One of the most controversial risk factors for predicting progression is the severity of the baseline VF. Despite a number of prospective studies performed to investigate whether the initial VF had any predictive power for subsequent progression, different conclusions were reached. In the CIGTS, it was found that patients with higher VF scores at baseline had higher VF scores during follow-up.
30 This was repeated by the results in the Early Manifest Glaucoma Trial (EMGT), which reported an increased risk for progression in patients with MD worse than –4 dB.
9 Conversely, the AGIS found that lesser VF defect increased the risk for additional VF loss.
31 Interestingly, using the same AGIS VF scoring system, Chen and Park
10 showed that an increased initial AGIS score was associated with progression. Although most studies supported the finding that increased severity of initial visual field was associated with further visual field worsening,
9 10 11 12 30 32 others showed no association,
6 7 8 and a few arrived at the same conclusions reported in the AGIS.
33 34 In the present study, regression analysis revealed that first-order inverse regression best described the relationship between the AGIS/CIGTS VF scores and StratusOCT-measured RNFL thickness
(Figs. 5B 6B) . Assuming the rate of loss of the retinal ganglion cell and its nerve fiber in glaucoma is constant during progression, our results provide an explanation for the findings in those longitudinal studies showing that increased severity of VF defect (documented by the AGIS/CIGTS VF scores or MD) at baseline indicates higher risk for progression. For the same degree of structural damage (reduction in RNFL thickness), the decrease in VF score or decibel is more dramatic in the advanced stages of the disease than in the early stages. For example, based on the regression functions in the study
(Figs. 5B 6B) , a reduction in RNFL thickness from 80 to 70 μm (in the early stage) would lead to a corresponding increase in the AGIS score of 2.0 and in the CIGTS score of 2.1. When the RNFL thickness is reduced from 50 to 40 μm (in the advanced stage), the corresponding increase in the AGIS and the CIGTS scores would be 5.7 and 5.9, respectively. Therefore, it is easier to detect the change in VF progression in VF scores during the moderate/advanced stages of disease, leaving the impression of increased risk for progression when the baseline VF scores are high. Therefore, the current AGIS and CIGTS scoring systems are considered less sensitive for detecting progression in the early stages of glaucoma because the steps for progression (an increase in score of 4 in the AGIS and 3 in the CIGTS) is defined independently of the disease stage. Consistent with earlier investigations, we demonstrated the CIGTS VF scores were systematically higher than the AGIS VF scores, and both scorings were highly correlated with each other and with the VF MD.
35 36 Our results are also consistent with the findings of longitudinal studies showing that the CIGTS scoring method leads to higher rates of detection of disease progression than the AGIS scoring system.
35 37