The influence of sampling errors on test-retest variability in Perimetry

Ted Maddess*

*Corresponding author for this work

    Research output: Contribution to journalArticlepeer-review

    34 Citations (Scopus)

    Abstract

    PURPOSE. To determine whether visual fields measured by standard automated perimetry (SAP) can be distorted by higherspatial-frequency image components and, in particular, whether test-retest variability of SAP fields can be explained by the combination of small scale fixational drift, small stimulus size, and coarse spatial sampling of the visual fields. METHODS. Standard SAP test patterns have points 6° apart. The amplitude spectra of the perimeter's 10-2 fields (model 511 Humphrey Field Analyser [HFA]; Carl Zeiss Meditec, Inc., North Ryde, NSW, Australia) were assessed to see whether their finer grained sampling revealed spatial frequencies that could cause distortions of standard fields because of undersampling. Model visual fields were then constructed whose spectra were similar to the 10-2 fields, and test-retest variability was examined for Goldmann sizes III to VI stimuli and Gaussian fixational drift with standard deviations of 0.075° to 0.3°. RESULTS. The 10-2 fields showed significant spatial frequency content up to 0.25 cyc/deg, three times the highest frequency that a 30-2 or 24-2 sample grid can resolve. As reported for SAP, test-retest variability increased with scotoma depth, and increasing the stimulus size from III to VI caused a reduction in test-retest variability, as did reduced fixation jitter. CONCLUSIONS. With fixation drift half the size of that exhibited by good fixators, many of the features of SAP test-retest variability were reproduced. Reducing test-retest variability may therefore involve using large test stimuli that are blurry in appearance and that overlap somewhat when placed on the perimetric test grid. Overlap across the meridians should perhaps be avoided.

    Original languageEnglish
    Pages (from-to)1014-1022
    Number of pages9
    JournalInvestigative Ophthalmology and Visual Science
    Volume52
    Issue number2
    DOIs
    Publication statusPublished - Feb 2011

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