Restoring Visual Acuity in Dynamic Conditions with a Vestibular Implant.

Vestibular implants are devices designed to rehabilitate patients with a bilateral vestibular loss (BVL). These patients lack a properly functioning vestibulo-ocular reflex (VOR), which impairs gaze stabilization abilities and results in an abnormal loss of visual acuity (VA) in dynamic situations (i.e., severely limiting the patient's ability to read signs or recognize faces while walking). We previously demonstrated that the VOR can be artificially restored in a group of BVL patients fitted with a prototype vestibular implant. This study was designed to investigate whether these promising results could be translated to a close-to-reality task, significantly improving VA abilities while walking. Six BVL patients previously implanted with a vestibular implant prototype participated in the experiments. VA was determined using Sloan letters displayed on a computer screen, in four conditions: (1) with the patient standing still without moving (static), (2) while the patient was walking on a treadmill at constant speed with the vestibular implant prototype turned off (systemOFF), (3) while the patient was walking on a treadmill at constant speed with the vestibular implant prototype turned on providing coherent motion information (systemONmotion), and (4) a "placebo" condition where the patient was walking on a treadmill at constant speed with the vestibular implant prototype turned on providing reversed motion information (systemONsham). The analysis (one-way repeated measures analysis of variance) revealed a statistically significant effect of the test condition [F(3, 12) = 30.5, p < 0.001]. Significant decreases in VA were observed with the systemOFF condition when compared to the static condition (Tukey post-hoc p < 0.001). When the vestibular implant was turned on, delivering pertinent motion information (systemONmotion) the VA improved to close to normal values. The improvement disappeared in the placebo condition (systemONsham) and VA-values also dropped significantly in this condition (Tukey post-hoc p < 0.001). These results are a significant step forward in the field, demonstrating for the first time in humans that gaze stabilization abilities can be restored with a vestibular implant prototype. The vestibular implant shows considerable promise of being the first-ever effective therapeutic alternative for patients with a BVL in the near future.

Vestibular Implants: 8 Years of Experience with Electrical Stimulation of the Vestibular Nerve in 11 Patients with Bilateral Vestibular Loss.

BACKGROUND: The concept of the vestibular implant is primarily to artificially restore the vestibular function in patients with a bilateral vestibular loss (BVL) by providing the central nervous system with motion information using electrical stimulation of the vestibular nerve. Our group initiated human trials about 10 years ago. METHODS: Between 2007 and 2013, 11 patients with a BVL received a vestibular implant prototype providing electrodes to stimulate the ampullary branches of the vestibular nerve. Eye movements were recorded and analyzed to assess the effects of the electrical stimulation. Perception induced by electrical stimulation was documented. RESULTS: Smooth, controlled eye movements were obtained in all patients showing that electrical stimulation successfully activated the vestibulo-ocular pathway. However, both the electrical dynamic range and the amplitude of the eye movements were variable from patient to patient. The axis of the response was consistent with the stimulated nerve branch in 17 out of the 24 tested electrodes. Furthermore, in at least 1 case, the elicited eye movements showed characteristics similar to those of compensatory eye movements observed during natural activities such as walking. Finally, diverse percepts were reported upon electrical stimulation (i.e., rotatory sensations, sound, tickling or pressure) with intensity increasing as the stimulation current increased. CONCLUSIONS: These results demonstrate that electrical stimulation is a safe and effective means to activate the vestibular system, even in a heterogeneous patient population with very different etiologies and disease durations. Successful tuning of this information could turn this vestibular implant prototype into a successful artificial balance organ.

Simultaneous development of 2 oral languages by child cochlear implant recipients.

