Analysis of the retinal sensitivity distribution in MP-3 perimetry revealed that a lower VF sensitivity in the MP-3 corresponded to the larger discrepancy in the VF sensitivity between the HFA 10-2 and MP-3. The difference in retinal sensitivity caused by increased test–retest and intra-test variability with disease severity, as previous reports suggest,
29,30 is a possible reason. By contrast, the misalignment of the retinal sensitivity distribution tended to be more frequent in patients with milder POAG. Additionally, there was no statistical correlation between the misaligned VF sensitivity distribution and age or HFA 10-2 reliability indices such as FL, FP, or FN rates. It is possible that factors other than reliability indices or age were involved. We propose the influence of eye movements as a contributing factor to the difference in distribution. Previous reports have shown that eye movements within 2° occurred in approximately 70% of the overall fixation time in patients with glaucoma
4,14; however, it has also been reported that small eye movements (i.e., less than 3°) during VF measurement are unavoidable, even in well-trained healthy individuals.
31,32 It was reported that patients with glaucoma can have multiple defects in different areas of the visual field and make rather fewer saccades than healthy controls.
33 We hypothesized that, in patients with advanced POAG, in whom the extent or depth of visual field defects is greater, the areas of the retina capable of fixation are limited; thus, the shift in the distribution of retinal sensitivity tends to be less pronounced. FLs are considered to be elevated consistently after the third decade of life,
34 and our results showed significant difference in the age of patients with severe POAG (
P = 0.04). However, there was no significant difference in FL rates across POAG severities (
P = 0.26), which would support this hypothesis. It is difficult to define an appropriate compensatory eye movement strategy for glaucoma solely using the parameters equipped in the HFA 10-2 and MP-3. Several tracking recording methods have been proposed to measure eye movements that may affect the reliability of VF measurements.
4,35 Validations with the addition of such parameters by implementing gaze-tracking or eye- and head-tracking technologies in the MP-3 can be a topic for further study.