Journal List > J Korean Ophthalmol Soc > v.54(2) > 1009591

Rhew and Choi: Corneal Biomechanical Properties of Normal Tension Glaucoma in Young Patients Evaluated with the Ocular Response Analyzer

Abstract

Purpose

To evaluate the corneal biomechanical properties and clinical characteristic of normal tension glaucoma (NTG) in young patients.

Methods

We compared corneal biomechanical properties using an Ocular response analyzer (ORA) of under age 40 of 37 eyes of patients with NTG and 42 eyes of normal group.

Results

The mean corneal resistance factor (CRF) and mean corneal hysteresis (CH) were significantly lower in NTG eyes (CRF, 9.2 ± 2.1 mm Hg; CH, 9.8 ± 1.8 mm Hg) than in normal eyes (CRF, 10.7 ± 2.3 mm Hg; CH, 10.9 ± 2.0 mm Hg; p = 0.01, p < 0.01). CH and CRF were associated with central corneal thickness (CCT) (CH; β = 0.354, p < 0.01, CRF; β = 0.348, p < 0.01) and glaucoma status (p < 0.01, p < 0.01).

Conclusions

The CRF and CH were significantly lower in NTG group while IOP cc was not significantly different between the group. In diagnosing the NTG in young patients, ORA maybe useful for distinguishing between the glaucoma eyes and normal eyes.

References

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Figure 1.
Intraocular pressure values of obtained with Ocular Response Analyzer and Goldman applanation tonometry in normal and normal tension glaucoma patient groups. N = Normal group; NTG = Normal tension glaucoma group; GAT = Goldmann applanation tonometer; IOP cc = cor-neal-compensated IOP; IOP g = Goldmann-correlated IOP.
jkos-54-280f1.tif
Table 1.
Clinical and ocular characteristics of the normal and normal tension glaucoma patient groups
  N (n = 42) NTG (n = 37) p-value
Age (years), mean ± SD 30.7 ± 4.7 27.9 ± 0.10*
range (24-39) 9.7 (12-39)  
Gender, n (%)     0.82
Male 20 (47.6) 19 (51.4)  
Female 22 (52.4) 18 (48.6)  
SE (diopters), mean ± SD -2.4 ± 1.6 -5.1 ± 2.4 <0.01*
Mean K (diopters), mean ± SD 42.3 ± 5.4 42.9 ± 1.8 0.50*
CCT (μm), mean ± SD 549.8 ± 29.1 554.3 ± 31.1 0.52*
Mean Astig (diopters), mean ± SD 1.0 ± 0.6 1.4 ± 0.9 0.08*
Topical glaucoma medications, n (%) 0 37 (100)  
Visual field index      
MD (dB)   -4.4 ± 5.3  
PSD (dB)   5.2 ± 4.7  

N = Normal group; NTG = Normal tension glaucoma group; Astig = Corneal astigmatism; CCT = central corneal thickness; K = keratometry; SD = standard deviation; SE = spherical equivalent.

* Independent t-test

Chi-square test.

Table 2.
Corneal biomechanical parameters by Ocular Response Analyzer in normal and normal tension glaucoma patient groups
  N (n = 42) NTG (n = 37) p-value
GAT (mm Hg)      
mean ± SD 14.7 ± 2.2 14.0 ± 2.6 0.18*
Min-Max 11-20 10.0-20.0  
IOP cc (mm Hg), mean ± SD      
mean ± SD 14.9 ± 3.4 14.5 ± 3.5 0.60*
Min-Max 8.4-26.8 7.0-22.5  
IOP g (mm Hg), mean ± SD      
mean ± SD 14.6 ± 3.4 13.1 ± 3.8 0.05*
Min-Max 8.8-22.7 5.9-19.7  
CRF (mm Hg), mean ± SD      
mean ± SD 10.7 ± 2.3 9.2 ± 2.1 <0.01*
Min-Max 6.1-18.4 6.3-12.8  
CH (mm Hg), mean ± SD      
mean ± SD 10.9 ± 2.0 9.8 ± 1.8 0.01*
Min-Max 7.9-15.9 5.7-14.9  

N = Normal group; NTG = Normal tension glaucoma group; IOP = intraocular pressure; GAT = Goldmann applanation tonometer; IOP cc = corneal-compensated IOP; IOP g = Goldmann-correlated IOP; CRF = corneal resistance factor; CH = corneal hysteresis; SD = standard deviation.

