Purpose
To assess rates of abnormal SD-tVEP amplitude and latency findings in adults with chronic glaucoma using the Diopsys Nova-LX P100/N75-referenced high (Hc) and low (Lc) contrast stimuli.
Methods
Clinical records of adults with chronic glaucoma undergoing SD-tVEP evaluation with the Diopsys Nova system between Aug 2013 and Apr 2014 were reviewed. In addition to demographic information, the amplitude and latency of the SD-tVEP under both Lc and Hc stimuli conditions were collected, as was whether the VEP findings were interpreted by the device as being normal or abnormal. The mean defect (MD) of the most recent Humphrey 30-2 visual field was used to stage the severity of the glaucoma as being mild (MD > -6dB), moderate (-6dB ≥ MD > -12dB) or severe (MD ≤ -12dB).
Results
Complete data were available for 98 glaucomatous eyes of 85 patients (49 eyes mild, 16 moderate, 33 severe). The mean age was 68.2±1.3 yrs. Mean amplitudes were reported as normal in >85% of eyes. The Lc rate of amplitude abnormality was mild: 8.6%; moderate: 5.0%; severe: 7.9% (R2 = 0.008, P = 0.94). The Hc amplitude abnormality rate was mild: 5.7%; moderate: 0.0%; severe: 21.1% (R2 = 0.584, P = 0.45). Lc and Hc latency abnormality rates both showed strong associations with perimetric staging, but Hc latency deficits were far more common (P = 0.02). The Lc rate of latency abnormality was mild: 12.2%; moderate: 18.8%; severe: 33.3% (R2 = 0.991, P = 0.06). The Hc latency abnormality rate was mild: 18.4%; moderate: 31.3%; severe: 57.6% (R2 = 0.994, P = 0.05).
Conclusions
Using the Diopsys NOVA-LX integrated analysis software, rates of significant SD-tVEP latency abnormality increased with glaucoma severity, with Hc deficits being significantly more common than Lc defects. This Hc>Lc latency defect preponderance arose at all stages, afflicting a majority of eyes with severe glaucoma. SD-tVEP latency thus appears to have far greater clinical relevance to glaucoma than amplitude, for which there was no observed relationship with disease severity.