect of the misalignment with zero boresight. It is demonstrated that cooperative communications are able to achieve not only a better performance in terms of the error rate performance as well as outage probability than direct transmission, but also in terms of the channel capacity in the context of FSO systems without much increase in hardware. In this way, a 3-way FSO communication setup is considered, in which the cooperative protocol can be applied to achieve a greater ergodic capacity compared to a direct transmission. It can be concluded that a greater and robust capacity strongly dependent on the relay location is achieved compared to a direct transmission without cooperative communication when line of sight is available. Here, the line of sight is taken into account in order to achieve a significant robustness under different turbulence conditions and more severe pointing errors regardless of the relay location. Simulation results are further demonstrated to confirm the accuracy and usefulness of the derived results.

On the capacity of MISO FSO systems over gamma-gamma and misalignment fading channels.

In this work, the ergodic capacity performance for multiple-input/single-output (MISO) free-space optical (FSO) communications system with equal gain combining (EGC) reception is analyzed over gamma-gamma and misalignment fading channels, which are modeled as statistically independent, but not necessarily identically distributed (i.n.i.d.). Novel and analytical closed-form ergodic capacity expression is obtained in terms of H-Fox function by using the well-known inequality between arithmetic and geometric mean of positive random variables (RV) in order to obtain an approximate closed-form expression of the distribution of the sum of M gamma-gamma with pointing errors variates. In addition, we present an asymptotic ergodic capacity expression at high signal-to-noise ratio (SNR) for the ergodic capacity of MISO FSO systems. It can be concluded that the use of MISO technique can significantly reduce the effect of the atmospheric turbulence as well as pointing errors and, hence, provide significant capacity gain over the direct path link (DL). The impact of pointing errors on the MISO FSO system is also analyzed, which only depends on the number of laser sources and pointing error parameters. Moreover, it can be also concluded that the ergodic capacity performance is dramatically reduced as a consequence of the severity of pointing error effects. Simulation results are further demonstrated to confirm the analytical results.

Impact of relay placement on diversity order in adaptive selective DF relay-assisted FSO communications.

The impact of relay placement on diversity order in adaptive selective decode-and-forward (DF) cooperative strategies is here investigated in the context of free-space optical (FSO) communications over atmospheric turbulence channels with pointing errors when line of sight is available. The irradiance of the transmitted optical beam here considered is susceptible to moderate-to-strong turbulence conditions, following a gamma-gamma (GG) distribution together with a misalignment fading model where the effect of beam width, detector size and jitter variance is considered. Novel closed-form approximate bit error-rate (BER) expressions are obtained for a cooperative FSO communication setup with N relays, assuming that these relays are located in an area similar to an annulus around source or destination node. An analytical expression is here found that determines the best selection criterion based on the knowledge of the channel state information (CSI) of source-relay or relay-destination links in order to significantly increase the diversity order corresponding to the cooperative strategy under study. It is concluded that the highest diversity order is achieved when the relation ß(SR(min)) > ß(SD) + ß(R(min)D) is satisfied, wherein ß(SR(min)), ß(R(min)D) and ß(SD) are parameters corresponding to the atmospheric turbulence conditions of source-relay and relay-destination link with the greatest scintillation index, and source-destination link, respectively.

Transmit alternate laser selection with time diversity for FSO communications.

In this paper, a new transmit alternate laser selection (TALS) scheme for FSO communication systems using intensity modulation and direct detection (IM/DD) over atmospheric turbulence and misalignment fading channels is presented when limited time diversity is available in the turbulent channel. Assuming channel state information (CSI) at the transmitter and receiver and a time diversity order (TDO) limited, we propose the transmit diversity technique based on the rotating selection of TDO out of the available L lasers corresponding to the optical paths with greater values of scintillation. Implementing repetition coding with blocks of TDO information bits, each information bit will be retransmitted TDO times using the TDO largest order statistics in an alternating way. Closed-form asymptotic bit error-rate (BER) expressions are derived when the irradiance of the transmitted optical beam is susceptible to moderate-to-strong turbulence conditions, following a gamma-gamma (GG) distribution, and pointing error effects, following a misalignment fading model where the effect of beam width, detector size and jitter variance is considered. Fully exploiting the potential time-diversity TDO available in the turbulent channel, a significant diversity gain is achieved, providing a diversity order of (2L + 1 - TDO)TDO/2.

