Comparing threshold visual fields between the Dicon TKS 4000 automated perimeter and the Humphrey Field Analyzer

The automated perimeter is becoming the instrument of choice in the analysis of the visual field. There are a number of different perimeters in use and it can be difficult to compare results from different instruments. The purpose of this study was to compare visual field threshold measurements determined by the Humphrey Field Analyzer and the Dicon TKS 4000.

This study provided a statistical comparison of field test results from the Dicon TKS 4000 Automated Perimeter (program number 9) and the Humphrey Field Analyzer (30-2 threshold using FastPac). Central 30 degree, 76 point full threshold fields were performed on 20 non-dilated optometry students (age range 21 to 32 years, mean age 25.1 years) using both instruments. For the purpose of statistical analysis, the visual field was divided into 24 sectors, each measuring 10 degrees by 10 degrees. The mean threshold value of each group of points was compared between instruments.

A difference was found between instruments (significant at P&0.0001) for 19 of 24 sectors. In addition, the Humphrey Field Analyzer threshold values were consistently higher (average difference 2.47 dB) than the Dicon values. Each subject was tested twice on each instrument; both instruments showed high test-retest correlations: 0.970 for the Humphrey and 0.971 for the Dicon. Test administration times were comparable (average 435.2 seconds for the Humphrey Field Analyzer and 430.2 seconds for the Dicon), although the Dicon averaged 41.5 fewer presentations tested per examination. Fixation losses were higher with the Dicon instrument.

A practitioner may be reluctant to directly compare test results between the two instruments since they produce threshold values of statistically significant differences. The Dicon TKS 4000 was subjectively preferred over the Humphrey Field Analyzer by most subjects.