Upprepade ljusstimuli orsakar interferens i mörkeradapterade elektroretinogram hos hund
Electroretinography is an examination method where the function of the retina is objectively assessed. In 2002 the European College of Veterinary Ophthalmology (ECVO) published a proposition to a standard on how to perform ERG examinations, to facilitate comparison of results and to make it possible...
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| Formato: | Otro |
| Lenguaje: | sueco sueco |
| Publicado: |
2005
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| Materias: | |
| Acceso en línea: | https://stud.epsilon.slu.se/11857/ |
| Sumario: | Electroretinography is an examination method where the function of the retina is objectively assessed. In 2002 the European College of Veterinary Ophthalmology (ECVO) published a proposition to a standard on how to perform ERG examinations, to facilitate comparison of results and to make it possible to repeat examinations.
The purpose of this study was to validate parts of the canine ERG protocol suggested by the ECVO. Our principal aim was to study if there is any interference at the recommended stimulus intervals for dark-adapted rod- and combined rod-/cone responses.
The results show that there is an effect on the a- and b-wave amplitudes when different stimulus intervals are employed. When all examined intervals are pooled, there is an increase in the median b-wave to each consecutive dim, white (rod) stimulus in a series of four. When bright stimuli were used, there is an initial increase and then a decrease in the median b-wave amplitude. In contrast, the a-wave amplitudes decreased for each consecutive stimulus. We believe that the decrease in a-wave amplitude and later b-wave amplitudes in response to bright stimuli is due to light adaptation of the rods. However, the increase in dark-adapted b-wave amplitude to dim stimuli has, to our knowledge, not been described previously. It may be caused by contribution from the cone system or other post-receptoral circuits in the retina, but this requires further investigation. The clinical relevance is probably limited, but may certainly add to the variation between individuals and therefore limit the possibility for diagnosing more subtle abnormalities of the canine retina. Furthermore, we found that the maximum impedance recommended by the ECVO, 2 kΩ, can be exceeded without any obvious effect on the quality and reproducibility of the ERG. Thus we suggest that the maximum impedance has to be less than 7 kΩ and preferably less than 5 kΩ. |
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