OBJECTIVE: To study the development French as a mainstream language by children with a cochlear implant who belong to non-French speaking families. STUDY DESIGN: Matched pairs comparison of postoperative hearing perception and speech development data of monolingual and bilingual children with cochlear implants. SETTING: University medical center. PATIENTS: Fourteen congenital profoundly deaf children. Seven were exclusively French speaking and seven bilingual (French-Portuguese, Arab, Turkish, or Serbo-Croatian) children. INTERVENTIONS: Cochlear implantation before the age of 5 ½ years. MAIN OUTCOME MEASURES: Subjects were evaluated using standard hearing perception and oral language development tests. RESULTS: Both monolingual and bilingual groups obtained excellent hearing perception results with the cochlear implant. Monolingual children showed oral language development results equivalent to those of normal hearing children of the same age, except for the morpho-syntax test where they were slightly below average. Bilingual children scored below average in all oral language development tests. CONCLUSION: Despite the excellent hearing perception obtained with cochlear implants, the acquisition of a second language at home seems to slow down the development of the French mainstream language. Comparison of our results with those of previous studies indicates that bilingual children require intensive and correct input in both languages. Parents' involvement in rehabilitation efforts also appears as an important factor for successful oral language development.

Artificial balance: restoration of the vestibulo-ocular reflex in humans with a prototype vestibular neuroprosthesis.

The vestibular system plays a crucial role in the multisensory control of balance. When vestibular function is lost, essential tasks such as postural control, gaze stabilization, and spatial orientation are limited and the quality of life of patients is significantly impaired. Currently, there is no effective treatment for bilateral vestibular deficits. Research efforts both in animals and humans during the last decade set a solid background to the concept of using electrical stimulation to restore vestibular function. Still, the potential clinical benefit of a vestibular neuroprosthesis has to be demonstrated to pave the way for a translation into clinical trials. An important parameter for the assessment of vestibular function is the vestibulo-ocular reflex (VOR), the primary mechanism responsible for maintaining the perception of a stable visual environment while moving. Here we show that the VOR can be artificially restored in humans using motion-controlled, amplitude modulated electrical stimulation of the ampullary branches of the vestibular nerve. Three patients received a vestibular neuroprosthesis prototype, consisting of a modified cochlear implant providing vestibular electrodes. Significantly higher VOR responses were observed when the prototype was turned ON. Furthermore, VOR responses increased significantly as the intensity of the stimulation increased, reaching on average 79% of those measured in healthy volunteers in the same experimental conditions. These results constitute a fundamental milestone and allow us to envision for the first time clinically useful rehabilitation of patients with bilateral vestibular loss.

Ethical, anatomical and physiological issues in developing vestibular implants for human use.

Effort towards the development of a vestibular implant for human use are being made. This paper will summarize the first important steps conducted in Geneva towards this ambitious goal. Basically, we have faced three major issues. First, an ethical issue. While it was clear that such development would require the collaboration of human volunteers, it was also clear that stimulation of the vestibular system may produce periods of significant incomfort. We know today how to minimize (and potentially eliminate) this type of incomfort. The second issue was anatomical. The anatomical topology of the vestibular system is complex, and of potentially dangerous access (i.e. facial nerve damage). We choose not to place the electrodes inside the ampullae but close the vestibular nerve branches, to avoid any opening of the inner ear and limit the risk of hearing loss. Work on cadaver heads, confirmed by acute stimulations trials on patients undergoing ear surgery under local anesthesia, demonstrated that it is possible to stimulate selectively both the posterior and lateral ampullary nerves, and elicit the expected vertical and horizontal nystagmic responses. The third issue was physiological. One of the goal of a vestibular implant will be to produce smooth eye movements to stabilize gaze direction when the head is moving. Indeed, after restoring a baseline or "rest" activity in the vestibular pathways with steady-state electrical stimulation, we demonstrated that modulation of this stimulation is producing smooth eye movements. In conclusion, humans can adapt to electrical stimulation of the vestibular system without too much discomfort. Surgical access to the posterior and lateral ampullary nerves have been developed and, electrical stimulation of the vestibular system can be used to artificially elicit smooth eye movements of different speeds and directions, once the system is in adapted state. Therefore, the major prerequisites to develop a prototype vestibular implant for human use are fulfilled.

