If a convert wore contact lenses during the mikvah immersion, is the conversion still valid? Does it depend on whether the contact lenses are disposable (not the one you wear for more than 30 days)?
On a similar question about a woman's regular mikvah immersion, Daily Halacha reports several opinions (emphasis mine):
Hacham Ovadia Yosef addresses this question in his work Taharat Habayit (vol. 3, p. 26), where he cites a responsum from the work Shebet Halevi (Rabbi Shemuel Wosner, contemporary). The Shebet Halevi distinguishes in this regard between contact lenses that are normally removed each night, and lenses which are made to remain in the eyes for an extended period. When it comes to lenses that are removed daily, although they do not, strictly speaking, constitute a Hasisa (interruption) between the woman’s body and the water, she should nevertheless remove them before immersing. Rav Moshe Feinstein (Russia-New York, 1895-1986), in his work Iggerot Moshe (Yore De’a 104), rules that if a woman immersed without removing the contact lenses, she need not repeat the immersion. The Shebet Halevi, however, writes that it is preferable for the woman to repeat the immersion, unless she had already been with her husband, in which case she does not repeat the immersion.
Several "mikvah checklists" I found remind people to remove contact lenses. It appears, however, that if one did not do so, the immersion is still valid. In the note at the end the Shevet Halevi calls for repeating the immersion if it hasn't already become "overcome by events", you might say; for geirut I suspect that if you notice immediately (while still in the pool) you'd take them out and repeat,1 but if you've since left and begun your life as a Jew, then, like the wife who has been with her husband, it doesn't make sense to repeat now. This is my own reasoning.
1 Whether you would repeat either b'racha in that case, I do not know.