Korean J Ophthalmol Vol.24, No.1, 2010 Differences between the two groups in the parameters at baseline OCT were evaluated. All seven of the OCT parameters were then compared among the control and diabetic subjects. Correlation analy- sis was also applied in order to characterize on a loga- rithmic scale the relationship between the OCT parameters and the best-corrected visual acuity. The efficacy of the OCT parameters as index variables for the discrimination of DR stage and as a predictive var- iable for discrimination between eyes with and without PRP within 6 months of baseline OCTs was determined via receiver operating characteristic (ROC) analysis. The area under the ROC curve (AUC) was calculated for each OCT parameter. The best model, as defined by the largest AUC and cutoff value characterized by the best trade-off between sensitivity and specificity, was determined. The statistical calculations were conducted using a SPSS ver. 11.5 (SPSS Inc., Chicago, IL, USA). The p-values of less than 0.05 were considered significant. Results A total of 129 consecutive diabetics with DR (129 eyes) and 20 diabetics without DR (20 eyes) were enrolled in this study. The control group consisted of 50 non-diabetic, age- and sex-matched normal subjects (50 eyes). The clinical characteristics of the three groups are sum- marized in Table 1. The mean age, gender ratio, and re- Fig. 2. Retinal thickness (µm) in the normal population, diabetic pa- tients without retinopathy, and four groups of diabetic patient with retinopathy. DM=diabetes; DR=diabetic retinopathy; NPDR=non-proliferative diabetic retinopathy; PDR=proliferative diabetic retinopathy; H= horizontal in macula; V=vertical in macula; S=superior to optic disc; I=inferior to optic disc; N=nasal to optic disc; D=circular concentric to optic disc; CMT=central macular thickness at foveal pit. fractive errors did not differ among the three groups. Based on the initial fundus examinations and fluorescein angiography, the 129 diabetics with DR were classified as Table 1. Characteristics of diabetic patients and normal subjects Diabetes with retinopathy (N=129) Age (yr) 62.3±7.3 Sex (M/F) 75/64 Refractive error (D) -0.1±0.3 Values for the diabetic patients and the controls are presented as mean±SD. D=diopter; NS=not significant. *Kruskal-Wallis test; †Chi-square test. Diabetes without retinopathy (N=20) 60.3±9.7 9/11 -0.4±0.7 Normal population (N=50) 59.3±10.8 28/22 -0.3±0.8 p-value* NS* NS† NS* Table 2. Retinal thickness (µm) in the normal population, diabetic patients without retinopathy and four groups of diabetic patients with retinopathy Normal population Diabetes without DR Mild NPDR Moderate NPDR Severe NPDR PDR p-value* (N=50) (N=20) (N=20) (N=38) (N=50) (N=21) H 219.2±16.0 207.9±17.8 205.4±17.5 225.3±32.5 251.2±46.8 266.1±77.3 <0.001 V 220.1±18.8 209.3±19.3 206.6±15.3 224.4±36.7 246.5±41.3 258.0±63.2 <0.001 S 192.5±21.1 185.6±13.4 193.6±17.9 200.7±18.4 216.0±22.9 222.5±33.1 <0.001 I 197.2±17.9 195.4±16.3 201.5±15.2 197.0±23.2 219.0±22.3 228.5±55.7 <0.001 N 171.0±22.5 171.3±13.6 162.0±17.6 180.5±22.0 203.6±39.8 202.0±55.0 <0.001 D 203.3±14.4 192.4±15.1 192.5±17.4 200.3±14.8 217.1±26.9 227.7±44.2 <0.001 CMT 141.5±15.3 149.8±14.7 146.9±18.6 182.5±69.8 193.6±77.4 232.1±148.6 <0.001 Mean±SD of retinal thickness is presented in microns. DR=diabetic retinopathy; NPDR=non-proliferative diabetic retinopathy; PDR=proliferative diabetic retinopathy; H=horizontal in macula; V=vertical in macula; S=superior to optic disc; I=inferior to optic disc; N=nasal to optic disc; D=circular concentric to optic disc; CMT =central macular thickness at foveal pit. *Kruskal-Wallis test or ANOVA. 18