Temporal properties of visual perception on electrical stimulation of the retina.

PURPOSE: To investigate the elementary temporal properties of electrically evoked percepts in blind patients chronically implanted with an epiretinal prosthesis. METHODS: Nine subjects were presented with isolated stimuli of variable duration and pulse rate. Stimulation amplitude was set to the upper comfortable level and a group of 2 × 2 adjacent electrodes was simultaneously activated. First, subjects were asked to verbally describe their visual perception paying particular attention to the time-course of brightness. Then, in subsequent trials, they described the brightness time dependence using a joystick while auditory feedback of joystick position was provided. RESULTS: All subjects described a bright, well-localized percept at stimulus onset. Only one subject reported such a bright, well-localized visual sensation during an entire 10-second stimulation trial. For the remaining eight subjects, it faded more or less rapidly (in four cases <0.5 second) and was often followed by a percept described as less bright, poorly localized, and having different color. Only initial percepts at stimulation onset seemed bright and localized enough to reconstruct a patterned image. Changing stimulation pulse rate influenced the time course of perception only in some cases but the effect was not systematic. CONCLUSIONS: Percepts differed considerably across subjects, probably because of the considerable variations in the progression and remodeling processes associated with the disease. Appropriate coding of a patterned image under such conditions appears challenging. Further research of the underlying mechanisms of visual perception upon electrical stimulation of the retina is required to optimize stimulation paradigms and to better establish patient selection criteria.

Tinnitus before and 6 months after cochlear implantation.

In this prospective multicenter study, tinnitus loudness and tinnitus-related distress were investigated in 174 cochlear implant (CI) candidates who underwent CI surgery at a Swiss cochlear implant center. All subjects participated in two session, one preoperatively and one 6 months after device activation. In both sessions, tinnitus loudness was assessed using a visual analogue scale and tinnitus distress using a standardized tinnitus questionnaire. The data were compared with unaided pre- and postoperative pure tone thresholds, and postoperative speech reception scores. 71.8% of the subjects reported tinnitus preoperatively. Six months after CI surgery 20.0% of these reported abolition of their tinnitus, 51.2% a subjective improvement, 21.6% no change and 7.2% a deterioration. Of the 49 (28.2%) subjects with no tinnitus preoperatively, 5 developed tinnitus 6 months after CI. These 5 had poorer speech understanding after CI surgery with their device than the group who remained tinnitus free. We found no correlation between tinnitus improvement, age, duration of tinnitus, or change in unaided hearing thresholds between the two sessions.

Reading with a simulated 60-channel implant.

First generation retinal prostheses containing 50-60 electrodes are currently in clinical trials. The purpose of this study was to evaluate the theoretical upper limit (best possible) reading performance attainable with a state-of-the-art 60-channel retinal implant and to find the optimum viewing conditions for the task. Four normal volunteers performed full-page text reading tasks with a low-resolution, 60-pixel viewing window that was stabilized in the central visual field. Two parameters were systematically varied: (1) spatial resolution (image magnification) and (2) the orientation of the rectangular viewing window. Performance was measured in terms of reading accuracy (% of correctly read words) and reading rates (words/min). Maximum reading performances were reached at spatial resolutions between 3.6 and 6 pixels/char. Performance declined outside this range for all subjects. In optimum viewing conditions (4.5 pixels/char), subjects achieved almost perfect reading accuracy and mean reading rates of 26 words/min for the vertical viewing window and of 34 words/min for the horizontal viewing window. These results suggest that, theoretically, some reading abilities can be restored with actual state-of-the-art retinal implant prototypes if "image magnification" is within an "optimum range." Future retinal implants providing higher pixel resolutions, thus allowing for a wider visual span might allow faster reading rates.

Adaptation to steady-state electrical stimulation of the vestibular system in humans.