Adaptive selective relaying in cooperative free-space optical systems over atmospheric turbulence and misalignment fading channels.

In this paper, a novel adaptive cooperative protocol with multiple relays using detect-and-forward (DF) over atmospheric turbulence channels with pointing errors is proposed. The adaptive DF cooperative protocol here analyzed is based on the selection of the optical path, source-destination or different source-relay links, with a greater value of fading gain or irradiance, maintaining a high diversity order. Closed-form asymptotic bit error-rate (BER) expressions are obtained for a cooperative free-space optical (FSO) communication system with Nr relays, when the irradiance of the transmitted optical beam is susceptible to either a wide range of turbulence conditions, following a gamma-gamma distribution of parameters α and ß, or pointing errors, following a misalignment fading model where the effect of beam width, detector size and jitter variance is considered. A greater robustness for different link distances and pointing errors is corroborated by the obtained results if compared with similar cooperative schemes or equivalent multiple-input multiple-output (MIMO) systems. Simulation results are further demonstrated to confirm the accuracy and usefulness of the derived results.

Improved BDF relaying scheme using time diversity over atmospheric turbulence and misalignment fading channels.

A novel bit-detect-and-forward (BDF) relaying scheme based on repetition coding with the relay is proposed, significantly improving the robustness to impairments proper to free-space optical (FSO) communications such as unsuitable alignment between transmitter and receiver as well as fluctuations in the irradiance of the transmitted optical beam due to the atmospheric turbulence. Closed-form asymptotic bit-error-rate (BER) expressions are derived for a 3-way FSO communication setup. Fully exploiting the potential time-diversity available in the relay turbulent channel, a relevant better performance is achieved, showing a greater robustness to the relay location since a high diversity gain is provided regardless of the source-destination link distance.

Asymptotic error-rate analysis of FSO links using transmit laser selection over gamma-gamma atmospheric turbulence channels with pointing errors.

Since free-space optical (FSO) systems are usually installed on high buildings and building sway may cause vibrations in the transmitted beam, an unsuitable alignment between transmitter and receiver together with fluctuations in the irradiance of the transmitted optical beam due to the atmospheric turbulence can severely degrade the performance of optical wireless communication systems. In this paper, asymptotic bit error-rate (BER) performance for FSO communication systems using transmit laser selection over atmospheric turbulence channels with pointing errors is analyzed. Novel closed-form asymptotic expressions are derived when the irradiance of the transmitted optical beam is susceptible to either a wide range of turbulence conditions (weak to strong), following a gamma-gamma distribution of parameters α and ß, or pointing errors, following a misalignment fading model where the effect of beam width, detector size and jitter variance is considered. Obtained results provide significant insight into the impact of various system and channel parameters, showing that the diversity order is independent of the pointing error when the equivalent beam radius at the receiver is at least 2(min{α,ß})(1/2) times the value of the pointing error displacement standard deviation at the receiver. Moreover, since proper FSO transmission requires transmitters with accurate control of their beamwidth, asymptotic expressions are used to find the optimum beamwidth that minimizes the BER at different turbulence conditions. Simulation results are further demonstrated to confirm the accuracy and usefulness of the derived results, showing that asymptotic expressions here obtained lead to simple bounds on the bit error probability that get tighter over a wider range of signal-to-noise ratio (SNR) as the turbulence strength increases.

Outage performance of MIMO FSO links over strong turbulence and misalignment fading channels.

Atmospheric turbulence produces fluctuations in the irradiance of the transmitted optical beam, which is known as atmospheric scintillation, severely degrading the performance over free-space optical (FSO) links. Additionally, since FSO systems are usually installed on high buildings, building sway causes vibrations in the transmitted beam, leading to an unsuitable alignment between transmitter and receiver and, hence, a greater deterioration in performance. In this paper, the outage probability as a performance measure for multiple-input/multiple-output (MIMO) FSO communication systems with intensity modulation and direct detection (IM/DD) over strong atmospheric turbulence channels with pointing errors is analyzed. Novel closed-form expressions for the outage probability as well as their corresponding asymptotic expressions are presented when the irradiance of the transmitted optical beam is susceptible to either strong turbulence conditions, following a negative exponential distribution, and pointing error effects, following a misalignment fading model where the effect of beam width, detector size and jitter variance is considered. Obtained results show that the diversity order is independent of the pointing error when the equivalent beam radius at the receiver is at least twice the value of the pointing error displacement standard deviation at the receiver. Simulation results are further demonstrated to confirm the analytical results. Additionally, since proper FSO transmission requires transmitters with accurate control of their beamwidth, asymptotic expressions here obtained for different diversity techniques are used to find the optimum beamwidth that minimizes the outage performance.

