Duane R. Geruschat

Long-Term Results from an Epiretinal Prosthesis to Restore Sight to the Blind

PURPOSE Retinitis pigmentosa (RP) is a group of inherited retinal degenerations leading to blindness due to photoreceptor loss. Retinitis pigmentosa is a rare disease, affecting only approximately 100 000 people in the United States. There is no cure and no approved medical therapy to slow or reverse RP. The purpose of this clinical trial was to evaluate the safety, reliability, and benefit of the Argus II Retinal Prosthesis System (Second Sight Medical Products, Inc, Sylmar, CA) in restoring some visual function to subjects completely blind from RP. We report clinical trial results at 1 and 3 years after implantation. DESIGN The study is a multicenter, single-arm, prospective clinical trial. PARTICIPANTS There were 30 subjects in 10 centers in the United States and Europe. Subjects served as their own controls, that is, implanted eye versus fellow eye, and system on versus system off (native residual vision). METHODS The Argus II System was implanted on and in a single eye (typically the worse-seeing eye) of blind subjects. Subjects wore glasses mounted with a small camera and a video processor that converted images into stimulation patterns sent to the electrode array on the retina. MAIN OUTCOME MEASURES The primary outcome measures were safety (the number, seriousness, and relatedness of adverse events) and visual function, as measured by 3 computer-based, objective tests. RESULTS A total of 29 of 30 subjects had functioning Argus II Systems implants 3 years after implantation. Eleven subjects experienced a total of 23 serious device- or surgery-related adverse events. All were treated with standard ophthalmic care. As a group, subjects performed significantly better with the system on than off on all visual function tests and functional vision assessments. CONCLUSIONS The 3-year results of the Argus II trial support the long-term safety profile and benefit of the Argus II System for patients blind from RP. Earlier results from this trial were used to gain approval of the Argus II by the Food and Drug Administration and a CE mark in Europe. The Argus II System is the first and only retinal implant to have both approvals.

Direction of gaze while walking a simple route : Persons with normal vision and persons with retinitis pigmentosa

Purpose. The purpose of this study was to determine whether persons with advanced vision impairment, when walking an unfamiliar route, visually sample the environment in a different manner than do persons with normal vision. Methods. Direction of gaze was measured in six persons with retinitis pigmentosa (RP) and in three persons with normal vision as they walked an unfamiliar, obstacle-free route while viewing the environment in a head-mounted display. Results. Persons with RP fixated over a larger area in the environment and at different features than did persons with normal vision. Persons with normal vision directed their gaze primarily ahead or at the goal, whereas persons with RP directed their gaze at objects on the walls, downward, or at the layout (i.e., edge-lines or boundaries between walls). The results also showed a significant negative correlation between the horizontal visual field extent of the RP subjects and the proportion of downward-directed fixations. Conclusions. Persons with advanced vision impairment as a result of RP visually sample the environment in a manner different from persons with normal vision.

Mental effort required for walking : Effects of retinitis pigmentosa

Purpose. To determine whether retinitis pigmentosa (RP) increases the mental effort required for walking. Methods. A dual‐task methodology was used; walking speed and reaction time (RT) to randomly emitted tones were measured in 13 persons with RP and 29 persons with normal vision. Measures of RT were used to estimate the mental effort required for walking. In a second experiment, 15 persons with RP and 17 persons with normal vision navigated a “simple” and a “complex” route. Results. The RP subjects had longer RT compared with the normal‐vision subjects when walking the complex but not the simple route. Normalized to each persons baseline, RT while walking the complex route was significantly correlated with log contrast sensitivity (r = —0.63) and log retinal area (r = —0.64) in the RP group. The amount of mental effort required for walking was shown to also depend on familiarity with the route. Conclusions. Route complexity is critical in determining whether walking requires more mental effort for persons with RP than for persons with normal vision. The magnitude of mental effort required for mobility covaries with the visual impairment measures which correlate with mobility performance in RP. (Optom Vis Sci 1998;75:879–886)

Gaze Behavior while Crossing Complex Intersections

Background. Crossing the street is a complex task that involves gathering, processing, and acting on information that is time dependent. The gaze behavior of subjects has been previously studied on increasingly complex and dynamic tasks such as making tea, walking indoors, and driving. The purpose of this study was to assess how normally sighted people use their vision to cross a street safely. Specifically, we identified the environmental features people look at when crossing two types of intersections. Method. We measured the eye movements and head directions of 12 normally sighted people as they approached, evaluated, and crossed a light-controlled “plus” intersection and a roundabout. The primary measures were percentage of fixations and head direction. Results. Crossing the street can be divided into three phases, walking to the curb, standing at the curb, and crossing the street. We found that while moving, subjects fixated primarily on crossing elements and when standing at the curb, they fixated primarily on vehicles. At the plus intersection, fixation behavior corresponded with crossing strategy; the subjects who crossed early fixated on cars, and the subjects who waited for the light to change fixated on traffic controls. At the roundabout, all subjects determined an appropriate time to cross from vehicular traffic flow by directing the majority of their fixations on cars. When moving, the head position of subjects was predominately centered. Subjects also made head turns in both directions before crossing and directed the head toward the danger zone while crossing. Conclusion. Crossing the street is a complex task that can be described in three phases. Common head and eye behaviors were found near the critical moments of crossing the street. Fixation behavior was closely related to street crossing behavior.

