Características clínicas y evolutivas de pacientes rehabilitados con prótesis oculares / Clinical and evolutive characteristics of patients rehabilitated with ocular prosthesis

Introducción: La prótesis ocular es un medio artificial con fines funcional y estético, que posibilita la rehabilitación física, psíquica y social de pacientes con defectos en los ojos. Objetivo: Describir la evolución de los pacientes con prótesis ocular según signos de infección en las cavidades oculares rehabilitadas, factores de riesgos asociados, así como modificaciones en la forma de la cavidad y/o en la prótesis ocular. Métodos: Se realizó un estudio observacional, longitudinal y prospectivo de 74 pacientes aquejados por defectos oculares, que recibieron tratamiento protésico en el período de 2018 a 2019 en la Clínica de Rehabilitación Bucomaxilofacial de Santiago de Cuba, los cuales fueron evaluados a través de una encuesta y un examen clínico en tres momentos durante un año de evolución. Para establecer la asociación entre variables, se emplearon la prueba de la Χ2 de Pearson y la exacta de Fisher de acuerdo con el cumplimiento de supuestos. Resultados: De los 222 exámenes efectuados a las cavidades oculares rehabilitadas, 31 revelaron la presencia de secreciones en 23 pacientes, con recurrencia en 8 de ellos; dicho signo clínico se manifestó de manera similar a la hipercoloración de la conjuntiva en cuanto al momento del hallazgo y al grupo etario afectado, con mayores porcentajes al año de evolución y una incidencia superior en los pacientes de 60 y más años de edad. Asimismo, se constató una asociación estadísticamente significativa de las variables higiene diaria de la cavidad y de la prótesis con la existencia de secreciones, para un intervalo de confianza de 95 %. Conclusiones: Se demostró la ventaja del aseo semanal de la cavidad ocular y de la prótesis en sus portadores, pues con ello se disminuye la frecuencia de los signos inflamatorios e infecciosos de la mucosa, lo que debe observarse con mayor rigurosidad en los ancianos, quienes resultan ser los más afectados.

Introduction: Ocular prosthesis is an artificial means with functional and cosmetic ends that facilitates the physical, psychic and social rehabilitation of patients with eyes defects. Objective: To describe the evolution of patients with ocular prosthesis according to infection signs in the rehabilitated ocular cavities, associated risk factors, as well as modifications in the form of the cavity and/or in the ocular prosthesis Methods: An observational, longitudinal and prospective study of 74 patients suffering from eye defects that received prosthetist treatment from 2018 to 2019 in the oral maxillofacial Rehabilitation Clinic was carried out in Santiago de Cuba, who were evaluated through a survey and a clinical exam in three moments during a year of evolution. To establish the association between variables, the Pearson chi-square and Fisher exact tests were used with the fulfillment of suppositions. Results: Of the 222 exams made to the rehabilitated ocular cavities, 31 revealed the presence of secretions in 23 patients, with recurrence in 8 of them; this clinical sign became evident in a similar way to the hypercoloring of the conjunctiva as for the moment of the finding and the age group affected, with higher percentages at the year of evolution and a higher incidence in the patients of 60 years and over. Also, an association statistically significant of the daily hygiene of the cavity and prosthesis variables with the existence of secretions was verified, for a confidence interval of 95 %. Conclusions: The advantage of the ocular cavity and prosthesis weekly personal cleanliness was demonstrated, because with it the frequency of the inflammatory and infectious signs of the mucous is reduced, what should be strictly observed in elderly, who are the most affected.

