Morphometric Analysis of the Macula in Eyes With Disciform Age-Related Macular Degeneration

Kim, S. Y.; Sadda, Srini Vas R.; Pearlman, Joel; Humayun, Mark S.; Juan, Eugene de; Melia, B. Michele; Green, W. R.

doi:10.1097/00006982-200208000-00012

Cited by 153 publications

(93 citation statements)

References 20 publications

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“…(3) Despite a near-total loss of the macular photoreceptors in the outer nuclear layer and even in the final stage of RP or ARMD, there are reports that the inner nuclear and retinal ganglion layers are partially preserved, retaining nearly 30 to 80% of the neurons found in a healthy eye. (4)(5)(6) Also, these results support that the approach of restoring vision by electrical stimulation of the surviving neurons using neural prosthetic devices may be viable as a vision-recovery methodology in retinal degenerative diseases. (7,8) The electrical stimulation typically involves a biphasic current waveform for the purpose of driving a constant current through the tissue followed by the reverse current to maintain charge balance.…”

Section: Introductionsupporting

confidence: 53%

Fabrication and Evaluation of Silicon Nanowire Photodetectors on Flexible Substrate for Retinal Prosthetic System

Lee

Jung

Park

et al. 2012

Sensors and Materials

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Retinal degenerative diseases result in a progressive degeneration of photoreceptors in the retina and eventually lead to complete blindness. In this study, we develop a novel silicon nanowire photodetector on a flexible substrate to replace the function of photoreceptors on the retina and restore vision for the blind. An extremely high surfaceto-volume-ratio characteristic of the nanowire enables the development of highly sensitive photonic sensors. Therefore, a nanowire-based photodetector can be used as a stand-alone retinal stimulation system without an external camera. The fabricated silicon nanowire photodetector is measured to have an average photoresponsivity of 1×10 4 A/W in a wide range of light intensities and wavelengths. Also, the optical characteristics of the silicon nanowire photodetector are well maintained on a flexible substrate, which is verified by comparing the photosensitivity before and after the substrate transfer from a rigid form to a flexible form. To evaluate the mechanical durability of the flexible silicon nanowire photodetector, mechanical bending tests are performed. The optical performance of the flexible photodetector is well preserved during bending for 200 times. The presented performance evaluation results show that the proposed nanowire-based photodetector can be used for the implementation of the retinal prosthetic system. The results of this proposed novel method can point the way to a revolutionary break-through in artificial retina research.206

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Section: Introductionsupporting

confidence: 53%

Fabrication and Evaluation of Silicon Nanowire Photodetectors on Flexible Substrate for Retinal Prosthetic System

Lee

Jung

Park

et al. 2012

Sensors and Materials

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“…Taken together, these diseases are the leading causes of retinal blindness. While there is significant degeneration of the outer retina and anatomical remodeling of the remnant inner retina [4], postmortem anatomical studies of patients with RP [5], [6] and AMD [7] have found that some inner retinal cells (78.4%) and ganglion cells (29.7%) can survive. This has led many research groups to investigate extracellular electrical stimulation as a means of restoring visual function to patients by implanting an epiretinal [8] or subretinal [9]- [11] microelectrode array.…”

Section: Introductionmentioning

confidence: 99%

AnIn VitroModel of a Retinal Prosthesis

Ahuja

Behrend

Kuroda

et al. 2008

IEEE Trans. Biomed. Eng.

103

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Epiretinal prostheses are being developed to bypass a degenerated photoreceptor layer and excite surviving ganglion and inner retinal cells. We used custom microfabricated multielectrode arrays with 200-μm-diameter stimulating electrodes and 10-μm-diameter recording electrodes to stimulate and record neural responses in isolated tiger salamander retina. Pharmacological agents were used to isolate direct excitation of ganglion cells from excitation of other inner retinal cells. Strength-duration data suggest that, if amplitude will be used for the coding of brightness or gray level in retinal prostheses, shorter pulses (200 μs) will allow for a smaller region in the area of the electrode to be excited over a larger dynamic range compared with longer pulses (1 ms). Both electrophysiological results and electrostatic finite-element modeling show that electrodeelectrode interactions can lead to increased thresholds for sites half way between simultaneously stimulated electrodes (29.4 ± 6.6 nC) compared with monopolar stimulation (13.3 ± 1.7 nC, p < 0.02). Presynaptic stimulation of the same gan-glion cell with both 200-and 10-μm-diameter electrodes yielded threshold charge densities of 12 ± 6 and 7.66 1.30 nC/cm 2 , respectively, while the required charge was 12.5 ± 6.2 and 19 ± 3.3 nC.

