4.4 Foveal Thickness and Focal Macular ERG 213
The results of focal macular ERGs and OCTs from patients with central serious chori- oretinopathy, aphakic or pseudophakic CME, and IEM have some findings in common that contribute to our understanding of the relation between macular morphology and macular ERG. The macula OPs at the early stage of aphakic or pseudophakic CME and IEM are selectively reduced, and this reduction was observed during the convalescent stage of central serous chorioretinopathy even after the submacular fluid had been resorbed. The common change in these patients was the increase in the OCT-determined thickness of the macula, which was due to macular edema.
These observations indicate that the macular OPs are the most sensitive indicator among the focal macular ERG components when the macula is edematous with minimal systemic pathology.
It was also determined that macular OPs have the slowest recovery following treatment of macular edema. This relation was confirmed by the significant correlation between the macular thickness measured by OCT and the amplitude of macular OPs in many patients with IEM after vitrectomy (Fig. 4.17).
When macular edema is long-standing or severe, the b-wave and then the a-wave may also become depressed. These findings indicate that the pathological process first affects the OPs, followed by the b-wave, and finally the a-wave as the macula thickness increases. The recovery process follows the reverse course; the a-wave recovers first, followed by the b-wave, and finally the OPs. This rule is important when analyzing complicated cases of macula edema associated with significant background pathol- ogy, such as diabetic macular edema (see Section 3.2.3).
4.4 Foveal Thickness and Focal Macular ERG
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