Evaluation of the LKC stimulator for focal ERG testing

Numerous studies have demonstrated the ability of focal ERGs to diagnose abnormally functioning maculae in the absence of funduscopic and angiographic signs, as well as to confirm diagnoses of clinically suspected macular disease. We present normative data on the second commercially available focal ERG stimulator (FCS-500, LKC Technologies), which may be added to the standard full field ERG systems currently used in many laboratories. The stimulator uses a monocular indirect ophthalmoscope to present a 5° white stimulus flickering at 31.25 Hz in a 20° background field. We have established a range of normal amplitudes (747–3000 nV) and implicit times (30.5–37.5 ms) for the instrument based on tests of 45 eyes of 45 normal patients. To confirm the validity of this test for diagnosis of ocular dysfunction we compared these normals to 46 eyes of 46 patients with macular disease and decreased acuity, and to 49 eyes of 49 patients with retinitis pigmentosa. Using Focal ERG amplitude alone, we found overall accuracy of 85% in diagnosing macular disease associated with decreased acuity. These findings confirm the validity and efficacy of the system we have evaluated.