Table 2.
Changes in Visual Acuity (LogMAR) at Different Levels of Illumination*
| Level of Illumination | Normal (100%) | Low (4%) | Very Low (0.1%) | |||
| Covariates§ | Coefficient¶ (95% CI) | P value | Coefficient (95% CI) | P value | Coefficient (95% CI) | P value |
| Treatment† | -0.0002 (-0.0131,0.0128) | 0.981 | 0.0054 (-0.0137,0.0246) | 0.578 | -0.0762 (-0.139, -0.0131) | 0.018 |
| Period | -‡ | - | -0.0448 (-0.083,-0.0066) | 0.022 | -0.0654 (-0.134, -0.0132) | 0.061 |
| Time† (number of weeks) | -0.0010 (-0.0026, 0.0007) | 0.250 | -0.0026 (-0.0048,-0.0003) | 0.025 | -0.0014 (-0.0027,-0.0001) | 0.037 |
| Age | - | - | - | - | - | - |
| Vitamin A Use | - | - | -0.0701 (-0.1357,-0.0046) | 0.036 | - | - |
| Iris color | - | - | - | - | - | - |
| Period × Treatment | - | - | - | - | 0.1452 (0.0339, 0.2565) | 0.011 |
| Treatment × Time | - | - | - | - | - | - |
| Period × Time | - | - | 0.0023 (0.0001, 0.0046) | 0.044 | - | - |
| Baseline LogMAR | 0.9783 (0.8933, 1.0634) | <0.001 | 1.0086 (0.8909, 1.1268) | <0.001 | 0.9290 (0.8416,1.0164) | <0.001 |
| Intercept | 0.108 (-0.187, 0.402) | 0.474 | 0.0265 (-0.0386, 0.0916) | 0.424 | 0.0949 (0.0088, 0.181) | 0.031 |
* Based on the GEE linear regression model
† Covariates forced to the model.
‡ Covariate removed due to non-significant contribution to the model (p value > 0.05).
§Description of covariates:
• Period: 0 in the first 24 weeks of the study, 1 in the second 24 weeks
• Treatment: 0 for placebo, 1 for lutein supplementation
• Time: Elapsed time within each 24-week period of the study (in weeks)
• Age: Age of the patients at baseline (in years)
• Vitamin A Use: 0 for participants not using, 1 for those using vitamin A supplements
• Iris color: Categorical variable: 1. Light/Dark Blue 2. Green/Hazel 3. Light/Dark Brown
¶The coefficient indicates the change in LogMAR units per unit change in the covariate.