OBJECTIVES: Efforts are being made toward the development of a vestibular implant. If such a device is to mimic the physiology of the vestibular system, it must first be capable of restoring a baseline or "rest" activity in the vestibular pathways and then modulating it according to the direction and velocity of head movements. The aim of this study was to assess whether a human subject could adapt to continuous electrical stimulation of the vestibular system, and whether it was possible to elicit artificial smooth oscillatory eye movements via modulation of the stimulation. METHODS: One bilaterally deaf patient with bilateral vestibular loss received a custom-modified Med-E1 cochlear implant in which one electrode was implanted in the vicinity of the left posterior ampullary nerve. This electrode was activated with biphasic pulse trains of 400-micros phase duration delivered at a repetition rate of 200 pulses per second. The resulting eye movements were recorded with 2-dimensional binocular video-oculography. RESULTS: Successive "on-off" cycles of continuous electrical stimulation resulted in a progressively shorter duration of the nystagmic response. Once the adapted state was reached upon constant stimulation, amplitude or frequency modulations of electrical stimulation produced smooth oscillatory conjugated eye movements. CONCLUSIONS: Although this is a case study of one patient, the results suggest that humans can adapt to electrical stimulation of the vestibular system without too much discomfort. Once the subject is in the adapted state, the electrical stimulation can be modulated to artificially elicit smooth eye movements. Therefore, the major prerequisites for the feasibility of a vestibular implant for human use are fulfilled.

Eye movements in response to electrical stimulation of the lateral and superior ampullary nerves.

OBJECTIVES: Recently, we demonstrated that it was possible to elicit vertical eye movements in response to electrical stimulation of the posterior ampullary nerve. In order to develop a vestibular implant, a second site of stimulation is required to encode the horizontal movements. METHODS: Three patients with disabling Meniere's disease were included in the study. Before a labyrinthectomy via a standard transcanal approach was performed, their lateral and anterior ampullary nerves were surgically exposed under local anesthesia through a procedure we recently developed. The attic was opened, the incus and malleus head were removed, and a small well was drilled above the horizontal portion of the facial nerve canal to place an electrode. This electrode was used to deliver balanced biphasic trains of electrical pulses. RESULTS: The electrical stimuli elicited mainly horizontal nystagmus without simultaneous stimulation of the facial nerve. CONCLUSIONS: It is possible to stimulate electrically the lateral and superior ampullary nerves without simultaneous stimulation of the facial nerve. Because the nerves run close to each other, electrical stimulation provoked eye movements that were not purely horizontal, but also had some vertical components. Nevertheless, this site can be used to encode horizontal movements, because central adaptation may correct unnatural afferent vestibular cues delivered by a prosthetic sensor. The range of stimulus intensities that produced a response was broad enough for us to envision the possibility of encoding eye movements of various speeds.

Simulations to study spatial extent of stimulation and effect of electrode-tissue gap in subretinal implants.

We present a finite element based simulation and analysis method to describe the spatial extent of stimulation and the effects of electrode-tissue interactions in subretinal prostheses. In particular, we estimate the threshold stimulation current needed to depolarise and evoke action potentials in the ganglion cells to be stimulated at a particular distance from the electrode. This is achieved through the application of a threshold electric field to a spherical neuronal soma model of a retinal ganglion cell under consideration. Threshold stimulation currents and the lateral extent of the stimulation zone were computed for disc microelectrodes in subretinal stimulation mode. Recent evidence indicates a decrease in threshold charge with time following subretinal implantation. Consequently, to explain the variation in threshold stimulation currents, we propose a hypothesis based on an electrode-tissue gap. Threshold stimulation currents and impedances for different electrode-tissue gaps were computed. We validate the hypothesis with our simulation results that the changes in impedance observed with time in vivo can be mainly attributed to the varying distance of the ganglion cells from electrodes due to changes in electrode-tissue gap. Our simulation framework proposes a convenient and practical method applicable for studying different electrode geometries used for retinal stimulation.

