What do you see? That question is so complex it may be impossible to answer. But when Vanessa Potter lost her sight because of a rare condition, she became obsessed with describing the experience of both literal and inner vision.

Patient H69: The Story of My Second Sight Book by Vanessa Potter

Her new book, “Patient H69,” tracks Potter’s progression from advertising producer to patient. But her memoir shows how a medical ordeal also turned her into a scientific detective, advocate and artist.

In 2012, Potter suddenly lost her sight. The first half of her book tracks her terrifying loss of vision and illustrates the psychological toll that accompanies the transition from healthy person to patient.

Potter’s ailment turned out to be neuromyelitis optica, a disorder also known as Devic’s disease. People with the autoimmune disorder experience inflammation of the optic nerve, temporary blindness and spinal cord inflammation that can cause pain and sensory loss.

Determined to regain her sight and understand her illness, Potter collaborated with scientists as her optical nerve healed.Along the way, she documented her experience.

Her descriptive powers serve her well as she illustrates what it’s like to experience the development of sight in real time — a progression that, for Potter, included synesthesia (a blending of the senses in which a word may be seen as a certain color, for example), self-hypnosis and plenty of emotion.

That emotional journey eventually led Potter to art. Her recovery inspired her to create a series of installations that translate brain waves into images, and Potter casts her slow progression toward sight as an art project of its own.

“What I have uncovered has opened my eyes, in every sense of the word,” she writes. There truly is an art in seeing — and Potter’s evocative chronicle of what it’s like to lose, then find, a sense reveals just how complicated sight can be.