Eye Studies is a book found in the 4th Floor Piano Room. The book serves as a hint to how to solve the Piano Puzzle.
It tells about different woman with different eye colur and hair colour, but it doesn't really say which one has which, that you have to found out on your own.
In Extra mode, this book is more important since the whole puzzle is around woman missing their eyes, you have to return the correct eyes to the correct woman.
You can say it's a book you need to read to complete the puzzle.
Eye Studies"People have different eye colours.
We know the following about woman in this region in particular.
A woman's eye colour depends on her hair.
The four hair colours are silver, black, gold and red.
The four eye colours are brown, green, blue and red.Silver-haired women have red eyes, and brown hair women can have either blonde or red hair."