Gaze behavior of the visually impaired during street crossing.

Purpose. This study explored the gaze patterns of fully sighted and visually impaired subjects during the high-risk activity of crossing the street. Methods. Gaze behavior of 12 fully sighted subjects, nine with visual impairment resulting from age-related macular degeneration and 12 with impairment resulting from glaucoma, was monitored using a portable eye tracker as they crossed at two unfamiliar intersections. Results. All subject groups fixated primarily on vehicles and crossing elements but changed their fixation behavior as they moved from “walking to the curb” to “standing at the curb” and to “crossing the street.” A comparison of where subjects fixated in the 4-second time period before crossing showed that the fully sighted who waited for the light to change fixated on the light, whereas the fully sighted who crossed early fixated primarily on vehicles. Visually impaired subjects crossing early or waiting for the light fixate primarily on vehicles. Conclusions. Vision status affects fixation allocation while performing the high-risk activity of street crossing. Crossing decision-making strategy corresponds to fixation behavior only for the fully sighted subjects.

Fixation behavior while walking: persons with central visual field loss.

The aim of this study was to determine the effect of central visual field loss (CFL) on fixation patterns of a person walking towards a target. Subjects were four visually normal persons and 10 persons with CFL. Eye position on scene was recorded and classified into 20 scene categories. The distributions of fixations among scene categories were compared across the two subject groups. For all but two CFL subjects, who fixated primarily at the floor, the distributions of fixations for the CFL subjects ranged from being moderately to strongly correlated with that of the visually normal mean. An analysis of the similarity in the sequence of fixations (or gaze pattern) of the CFL subjects to the visually normal subjects showed a range of 7-66%. Excluding the one CFL subject who had a functioning fovea, sequence similarity was strongly correlated with the logarithm of the minimum angle of resolution (logMAR). The better a persons logMAR, the more closely his or her gaze pattern matched that of the visually normal subjects. Finally, the CFL data were tested against two current models of oculomotor strategy, visual salience and guided search. Similar to what was found with visually normal subjects, CFL subjects appear to use the expected features and general location of the target to guide their fixations, the guided-search strategy.

FLORA™: Phase I development of a functional vision assessment for prosthetic vision users

Research groups and funding agencies need a functional assessment suitable for an ultra‐low vision population to evaluate the impact of new vision‐restoration treatments. The purpose of this study was to develop a pilot assessment to capture the functional visual ability and well‐being of subjects whose vision has been partially restored with the Argus II Retinal Prosthesis System.

Worldwide Argus II implantation: recommendations to optimize patient outcomes.

BackgroundA position paper based on the collective experiences of Argus II Retinal Prosthesis System investigators to review strategies to optimize outcomes in patients with retinitis pigmentosa undergoing retinal prosthesis implantation.MethodsRetinal surgeons, device programmers, and rehabilitation specialists from Europe, Canada, Middle East, and the United States were convened to the first international Argus II Investigator Meeting held in Ann Arbor, MI in March 2015. The recommendations from the collective experiences were collected. Factors associated with successful outcomes were determined.ResultsFactors leading to successful outcomes begin with appropriate patient selection, expectation counseling, and preoperative retinal assessment. Challenges to surgical implantation include presence of staphyloma and inadequate Tenon’s capsule or conjunctiva. Modified surgical technique may reduce risks of complications such as hypotony and conjunctival erosion. Rehabilitation efforts and correlation with validated outcome measures following implantation are critical.ConclusionsBringing together Argus II investigators allowed the identification of strategies to optimize patient outcomes. Establishing an on-line collaborative network will foster coordinated research efforts to advance outcome assessment and rehabilitation strategies.

An analysis of observer‐rated functional vision in patients implanted with the Argus II Retinal Prosthesis System at three years

The purpose of this analysis was to compare observer‐rated tasks in patients implanted with the Argus II Retinal Prosthesis System, when the device is ON versus OFF.

Traffic Gap Detection for Pedestrians with Low Vision

Purpose. Pedestrians with low vision have identified crossing the street as a difficult task. With the increasing complexity of the crossing environment (actuated signals and roundabouts), the challenges are increasing. The purpose of this study was to evaluate the effect of two types of vision loss (central or peripheral) on the ability to detect gaps in traffic. Methods. Forty-one subjects participated with 14 being fully sighted (FS), 10 having central vision loss from age-related macular degeneration (AMD), and 17 having peripheral vision loss from either retinitis pigmentosa or glaucoma. Standing at entry and exit lanes of a roundabout, subjects depressed a handheld trigger to indicate when there was a sufficient gap in traffic to cross the street. A total of twelve 2-min intervals were completed including four of those intervals with occluded hearing. Results. No difference was found in the ability of the three subject groups to identify crossable or short gaps. There were significant differences in latency and safety margin. The AMD subjects did not perform as well as the FS or the subjects with retinitis pigmentosa/glaucoma. When hearing was occluded, the two vision loss groups did not show a change in sensitivity but the FS group did, being more sensitive when hearing was occluded. Conclusions. The purpose of this study was to evaluate the effect of low vision on the ability to detect crossable gaps in traffic. The findings suggest that subjects with AMD have an increased risk because they show significant latency in their identification of gaps and this in turn results in a reduction of safety margin.