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I'm not quite sure if this tip will prove helpful or not, but I usually clean my screen with a slightly dampened t-shirt, making sure to use the dry side of the shirt to give it a glossy shine ^____^ It has helped me significantly so far and I don't have any worries since I'm pretty sure the water I use contains no abrasive solvents.

This has worked for me with hanes or fruit of the loom type undershirts, (laundered of course) 100% cotton and DISTILLED water.
 
Glass Plus(tm) and a cloth towel. It doesn't have ammonia in it. Use it on the entire mac as well. It sure beats spitting on the screen and wiping with a shirt sleeve.

I'm guessing the OP has other problems not related to cleaning. It sounds like there's some kind of fog built up behind the glass.
 
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