Yes I recall Biotin, I've heard of it, and yes your description sounds familiar

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Yes Egg Yolks also contain Lutein, a very good Carotenoid source which helps with the Eyes, not to mention things like Protein and Vitamins / Minerals, but there is LDL bad cholesterol in them, so limitation is a good policy.
I don't know about the 4 yolks a week thing, I generally have about 6 a week tops, but I am not certain exactly of a healthy maximum limit. That's why though I would heed caution. If someone attempts two Yolks a day, perhaps only 3 times a week, or one day only, but perhaps every day could be okay, with a one a day strategy.