Asymmetries in the contributions of On- and Off-mechanisms to the ERG signal

ERG responses were recorded to rapid-on and rapid-off L- and M-cone isolating sawtooth stimuli of different cone contrasts. In addition, the responses were recorded to simultaneous in-phase stimulation of the L- and M-cones at equal cone contrast. Linear responses to mirror imaged rapid-on and rapid-off sawtooth stimuli are also mirror imaged. By adding on- and off-responses, linear response components will cancel and nonlinearities will remain. Because nonlinearities that occur at a certain stage of visual processing will influence subsequent stages, linear response components will probably have an outer retinal origin and nonlinearities probably originate mainly in the inner (post-receptoral) retina...

Multifocal Electroretinograms in Amblyopic Patients

PURPOSE: To evaluate the results of amblyopia on multifocal electroretinogram (mfERG). METHODS: The mfERG procedure was performed on nineteen monocular amblyopic patients (age ranged from 7 to 42 years) using the VERIS(TM) (EDI, San Mateo, CA) system. The central 30 degrees of ocular fundus were stimulated by an array of 103 hexagonal elements for four minutes. The responses of six concentric rings (rings 1 to 6) radiating from the foveal center were averaged, and the latencies and amplitudes of N1, P1 and N2 were compared with the findings of the normal contralateral eyes. The mfERG procedure was recorded again after improvement of vision in one patient (No. 4) who underwent occlusion treatment for one month. RESULTS: There were no significant differences of N1, P1 and N2 latencies between normal contralateral and amblyopic eyes (P>0.05). However, P1 amplitudes of the amblyopic eyes were reduced significantly compared with those of the normal contralateral eyes on rings 1 and 2 (P<0.05). N1 and N2 amplitudes of the amblyopic eyes were also reduced, but not significantly. After the successful occlusion treatment of patient No. 4, the responses of the amblyopic eye were improved but not the level of the contralateral normal eye. CONCLUSIONS: These results suggest that amblyopia may cause some changes in mfERG responses, especially in terms of amplitudes of the central retina. Further investigation is needed to determine whether these results are due to the physiologic change(s) of the amblyopia itself or to fixation instability during the test.

Changes of Multifocal Electroretinograms after Macular Hole Surgery

PURPOSE: To evaluate macular function before and after surgical closure of idiopathic macular hole using multifocal electroretinogram (mfERG). METHODS: The mfERGs were performed on nine patients, who had been diagnosed with idiopathic macular hole, before and after vitrectomy (average 2.9+/-0.6 mo) and gas (C3F8) injection. VERISTMsystem (EDI: San Mateo, CA, USA) was used to record the mfERGs. The central 30 degrees of the ocular fundus were stimulated by an array of 103 hexagonal elements for 4 minutes. The responses of six concentric rings (rings 1 to 6) radiating from the foveal center were averaged. Preoperative and postoperative responses of mfERG were compared. Statistical differences were analyzed with the paired two sample t-test. RESULTS: N1, P1 and N2 amplitudes of rings 1 and 2 increased after surgery significantly (p0.05). The changes of mfERG responses were not correlated with the changes of visual acuities after surgery. Visual acuity was improved in seven patients but deteriorated in the other two, one of whom developed RPE degeneration and another cataract. CONCLUSIONS: The mfERG responses improved after macular hole surgery. These results suggest that mfERG may be a useful method to assess macular function changes after macular hole surgery, although the responses were not correlated with visual acuity.

Multifocal Electroretinograms in Patients with Branch Retinal Vein Occlusion

PURPOSE: To evaluate the damage to the inner retina in patients with branch retinal vein occlusion (BRVO), we recorded multifocal electroretinograms (mfERG) and analyzed the waveform changes of the first and the second order kernel responses. METHODS: Eight eyes of patients with unilateral BRVO were included. Fourteen eyes of 14 normal subjects were also tested as controls. VERIS system was used to record mfERG. The first and the second order kernel responses of each quadrant were averaged. Averaged responses were compared with those of the contralateral eyes and normal control eyes. RESULTS: The amplitudes of averaged tracing decreased in the N1, P1, and N2 of the first order kernel responses in the affected quadrant in comparison with those of contralateral and normal control eyes (P<0.05). Prolongation of latency was noted in N1, P1 and N2 in the affected quadrant. In the second order kernel responses of the affected quadrant, no responses were found in four patients. The delay in latency and the decrease in amplitude were more marked in the second order kernel responses than in the first order kernel responses (P<0.01). CONCLUSIONS: The first order mfERG components decreased in amplitude and increased in latency, with N2 being the most severely affected. And the second order mfERG components were more decreased in the affected area in patients with BRVO. These results suggested that the second order kernel responses may reflect the condition of the inner retina better than the first order kernel responses.