Rate-adaptive FSO links over atmospheric turbulence channels by jointly using repetition coding and silence periods.

In this paper, a new and simple rate-adaptive transmission scheme for free-space optical (FSO) communication systems with intensity modulation and direct detection (IM/DD) over atmospheric turbulence channels is analyzed. This scheme is based on the joint use of repetition coding and variable silence periods, exploiting the potential time-diversity order (TDO) available in the turbulent channel as well as allowing the increase of the peak-to-average optical power ratio (PAOPR). Here, repetition coding is firstly used in order to accommodate the transmission rate to the channel conditions until the whole time diversity order available in the turbulent channel by interleaving is exploited. Then, once no more diversity gain is available, the rate reduction can be increased by using variable silence periods in order to increase the PAOPR. Novel closed-form expressions for the average bit-error rate (BER) as well as their corresponding asymptotic expressions are presented when the irradiance of the transmitted optical beam follows negative exponential and gamma-gamma distributions, covering a wide range of atmospheric turbulence conditions. Obtained results show a diversity order as in the corresponding rate-adaptive transmission scheme only based on repetition codes but providing a relevant improvement in coding gain. Simulation results are further demonstrated to confirm the analytical results. Here, not only rectangular pulses are considered but also OOK formats with any pulse shape, corroborating the advantage of using pulses with high PAOPR, such as gaussian or squared hyperbolic secant pulses. We also determine the achievable information rate for the rate-adaptive transmission schemes here analyzed.

Individualización de pacientes con baja visión en el Centro Oftalmológico del Hospital General Docente Dr Juan Bruno Zayas Alfonso / Individualization of low vision patients in Dr Juan Bruno Zayas Alfonso Teaching General Hospital Ophthalmologic Center

Se efectuó un estudio descriptivo y transversal de 73 pacientes con baja visión, que asistieron a la consulta del Centro Oftalmológico del Hospital General Docente Dr Juan Bruno Zayas Alfonso de Santiago de Cuba, desde julio hasta diciembre del 2009, a fin de describir algunas características clínicas y demográficas. La degeneración macular asociada a la edad primó en más de 25,0 por ciento de los integrantes de la casuística, seguida por el glaucoma crónico simple y la miopía degenerativa y, según lugar de procedencia, los pertenecientes al municipio de Santiago de Cuba representaron 73,0 por ciento del total. Se logró rehabilitar a 89,0 por cientode los pacientes examinados y tratados(AU)

A descriptive and cross sectional study of 73 patients with low vision who visited the Ophthalmologic Center at Dr Juan Bruno Zayas Alfonso Teaching General Hospital in Santiago de Cuba was carried out from July to December 2009 in order to describe some clinical and demographic characteristics. Macular degeneration associated with age prevailed in more than the 25,0 per cent of the case material, followed by simple chronic glaucoma and degenerative myopia and, according to origin place, those belonging to Santiago de Cuba municipality represented 73,0 per cent of the total. It was possible to rehabilitate the 89,0 per cent of the examined and treated patients(AU)

Individualización de pacientes con baja visión en el Centro Oftalmológico del Hospital General Docente Dr Juan Bruno Zayas Alfonso / Individualization of low vision patients in Dr Juan Bruno Zayas Alfonso Teaching General Hospital Ophthalmologic Center

Se efectuó un estudio descriptivo y transversal de 73 pacientes con baja visión, que asistieron a la consulta del Centro Oftalmológico del Hospital General Docente Dr Juan Bruno Zayas Alfonso de Santiago de Cuba, desde julio hasta diciembre del 2009, a fin de describir algunas características clínicas y demográficas. La degeneración macular asociada a la edad primó en más de 25,0 por ciento de los integrantes de la casuística, seguida por el glaucoma crónico simple y la miopía degenerativa y, según lugar de procedencia, los pertenecientes al municipio de Santiago de Cuba representaron 73,0 por ciento del total. Se logró rehabilitar a 89,0 por cientode los pacientes examinados y tratados

