AMNA NAWAZ: Finally tonight, the story of a man who found meaning in darkness.

In this story from KPBS' Kori Suzuki and Carolyne Corelis, we visit the Tijuana River Estuary in Southern California, where a volunteer is leading a tour that encourages visitors to experience nature a little differently.

RON PETERSON, Volunteer Docent: Ron Peterson Good question.

Yes, this is lemonade berry.

And the reason I know it's lemonade berry is because the leaves are thick and leathery, almost like the tongue of a leather shoe.

I have learned to identify about almost 40 plants just by touch and also smell.

All right, Gidget, here we go.

My name is Ron Peterson.

I'm 73 years old.

I'm a retired scientist and engineer.

I live here in Imperial Beach, and I am blind.

And we are here at the Tijuana Estuary.

This is one of my homes away from home.

There's several nature walks and there's several bird walks.

And one of those nature walks is mine.

I'm a docent for this nature walk called the Eye-Opening Experience Without Sight, where a blind person leads a nature walk and introduces visitors to the native plants with the emphasis on the other four senses besides sight.

Well, let's start over here with a very special plant right over here.

Everyone take a whiff and tell me what you think.

WOMAN: I don't love it.

RON PETERSON: Oh, OK, we have a "I don't love it."

Most people don't care for it all that much.

And this plant is actually called bladderpod, and I think you can see why it has the name bladderpod.

(LAUGHTER) RON PETERSON: One reason I know this is buckwheat is, I can -- I have worked here as a volunteer for about nine years planting native plants and clearing trails.

But then, five years ago, things kind of went south for me, glaucoma.

I lost my vision.

And I couldn't work here anymore.

I couldn't do the things that I was doing.

A couple of years ago, the idea came along that, since I had already learned many of these plants by sight, I could learn these plants by touch and smell and then share that with people.

WOMAN: Oh, wow.

RON PETERSON: It's the wonderful feel and the speciality of the smells.

And there's even sounds.

Come on closer, folks.

Come on closer.

So we -- the shape of these leaves, if there's a strong breeze, they will vibrate a little bit.

It's really an aerodynamics thing.

And that vibration causes the tree to kind of shimmer, some people say murmur in a breeze.

Feel this and smell this wonderful plant.

The thing about giving to others is, not only is it a good thing to do, it's the right thing to do, but also it takes the focus off of yourself to -- so you don't feel sorry for yourself.

But it has helped me to wake up with a smile on my face, to wake up looking forward to the day, and feeling like I accomplished something at the end of each day, that I did something for someone besides me.