[Technical factors that influence multifocal electroretinogram (mfERG) recording].
OBJECTIVE
To describe the main intervening factors observed during the acquisition and analysis of multifocal electroretinogram (mfERG), that could affect the recorded signal, the obtained responses and their analysis.


METHODS
The error factors observed during the acquisition of 100 sequential multifocal electroretinogram tests, in the period of May to July, 2005 were analyzed. The examinations of multifocal electroretinogram were carried out in agreement with international guideline recommendations, taking into account the established parameters of equipment, with 61 elements, and visual angle of 30 degrees. All patients had been submitted to complete ophthalmologic examination, excluding those with inadequate transparency of ways, flat corneas and those incapable to visualize a central fixation target.


RESULTS
The intervening factors, that could cause artifacts and errors in the interpretation of the obtained results, observed and corrected during the acquisition of multifocal electroretinogram were: eccentric or poor fixation, eye movements, orbicular contraction, cervical muscle contraction, inadequate transparency of the corneal electrode, electrode displacement, lens support decentralization, inadequate viewing distance in patients with high refractive errors, eye height inadequacy in relation to the center of the screen, electrical noise in 60 HZ frequency and electromagnetic field and high impedances. Excessive use of filters in wave processing for noise and artifact removal can interfere with the analysis of the obtained results.


CONCLUSIONS
Simple observational cares during signal acquisition are of significant importance to ensure accuracy of the topographical electroretinogram information, good waveform morphology and low noise level register. Through their ready correction, the correct and adjusted analysis of the amplitude and of implicit time of peaks N1, P1 and N2 is reliable. Digital smooth system with specific frequency peak removal supply waves with more defined morphology with lower amplitude reduction than other available resources.
Oyamada
Maria Kiyoko
MK
Departamento de Oftalmologia, Hospital das Clínicas, Faculdade de Medicina, Universidade de São Paulo, São Paulo, SP, Brasil. kyoko.ops@terra.com.br
Dotto
Patrícia de Freitas
Pde F
Abdalla
Milena
M
D004596:Electroretinography / Q000295:instrumentation / Q000379:methods*; D005133:Eye Movements / Q000502:physiology; D005403:Fixation, Ocular / Q000502:physiology; D006801:Humans