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“…[40][41][42] Similar results have been found in patients with AMD. 44 Given that there is limited transsynaptic neuronal degeneration, it does seem feasible to stimulate the remaining retinal neurons.…”

Section: Retinal Prosthesesmentioning

confidence: 99%

Intraocular retinal prosthesis

Weiland

Humayun

2006

IEEE Eng. Med. Biol. Mag.

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Purpose: An electronic implant that can bypass the damaged photoreceptors and electrically stimulate the remaining retinal neurons to restore useful vision has been proposed. A number of key questions remain to make this approach feasible. The goal of this thesis is to address the following 2 specific null hypotheses: (1) Stimulus parameters make no difference in the electrically elicited retinal responses. (2) Just as we have millions of photoreceptors, so it will take a device that can generate millions of pixels/light points to create useful vision.Methods: For electrophysiologic experiments, 2 different setups were used. In the first setup, charge-balanced pulses were delivered to the retinal surface via electrodes inserted through an open sky approach in normal or blind retinal degenerate (rd) mice. In the second setup, the rabbit retina was removed under red light conditions from an enucleated eye and then maintained in a chamber while being superfused with oxygenated, heated Ames media. In both setups, stimulating electrodes and recording electrodes were positioned on the retinal surface to evaluate the effect of varying stimulation parameters on the orthodromic retinal responses (ie, recording electrode placed between stimulating electrodes and optic nerve head).For psychophysical experiments, visual images were divided into pixels of light that could be projected in a pattern on the retina in up to 8 sighted volunteers. Subjects were asked to perform various tasks ranging from reading and face recognition to various activities of daily living.Results: Electrophysiologic experiments: In a normal mouse, a single cycle of a 1-kHz sine wave was significantly more efficient than a 1-kHz square wave (P <.05), but no such difference was noted in either of the 8-or 16-week-old rd mouse groups (8-week-old, P =.426; 16-week-old, P =.078). Charge threshold was significantly higher in 16-week-old rd mouse versus both 8-week-old rd and normal mouse for every stimulus duration (P <.05). In all groups, short duration pulses (40, 80, and 120 s) were more efficient in terms of total charge (the product of pulse amplitude and pulse duration) than longer (500 and 1,000 s) pulses (P <.05). In all groups, applying a pulse train did not lead to more efficient charge usage (P <.05).Psychophysical experiments: In high-contrast tests, facial recognition rates of over 75% were achieved for all subjects with dot sizes of up to 31.5 minutes of arc when using a 25 x 25 grid with 4.5 arc minute gaps, a 30% dropout rate, and 6 gray levels. Even with a 4 x 4 array of pixels, some subjects were able to accurately describe 2 of the objects. Subjects who were able to read the 4-pixel letter height sentences (on the 6 x 10 and 16 x 16 array) seemed to have a good scanning technique. Scanning at the proper velocity tends to bring out more contrast in the lettering. The reading speed for the 72-point font is a bit slower than for the next smaller font. This may be due to the limited number of letters (3) visible in the window with t...

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Morphometric Analysis of the Macula in Eyes With Disciform Age-Related Macular Degeneration

Cited by 153 publications

References 20 publications

Fabrication and Evaluation of Silicon Nanowire Photodetectors on Flexible Substrate for Retinal Prosthetic System

Fabrication and Evaluation of Silicon Nanowire Photodetectors on Flexible Substrate for Retinal Prosthetic System

AnIn VitroModel of a Retinal Prosthesis

Intraocular retinal prosthesis

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