Anterior segment optical coherence tomography findings in type I Boston keratoprosthesis / Achados de tomografia de coerência óptica do seguimento anterior em ceratoprótese de Boston tipo I

ABSTRACT Purpose: To report the results of high-resolution anterior segment optical coherence tomography of patients implanted with a type 1 Boston keratoprosthesis (KPro). Methods: The retrospective study cohort included 11 eyes of 11 patients (average age, 58.4 years; range, 34-83 years). All subjects underwent anterior segment optical coherence tomography at a single posteoperative time point. The main outcome measures were retro-backplate and retro-optic membrane formation, thinning and gap formation of the corneal carrier graft (melting), and degree of angle closure. Results: Preoperative diagnoses included chemical burn (55%), failed corneal transplant (36%), and Stevens-Johnson syndrome (9%). The mean postoperative follow-up duration was 38.5 (range, 12-72) months. The most frequent findings of anterior segment optical coherence tomography were retroprosthetic membrane formation (63%, 7/11), thinning of the corneal carrier graft (melting; 55%, 6/11), and a narrow or closed angle (91%, 10/11). Other less common findings were epithelial growth over the optic surface and periprosthetic cyst formation. Retroprosthetic membrane formation was observed in all patients with melting (6/11). Conclusions: Detailed postoperative examination and visualization of subtle changes of keratoprosthesis implanted eyes by slit lamp biomicroscopy are often difficult. Anterior segment optical coherence tomography is a useful, noninvasive, and quantitative imaging technique that provides useful information to postoperatively monitor the anatomic stability of an implanted keratoprosthesis.

RESUMO Objetivos: Reportar os resultados das imagens de pacientes com Ceratoprótese de Boston tipo I (KPro) usando tomografia de coerência óptica de alta resolução do seguimento anterior (AS-OCT). Métodos: Nós realizamos um estudo retrospectivo de pacientes submetidos à KPro. Um total de 11 olhos de 11 pacientes foram incluídos. As imagens de AS-OCT foram realizadas em um único tempo de pós-operatório. Os principais resultados incluem formação de membrana retroprostética atrás do prato posterior e atrás do cilindro ótico, afinamento e lacunas na córnea doadora (melt) e graus de ângulo fechado. Resultados: Os diagnósticos pré-operatórios inclui queimadura química (55%), falência pós transplante de córnea (36%) e síndrome de Stevens Johnson (9%). A idade média foi de 58.4 anos (escala, 34-83 anos). A média de tempo de pós-operatório foi de 38.5 meses (escala, 12-72 meses). Os achados mais frequentes de AS-OCT foram: membrana retroprostética, 63% (7/11); afinamento da córnea doadora (melting), 55% (6/11); angulo estreito ou fechado, 91% (10/11). Outros achados menos comuns foram crescimento epitelial sobre a superfície ótica e cistos periprostéticos. Todos os pacientes com melting (6/11) apresentaram membrana retroprostética. Conclusões: O exame pós-operatório e a visualização detalhada das mudanças em olhos com KPro pela lâmpada de fenda pode ser difícil. AS-OCT é uma técnica de imagem útil, não invasiva e quantitativa que permite o monitoramento da estabilidade anatômica no seguimento de KPro implantadas.

The advantage of topographic prominence-adopted filter for the detection of short-latency spikes of retinal ganglion cells

Electrical stimulation through retinal prosthesis elicits both short and long-latency retinal ganglion cell (RGC) spikes. Because the short-latency RGC spike is usually obscured by electrical stimulus artifact, it is very important to isolate spike from stimulus artifact. Previously, we showed that topographic prominence (TP) discriminator based algorithm is valid and useful for artifact subtraction. In this study, we compared the performance of forward backward (FB) filter only vs. TP-adopted FB filter for artifact subtraction. From the extracted retinae of rd1 mice, we recorded RGC spikes with 8×8 multielectrode array (MEA). The recorded signals were classified into four groups by distances between the stimulation and recording electrodes on MEA (200-400, 400-600, 600-800, 800-1000 µm). Fifty cathodic phase-1(st) biphasic current pulses (duration 500 µs, intensity 5, 10, 20, 30, 40, 50, 60 µA) were applied at every 1 sec. We compared false positive error and false negative error in FB filter and TP-adopted FB filter. By implementing TP-adopted FB filter, short-latency spike can be detected better regarding sensitivity and specificity for detecting spikes regardless of the strength of stimulus and the distance between stimulus and recording electrodes.

