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J. Zheng, J. Racine, P. Lachapelle; Clinical Analysis of the ERG OPs: Individual vs. Collective Assessment. Invest. Ophthalmol. Vis. Sci. 2010;51(13):1493.
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A naive observer (JZ) was asked to conduct a retrospective study in order to verify if individual OP analysis added anything to the ERG interpretation.
We compared the relative amplitude (OPx/SumOPs) of each of the 3 major OPs (OP2, OP3, OP4) obtained at the peak of the Photopic Hill (flash: 0.69 or 1 log cd.sec.m-2; background : 30 cd.m2 ) in normal subjects (n=30) and patients (n=126) affected with a variety of retinal disorders. Results were compared to diagnosis and visual field configuration [central scotoma (CS), mid-periphery scotoma (MPS) and peripheral constriction (PC)].
In normal subjects, the amplitude of the SumOPs (OP2+OP3+OP4) is 62±9 µV and the relative amplitudes of OP2, OP3 and OP4 are 24±3%, 27±6% and 49±8%, respectively. The SumOPs breakdown of our patient population was as follows: 3% with normal SumOPs, 10% with SumOPs between 75-99%, 16% between 50-74%, 19% between 25-49% and 52% between 0-24% of normal. Of those, 23% had a normal OP profile, 4% had an extinguished OP response and 22%, 12% and 38% had an OP2, OP3 or OP4 specific attenuation. CS was most frequent in OP2 anomaly (48% of the cases), MPS in OP3 anomaly (41% of the cases) and PC in OP4 anomaly (31% of the cases). There was no evidence of an OP specific signature for a given retinopathy. Finally, in several of our patients presenting with a nearly extinguished response, the narrowband OP response was almost identical to the broadband ERG response.
Our analysis failed to reveal OP patterns that were pathognomonic for a given retinopathy. Even the typical CSNB pattern could be reproduced in other conditions. Nevertheless, individual rather than collective assessment of OPs does add five new diagnostic categories (normal OP pattern, extinguished OPs, OP2, OP3 and OP4 related pathologies), thus significantly adding to the diagnostic possibilities and may become clinically more relevant if used more widely. Of interest, the association of a given OP pattern with the visual field anomaly could suggest, as previously advanced, a concentric organization of OP generators. Reasons as to why this is not always verified (such as in CSNB) are currently investigated. Finally, the fact that the OP signal appears to be the only electrophysiological sign remaining in some advanced retinopathies strongly points to a major role played by the OPs in signalling retinal function.
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