If we assume that
Fc and EVP are constant between C57BL/6J, BALB/cJ, and CBA/J mice, then the regression in
Figure 5A predicts (excluding the outlier) that
Fc = 0.068 ± 0.044 μL/min and EVP = 7.1 ± 3.2 mm Hg (mean ± SD). Whether
Fc and EVP truly are constant between strains is an open question. However, the strong agreement between
Equation 5 and our data (
R2 = 0.70,
N = 13 mice) suggests that
Fc and EVP are reasonably consistent between C57BL/6, BALB/cJ, and CBA/J strains, or that any variation in
Fc and EVP between strains has relatively minor influence (≤30%) on IOP compared to the principal dependence of IOP on 1/
C. We point out that a portion of the remaining 30% influence is likely attributable to experimental uncertainty in the measurements themselves. The value of EVP estimated by linear regression (7.1 mm Hg) agrees fairly well, but tends to be slightly higher than published values from the same strains using the blood-reflux technique
21 (compare to 5.4 mm Hg for BALB/cJ
8 and 6.3 mm Hg for C57BL/6J
35) that requires anesthesia where EVP may be depressed artificially. The value of
Fc estimated by linear regression (0.068 μL/min) also fits within the published range for
Fc that varies 3-fold between strains (0.032 μL/min in NIH Swiss White,
21 0.060 μL/min for C57BL/6,
35 and 0.111 μL/min for BALB/cJ
8), which may be related to methodologic differences between studies or true physiologic differences between strains. It should be pointed out that
Fc lumps effects of
Fin and
Fu , such that variations in
Fin between strains may be masked by compensatory differences in
Fu (or vice versa), and this approach, therefore, is unable to make inferences about
Fin or
Fu without additional data beyond
C and IOP. We attempted to perform regression analysis on each strain individually, so as to estimate values of
Fc and EVP for each strain, but the small numbers of mice (3–6 per strain) made this analysis unreliable.