Measurement of dynamic visual acuity in patients with vestibular areflexia.

CONCLUSION: The test is simple and sensitive enough to separate normal subjects from patients suffering from a vestibular loss. There was also a good correlation between the objective results and the subjective complaint of oscillopsia. OBJECTIVES: Oscillopsia (i.e. blurred vision while walking) is often reported by patients suffering from vestibular loss. We developed a test to quantify oscillopsia. METHODS: Visual acuity was determined in 16 normal subjects and in 8 patients suffering from a bilateral vestibular loss, at rest and while walking at increasing speed on a treadmill. Snellen optotypes were randomly projected on a screen and the visual acuity was determined with an adaptative staircase algorithm. RESULTS: In normal subjects, the visual acuity did not decrease markedly during walking, but decreased significantly in patients with a vestibular loss.

What can be expected from a late cochlear implantation?

OBJECTIVE: Verify if late cochlear implantation allows pre-lingual deafs to convert from visual to oral communication mode only. METHOD: Thirteen pre-lingual profoundly deaf patients implanted the ages of 8 and 22 years were included in the study. Before cochlear implantation, none of the patients used the oral language. Six patients used cued speech and seven used the sign language to communicate. Evaluations were made with measures of hearing thresholds, phoneme identification, categories of auditory performance and rating of the intelligibility of speech before and after implantation. Changes in principal mode of communication (i.e. oral, cued speech or sign language) were also monitored. RESULTS: The former users of cued speech benefited significantly more from cochlear implantation than the sign language users for phoneme identification and categories of auditory performance, although all had similar hearing thresholds before and after cochlear implantation. After a mean implant use of 4.5 years, four out of six cued speech users converted to exclusive use of the oral language, while only one out of seven former users of the sign language converted to the use of the oral language. DISCUSSION: It is possible for pre-lingual or congenital deafs to convert totally from a visual to an oral communication mode even in case of late cochlear implantation. Previous awareness of the structure of the oral language, even without hearing (e.g. via cued speech) influences positively the outcome of delayed implantations. We recommend the adoption of oral communication with the cued speech code in cases where a late cochlear implantation is envisioned.

Simulation of artificial vision: IV. Visual information required to achieve simple pointing and manipulation tasks.

Retinal prostheses attempt to restore some amount of vision to totally blind patients. Vision evoked this way will be however severely constrained because of several factors (e.g., size of the implanted device, number of stimulating contacts, etc.). We used simulations of artificial vision to study how such restrictions of the amount of visual information provided would affect performance on simple pointing and manipulation tasks. Five normal subjects participated in the study. Two tasks were used: pointing on random targets (LEDs task) and arranging wooden chips according to a given model (CHIPs task). Both tasks had to be completed while the amount of visual information was limited by reducing the resolution (number of pixels) and modifying the size of the effective field of view. All images were projected on a 10 degrees x 7 degrees viewing area, stabilised at a given position on the retina. In central vision, the time required to accomplish the tasks remained systematically slower than with normal vision. Accuracy was close to normal at high image resolutions and decreased at 500 pixels or below, depending on the field of view used. Subjects adapted quite rapidly (in less than 15 sessions) to performing both tasks in eccentric vision (15 degrees in the lower visual field), achieving after adaptation performances close to those observed in central vision. These results demonstrate that, if vision is restricted to a small visual area stabilised on the retina (as would be the case in a retinal prosthesis), the perception of several hundreds of retinotopically arranged phosphenes is still needed to restore accurate but slow performance on pointing and manipulation tasks. Considering that present prototypes afford less than 100 stimulation contacts and that our simulations represent the most favourable visual input conditions that the user might experience, further development is required to achieve optimal rehabilitation prospects.

Partial withdrawal of deeply inserted cochlear electrodes: observations of two patients.

