THE VALUE OF BLUE-ON-YELLOW VEP FOR THE E ARLY DIAGNOSIS OF GLAUCOMA - BIOSTATISTICAL CONSIDERATIONS AND RESULTS

Background: In the Erlangen glaucoma study, the blue-on-yellow VEP was shown to be able to discriminate between controls and manifest glauco ma patients. Scientific questions and aims: In our investigation,we as sessed the validity of the blue-on-yellow VEP for early diagnosis of g laucoma. With this aim, we compared different subgroups of glaucoma su spects. The main issue of the investigation was the biostatistical asp ects of early diagnosis of glaucoma. Material, methods and results: Wi thin a group of patients who were suspected of having ocular hypertens ive glaucoma without visual field loss we compared 109 patients with o ptic disc damage [preperimetric (PPM) 47+/-11 years] and 91 patients w ithout optic disc damage [ocular hypertension (OHT) 45+/-10 years]. We evaluated the N 1-amplitude and the peak latency of the blue-on-yello w VEP. The peak latency was significantly longer in the PPM group (fir st examination:OHT 118.4+/-9.5 ms, PPM 122.0+/-10.5 ms;second examinat ion: 119.1+/-7.4/121.9+/-11.0 ms;third examination: 118.5+/-9.1/122.4/-10.9 ms). The amplitude was reduced in the PPM group (P = 0.08). The differences between the two groups only allowed limited individual se paration: (sensitivity of 42% for advanced optic disc damage with 80% specificity among OHT patients). Conclusions: The reduced sensitivity of a diagnostic procedure within a group of glaucoma suspect patients compared with patients with manifest glaucoma might be explained by: ( 1) possible misclassifications of patients and (2) a smaller degree of loss of visual function in the early stages of the disease.