Research progress of visual prosthesis / 生理学报

Vision is one of the most important human sensations about the surrounding world. Visual deprivation not only markedly affects the life of blind people, but also gives a heavy burden to their family and the society. A visual prosthesis is an electronic device that helps the blinds to regain visual perception by directly stimulating the visual pathway using the microelectrodes implanted into the body. In recent years, visual prostheses have been developed rapidly and some devices have already become clinically available. In this paper, we reviewed the history of visual prosthesis, introduced different visual prostheses classified according to the location of the implanted stimulating electrodes. Clinical study results as well as the functional status of the currently available visual prosthesis devices were also summarized.

Effect of Stimulus Waveform of Biphasic Current Pulse on Retinal Ganglion Cell Responses in Retinal Degeneration (rd1) mice

A retinal prosthesis is being developed for the restoration of vision in patients with retinitis pigmentosa (RP) and age-related macular degeneration (AMD). Determining optimal electrical stimulation parameters for the prosthesis is one of the most important elements for the development of a viable retinal prosthesis. Here, we investigated the effects of different charge-balanced biphasic pulses with regard to their effectiveness in evoking retinal ganglion cell (RGC) responses. Retinal degeneration (rd1) mice were used (n=17). From the ex-vivo retinal preparation, retinal patches were placed ganglion cell layer down onto an 8x8 multielectrode array (MEA) and RGC responses were recorded while applying electrical stimuli. For asymmetric pulses, 1st phase of the pulse is the same with symmetric pulse but the amplitude of 2nd phase of the pulse is less than 10 microA and charge balanced condition is satisfied by lengthening the duration of the pulse. For intensities (or duration) modulation, duration (or amplitude) of the pulse was fixed to 500 micros (30 microA), changing the intensities (or duration) from 2 to 60 microA (60 to 1000 micros). RGCs were classified as response-positive when PSTH showed multiple (3~4) peaks within 400 ms post stimulus and the number of spikes was at least 30% more than that for the immediate pre-stimulus 400 ms period. RGC responses were well modulated both with anodic and cathodic phase-1st biphasic pulses. Cathodic phase-1st pulses produced significantly better modulation of RGC activity than anodic phase-1st pulses regardless of symmetry of the pulse.

Cavidades anoftálmicas atípicas en el Instituto Cubano de Oftalmología "Ramón Pando Ferrer" / Atypical anophthalmic cavities observed in patients seen at "Ramón Pando Ferrer" Cuban Institute of Ophthalmology

OBJETIVO: describir el comportamiento de las cavidades anoftàlmicas atípicas. MÉTODOS: se realizó un estudio descriptivo prospectivo en pacientes con cavidades anoftálmicas atípicas atendidos en la consulta de Cirugía Plástica Ocular, en el período de enero de 2009 a julio de 2010. Se analizaron diferentes variables como sexo, edad, alteraciones de la cavidad y tratamiento quirúrgico. RESULTADOS: del total de los pacientes vistos en la consulta, 57 % pertenecían al sexo masculino. El 43 % se encontraba entre los 30 y 49 años. El 90,2 % presentó alteraciones conjuntivales, y la de mayor representatividad fue la retracción del fornix inferior, con el 33,8 %. Dentro de las técnicas quirúrgicas, la reinserción conjuntival del fondo de saco fue la más utilizada y se realizó en el 38 % de los pacientes. CONCLUSIONES: el mayor número de pacientes vistos pertenecen al sexo masculino y al grupo de edades entre 30 y 49 años. Predominaron las alteraciones conjuntivales y dentro de ellas la retracción del fornix inferior. La técnica más utilizada fue la reinserción de la conjuntiva.