Three patients implanted in our department received the preformed Clarion S-Series cochlear implant with the electrode Positioning System (EPS). The EPS is a device designed to bring the electrode array closer to the modiolus and deeper into the cochlea. Two of these patients still complained because they were perceiving too low pitch sounds, and because of the presence of echoes and poor discrimination after 3 years of implant use and many tuning sessions. We hypothesized that the electrode array was too deeply inserted and could be stimulating overlapping populations of neurons in the low frequency range. The EPS was removed through a transcanal tympanotomy under local anesthesia and the array was pulled 2-3 mm out of the cochlea. The angle of electrode insertion into the cochlea and the patients' performances on consonant identification tests were evaluated before and after the removal surgery and over the long term, 3 years after the surgery. Immediately after the removal surgery the angle of insertion of the electrode array decreased from 720 degrees to 485 degrees in one case and from 675 degrees to 485 degrees in the other. Both patients reported subjective improvements after the removal which were confirmed by tests of performance at the long term by one of the patients. These observations show that (1) the electrode array can be moved without deterioration of performances even several years after being implanted; revision surgery may be beneficial in some cases, (2) neighboring electrodes might stimulate overlapping populations of neurons, inducing a deterioration of performances; for anatomical reasons, this is most likely to occur in the apex of the cochlea and (3) tuning of the external processor should be a customized procedure.

Processes involved in oculomotor adaptation to eccentric reading.

PURPOSE: Adaptation to eccentric viewing in subjects with a central scotoma remains poorly understood. The purpose of this study was to analyze the adaptation stages of oculomotor control to forced eccentric reading in normal subjects. METHODS: Three normal adults (25.7 +/- 3.8 years of age) were trained to read full-page texts using a restricted 10 degrees x 7 degrees viewing window stabilized at 15 degrees eccentricity (lower visual field). Gaze position was recorded throughout the training period (1 hour per day for approximately 6 weeks). RESULTS: In the first sessions, eye movements appeared inappropriate for reading, mainly consisting of reflexive vertical (foveating) saccades. In early adaptation phases, both vertical saccade count and amplitude dramatically decreased. Horizontal saccade frequency increased in the first experimental sessions, then slowly decreased after 7 to 15 sessions. Amplitude of horizontal saccades increased with training. Gradually, accurate line jumps appeared, the proportion of progressive saccades increased, and the proportion of regressive saccades decreased. At the end of the learning process, eye movements mainly consisted of horizontal progressions, line jumps, and a few horizontal regressions. CONCLUSIONS: Two main adaptation phases were distinguished: a "faster" vertical process aimed at suppressing reflexive foveation and a "slower" restructuring of the horizontal eye movement pattern. The vertical phase consisted of a rapid reduction in the number of vertical saccades and a rapid but more progressive adjustment of remaining vertical saccades. The horizontal phase involved the amplitude adjustment of horizontal saccades (mainly progressions) to the text presented and the reduction of regressions required.

Acoustic to electric pitch comparisons in cochlear implant subjects with residual hearing.

The aim of this study was to assess the frequency-position function resulting from electric stimulation of electrodes in cochlear implant subjects with significant residual hearing in their nonimplanted ear. Six cochlear implant users compared the pitch of the auditory sensation produced by stimulation of an intracochlear electrode to the pitch of acoustic pure tones presented to their contralateral nonimplanted ear. Subjects were implanted with different Clarion electrode arrays, designed to lie close to the inner wall of the cochlea. High-resolution radiographs were used to determine the electrode positions in the cochlea. Four out of six subjects presented electrode insertions deeper than 450 degrees . We used a two-interval (one acoustic, one electric), two-alternative forced choice protocol (2I-2AFC), asking the subject to indicate which stimulus sounded the highest in pitch. Pure tones were used as acoustic stimuli. Electric stimuli consisted of trains of biphasic pulses presented at relatively high rates [higher than 700 pulses per second (pps)]. First, all electric stimuli were balanced in loudness across electrodes. Second, acoustic pure tones, chosen to approximate roughly the pitch sensation produced by each electrode, were balanced in loudness to electric stimuli. When electrode insertion lengths were used to describe electrode positions, the pitch sensations produced by electric stimulation were found to be more than two octaves lower than predicted by Greenwood's frequency-position function. When insertion angles were used to describe electrode positions, the pitch sensations were found about one octave lower than the frequency-position function of a normal ear. The difference found between both descriptions is because of the fact that these electrode arrays were designed to lie close to the modiolus. As a consequence, the site of excitation produced at the level of the organ of Corti corresponds to a longer length than the electrode insertion length, which is used in Greenwood's function. Although exact measurements of the round window position as well as the length of the cochlea could explain the remaining one octave difference found when insertion angles were used, physiological phenomena (e.g., stimulation of the spiral ganglion cells) could also create this difference. From these data, analysis filters could be determined in sound coding strategies to match the pitch percepts elicited by electrode stimulation. This step might be of main importance for music perception and for the fitting of bilateral cochlear implants.

