The idea of implanting microphotodiode arrays as visual prostheses has aroused controversy on its feasibility from the moment it appeared in print. We now present results which basically support the concept of replacing damaged photoreceptors with subretinally implanted stimulation devices. Network activity in degenerated rat retinae could be modulated through local electrical stimulation in vitro. We also investigated the long term stability and biocompatibility of the subretinal implants and their impact on retinal physiology in rats. Ganzfeld electroretinograms and histology showed no significant side effect of subretinal implants on retinal function or the architecture of the inner retina.

There are presently several concepts to restore vision in blind or highly visually handicapped persons by implanting electronic devices into the eye in order to partially restore vision. Here, the approach to replace retinal photoreceptors by a sub-retinally implanted microphotodiode array (MPDA) is summarized. A survey is given on the present state of the development of MPDAs, the possibility of in vitro and in vivo tests as well as first results on biocompatibility and histology. Additionally, electrophysiological recordings in rabbits and rats are presented which have received such subretinal implants.

The international Standard for Clinical Electroretinography requires a minimum of 5 standard response types. In a sample of 20 healthy subjects, the normative values according to this standard were established. Since the distribution of amplitude and implicit time does not follow a Gaussian distribution, we have found the median value and the 1st to 99th percentile or the 5th to 95th percentile useful for determination of abnormality, presented here separately for intraindividual and interindividual variation. To improve quality and reliability, we propose that individual laboratories extend the minimum standard and record the standard responses as parts of a stimulus series of increasing intensity. The normal value of the b/a ratio can easily be established from the maximum response to the Standard for Clinical Electrophysiology standard flash, pointing to abnormalities especially in circulatory disturbances and in degenerative diseases of the retina. The b/a ratio is between 1.5 and 1.7. If flicker responses are recorded at the 1st and 10th minutes after the onset of the rod saturating adaptation light (25 cd/m2), an increase in amplitude can be observed, which in our sample has a relative value of 1.3. A reduced increase in cone response amplitudes during light adaptation might point to abnormality within the rod/cone interaction. Responses from the cone system can be further differentiated by the use of chromatic stimuli. With appropriate filters, short-wavelength cone-sensitive and long-wavelength cone-sensitive responses can be differentiated also in clinical daily practice, which might be helpful for further differentiation of cone disorders. Regular measurements of intraindividual variability can help to improve the quality of electroretinogram recordings. Medians and ranges between the 1st and 99th and the 5th and the 95th percentiles were determined for all recordings for interindividual, as well as for intraindividual variations.

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The International Standard of Clinical Electroretinography serves as standard protocol for recording electroretinographic responses in order to facilitate worldwide comparisons of examinations. To promote its distribution and acceptance throughout the German speaking countries, we established normal values for the five standard responses and added a German translation of the International Standard in the appendix. To determine normal values for electroretinographic data we suggest to use percentiles instead of parameters based on a Gaussian distribution. Patient-related (age, sex) and -unrelated (interstimulus-interval, diurnal rhythm) parameters proved to influence the data values significantly. With these variables taken into account one can increase the clinical value of electroretinography in terms of a greater reliability and predictiveness of data.