Comparison of Clinical Characteristics Between Korean and Western Normal-Tension Glaucoma Patients


To detect potential differences in the phenotypes between Western normal-tension glaucoma (NTG) and Korean NTG.


A retrospective, cross-sectional study.


One hundred eighty-four NTG eyes of 71 patients of the Jules Stein Eye Institute, University of California, Los Angeles, and 113 patients of the Seoul National University Hospital, Seoul, Korea, were studied after reviewing medical charts retrospectively. All eligible patients from both institutions who were evaluated between July 2007 and June 2008 were included. The groups were matched for stage of glaucoma severity based on the visual field mean deviation value. All patients underwent a complete ophthalmic examination, Humphrey perimetry, Heidelberg Retina Tomography, Stratus optical coherence tomography, and pachymetry. Structural and functional parameters between the 2 groups were compared.


There were no statistically significant differences in the baseline intraocular pressure, disc area, frequency of disc hemorrhage, or peripapillary atrophy ( P > .05). Cup-shape measure (by Heidelberg Retina Tomography), average RNFL thickness (by Stratus optical coherence tomography), and central corneal thickness were significantly different ( P < .002). The eyes of Korean NTG patients showed higher values for cup-shape measure, higher average RNFL thicknesses, and thinner central corneal thicknesses than Western NTG patients. The difference was significant ( P < .001) while controlling for age, sex, disc area, mean deviation, pattern standard deviation, and spherical equivalent with multivariate analysis.


Korean NTG patients showed steeper cup shapes, thicker RNFL thickness, and thinner central corneal thickness compared with Western NTG patients with similar amounts of visual field loss. This result may help clinicians understand the clinical characteristics of NTG patients and points to the heterogeneous character of the glaucomas.

Glaucoma is an irreversible, progressive, and heterogeneous optic neuropathy. Because it is apparent that there is a substantial diversity in glaucoma types according to race, the characterization population difference was investigated previously. Primary open-angle glaucoma (POAG) with high intraocular pressure (IOP) is the most common type in white persons; however, in some races, the proportion of normal-tension glaucoma (NTG) or angle-closure glaucoma is higher. Furthermore, retinal nerve fiber layer (RNFL) thickness profiles may differ according to ethnicity. The identification of such differences may provide clues to understanding the variation in racial susceptibility to glaucomatous damage.

NTG commonly is defined as open-angle glaucoma with untreated IOP of less than 22 mm Hg. In east Asia, NTG is the most common form of open-angle glaucoma. In a recent study, the prevalence of Japanese patients with POAG and IOP levels of 21 mm Hg or less was found to be 3.6%, whereas the prevalence of those with IOP levels of more than 21 mm Hg was 0.3%, and the average IOP for eyes with POAG was approximately 15 mm Hg. In Koreans, the estimated prevalence of POAG with an IOP of 21 mm Hg or less is 2.7%, and the estimated prevalence of POAG with an IOP of 22 mm Hg or more is 0.8%. The mean IOP for POAG eyes was 16.3 mm Hg in that same study. Patients have been found to differ with respect to structural differences as well. For example, black persons with ocular hypertension had significantly larger optic discs, deeper cups, thicker neuroretinal rims, and higher cup-to-disc ratios compared with other racial groups. In the present study, we investigated the potential differences in phenotype between Asians and white persons with NTG.


We retrospectively reviewed medical records in this cross-sectional study. Our study included 184 NTG eyes from 71 white patients who visited the Jules Stein Eye Institute, University of California, Los Angeles, and 113 patients who visited the Seoul National University Hospital, Seoul, Korea, for glaucoma and who did not have other ocular conditions aside from glaucoma. We also analyzed 30 normal control eyes from 30 patients at each institution who were diagnosed as healthy. We included only 1 eye of each patient in our analysis. If both eyes were eligible, we randomly selected 1 eye. For simplicity, we use the terminology Korean and Western in this study. Korean subjects were frequency matched for glaucoma severity with Western patients based on visual field mean deviation (MD). This study with retrospective review of patient data was approved by the Institutional Review Boards of the Seoul National University Hospital Clinical Research Institute and the University of California at Los Angeles, was performed in accordance with the tenets of the Declaration of Helsinki, and is in compliance with the Health Insurance Portability and Accountability rules and regulations governing such work.

