In medical practice, glaucoma severity is usually measured using the Advanced Glaucoma Intervention Studies (AGIS) metric. In a previous study, we replicated the work of Montolio et al.,and demonstrated that, for a larger dataset, time of day of test using the AGIS metric did make a difference to the measurement of glaucoma, supporting Montolio et al’s work. However, in our earlier study, we used the AGIS scores for both eyes combined. In this paper, we use the measurement from just one eye at a time. A dataset of 14,389 left eye AGIS scores and the same number for the right eye from 2468 Moorfield Eye Hospital patients was used as the empirical basis. We then re-compared time of test results with those of Montolio’s study. Results revealed that using the values from just one eye (as opposed to both) may give a distorted picture of the AGIS scores; differences in the same time period were found between the two eyes. This may have implications for choice of sampling data and analysis of glaucoma using the AGIS metric.