Jörg Sommerhalder

Primary Vitrectomy without Scleral Buckling for Pseudophakic Rhegmatogenous Retinal Detachment

PURPOSE To report the anatomic and functional results of primary vitrectomy without scleral buckling for the treatment of pseudophakic rhegmatogenous retinal detachment (PsRD). DESIGN Prospective, nonrandomized surgical technique study. METHODS One hundred eyes of 98 patients with PsRD were operated by vitrectomy alone. Internal subretinal fluid drainage, cryocoagulation and/or endolaser and fluid-air exchange with sulfur hexafluoride 20% was applied in all cases. The preoperative and postoperative characteristics were analyzed. Main outcome measures were anatomic success rates after initial surgical intervention and after reoperation for primary failures, visual outcome at the last follow-up visit, and complications. RESULTS Mean follow-up +/- standard deviation (SD) was 12 +/- 6.3 months (range, seven to 36 months). Mean final visual acuity +/- SD was 0.42 +/- 0.45 logarithm of the minimum angle of resolution (logMAR) compared with 0.95 +/- 0.73 logMAR before surgery (P < .01). Mean number +/- SD of retinal breaks found before surgery was 1.36 +/- 1.12 (range, zero to five), and an additional 1.58 +/- 2.26 (range, zero to 15) retinal breaks were found during surgery. The retina was reattached successfully after a single surgery in 92 eyes (92%). Recurrence of retinal detachment occurred in eight eyes (8%), caused by proliferative vitreoretinopathy in six eyes (75%) and by new breaks in two eyes (25%). Final anatomic reattachment was obtained in these cases after a mean of 1.75 subsequent operations. Three eyes required permanent silicone oil tamponade so that final anatomic success was achieved in 97 eyes (97%). The most common postoperative complication was ocular hypertonia of more than 21 mm Hg, observed in 36 (36%) eyes, which was managed successfully. CONCLUSIONS Primary vitrectomy without scleral buckling provides a high anatomic success rate in eyes with PsRD and is associated with few complications.

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.

Subretinal electrode implantation in the P23H rat for chronic stimulations

Background: In age related macular degeneration and inherited dystrophies, preservation of retinal ganglion cells has been demonstrated. This finding has led to the development of various models of subretinal or epiretinal implant in order to restore vision. This study addresses the development of a polyimide subretinal electrode platform in the dystrophic P23H rat in vivo. Methods: A technique was developed for implanting a subretinal electrode into the subretinal space and stabilising the distal extremity of the cabling on the rat cranium in order to allow future electrical stimulations of the retina. Results: In vivo imaging of the retina with the scanning laser ophthalmoscope demonstrated reabsorption of the surgically induced retinal detachment and the absence of major tissue reactions. These in vivo observations were confirmed by retinal histology. The extraocular fixation system on the rat cranium was effective in stabilising the distal connector for in vivo stimulation. Conclusion: This study demonstrates that a retinal implant can be introduced into the subretinal space of a dystrophic rat with a stable external connection for repeatable electrical measurements and stimulation. This in vivo model should therefore allow us to evaluate the safety and efficacy of electrical stimulations on dystrophic retina.

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.

Coupling of HRT II and AS-OCT to evaluate corneal endothelial cell loss and in vivo visualization of the Ahmed glaucoma valve implant.

AimsTo report corneal endothelial cell loss and in vivo visualization of the Ahmed glaucoma valve implant in eyes with refractory glaucoma.MethodsTen eyes underwent Ahmed valve implant surgery and were followed-up for 12 months. Data collected included intraocular pressure (IOP), number of antiglaucoma medications and surgery-related complications. At 6 and 12 months postoperatively, the intracameral length of the drainage tube (ICL) and the distance between the tube and the cornea (T–C distance), and the iris (T–I distance) were assessed using anterior segment optical coherence tomography (AS-OCT). Heidelberg cornea tomograph II (HRT II) was used to measure the corneal endothelial cell density.ResultsMean (±SEM) preoperative IOP was 29.5±4 mmHg. Mean postoperative IOP was 11.6±2 at 12 months (P<0.01). Over a 6-month period, mean corneal endothelial loss was 7.9%±2.5 in the central and 7.5%±2.4 in the peripheral cornea (P<0.01). There was no correlation between central or peripheral corneal endothelial cell loss and the T–C, T–I distance or the ICL of the tube.ConclusionsCorneal endothelial cell loss occurs following Ahmed valve implant surgery, this appears to be multifactorial. AS-OCT and HRT II are promising methods for the follow-up of patients with a glaucoma drainage device.

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.

ARVO Annual Meeting 2008: Visual Prostheses Research

The first visual prostheses were conceived approximately 40 years ago, but interest in the field of artificial vision has particularly increased over the last 10–15 years. Recent progress in microtechnology has made it possible to envision extremely small and highly integrated neurostimulators dedicated to restoring some useful vision to blind patients. A number of research groups – essentially multidisciplinary consortia – are presently working on projects aiming at the development of a visual prosthesis stimulating either surviving retinal neurons, fibers of the optic nerve or the visual cortex itself. The annual meeting of the Association for Research in Vision and Ophthalmology (ARVO) is one of the largest ophthalmic research events and provides an excellent update of current work. Approximately 15 years ago, research on visual prostheses was practically unreported at ARVO. Nowadays, there are numerous presentations and several sessions on the topic. At this year’s ARVO meeting, artificial vision was introduced in the ‘Innovations in restoring vision’ paper session on the first day. Over the following days, four sessions (two poster and two paper sessions, totaling 67 presentations) were dedicated to visual prostheses. The aim of this report is to summarize these presentations. The numbers in brackets refer to ARVO program numbers.

How to Restore Reading With Visual Prostheses

In daily life sight is used for mainly two types of tasks. Those requiring the recognition of small forms or objects as it is specifically done in reading and those requiring spatial orientation and localization in three-dimensional environments, such as whole body mobility and visuo-motor coordination. For the former the central part of the visual field is mainly used, whereas the latter rely for an essential part on the peripheral visual field. Both have to be seriously considered when developing useful vision aids for low vision and/or blind patients. This chapter is dedicated to the particular question: What are minimum requirements for visual prostheses to restore useful reading abilities to blind patients?

Heterochromatic luminance matches in automated Rayleigh and Moreland equations

We have developed an automated color vision examination consisting of Rayleigh and Moreland matches on a computer-controlled anomaloscope. With this system, it is possible to vary automatically the radiance (and saturation) of the test field when a given ratio of primaries is presented in the mixture field. The aim of these experiments was to test different methods of heterochromatic luminance matches so that a correct radiance of the test field could be used during the automated color vision examination itself.

Prospects and Limitations of Spatial Resolution

Our sense of vision permanently captures, transmits and interprets enormous amounts of visual information. The amount of visual information that can be transmitted to the brain by the means of visual prosthesis will be severely limited and thus also limit the rehabilitation prospects of such devices. While several parameters contribute to the information content of visual stimuli, this chapter concentrates essentially on spatial resolution.