Patient demographic characteristics, including gender, age, and medical histories, were collected. Each patient underwent a complete ophthalmic examination, including funduscopy. Gonioscopic angle evaluation was performed to exclude angle-closure patients. Inclusion criteria included patients with glaucoma with glaucomatous optic nerve head damage, retinal nerve fiber layer abnormalities that corresponded to the visual field defects, or both. Exclusion criteria included a history of intraocular disease, ocular injuries, intraocular or extraocular surgery, laser treatment, optic nerve disease other than glaucoma, or abnormal optic nerve shape (e.g., coloboma, optic nerve hypoplasia, morning glory disc anomaly, etc.). Eyes with IOPs of more than 22 mm Hg and best-corrected visual acuity of 20/40 or worse also were excluded.

We measured RNFL thickness with the same imaging devices at both sites, the Stratus optical coherence tomography (OCT) device (version 4.0; Carl Zeiss Meditec, Dublin, California, USA) and the Heidelberg Retina Tomography (HRT III) device (Heidelberg Engineering, Heidelberg, Germany). Fundus photographs of the retina and stereo disc photographs were obtained with a Zeiss fundus camera. Visual field tests were performed using the 24-2 program of the Humphrey visual field analyzer (Zeiss Inc, San Leandro, California, USA) with the standard Swedish interactive threshold algorithm. Central corneal thickness (CCT) was measured with an ultrasonic pachymeter (Cinescan; Quantel Medical, Bozeman, Montana, USA), and the average of 3 measurements was recorded. Measurements of axial length were performed with the IOLMaster (Carl Zeiss Meditec, Jena, Germany).

We analyzed the data with chi-square and independent t tests using a commercially available statistical software package (SPSS version 17.0; SPSS, Inc, Chicago, Illinois, USA). All P values were 2-sided and were considered statistically significant when less than .05.


Demographic characteristics for the NTG patients are shown in Table 1 . There was a significant difference in age, with Western NTG patients being older ( P < .001). The gender, refractive error, baseline IOP, and MD value and pattern standard deviation value of the visual field did not show clinically significant difference. Of the baseline characteristics ( Table 2 ), Korean NTG patients have significantly less family history ( P < .001). There were no clinically significant differences in the prevalence of systemic hypertension, hypotension, diabetes, migraine, or cold hands. Several parameters differed significantly between groups. Of the ocular parameters, the cornea was thicker in Western NTG patients than in Korean NTG patients ( P < .001). Disc hemorrhage, peripapillary atrophy, and axial length did not show significant differences ( Table 3 ). The HRT parameters for NTG patients are shown in Table 4 . Cup-shape measure parameters showed that Korean NTG patients have significantly steeper cups ( P = .001), whereas the disc area and rim area were not different between the 2 groups. Of the OCT parameters, all tested OCT thickness parameters were significantly different ( Table 5 ; P < .05). In multivariate analysis after adjusting for age, sex, disc area, MD, pattern standard deviation, and spherical equivalent ( Table 6 ), cup-shape measure, average RNFL thickness assessed by OCT, and central corneal thickness showed significant differences between the groups ( P < .05). Figures 1 and 2 show the scatterplots of cup-shape measure obtained by HRT and the average RNFL thickness measured by OCT versus MD of the visual field, respectively. In comparison with the control groups, normal Korean subjects have significantly thicker RNFL than normal Western subjects ( Table 7 ; P < .05).

Table 1

Baseline Ocular and Demographic Characteristics of Western and Korean Normal-Tension Glaucoma Patients

Western Korean P Value a
No. of patients 71 113
Age (y) 65.1 ± 10.4 52.9 ± 12.3 <.001
Gender (% male) 43.7 55.8 .111
Spherical equivalent (D) −2.40 ± 3.85 −2.23 ± 3.56 .771
Baseline IOP 14.5 ± 2.1 14.5 ± 3.1 .856
Humphrey visual field
Mean deviation −6.62 ± 6.06 −6.63 ± 5.34 .991
Pattern standard deviation 6.78 ± 4.31 7.71 ± 4.75 .188

D = diopters; IOP = intraocular pressure.

a Independent sample test.

