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K. Bradshaw, R. Hanitzsch; Contribution of Post-Receptoral Cells to the Cone A-Wave of the Human ERG in CSNB and Auto-Immune Retinopathy. Invest. Ophthalmol. Vis. Sci. 2010;51(13):3274.
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Hyperpolarising cells contribute to the later part of the cone a-wave of the ERG. We tested patients with abnormal inner retinal ERGs to determine whether the a-wave was also affected by the altered contribution of potentials of these secondary cells.
Standard clinical ERGs were recorded in 2 patients with auto-immune retinopathy (AI) and 3 patients with CSNB; results were compared with those of 26 normals. ERGs were also recorded in the same patients to a red stimulus flash (0.8ph.cd.s.m-2) presented either against a steady blue background (39sc.cd.m-2) or 0-300ms after extinguishing the background; responses were compared with those of 8 normals.
(a) Clinical ERGs. All ON and OFF inner retinal rod and cone responses were abnormal in both AI patients. ERG responses in patients with CSNB were characteristic of results in CSNB1 (ON pathway abnormality) in 2 patients and CSNB2 (ON and OFF pathway abnormality) in 1 patient. (b) Red flash ERGs. In all normal subjects the cone a-wave increased in amplitude after 50-100ms darkness. In AI patients the a-wave was sub-normal when recorded against a steady background but increased in amplitude in the dark; maximal amplitude was normal in 1 patient and slightly reduced in the other. The cone a-wave showed a normal increase in amplitude in the dark in the CSNB2 patient. There was no significant increase in a-wave amplitude in the dark in either patient with CSNB1.
The increase in a-wave amplitude in the dark in normals is due to a contribution from secondary hyperpolarising cells. These cells are affected differently in the 3 diseases. In CSNB1 the absence of a-wave amplitude increase in the dark provides new evidence of OFF pathway abnormality in at least some patients. The normal increase in a-wave amplitude in CSNB2 indicates a continuing hyperpolarising cell contribution at light ON despite abnormality of OFF components of the ERG. In AI patients a-wave amplitude increased despite severe abnormality of all other OFF components of the ERG. The procedures we describe provide a novel method for probing post-receptoral cone pathway function.
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