Analyzing the location of glaucomatous visual field defects using first, second and third order moments.

الملخص

Purpose : To assess whether measuring the moments of a visual field has utility in describing the location and shape of visual field loss. Methods : This was a cross-sectional study involving participants from a prospective longitudinal study designed to evaluate optic nerve structure and visual function in glaucoma. The study involved the analysis of SAP results for 180 eyes of 107 subjects with a mean age of 61.6 ± 16.8 years, including 90 glaucomatous eyes of 60 subjects and 90 healthy eyes of 47 subjects. SAP testing was performed using the SITA Standard 24-2 strategy of the Humphrey visual field analyzer. The initial step in calculating the moments of the visual field was to convert the threshold values into linear units. All statistical analyses were performed with commercially available software (STATA, version 12; StataCorp LP. Results : The glaucomatous eyes had an average MD of -5.8 ± 6.6dB (range -25.4 to 1.2dB) compared to 0.3 ± 0.8 dB (range -1.0 to 2.5dB) in healthy eyes. The coordinates of the center of mass of threshold values (remaining visual field) and the center of visual field defects were calculated using the first moment .The coordinates of the center of visual field defects showed good correspondence to the location of the visual field defect seen on the SAP total deviation map. In each case the first moment coordinates show a good spatial relationship to the defect. There was reasonable agreement between the average coordinates for the center of remaining vision assigned by the graders and the first moment. There was also reasonable agreement between the average coordinates for the center of the visual field defect assigned by the graders and the first moment. The second moment has been proposed as a measure of the centrality of visual field defect it is strongly affected by disease severity. There was a similar relationship between the third and fourth moments, disease severity and the presence or Page 12 Mauritanie Médicale - Novembre 2018 ; 2, Vol1 : 012 - 022 Revue scientifique de la Faculté de Médecine de Nouakchott absence of central defects as that found for the second order moment. Conclusion : The first moments of visual field thresholds and deviation values are useful objective measures of the shape of the hill of vision.