Intra- and interrater agreement and reliability of the Functional Field Score

In 2001, the American Medical Association adopted the Functional Vision Score (FVS). It is built on Functional Acuity Scores (FAS) and Functional Field Scores (FFS). The purpose of this study was to evaluate the intra- and interrater reproducibility of the FFS. The study sample was composed of 62 persons, mean age 41.8 years, from the population of patients who visited a rehabilitation centre for visually impaired adults. We analysed 30 FFSs of isopter III-4e and 58 of isopter V-4e. Two raters independently scored the plots. The smallest detectable difference (SDD) and the weighted kappa quantified agreement. The SDDs were smaller than the minimal clinically important difference (MCID) of 10 points. Thus, the MCID can be distinguished from measurement error. The intraclass correlation coefficient (ICC) quantified reliability. The intra- and inter ICCs were high (ICCs > 0.98). We concluded that both intra- and interrater reliability of the FFS were excellent.