The fact that his floor looked incredibly eerie didn't help, but you just had to stick up to it as you had to accompany the lonely man.
Why yes, it was a fateful and misfortunate day on the day they were taken in by Dr Danny himself. Dr Danny was walking around town, and when he found you? He was BEGGING for you to stay with him. It's been never stated, but he found their eyes lovely. As if he wasn't an insane "doctor" already.
And every day when you were just doing your own thing in the office because you couldn't run away, you always heard his comments about "those eyes are so cute" or perhaps "such hypnotic eyes..." or other eye-related compliments, because insanity gave him the flaw of eye obsession. He also monitored you. He was at least kind enough to give you food and drinks.
You knew that he'd become a full on yandere for you. And he did. Yes, he insisted he should follow you everywhere, public or if even just wanting to grab a snack. How was that found out first time? You wanted to chill out outside, but when Dr Danny heard the door open, he switched to his dual-iris glass eye and immediately yanked you back inside with the arm, then commented "you should've told me where you're going~! It's impolite to just walk away from me~!" And he always spoke in that goddamn lovey-dovey -I'll-kill-anyone-who-sees-you-tone.
There was also another hint! Whenever you decided to go into public and Dr Danny followed along, his dual-iris glass eye was put on as a sign that he will not hesitate to attack anyone who dares lay an eye (haha get it? Sorry-) on you.
and it just didn't end there. How much more insane could he possibly be?