The median of UCVA (approxETDRS letter scores) of pterygia eyes was 69, with upper and lower quartiles of 65, 73. The median of UCVA (approxETDRS letter scores) of control eyes was 80, with upper and lower quartiles of 73, 84. UCVA was significantly lower in the pterygia eyes (P<0.001). BCVA was comparable between the two groups (P=0.509). (Table 1).
Table 1 Visual Acuities (approxETDRS letter scores) in the two groups
|
|
Pterygium eye
median( QR )
|
Control eye
median( QR )
|
P*
|
UCVA(approxETDRS letter scores)
|
69( 65, 73)
|
80( 73, 84)
|
<0.001
|
BCVA(approxETDRS letter scores)
|
77( 69, 82)
|
80(73, 84)
|
0.509
|
*Mann–Whitney U test (median( upper QR, lower OR )
|
|
|
|
|
The HL of pterygium ranged from 0.33 to 5.06 mm, with a mean of 2.00±1.12 mm. The VL of pterygium ranged from 2.38 to 8.92 mm, with a mean of 5.11±1.17 mm. The thickness of pterygium ranged from 36 µm to 458 µm, with a mean of 192.93±118.42. Pterygia HL (Rho: -0.531 and P< 0.001) , VL (Rho: -0.322 and P=0.012) and thickness (Rho: -0.399 and P=0.002) of pterygia were found to be negatively correlated with UCVA (Table 2). There were no statistically correlation between the indices and the BCVA of pterygium (Table 2).
Table 2. Corneal refractive power (D) in the two groups
|
|
Pterygium eye
|
Control eye
|
P
|
Front (3mm)
|
43.17± 2.68
|
44.39± 1.53
|
<0.01#
|
Back (3mm)
|
-6.36( -6.55, -6.10)
|
-6.36( -6.34,-6.21)
|
0.98*
|
Front (7mm)
|
42.07± 2.66
|
44.12± 1.39
|
<0.01#
|
Back (7mm)
|
-5.98( -6.23, -5.35)
|
-6.23( -6.33, -6.09)
|
<0.01*
|
Sim K
|
43.12( 41.97, 44.29)
|
44.09( 43.37, 45.27)
|
<0.01*
|
*Mann–Whitney U test (median( upper QR, lower OR )
# Independent samples t test (x̄±s)
QR: quartile range
|
In pterygium and control group, the mean ± SD pupil diameters measured with Sirius Scheimpflug Analyzer under scotopic conditions were 6.88±0.60 mm and 6.87±0.67 mm. There were no statistical difference of the pupil diameters between the two groups(P=0.943, independent samples t test). Therefore, for corneal astigmatism value and aberration analysis in the natural-light and low-light condition, the corneal zone of 3mm and 7mm were selected .
Corneal refractive power of front cornea were significantly lower in the pterygium group compared with control group. For corneal refractive power of back cornea in the 3mm zone, there were no statistical difference between the two groups. For the corneal refractive power of back cornea in the 7mm zone, K values of were significantly higher in the pterygium group compared with contol group. Detailed data about the K values of front and back cornea and Sim K was presented in Table 2.
The astigmatigmatism values of front cornea both at 3mm and 7mm zone, back cornea at 7mm zone and Sim K were significantly higher in the pterygium group compared with control eyes. For the astigmatism of the back cornea at 3mm zone, there were no significant difference between the two groups (Table 3). The HL and thickness of cornea vere positively correlated with all the astigmatic values. There were also a relatively weak positive correlation between the VL and astigmatic values except for the astigmatic values of the back cornea at 3mm zone(table 4).
