Instruct: Classify Amazon reviews into positive or negative sentiment
Query: I found the book to fall short of being usefull

I was looking for a book that explains the technical differences in various types of lenses. Multifocal, bifocal, aspherical, high index, polycarb, plastic, glass, abbe numbers etc. How does one choose and what are the advantages and disadvantages of each type and manufacturers design. I was also interested in the differences in contacts. Torics, bifocals, etc etc. The book is technically lame. It was no help whatsoever. Ask your optometrist was the redcomendation. I learned nothing from this book! Nothing!