Simulation of artificial vision, III: do the spatial or temporal characteristics of stimulus pixelization really matter?

PURPOSE: In preceding studies, simulations of artificial vision were used to determine the basic parameters for visual prostheses to restore useful reading abilities. These simulations were based on a simplified procedure to reduce stimuli information content by preprocessing images with a block-averaging algorithm (square pixelization). In the present study, how such a simplified algorithm affects reading performance was examined. METHODS: Five to six volunteers with normal vision were asked to read full pages of text with a 10 degrees x 7 degrees viewing window stabilized in central vision. In a first experiment, reading performance with off-line and real-time square pixelizations was compared at different resolutions. In a second experiment, off-line square pixelization was compared with off-line Gaussian pixelization with various degrees of overlap. In a third experiment, real-time square pixelization was compared with real-time Gaussian pixelization. RESULTS: Results from the first experiment showed that real-time square pixelization required approximately 30% less information (pixels) than its off-line counterpart. Results from the second experiment, using off-line processing, revealed a restricted range of Gaussian widths for which performances were equivalent or significantly better than that obtained with square pixelization. The third experiment demonstrated, however, that reading performances were similar in both real-time pixelization conditions. CONCLUSIONS: This study reveals that real-time stimulus pixelization favors reading performance. Performance gains were moderate, however, and did not allow for a significant (e.g., twofold) reduction of the minimum resolution (400-500 pixels) needed to achieve useful reading abilities.

Measurements of electrode position inside the cochlea for different cochlear implant systems.

CONCLUSIONS: This study demonstrates that the exact location of an electrode inside the cochlea needs to be assessed using two complementary measures, namely the length and angle of insertion, both of which are mandatory if one wants to prevent erroneous outcomes. Knowledge of the contact position may become very useful when tuning a cochlear implant processor in a patient with contralateral residual hearing, or in cases of binaural implants. OBJECTIVE: Multichannel cochlear implants restore useful hearing to deaf patients. However, several types of intracochlear electrodes are presently available, each featuring a specific technology or design. The aim of this study was to determine precisely the intracochlear position of the contacts for different electrode arrays. MATERIAL AND METHODS: Electrode array insertions were estimated using special radiographs. A total of 26 cochlear implantations were included in the study: 6 Ineraid; 5 Clarion HiFocus I; 11 Clarion HiFocus II; and 4 Med-El Combi40+. In each case, a measurable reference or marker ring placed close to the round window (within 2 mm) could be identified. Insertion lengths and angles were measured and then plotted on a graphl based on 3D reconstructions. RESULTS: Both Clarion HiFocus I and II electrode arrays were found to be placed close to the inner wall of the cochlea. Ineraid and Med-El Combi40+ electrode arrays were both placed close to the organ of Corti, the Med-El Combi40+ arrays demonstrating the deepest insertions overall. In spite of marked differences in the positions of the contacts, we did not find any correlation with speech perception performance for the different types of implants studied.