Table 3. Topographic Astigmatism in the two groups
|
|
Pterygium eye
|
Control eye
|
P*
|
Front corneal astigmatism(3mm)
|
1.67( 0.64, 4.36)
|
0.82(0.49, 1.28)
|
0.002
|
Back corneal astigmatism(3mm)
|
0.30( 0.18, 0.63)
|
0.34( 0.21, 0.45)
|
0.287
|
Front corneal astigmatism(7mm)
|
3.26( 1.08, 11.08)
|
0.68( 0.37, 1.13)
|
<0.001
|
Back corneal astigmatism(7mm)
|
0.77( 0.22, 2.97)
|
0.19(0.12, 0.30)
|
<0.001
|
Sim K astigmatism(D)
|
1.47( 0.72, 8.70)
|
0.69( 0.41, 1.18)
|
<0.001
|
*Mann–Whitney U test (median( upper QR, lower OR )
|
|
Table 4. The correlation between the pterygia sizes and corneal astigmatism and aberrations
|
|
HL
|
VL
|
Thickness
|
rs
|
p
|
rs
|
p
|
rs
|
p
|
Front corneal astigmatism(3mm)
|
0.636
|
<0.001
|
0.377
|
0.003
|
0.448
|
<0.001
|
Back corneal astigmatism(3mm)
|
0.452
|
<0.001
|
0.252
|
0.052
|
0.295
|
0.022
|
Front corneal astigmatism(7mm)
|
0.809
|
<0.001
|
0.556
|
<0.001
|
0.692
|
<0.001
|
Back corneal astigmatism(7mm)
|
0.574
|
<0.001
|
0.405
|
0.001
|
0.512
|
<0.001
|
Sim K astigmatism(D)
|
0.705
|
<0.001
|
0.422
|
0.001
|
0.566
|
<0.001
|
Total corneal abberation ( 3mm)
|
0.444
|
<0.001
|
0.244
|
0.06
|
0.337
|
0.008
|
Higher-order abberation( 3mm)
|
0.515
|
<0.001
|
0.283
|
0.029
|
0.354
|
0.006
|
Total corneal abberation ( 7mm)
|
0.456
|
<0.001
|
0.101
|
0.442
|
0.360
|
0.005
|
Higher-order abberation ( 7mm)
|
0.413
|
<0.001
|
0.105
|
0.425
|
0.402
|
0.001
|
rs: Spearman's rank correlation coefficient
|
Regarding the types of astigmatism of the front cornea, with-the-rule astigmatism ,against-the-rule astigmatism and oblique astigmatisam were present in 37 eyes (61.7%) ,12 eyes (21.7%) and 10 eyes (16.7%) in perygium eyes, and 25 eyes (41.7%), 22 eyes (36.7%) and 13 eyes (21.7%) in control eyes at 3mm zone (P=0.004, chi-square test). At 7mm zone, the 3 types of astigmatism were present in 50 eyes (83.3%), 5 eyes (8.3%) and 5 eyes (8.3%) and 18 eyes (30%), 25 eyes (41.7%) and 17 eyes (28.3%) in pterygium group and control group (P=0.015, chi-square test). (Fig 1).
The back corneal astigmatism was with-the-rule in 33 eyes (55%), against-the-rule in 10 eyes (16.7%) and oblique in 17 eyes (28.3%) at 3mm zone in pterygium group and these numbers were 55 eyes (91.7%), 2 eyes (3.3%) and 3 eyes (5%) respectively in control group (P<0.001, chi-square test). At 7mm zone, the 3 types of astigmatism were present in 51 eyes (85.0%), 4 eyes (6.7%), 5 eyes (8.3%) and 43 eyes (71.7%), 11 eyes (18.3%) , 6 eyes (10.0%) in pterygium group and control group (P<0.001, chi-square test). (Fig 2).
When RMS values were compared between the pterygium group and control group, all RMS values in the pterygium group were significantly higher than those in the control group (Table 4).These values were found to be positively correlated with both HL and thickness of pterygium. There was only a weak positive correlation between the pterygium VL and the was not statistically correlated with the RMS values of higher-order aberration at 3mm zone. The remaing RMS values werenot found to have any statistical correlation with the pterygium VL. Details of the correlation between the RMS values of optical aberrations and HL, VL and thickness of pterygium on the surface of the cornea were documented in Table 5.
Table 5. The Change of corneal HOAs and total aberrations between pterygia group and control group
|
Parameters (RMS)
|
Pterygium eye
|
Control eye
|
P*
|
Total abberations( 3mm)
|
0.42(0.26, 0.82)
|
0.27( 0.15, 0.40)
|
0.001
|
HOAs( 3mm)
|
0.21(0.14, 0.40)
|
0.11( 0.09, 0.19)
|
<0.001
|
Total abberations( 7mm)
|
3.94( 2.60, 5.61)
|
2.30( 1.87, 3.16)
|
<0.001
|
HOAs( 7mm)
|
2.96( 2.04, 5.03)
|
1.84( 1.54, 2.14)
|
<0.001
|
*Mann–Whitney U test (median( upper QR, lower OR )
|
Comparing the parameters of different corneal 3mm zone and 7mm, which represented the natural-light and low-light conditions, the difference between pterygia group and control group of anterior astigmatism, posterior astigmatism, total corneal aberrations and higher-order aberrations at 7mm zone were significantly larger than those at 3mm zone (P=0.003, P<0.001, P=0.003, P<0.001)(Fig 3).