* Independent t-test

Table 3.
Statistical correlations between CH, CRF and clinical/ocular characteristics in normal and normal tension glaucoma patient groups
  Age SE Mean K Astig CCT
N CH -0.085 (0.59) 0.107 (0.50) -0.018 (0.91) 0.231 (0.09) 0.327 (0.04)
CRF -0.013 (0.93) 0.157 (0.32) 0.024 (0.88) 0.245 (0.08) 0.263 (0.09)
NTG CH -0.220 (0.19) 0.092 (0.59) 0.478 (<0.01) -0.261 (0.12) 0.524 (<0.01)
CRF -0.301 (0.07) 0.013 (0.94) 0.449 (<0.01) -0.321 (0.06) 0.642 (<0.01)

N = Normal group; NTG = Normal tension glaucoma group; Astig = Corneal Astigmatism; CCT = central corneal thickness; CH = corneal hysteresis; CRF = corneal resistance factor; K = keratometry; SE = spherical equivalent.

Datas are presented as Pearson's coefficient (p-value).

Table 4.
Statistical correlations between GAT, IOP g, IOP cc and clinical/ocular characteristics in normal and normal tension glaucoma patient groups
  GAT IOP g IOP cc
N Age 0.115 (0.47) 0.187 (0.24) 0.230 (0.14)
SE -0.143 (0.16) 0.048 (0.76) 0.113 (0.47)
Mean K 0.093 (0.56) 0.012 (0.94) -0.079 (0.62)
Astig 0.185 (0.24) 0.136 (0.39) -0.006 (0.97)
CCT 0.208 (0.19) 0.275 (0.07) 0.041 (0.79)
CH 0.266 (0.08) 0.130 (0.41) -0.225 (0.15)
CRF 0.141 (0.38) 0.009 (0.95) -0.315 (0.04)
NTG Age -0.251 (0.14) -0.263 (0.12) -0.130 (0.44)
SE -0.065 (0.70) -0.098 (0.57) -0.144 (0.40)
Mean K 0.204 (0.23) 0.169 (0.32) -0.110 (0.52)
Astig -0.089 (0.60) -0.256 (0.13) -0.228 (0.68)
CCT 0.347 (0.04) 0.463 (<0.01) 0.154 (0.37)
CH 0.252 (0.13) 0.180 (0.29) -0.385 (0.02)
CRF 0.535 (<0.01) 0.682 (<0.01) 0.174 (0.30)

N = Normal group; NTG = Normal tension glaucoma group; Astig = Corneal Astigmatism; CCT = central corneal thickness; CH = corneal hysteresis; CRF = corneal resistance factor; GAT = goldmann applanation tonometer; IOP cc = Corneal-compensated intraocular pressure; IOP g = goldmann-correlated intraocular pressure; K = keratometry; SE = spherical equivalent.

Datas are presented as Pearson's coefficient (p-value).

Table 5.
Multiple linear regression models of factors associated with CH, CRF, IOP cc for the combined two groups
Parameter Partial regression coefficient (β) ± SE Standardized coefficients (β) p-value
CH (adjusted R2 = 0.275)
Age -0.029 ± 0.027 -0.109 0.29
Glaucoma status (0/1) -1.273 ± 0.410 -0.332 <0.01
GAT 0.111 ± 0.086 0.137 0.20
CCT 0.023 ± 0.007 0.354 <0.01
CRF (adjusted R2 = 0.332)
Age -0.038 ± 0.030 -0.123 0.22
Glaucoma status (0/1) -1.651 ± 0.463 -0.354 <0.01
GAT 0.188 ± 0.097 0.197 0.06
CCT 0.027 ± 0.008 0.348 <0.01
IOP cc (adjusted R2 = 0.250)
Age 0.023 ± 0.047 0.050 0.63
Glaucoma status (0/1) 0.301 ± 0.718 0.044 0.67
GAT 0.724 ± 0.151 0.518 <0.01
CCT -0.005 ± 0.012 -0.046 0.66

CH = corneal hysteresis; GAT = Goldmann applanation tonometer; CCT = Central corneal thickness; IOP cc = corneal-compensated IOP; CRF = corneal resistance factor.

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