OBJECTIVE: to describe the behavior of atypical anophthalmic cavities. METHODS: aprospective and descriptive study was conducted in patients with atypical anophthalmic cavities seen in the ocular plastic surgery service from January 2009 to July 2010. The analyzed variables were sex, age, cavity abnormalities, and surgical treatment. RESULTS: of all patients seen, 57 % were males and 43 % were 30 to 49 years-old. In this group, 90,2 % had conjunctival anomalies, being the inferior fornix retraction the most significant with 33.8 %. Among the surgical techniques used, the conjunctival reinsertion of the fornix was the most performed in 38% of cases. CONCLUSIONS: the highest number of patients was males and the predominant age group was 30-49 years; conjunctival alterations were predominant, mainly the inferior fornix retraction. The most used technique was the reintegration of the conjunctiva.

Finite element analysis of temperature field of retina by electrical stimulation with microelectrode array / 生物医学工程学杂志

We studied the influence of electrode array parameters on temperature distribution to the retina during the use of retinal prosthesis in order to avoid thermal damage to retina caused by long-term electrical stimulation. Based on real epiretinal prosthesis, a three-dimensional model of electrical stimulation for retina with 4 X 4 microelectrode array had been established using the finite element software (COMSOL Multiphysics). The steady-state temperature field of electrical stimulation of the retina was calculated, and the effects of the electrode parameters such as the distance between the electrode contacts, the materials and area of the electrode contact on temperature field were considered. The maximum increase in the retina steady temperature was about 0. 004 degrees C with practical stimulation current. When the distance between the electrode contacts was changed from 130 microm to 520 microm, the temperature was reduced by about 0.006 microC. When the contact radius was doubled from 130 microm to 260 microm, the temperature decrease was about 0.005 degrees C. It was shown that there were little temperature changes in the retina with a 4 x 4 epiretinal microelectrode array, reflecting the safety of electrical stimulation. It was also shown that the maximum temperature in the retina decreased with increasing the distance between the electrode contacts, as well as increasing the area of electrode contact. However, the change of the maximum temperature was very small when the distance became larger than the diameter of electrode contact. There was no significant difference in the effects of temperature increase among the different electrode materials. Rational selection of the distance between the electrode contacts and their area in electrode design can reduce the temperature rise induced by electrical stimulation.

Image processing strategies based on visual attention models under simulated prosthetic vision / 中国医疗器械杂志

Visual prostheses have the potential to restore partial vision for the blinds. The stimulating electrodes generate reproducible phosphenes. Still limited by the low resolution vision used in visual prostheses nowadays, it is important to optimize the image processing strategies in order to deliver better visual information to the patients. This paper presents a review of the current research progress on the image processing strategies based on visual attention models under simulated prosthetic vision and related psychophysics.

The research on high-density flexible microelectrode array of retinal prosthesis based on MEMS technology / 中国医疗器械杂志

The paper proposed a new method to design and fabricate a flexible neural microelectrode arrays (MEA) for retinal prosthesis, the ion-beam technology was introduced to decrease the width of conductive wires and the distances between wires, a high density MEA (120 microelectrodes with a matrix of 10 x 12) was fabricated on a single layer of polymer from this. The MEA was proved to possess a fine electrochemical property. In vitro test, the average impedance of MEA on 1 kHz was 16 k omega +/- 2 k omega and the average phase difference was -85 degrees +/-30 degrees.

Design and optimization of wireless power and data transmission for visual prosthesis / 中国医疗器械杂志

Boosting spatial resolution of visual prostheses is an effective method to improve implant subjects' visual perception. However, power consumption of visual implants greatly rises with the increasing number of implanted electrodes. In respond to this trend, visual prostheses need to develop high-efficiency wireless power transmission and high-speed data transmission. This paper presents a review of current research progress on wireless power and data transmission for visual prostheses, analyzes relative principles and requirement, and introduces design methods of power and data transmission.

