The demographic data and clinical characteristics of all participants are presented in Table 1. There were no significant differences in mean age and gender distribution among the NTG, POAG and normal groups (P = 0.375 for age and P = 0.212 for gender). Nine eyes of POAG and eight eyes of NTG were newly diagnosed and had not started medicine treatment when enrolled, and they did not have significant difference in age and gender distribution either (P = 0.485 for age and P = 0.707 for gender). Neither did the POAG patients with and without treatment (P = 0.544 for age and P = 0.907 for gender). The medication time for the POAG patients (prostaglandin analogs only or combined with beta-blockers) ranged from 1 to 50 months with the average of 17.86 ± 16.66 months.
Comparison of the CCM parameters of CSNP and LCs among the POAG, the NTG and the normal
Firstly, we analyzed all patients including treated and untreated as well as the healthy subjects. The NTG group had the longest nerve FL of 3494.60 ± 523.01 µm while it was 3156.79 ± 643.92 µm in the POAG and 3223.78 ± 617.06 µm in the normal. However, no significant difference was identified in the value of nerve FL among the three groups (Table 2). NTG also had the most BN (19.78 ± 5.56), and both POAG (17.55 ± 5.62) and NTG groups had more nerve BN than the normal (13.38 ± 5.44) with the P values of 0.008 and 0.003 respectively. The NTG group had the thinnest FW of 2.96 ± 1.20 µm and the POAG group had the thickest of 3.65 ± 0.69 µm. The difference between the two groups was significant (p = 0.043). The POAG had the highest FR of 153.09 ± 14.12, much brighter than the NTG (143.03 ± 14.01) and the normal (143.91 ± 15.91) (p = 0.069, and p = 0.033 respectively). The NTG had the highest total NT (1.09 ± 0.07) and the lowest local NT (125.10 ± 11.15) indicating the most bending and tortuous trend of the corneal nerve in the NTG. The normal subjects had the lowest total NT (1.06 ± 0.03) and the highest local NT (132.07 ± 11.00) suggesting a relatively straight direction of the nerve. The total and local NT of POAG (1.07 ± 0.03 and 130.56 ± 13.03) were in the middle of the NTG and the control (Table 2).
It showed no difference among three groups as for total LC, neither for the type 1 LC which was the mature form of the cell. However, type 2 LC existed in more POAG and NTG patients than in the control and the differences were significant (p = 0.024, p = 0.027 respectively).
Secondly, we analyzed each CNSP parameters between the untreated NTG and untreated POAG patients (both marked with m-) to exclude the potential impact of antiglaucoma eye drops.
The NTG m- group had the longest nerve FL of all three groups with a length of 3646.10 ± 457.09 µm, while it was 3026.25 ± 684.28 µm in the POAG m- and 3223.78 ± 617.06 µm in the normal. The differences were 0.047and 0.079 respectively. NTG m- group also had more BN (20.75 ± 5.86) than the other two groups, and the P values were 0.089 and 0.002 for POAG m- and the control respectively. The NTG m- had the thinnest FW of 2.52 ± 0.81 µm (p = 0.007 and p = 0.018 for the control and POAG m- respectively). The NTG m- had the lowest NR of 139.50 ± 13.30 while it was 143.91 ± 15.91 for the normal and 150.70 ± 14.89 for the POAG m-, but the difference was not significant among the three. Though POAG m- group had more BN, NW and NR than the normal the difference was not significant. The NTG m- had the highest total NT (1.10 ± 0.07) and the lowest local NT (121.56 ± 9.35) also suggesting a tortuous feature. The POAG m- showed similar NT to the control (Table 3).
The POAG m- and the NTG m- patients had more type 2 LC than the control (p = 0.08, p = 0.052 respectively). The NTG m- also showed more type 1 LC and total LC and the difference was significant when compared with the POAG m- (p = 0.03 and p = 0.024 respectively).
From the above results, the CSNP of NTG group no matter with or without medication could be described as thin and tortuous nerves with many branches and lower reflectivity. The POAG no matter with or without medication had CSNP more similar to that of the control with higher nerve reflectivity, wider nerve width, less nerve length, and less nerve branches and had a more straight trend than the NTG. Both the NTG and POAG patients had more type 2 LC than the normal (Fig. 1).
Comparison of CCM parameters of CSNP and LCs in treated and untreated POAG
We analyzed each CSNP parameters between the treated (marked as m+) and untreated (marked as m-) eyes in POAG group. Both POAG m + and m- patients had more nerve branches, wider nerve width, higher reflectivity than the control. However, the difference between POAG m- and the control group did not reach statistical significance (Table 2). The difference between POAG m + and the control was significant for BN and NR (p = 0.002, p = 0.036 respectively). Though POAG m + had longer nerve FL, more BN, FW, FR, more nerve tortuosity than POAG m-, the difference was not significant (Table 2).
POAG m + and POAG m- had more type2 LC than the control (p = 0.034 and p = 0.08 respectively), but the type 1 and total LC had no significant difference among three groups.
Correlation between CCM parameters and medication duration in the POAG
The correlation between each CCM parameters and the duration of anti-glaucoma medicine treatment in the POAG patients was analyzed and no significant association could be seen (Table 3).
Correlation analysis between CCM parameters and OCT findings in the POAG, the NTG and the normal
The correlation of peripapillary RNFL thickness and the corneal nerve parameters were analyzed in the POAG, NTG and the normal groups.
In POAG group, the nerve FL was associated with the superior quadrant of RNFL thickness (r = 0.547, p = 0.043). Both the superior and nasal quadrants of RNFL thickness were statistically correlated with nerve BN. (nasal: r = 0.568, P = 0.034; superior: r = 0.535, P = 0.049). The brightness of nerve FR had significant correlations with all but the nasal quadrant of RNFL thickness (Table 4). The nerve FW and NT were not associated with the thickness of peripapillary RNFL. Neither was the LC existence.
All but the temporal quadrants of RNFL thickness were statistically correlated with nerve BN in the NTG (Table 4). The total NT had significant correlation with the inferior and the nasal quadrants (inferior: r=-0.829, p = 0.042; nasal: r=-0.972, r = 0.001). The type 2 LC existence was associated with the superior quadrant of peripapillary RNFL thickness (r=-0.878, p = 0.021).
None but the inferior quadrants of RNFL thickness was statistically correlated with NR in the control (Table 4). No other correlations were identified.