Lutein supplementation in retinitis pigmentosa: PC-based vision assessment in a randomized double-masked placebo-controlled clinical trial [NCT00029289]

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.

ISSN: 1471-2415