For the young group, all within-subject factors were significant (head position F1,12 = 28.3, P < 0.001; drug F1,12 = 172, P < 0.001; accommodation F1,12 = 18.0, P = 0.001) and there was significant interaction between head position and drug state (P = 0.01). For the older group, all factors were significant (head position F1,9 = 19.3, P = 0.002; drug F1,9 = 16.8, P = 0.003; accommodation F1,9 = 9.9, P = 0.012) and there was significant interaction between head position and accommodation (P = 0.045). Prone head position, drug instillation, and maximum accommodation decreased ACD compared to upright head position, no drug instillation, and minimum accommodation, respectively.
The main finding for the young group is that head position affected ACD for all drug state and accommodation combinations (
Fig. 3c), but mean effects were small at 0.04 to 0.07 mm and much smaller than reported in the literature.
2,17–20 The main finding for the older group was that the head position affected ACD only when the drug pilocarpine was being used, with mean effects of only 0.10 to 0.12 mm (
Fig. 3c).