This observational, cross-sectional study examined how 3 reliability measures (false positives, false negatives and fixation losses) affect the global indices of visual field (VF) results in nonglaucomatous eyes.
Study design
Investigators included 830 adults (1,235 eyes) without visual impairment, glaucoma, significant cataract or major eye diseases from the population-based Singapore Chinese Eye Study.
Participants underwent a comprehensive ocular exam and VF testing with the Humphrey Field Analyzer II using the SITA Standard 24-2 program. The effects of false-negatives (FN), false-positives (FP) and fixation losses (FL) on mean deviation (MD) and pattern standard deviation (PSD) were analyzed using multivariable regression models.
Outcomes
Both FN and FP responses were independently associated with the MD and PSD, but in a nonlinear fashion.
An FN of greater than 15% had a larger effect on MD and PSD compared with lower FN frequencies (<15%). Likewise, a higher frequency of FP (≥15%) had a larger impact on MD than low frequencies of false answers (<15%). Lower FP frequencies had a negative association with PSD, but that association was not present at larger FP frequencies (≥15%).
FL had no significant associations with MD, and was only marginally associated with PSD.
Limitations
These analyses were based on normal eyes, and the findings may not necessarily be the same in eyes with established VF defects. Because normal MD and PSD values represent a spread of values distributed around a mean, it is inaccurate to assume that all deviations from a normal baseline may be due to changes in reliability indices.
Clinical significance
Physicians typically rely on cutoff values for reliability indices to categorize a VF result as "reliable" or "unreliable". However, these results show that “reliability” falls along a continuum. The findings will allow clinicians to better estimate to what degree the unreliable responses may affect the VF globally, at least in patients expected to have a normal VF and disc suspects.