The formula for the contrast threshold in CIELAB space

As indicated in the WCAG recommendations, the contrast ratio between the background and foreground colors should be at least 4.5: 1, as shown in http://www.w3.org/TR/WCAG20/Overview.html#IEC-4WD

But the above formula is for RGB format colors (Ctrl + f 'sRGB' to see the formula). I am dealing with a CIELAB space, so can this formula be transformed for a CIELAB space? Or can we get a similar threshold in remote form CIELAB?

My observations There is no comparison between the distance between CIELAB between two colors and the contrast ratio between two identical colors in RGB format.