Optimum design and performance evaluation of down-sampling algorithm for visual prosthesis imaging processing / 中国医疗器械杂志

According to analyses of the real-time performance of the visual prosthesis image processing system, down-sampling is a key factor which influences the processing speed. Based on these analyses, the algorithm of grid sampled averaging was proposed for down-sampling. Then the effect of grid parameters on the result and algorithm complexity was evaluated by using the regional-averaging algorithm as a reference. Our research shows that the grid-averaging algorithm could reduce the computation burden by 90% or more, with no significant difference from the regional-averaging algorithm.

Research on and design of visual prosthesis based on visual information processing / 生物医学工程学杂志

Induced by a variety of retinopathy, visual loss has become the most serious form of disability, which influences the quality of human life. With the rapid development and crossing among the information science, microelectronics, material science and biomedical disciplines, the visual prosthesis makes reparation possible for the visual blindness caused by retinitis pigmentosa, age-related macular degeneration, and other eye, retina, optic nerve and visual cortex lesions. With technology innovation, the prosthesis design, manufacturing and surgical technique are no longer the biggest obstacles to the future development of the visual prosthesis, but how to construct effective transmission of information between the brain and the prosthesis. However, due to the complex structure of the human visual system, the visual prosthesis manufacturing and visual information signal mapping are facing some difficulties. Thus, we can only study the representation strategy of image information and micro-electrode array stimulation basing on limited pixels of simulated prosthesis visual information. By studying the visual information processing of the visual prosthesis, we propose a visual prosthesis design which is based on biological, mechanical, and electronic integration.

Finite element analysis of electric field of extracellular stimulation of optic nerve with a spiral cuff electrode / 生物医学工程学杂志

In order to study the underlying electrode-nerve functional mechanism, optimize the electrode design and guide the prosthesis application, we applied finite element method to analyze the spatial distribution of electric field generated by optic nerve electrical stimulation with spiral cuff electrode. A macroscopic cylindrical model of optic nerve was elaborated, taking into account of electrode contact configurations and possible variations of the thickness of cerebrospinal fluid (CSF). By building an appropriate mesh on this model and under some boundary conditions, the finite element method was applied to compute the 3D electric field generated by the electrode with finite element software COMSOL Multiphysics. The stimulation results indicated that, under the same conditions of stimulation, the longitudinal tripolar electrode structure could generate larger current density than that of biopolar electrode structure (located in the opposite of nerve trunk). However biopolar electrode structure requirs less leads, and is more easily implanted. By means of parametric sweep, the results suggest that, with the increase of the CSF thickness and a higher conductivity of CSF than those of other tissues, the distribution of electric field generated by electrodes is extended but scattered, and the diffuse current distribution makes nerve stimulation less effective.

Image processing system of visual prostheses based on digital signal processor DM642 / 中国医疗器械杂志

This paper employed a DSP platform to create the real-time and portable image processing system, and introduced a series of commonly used algorithms for visual prostheses. The results of performance evaluation revealed that this platform could afford image processing algorithms to be executed in real time.

Design of power and data telemetry system utilizing Class-E amplifier for visual prosthesis / 中国医疗器械杂志

A wireless transmission system for visual prosthesis is introduced. Power and data are transmitted through inductive link between only one pair of coils, in order to reduce the size of the device. The transmitter is based on Class-E power amplifier due to its high efficiency, and a modulation circuit is added to control the dc supply of the Class-E amplifier to achieve ASK modulation of data with modulation depth of 25%. In addition, an experimental system is implemented, and test shows that it sufficiently supports a 16-channel micro-stimulator on power delivery and data transfer rate.