A descriptive and cross sectional study of 73 patients with low vision who visited the Ophthalmologic Center at Dr Juan Bruno Zayas Alfonso Teaching General Hospital in Santiago de Cuba was carried out from July to December 2009 in order to describe some clinical and demographic characteristics. Macular degeneration associated with age prevailed in more than the 25,0 per cent of the case material, followed by simple chronic glaucoma and degenerative myopia and, according to origin place, those belonging to Santiago de Cuba municipality represented 73,0 per cent of the total. It was possible to rehabilitate the 89,0 per cent of the examined and treated patients

Average capacity of FSO links with transmit laser selection using non-uniform OOK signaling over exponential atmospheric turbulence channels.

A new upper bound on the capacity of power- and bandwidth-constrained optical wireless links using selection transmit diversity over exponential atmospheric turbulence channels with intensity modulation and direct detection is derived when non-uniform on-off keying (OOK) formats are used. In this strong turbulence free-space optical (FSO) scenario, average capacity is investigated subject to an average optical power constraint and not only to an average electrical power constraint when the transmit diversity technique assumed is based on the selection of the optical path with a greater value of irradiance. Simulation results for the mutual information are further demonstrated to confirm the analytical results for different diversity orders.

Space-time trellis coding with transmit laser selection for FSO links over strong atmospheric turbulence channels.

Atmospheric turbulence produces fluctuations in the irradiance of the transmitted optical beam, which is known as atmospheric scintillation, severely degrading the link performance. In this paper, a scheme combining transmit laser selection (TLS) and space-time trellis code (STTC) for multiple-input-single-output (MISO) free-space optical (FSO) communication systems with intensity modulation and direct detection (IM/DD) over strong atmospheric turbulence channels is analyzed. Assuming channel state information at the transmitter and receiver, we propose the transmit diversity technique based on the selection of two out of the available L lasers corresponding to the optical paths with greater values of scintillation to transmit the baseline STTCs designed for two transmit antennas. Based on a pairwise error probability (PEP) analysis, results in terms of bit error rate are presented when the scintillation follows negative exponential and K distributions, which cover a wide range of strong atmospheric turbulence conditions. Obtained results show a diversity order of 2L-1 when L transmit lasers are available and a simple two-state STTC with rate 1 bit/(s .Hz) is used. Simulation results are further demonstrated to confirm the analytical results.

Consideraciones oftalmológicas y genéticas sobre la asociación de retinosis pigmentaria con glaucoma / Genetic and ophthalmologic considerations on the association of retinitis pigmentosa with glaucoma

Se realizó un estudio descriptivo, retrospectivo y longitudinal de 1 119 pacientes con retinosis pigmentaria asociada a glaucoma, atendidos en el Centro Provincial de Retinosis Pigmentaria de Santiago de Cuba desde el 2004 hasta el segundo trimestre del 2005, procedentes de los centros provinciales de retinosis pigmentaria del territorio oriental. Entre las variables analizadas figuraron: edad, sexo, clasificación cubana de la retinosis pigmentaria, tipo de glaucoma, herencia y variantes terapéuticas. Del total de pacientes, en 5,4 porciento se encontró asociación de retinosis pigmentaria con glaucoma, sobre todo en mujeres y en el grupo etario de 41 a 60 años. Los resultados de la investigación revelaron que es muy importante tener en cuenta estas 2 enfermedades que poseen características comunes, provocan gran discapacidad visual y agravan el pronóstico cuando se asocian

A descriptive, retrospective and longitudinal study was conducted in 1 119 patients with retinitis pigmentosa associated with glaucoma, who were attended at the Provincial Center of Retinitis Pigmentosa of Santiago de Cuba from 2004 to the second trimester of 2005 and who came from provincial centers of retinitis pigmentosa of the eastern territory. Some of analyzed variables were age, sex, and Cuban classification of the retinitis pigmentosa, type of glaucoma, inheritance and therapeutic variants. Of the total of patients in 5,4 percent association of retinitis pigmentosa with glaucoma was found, mainly in women and in the group between 41-60 years of age. Results of the investigation revealed that it is very important to take into account both diseases, which have common characteristics, cause a significant visual disability and worsen the prognosis when they are associated