بنام خداوند بخشنده مهربان دکتر غلامعلی نادریان گروه چشم دانشگاه علوم پزشکی اصفهان
Electeroretinogram Electro – oculogram
Electeroretinogram The clinical electroretinogram is a mass response evoked from the entire retina by a brief flash of light
The ERG is characterized by a negative waveform ( a-wave ) that represents the response of photo receptors , followed by a positive waveform ( b-wave ) generated by combination of cells in the Muller and bipolar cell layer
The duration of the entire response is usually less than 150 msec
a-Wave amplitude is measured from baseline to the a-wave trough
b- Wave amplitude is measured from the a – wave trough to the b- wave peak
The implicit time ( t) the time to reach a peak , is measured from the onset of the stimulus to the trough of the a- wave or the peak of the b- wave
Use of a corneal contact lens electrode to record the ERG gives the most accurate and reproducible results
The pupils should be dilated and light flashes presented full field to the entire retina A bowl similar to that of a perimeter is used to illuminate the entire retina
Dark – adapted testing The rod response is produced by dark- adapting the patient for at least 20 minutes and stimulating the retina
Light adapted testing The single flash cone response or photopic ERG is obtained by maintaining the patient in a light – adapted state and stimulating the retina with a bright white flash
Electro – oculogram (EOG) The EOG is an eye movement dependent voltage recorded between electrodes placed near the eye
The corneafundal potential results from the metabolic activity of several epithelial contribute to this potential
The contributions of the cornea and lens are not photosensitive , but that of the RPE is substantially reduces during dark adaptation and increases during light adaptation
The individual should preadapted for approximately 15 minutes before the test
The EOG reflects the activity of the entire retina
The validity of the results depends on accurate and consistent tracking of the fixation light over 30 minutes , so this test is not appropriate for young children
The EOG is a useful adjunct to the ERG It is generally abnormal in any condition in which the ERG is abnormal
An abnormal ERG with normal EOG is the hallmark of Best,s disease and has also been repotted in cases of fundus flavimaculatus , pattern dystrophy , dominant drusen