[Diagnosis of retinal diseases. Comparison between multifocal ERG and fundus perimetry - a case study]

There are new methods available for function testing of the macula, i.e. multifocal Electroretinography (mfERG) as well as fundus perimetry with the scanning laser ophthalmoscope (SLO). The value and clinical impact of these methods have still to be evaluated. We wanted to compare the results from patients having undergone both examinations.

A total of 33 eyes from 25 patients (visual acuity 0.03-0.8) aged 14-79 years were examined using fundus perimetry with the SLO. In addition, multifocal ERG was performed in all eyes, where 61 local ERGs inside the 30 degrees visual field were recorded. We compared the depth of the scotoma with the reduction of the amplitudes during mfERG taking the fixation status into consideration.

Examination time was comparable for both examination techniques. There was good concordance for eyes with retinitis pigmentosa with only central response. In contrast, patients with juvenile macular dystrophy demonstrated different results with comparable size of the defect while sometimes an enlarged pathology during mfERG was observed. Correlation between pathology findings observed in mfERG and fundus changes was difficult due to the change of the point of fixation caused by central scotoma. In age-related macular degeneration correlation of the findings was less obvious.

The different setting with supra-threshold stimuli during ERG in contrast to near-threshold stimulus presentation during perimetry, might be the reason for differences even in the beginning of retinal diseases. In addition, reduced stability of fixation leads to artifacts during mfERG while it may be compensated for in fundus perimetry. Both methods are of additional value and demonstrate different results depending on the disease.