Автор работы: Пользователь скрыл имя, 15 Апреля 2012 в 12:05, реферат
Цель работы: Отыскать проекты, занимающиеся восстановлением зрения слепых людей, при помощи технологий искусственного зрения, а также ознакомиться с текущим прогрессом этих проектов.
Изучить принцип работы зрительного анализатора человека.
Ознакомиться с различными заболеваниями зрительного анализатора, и причинами их возникновений.
Поиск проектов занимающихся разработкой искусственного зрения.
Изучение текущего прогресса этих проектов, ознакомление со статистическими данными и планами исследований.
2.2.2 Три тестируемых модели
Model 1 (Argus™ I)
The Model 1 device [developed by Second Sight™ Medical Products, Inc. (SSMP)] was implanted in six blind patients between 2002 and 2004, whose ages ranged from 56 to 77 at time of implant and all of whom have retinitis pigmentosa. The device consists of a 16-electrode array in a one-inch package that allows the implanted electronics to wirelessly communicate with a camera mounted on a pair of glasses.(Рис. 17) It is powered by a battery pack worn on a belt. This implant enables patients to detect when lights are on or off, describe an object’s motion, count individual items, and locate objects in their environment. To evaluate the long-term effects of the retinal implant, five devices have been approved for home use.
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Рисунок 17. Изображение модели Argus™ I |
Model 2 (Argus™ II)
The smaller, more compact Model 2 retinal prosthesis (developed by SSMP with DOE contributions) is currently undergoing clinical trials to evaluate its safety and utility. This model is much smaller, contains 60 electrodes, and surgical implant time has been reduced from the 6 hours required for Model 1 to 2 hours.
Model 3
The Model 3 device, which will have more than 200 electrodes, has undergone extensive design and fabrication studies at the DOE national laboratories and is ready for preclinical testing. The new design uses more advanced materials than the two previous models and has a highly compact array. This array is four times more densely packed with metal contact electrodes and required wiring connecting to a microelectronic stimulator. Simulations and calculations indicated that the 200+ electrode device should provide improved vision for patients.
2.2.3 Принцип работы
Normal vision begins when light enters and moves through the eye to strike specialized photoreceptor (light-receiving) cells in the retina called rods and cones. These cells convert light signals to electric impulses that are sent to the optic nerve and the brain. Retinal diseases like age-related macular degeneration and retinitis pigmentosa destroy vision by annihilating these cells.
With the artificial retina device, a miniature camera mounted in eyeglasses captures images and wirelessly sends the information to a microprocessor (worn on a belt) that converts the data to an electronic signal and transmits it to a receiver on the eye. The receiver sends the signals through a tiny, thin cable to the microelectrode array, stimulating it to emit pulses.(Рис. 18)
Рисунок 18. Принцип работы Artificial Retina.
The artificial retina device thus bypasses defunct photoreceptor cells and transmits electrical signals directly to the retina’s remaining viable cells. The pulses travel to the optic nerve and, ultimately, to the brain, which perceives patterns of light and dark spots corresponding to the electrodes stimulated. Patients learn to interpret these visual patterns.
2.2.4 Технологические трудности в конструировании имплантата
Researchers face numerous challenges in developing retinal prosthetic devices that are effective, safe, and durable enough to last for the lifetime of the individual.
The retinal device bypasses the eye's lost light-gathering function of the rods and cones with a video camera. The information captured by the camera is used to electrically stimulate the part of the retina not destroyed by disease. Stimulation is done with a thin, flexible metal electrode array that has been patterned on soft plastic material similar to that of a contact lens.
The device must be biocompatible with delicate eye tissue, yet tough enough to withstand the corrosive effect of the salty environment. It should remain stably tacked to the retinal macula and not overly compress or pull at the tissue--the resilience of which can be compared to that of a wet Kleenex®. The apparatus also needs to be powered at a high enough level to stimulate the electrodes, yet not generate enough heat to damage the remaining functional retinal cells.(Рис. 19)
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Рисунок 19. Artificial retina. |
Moreover, just as the resolution of graphic images on a computer screen improves with greater pixel density, researchers assume that increased electrode densities will translate into higher-resolution images for patients. However, the area of the retina targeted for electrical stimulation is less than 5 mm by 5 mm. Consequently, as the number of electrodes increases, their size and spacing must decrease. (Рис. 20)
Furthermore, image processing needs to be performed in real time so there is no delay in interpreting an object in view. Development of effective surgical approaches is also critically important to ensure a successful implant (see sidebar, Ensuring Surgical Reproducibility, below).
In other words, engineering a retinal prosthesis is somewhat analogous to constructing a miniature iPod® on a foldable contact lens that works in seawater.
Рисунок 20. Увеличение разрешающей способности
As the DOE Artificial Retina Project moves forward, prospects for additional progress include developing a device with 1000 or more electrodes that can be scaled up using the knowledge gained in creating the 200+ model.(Рис. 21) Various advances and spinoffs from this work already are beginning to pay off in other biomedical applications as well as in a wide range of hybrid surveillance systems, including environmental sensors, and for plant and bacteria
Рисунок 21. Готовый массив на 200 электродов
Заключение
Ознакомившись с достижениями науки в сфере искусственного зрения, придём в выводу, что безусловно прогресс уже есть и причём немалый. Для восстановления зрения на сетчатку глаза вживляются уже более 100 электродов, что дают неплохое для слепого человека зрение, позволяющего обходить предметы и ориентироваться преград. Логично стремление ученых и вклад средств инвесторов в увеличение числа электродов, для более высокого разрешения изображения. Следует отметить, что немалые ресурсы вкладывают государства, в которых ведутся разработки. За этими технологиями определенно есть будущее. Причем радует то, что это явно ближайшее будущее. Уверен, что к концу второго десятилетия 21 века чип из 1000-2000 электродов будет свободно вживляться на сетчатки глаз слепых людей на уровне хирургической операции.
Список используемой литературы