Comparison of Retinal Ganglion Cell Responses to Different Voltage Stimulation Parameters in Normal and rd1 Mouse Retina / 의학물리

Retinal prostheses are being developed to restore vision for the blind with retinal diseases such as retinitis pigmentosa (RP) or age-related macular degeneration (AMD). Since retinal prostheses depend upon electrical stimulation to control neural activity, optimal stimulation parameters for successful encoding of visual information are one of the most important requirements to enable visual perception. Therefore, in this paper, we focused on retinal ganglion cell (RGC) responses to different voltage stimulation parameters and compared threshold charge densities in normal and rd1 mice. For this purpose, we used in vitro preparation for the retina of normal and rd1 mice on micro-electrode arrays. When the neural network of rd1 mouse retinas is stimulated with voltage-controlled pulses, RGCs in degenerated retina also respond to voltage amplitude or voltage duration modulation as well in wild-type RGCs. But the temporal pattern of RGCs response is very different; in wild-type RGCs, single peak within 100 ms appears while in RGCs in degenerated retina multiple peaks (~4 peaks) with ~10 Hz rhythm within 400 ms appear. The thresholds for electrical activation of RGCs are overall more elevated in rd1 mouse retinas compared to wild-type mouse retinas: The thresholds for activation of RGCs in rd1 mouse retinas were on average two times higher (70.50~99.87micronC/cm2 vs. 37.23~61.65micronC/cm2) in the experiment of voltage amplitude modulation and five times higher (120.5~170.6micronC/cm2 vs. 22.69~37.57micronC/cm2) in the experiment of voltage duration modulation than those in wild-type mouse retinas. This is compatible with the findings from human studies that the currents required for evoking visual percepts in RP patients is much higher than those needed in healthy individuals. These results will be used as a guideline for optimal stimulation parameters for upcoming Korean-type retinal prosthesis.

The research progress on microelectrode array (MEA) of retinal prosthesis / 中国医疗器械杂志

This review paper presents the current research progress, challenges and future development on microelectrode array of retinal prosthesis, including epi-retinal and sub-retinal implants.

Electrically-evoked Neural Activities of rd1 Mice Retinal Ganglion Cells by Repetitive Pulse Stimulation

For successful visual perception by visual prosthesis using electrical stimulation, it is essential to develop an effective stimulation strategy based on understanding of retinal ganglion cell (RGC) responses to electrical stimulation. We studied RGC responses to repetitive electrical stimulation pulses to develop a stimulation strategy using stimulation pulse frequency modulation. Retinal patches of photoreceptor-degenerated retinas from rd1 mice were attached to a planar multi-electrode array (MEA) and RGC spike trains responding to electrical stimulation pulse trains with various pulse frequencies were observed. RGC responses were strongly dependent on inter-pulse interval when it was varied from 500 to 10 ms. Although the evoked spikes were suppressed with increasing pulse rate, the number of evoked spikes were >60% of the maximal responses when the inter-pulse intervals exceeded 100 ms. Based on this, we investigated the modulation of evoked RGC firing rates while increasing the pulse frequency from 1 to 10 pulses per second (or Hz) to deduce the optimal pulse frequency range for modulation of RGC response strength. RGC response strength monotonically and linearly increased within the stimulation frequency of 1~9 Hz. The results suggest that the evoked neural activities of RGCs in degenerated retina can be reliably controlled by pulse frequency modulation, and may be used as a stimulation strategy for visual neural prosthesis.

A discussion about key issues in retinal prosthesis / 生物医学工程学杂志

Retinitis pigmentosa (RP) and age-related macular degeneration (AMD) are two predominant causes of visual deterioration. Retinal prosthesis embeds a micro-electric chip or a micro-photoelectric diode array in the sub-retina or epi-retina, which is used to stimulate the remainder of inner retina, so as to restore some degree of sight. Retinal prosthesis has attracted most attention in the field of artificial visual function recovery, and along with deep-going research, many issues need to be resolved. In this paper, the theory of retinal prosthesis and the status quo of research in many countries are introduced, the key issues which influence the application of the retinal prosthesis are discussed in detail, and some notions and advices are presented.

The development and challenge of vision prosthesis / 中国医疗器械杂志

This paper introduces the current development and challenges of vision prosthesis.