Among total 79 patients, 10 patients were excluded from final analysis. 8 patients excluded due to unreliable OBFA result and 2 patients showed unreliable DCT result.
Ultimately, 69 eyes in 69 patients were included in the analysis. Of them, 31 eyes of 31 patients and 38 eyes of 38 patients were divided into the normal and NTG groups, respectively. IOP measurements by the three devices were lower in the NTG group than in normal patients (p < 0.05), likely because all NTG patients were using topical IOP-lowering medications (average number of meds = 1.7 ± 1.1). OPA was also lower in the NTG group.
There were no significant differences in the ocular pulsatile component measurements by OBFA (PA, PV, and POBF) or ORF between normal and NTG groups (Table 1).
Table 1. Descriptive statistics of enrolled subjects.
*, T-test; †, Fisher’s exact test Values are presented in mean ± SD.
BFA, blood flow analyzer; CCT, central corneal thickness; DCT, dynamic contour tonometry; GAT, Goldmann applanation tonometry; IOP, intra ocular pressure; MAP, mean arterial pressure; MD, mean deviation; MOPP, mean ocular perfusion pressure; NTG, normal tension glaucoma; OPA, ocular pulse amplitude; ORF, Ocular rigidity-related factor;
PA, pulse amplitude measured by BFA; POBF, pulsatile ocular blood flow measured by BFA; PP, pulse pressure; PR, pulse rate; PSD, pattern standard deviation; PV, pulse volume measured by BFA; RNFLT, retinal nerve fiber layer thickness; SD, standard deviation; SE, spherical equivalent.
As shown in Table 2, all IOPs measured by each device were positively correlated with MAP, but PP and MOPP were not correlated with IOPs measured by all devices. OPA, PA and POBF were not correlated with MAP, PP, and MOPP whereas ORF significantly correlated with PP. CCT correlated positively with GAT IOP (r = 0.247, p = 0.041) but not with DCT IOP (r = 0.156, p = 0.199) and with OBFA IOP (r = 0.060, p = 0.623). CCT did not correlate significantly with OPA, PA, POBF, or ORF. SE of refractive error was significantly correlated with OPA, PA and POBF but not with ORF (Table 2).
Table 2. Correlations between IOP or OPA-derived parameters and systemic or other ocular parameters in total patients.
Age MAP PP MOPP CCT SE Values are presented in Pearson correlation coefficient R (P value in parenthesis).
BFA, blood flow analyser; CCT, central corneal thickness; DCT, dynamic contour tonometry;
GAT, Goldmann applanation tonometry; IOP, intraocular pressure; MAP, mean arterial pressure; MOPP, mean ocular perfusion pressure; OPA, ocular pulse amplitude measured by DCT; ORF, ocular rigidity-related factor; PA, pulse amplitude measured by BFA; POBF, pulsatile ocular blood flow measured by BFA; PP, pulse pressure; SE, spherical equivalent.
As shown in Table 3, DCT OPA correlated positively with GAT and DCT IOPs, and showed a significant correlation with PA (r = 0.753, p < 0.001) and POBF (r = 0.512, p <
0.001) measured by OBFA. In contrast, OBFA PA was not significantly correlated with any IOP measurements by the three devices. POBF showed a negative correlation with IOPs (r = -0.236 to -0.356, p < 0.05) but a positive correlation with OPA (r = 0.562, p < 0.001) and PA (r = 0.750, p < 0.001). ORF correlated positively with all IOPs (r = 0.262 to 0.434, p < 0.03), but negatively with PA (r = -0.298, p = 0.013) and POBF (r = -0.394, p = 0.001). Those inter-relationship of OPA and ORF with other parameters such as IOPs and OBFA measured factors are diagrammatically described in Fig. 1.
Table 3. Correlations between OPA-derived parameters and IOP measurements in total Values are presented in Pearson correlation coefficient R (P value in parenthesis).
BFA, blood flow analyzer; DCT, dynamic contour tonometry; GAT, Goldmann applanation tonometry; OPA, ocular pulse amplitude measured by DCT; ORF, ocular rigidity-related factor; PA, pulse amplitude measured by BFA; POBF, pulsatile ocular blood flow measured by BFA.
Fig. 1. Inter-relationship of OPA and ORF with IOPs and OBFA measured parameters in total patients. OPA showed statistically significantly positive relationship (straight line) with GAT, DCT IOP, PA, and POBF. PA and POBF showed positive correlation, too (left).
ORF showed significantly positive correlation with GAT and DCT IOP but negative correlation (dashed line) with PA and POBF (right). Pearson correlation coefficient R and P values were described in parenthesis. DCT, dynamic contour tonometry; GAT, Goldmann applanation tonometry; IOP, intraocular pressure; OBFA, ocular blood flow analyzer; OPA, ocular pulse amplitude measured by DCT; ORF, ocular rigidity-related factor; PA, pulse amplitude measured by OBFA; POBF, pulsatile ocular blood flow measured by OBFA.
In a subgroup analysis in the NTG group, OPA, PA and POBF did not show any significant correlation with MD, PSD, or RNFL thickness parameters. ORF was correlated significantly with nasal (r = -0.336, p = 0.039), inferior (r = -0.439, p = 0.006), and average (r = -0.372, p = 0.022) RNFL thickness. ORF showed a significant correlation with the MD determined by VF tests (r = -0.389, p = 0.016), but POBF did not (Table 4). Although correlation between ORF and RNFL thickness could not be evaluated in total patients because most of normal subjects did not take OCT exam, ORF was significantly correlated with MD by VF tests (r = -0.246, p = 0.042) in total patients. Diagrammatical relationship between ORF and the parameters indicating glaucoma severity is described in Fig. 2.
Table 4. Correlations between IOP or OPA-derived parameters and indices of glaucomatous damages in normal tension glaucoma patients.
MD PSD
Values are presented in Pearson correlation coefficient R (P value in parenthesis).
IOP, intraocular pressure; OPA, ocular pulse amplitude; GAT, Goldmann applanation tonometry; DCT, dynamic contour tonometry; BFA, blood flow analyzer; Inf, inferior;
MD, mean deviation; ORF, Ocular rigidity related factor; PA, pulse amplitude measured by BFA; POBF, pulsatile ocular blood flow measured by BFA; PSD, pattern standard deviation; RNFL, retinal nerve fiber layer; Sup, superior.
Fig. 2. Relationship between ORF and the parameters indicating glaucoma severity which is MD in Humphrey visual field test and RNFL thickness in Cirrus OCT test in NTG subgroup analysis and total patients. ORF showed significantly negative correlation (straight line) with MD from Humphrey VF and nasal, inferior and average RNFL thickness in cirrus OCT in NTG subgroup analysis. In total patients, ORF showed significantly negative correlation with MD from Humphrey VF. Pearson correlation coefficient R and P values were described in parenthesis. Other parameters such as PA, OPA or POBF did not show any clinically significant relationship. MD, mean deviation; OCT, optical coherence topography; OPA, ocular pulse amplitude measured by dynamic contour tonometry; ORF, ocular rigidity-related factor; PA, pulse amplitude measured by ocular blood flow analyzer;
POBF, pulsatile ocular blood flow measured by ocular blood flow analyzer; RNFL, retinal nerve fiber layer; VF, visual field test.