Madara describes his and Sasuke's Mangekyou patterning being a straight-tomoe pattern, or choku tomoe. Apparently this means that their tomoe doesn't have a comma shape, and it's patterning indicates the Mangkeyou's capabilities to some degree, as Madara observes that Sasuke's pattern makes his vision extra fluid and efficient, superior at detecting movement compared to other Mangekyou patterns.
As for what Madara actually means by "straight tomoe", I honestly have no clue. I've never been able to detect any visual similarity between Madara and Sasuke's Mangkeyou patterns, so I'm a little perplexed by what exactly Madara meant by there being a correlation between his and Sasuke's patterns, so I'm not much help on this particular topic.
What is important about this exchange is that Madara is basically sensing the connection between him and Sasuke, sensing on some level that they are both Indra's reincarnations, something unique to them. While Madara doesn't have knowledge of the Asura/Indra reincarnation cycle, he does sense it, and by extension, his connection to Sasuke, so that's the important thing to note about Madara's statements about the choku tomoe. And evidently there is some kind of pattern congruency between Indra's reincarnations that I'm not aware of.