Table 2

Baseline Medical Histories of Western and Korean Normal-Tension Glaucoma Patients

Western Korean P Value a
Hypertension (%) 32.4 21.2 .092
Hypotension (%) 5.6 0.9 .105
Diabetes (%) 5.6 6.2 .933
Family history (%) 45.1 5.3 <.001
Migraines (%) 7.0 8.8 .725
Cold hands (%) 8.5 7.1 .673

a Independent sample test.

Table 3

Comparison of Ocular Findings between Western and Korean Normal-Tension Glaucoma Patients

Western Korean P Value a
Disc hemorrhage (%) 11.3 11.5 .961
Peripapillary atrophy (%) 80.3 84.1 .512
Axial length (mm) 24.57 ± 1.79 24.92 ± 1.59 .412
Corneal thickness (μm) 558.4 ± 37.4 535.2 ± 27.5 <.001

a Independent sample test.

Table 4

Comparison of Heidelberg Retina Tomography Parameters between Western and Korean Normal-Tension Glaucoma Patients

HRT Parameter Western Korean P Value a
Disc area (mm 2 ) 2.330 ± 0.798 2.430 ± 0.622 .345
CDR 0.651 ± 0.170 0.682 ± 0.168 .236
CSM −0.097 ± 0.086 −0.056 ± 0.079 .001
Rim area (mm 2 ) 1.131 ± 0.456 1.164 ± 0.365 .596
Rim volume (mm 3 ) 0.242 ± 0.136 0.290 ± 0.165 .042

CDR = cup-to-disc ratio; CSM = cup-shape measure; HRT = Heidelberg Retina Tomography.

a Independent sample test.

Table 5

Comparison of Optical Coherence Tomography Parameters for Retinal Nerve Fiber Layer Thickness between Western and Korean Normal-Tension Glaucoma Patients

OCT Parameter Western Korean P Value a
Average 71.8 ± 17.7 85.0 ± 16.5 <.001
Temporal 57.0 ± 17.3 70.8 ± 17.5 <.001
Superior 87.4 ± 30.4 102.5 ± 25.6 .003
Nasal 60.7 ± 17.2 68.3 ± 15.5 .010
Inferior 82.9 ± 26.8 98.8 ± 26.5 .001

OCT = optical coherence tomography.

Data are presented in micrometers.

a Independent sample test.

Table 6

Univariate and Multivariate Analyses of Western and Korean Normal-Tension Glaucoma Patients

Variable Univariate Analysis Multivariate Analysis a
OR 95% CI P Value OR 95% CI P Value
Age 1.097 1.062 to 1.133 <.001 1.101 1.042 to 1.163 <.001
Male gender 1.626 0.894 to 2.957 .111
Disc area 0.805 0.514 to 1.262 .345
Mean deviation 1.000 0.948 to 1.056 .991
Pattern standard deviation 0.956 0.894 to 1.022 .188
Spherical error 0.988 0.909 to 1.073 .769
Cup-shape measure 0.002 0.000 to 0.105 .002 0.000 0.000 to 0.016 .002
OCT average RNFL thickness 0.955 0.933 to 0.978 <.001 0.932 0.896 to 0.969 <.001
Central corneal thickness 1.024 1.011 to 1.037 <.001 1.020 1.003 to 1.037 .018

CI = confidence interval; OCT = optical coherence tomography; OR = odds ratio; RNFL = retinal nerve fiber layer.

a Analysis was adjusted for age, gender, disc area, mean deviation value, pattern standard deviation value, and spherical equivalent.

Only gold members can continue reading. Log In or Register to continue

Stay updated, free articles. Join our Telegram channel

Jan 9, 2017 | Posted by in OPHTHALMOLOGY | Comments Off on Comparison of Clinical Characteristics Between Korean and Western Normal-Tension Glaucoma Patients

Full access? Get Clinical Tree

Get Clinical Tree app for offline access