Background: Differences in visual field characteristics between normal-tension glaucoma (NTG) and high-tension glaucoma (HTG) have not been established. This study re-examined the problem by pointwise between-group comparison of data obtained with the Humphrey 30-2 program.
Methods: Sixty-eight NTG cases with maximum intraocular pressure (IOP) of 21 mmHg or lower and 62 HTG cases with maximum IOP of 25 mmHg or greater with a mean deviation (STATPAC) greater than -10 decibels (dB) were included. Age, refraction, mean deviation, or sex ratio were matched between the two groups. Total deviation (STATPAC), the difference between the measured threshold and the age-corrected normal reference at each test point of the 30-2 program, was used for pointwise between-group comparisons. Another parameter, total deviation - mean total deviation, was introduced to normalize the total deviation by the overall visual field damage as an index of disease stage. Mean total deviation is the average of total deviations across the test field. Further, logistic discriminant analysis was applied to confirm that the difference at a questioned test point was due to the difference of disease type, but not disease stage, between the two groups.
Results: Comparison using total deviation and total deviation - mean total deviation gave similar results, which were collaborated by logistic discriminant analysis. For a given amount of visual field damage, an area just above the horizontal meridian was significantly more depressed in NTG, while HTG had significantly more diffuse visual field damage.
Conclusion: Visual field defect of NTG differs from that of HTG, which may suggest that different regions of the optic disc are more susceptible to damage in NTG.