I have a blind depressed character and I'd like to write a chapter that talks only about his internal conflict, i.e, struggling with his inner self, like going inside his mind, but I find difficulties not knowing on what should I focus and what should I describe exactly, so I can get people empathize with the character.
Apart from the previous answer, you could incorporate the character's thoughts in the way they interact with their world. For example, he might be fumbling with his bedsheets until he feels a fascinating embossed texture on it. He then wonders what that texture might look like, suddenly feeling frustrated that he might never know.
Or he could simply begin giving meaning to every little thing. The way he hears the wind blow through the trees, for example, could seem to him like the scuffling of feet from people rushing to get away from him. From that thought, he could begin contemplating his loneliness.
Key to these sort of character scenes is to make it seem a natural part of him. Depression, of course, is not something you'd wish to be someone's daily reality, but it is the brutal reality of your character. Establish a simple scene of him doing everyday activities and have his reactions to these activities mingle with his own dark thoughts. It gives a sense that this sort of struggle happens to him every day, in every little circumstance, and it's beyond his control.
Convey the gravity sensitively. For readers to empathize, don't go overboard with his misery. Instead, showcase that his heavy feelings can be triggered by small things and still make him completely miserable. Show and don't tell, as always, and know that the most powerful way to connect the readers with your character is for them to see themselves in him in some way. His condition is interfering with his life, not defining it.
All the best!