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

Jin Young Rhew; Kyu Ryong Choi

doi:10.3341/jkos.2013.54.2.280

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

Original Article

J Korean Ophthalmol Soc 2007;54(2):280-288.

Published online: 24 August 2007

DOI: https://doi.org/10.3341/jkos.2013.54.2.280

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

Jin Young Rhew, MD, Kyu Ryong Choi, MD, PhD

Department of Ophthalmology, Ewha Womans University School of Medicine, Ewha Institute of Ophthalmology and Optometry, EIOO, Seoul, Korea

Address reprint requests to Kyu Ryong Choi, MD, PhD Department of Ophthalmology, Ewha Womans University Medical Center #1071 Anyangcheon-ro, Yangcheon-gu, Seoul 158-710, Korea Tel: 82-2-2650-5154, Fax: 82-2-2654-4334, E-mail: ckrey02@ewha.ac.kr

Received 30 March 201211 September 2012 Accepted 24 January 2013

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

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.

Keywords: Normal tension glaucoma, Ocular Response Analyzer, Young

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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.

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)
N	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)
NTG	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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