gms | German Medical Science

102. Jahrestagung der DOG

Deutsche Ophthalmologische Gesellschaft e. V.

23. bis 26.09.2004, Berlin

Subretinal implants for restitution of vision: Tests for clinical trials

Meeting Abstract

  • corresponding author E. Zrenner - University Eye Hospital, Dept. II, Tuebingen, Germany
  • M. Bach - University Eye Hospital Freiburg, Germany
  • F. Gekeler - University Eye Hospital, Dept. II, Tuebingen, Germany
  • V.-P. Gabel - University Eye Hospital, Regensburg, Germany
  • H. Haemmerle - Natural and Medical Science Institute at the University of Tuebingen, Reutlingen, Germany
  • K. Kohler - University Eye Hospital, Dept. II, Tuebingen, Germany
  • C. Kuttenkeuler - University Eye Hospital, Dept. II, Tuebingen, Germany
  • W. Nisch - Natural and Medical Science Institute at the University of Tuebingen, Reutlingen, Germany
  • H. Sachs - University Eye Hospital, Regensburg, Germany
  • K. Shinoda - University Eye Hospital, Dept. II, Tuebingen, Germany
  • A. Stett - Natural and Medical Science Institute at the University of Tuebingen, Reutlingen, Germany
  • B. Wilhelm - STZ for Biomedical Optics and Function Testing, Tübingen, Germany

Evidenzbasierte Medizin - Anspruch und Wirklichkeit. 102. Jahrestagung der Deutschen Ophthalmologischen Gesellschaft. Berlin, 23.-26.09.2004. Düsseldorf, Köln: German Medical Science; 2004. Doc04dogSA.11.01

The electronic version of this article is the complete one and can be found online at:

Published: September 22, 2004

© 2004 Zrenner et al.
This is an Open Access article distributed under the terms of the Creative Commons Attribution License ( You are free: to Share – to copy, distribute and transmit the work, provided the original author and source are credited.




We have developed a powered "active" subretinal implant that has several advantages: In blindness caused by photoreceptor degeneration the remaining neuronal network of the retina can be utilized for signal processing; positioning and fixation of the Multiphotodioden-Arrays (MPDAs) in the subretinal space is relatively easy; no external camera and external image processing is required; eye movements can be used for localization of objects; semiconductor-based MPDAs are well tolerated by inner retina, as shown for 28 months, encapsulated implants remain intact after long term implantation. Safe ab externo surgical procedures have been developed (see H. Sachs and V.-P. Gabel).


Our goals are to replace degenerated photoreceptors by microphotodiode arrays consisting of approx. 1600 microphotodiodes on a 3 x 3 mm chip (100 µm thick) and 1600 amplifiers and electrodes which ensure stimulation and adaptation of the current output to the ambient light scene in a wide range. This chip in its foil bound powered version shall be used for a first clinical trial in 8 blind patients suffering from retinitis pigmentosa.


After the presentation of the technology and its rationale, the design of a first clinical trial shall be discussed, including the rationale for a particular "test battery" to assess the spatial and temporal abilities of patients' vision after implantation.


The expected resolution of a sensor array with 40 time 40 "pixels" separated by a distance of 70 micrometer requires special techniques of assessing the spatial and temporal characteristics of visual performance mediated by electronic retinal prosthesis. Based on the principles of the Freiburg visual acuity test (Fract), developed by M. Bach a Basic Light Localization and Motion test (BALM) was developed for threshold based automated assessment of visual functions in patients with very low vision. Four submodalities if vision are to be tested: light sensitivity, temporal resolution, localization and visual motion perception.


Common clinical tests insufficiently describe improvements gained by various chip-types, because these test settings are prone to a number of effects not necessarily related to chip-performance. It seems preferably to present visual targets adequately on a bright TFT screen. The patient's visual thresholds are assessed by varying brightness, spatial or temporal variables. The (2/4/8-) alternative forced-choice principle is crucial for reliable assessment of function. Hit rate (%) and reaction time (ms) for single locations/directions can be used as outcome measurement in terms of means ±SD of hit rate and average reaction time. We recommend this battery of computerized, standardized tests for patients with visual prostheses to quantify the functional outcome.

supported by BMBF 01K008 and Alexander von Humboldt Foundation IV-JAN/1112777STP