Difference between red, green and blue edge of blur

When using a -7.00/0.00 contact lens and measuring distance where double vision ceases I get (when recalculated from cm to D) depending on natural change of refraction:

Red: -8.75~-9.00
Green: -9.00~-9.50
Blue (ambient lighting): -9.50 (all other text on fridge is out of focus)
Violet-blue (no lighting besides itself) -9.50~-10.00

Is this normal to have such a big gap between different light color?


(why we have this 10 char limit? :slight_smile: )

What is meaning of red and green?When doctor asked what colour YouCan see better

No, red and green light scources.

Full discussion here.


The article is silent about blue and beyond blue light.

Not surprised. Even those with “20/20” vision often do not see blue sharply at distance. I find my red light prescription and green light prescription to be 0.25D apart (approximately). I find blue to be 0.5D or more further. Thus, I’d have to be 0.5 to 0.75D farsighted to see blue neon signs sharp from a distance, especially at night.

I’ve confirmed this with my astro glasses (which are about 0.5D farsighted). A blue LED clock is sharp(ish) at 20ft away. These clocks were picked up at a thrift store, and I can see why now, they are simply not sharp across the room unless you are naturally farsighted! :slight_smile:

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That’s why my take is


The ideal refraction in my opinion is +0.75, but prolonged close up and lack of blue light stimulus make most people on Earth slightly nearsighted.

It’s like many, if not most people have non-neutral sideways curvature of spine. It can be up to 10 degrees crooked. Abusing right hand makes spine to slightly curve to the right in thoracic region after adolescence. As well as abusing horizontal rectus muscles to make reading eye movements leads to with the rule astigmatism in most people of working age.