Extrapolating global visual field indices from local parameters in the nasal region

Abstract

The local mean and the average difference of four pairs of test locations within the 26 degrees visual field, situated above and below the horizontal nasal meridian, were used to predict the global field indices MD and CLV of the Gl glaucoma program. Out of 539 examinations (194 eyes suspected of having glaucoma), the local indices NDIFF (describing asymmetrical behavior around the nasal horizontal meridian), ND0 (the mean defect in the nasal region), and the global indices MD and CLV were calculated. Seven hundred fifty-five examinations (446 normal eyes) served as a control group. First and second examinations of 146 glaucoma suspect eyes were used to calculate the retest reliability scores for the indices in question. When analyzing the glaucoma suspects, the local index NDIFF, together with the local mean defect, ND0, yielded highly reliable estimates of the global indices MD and CLV, with a retest correlation r = 0.86 for NDIFF, and r = 0.96 for ND0. The covariance of NDIFF with CLV was r = 0.67, while the co-variance of MD with ND0 was r = 0.95. The ranges of the local indices ND0 and NDIFF were each classified into 'normal range' and 'range of suspected pathology', in analogy to the normal and pathological ranges of the global field indices. Equivalence of the local indices with the corresponding ranges of MD and CLV was investigated and the results are shown. The establishment of local indices may prove to be a powerful tool in early detection of glaucomatous damage.

Classification of Visual Field Abnormalities in the Ocular Hypertension Treatment Study

“…Automated perimetry has become an accepted standard of practice, allowing physicians to monitor the development of glaucomatous visual field loss. Very few longitudinal studies of any size and magnitude 12,[26][27][28][29][30][31][32][33][34][35] involving the classification of abnormal glaucomatous visual fields have been conducted. Previous investigators have developed classification systems to identify the pattern and severity of glaucomatous visual field loss.…”

Optimizing distribution and number of test locations in perimetry

“…A number of studies have reported surprisingly high sensitivities and specificities with few test locations only [3,5,12,13,17,22,24,25]. However, their authors have all selected the best test locations retrospectively.…”