Books like Duke-Elder's Practice of Refraction
Sir Stewart Duke- Elder
Duke-Elder's Practice of Refraction is 328 pages, about 6 hours 1 minute at 250 words a minute.
6 books to read next
How long each takes
The Fine Art of Prescribing Glasses Without Making a Spectacle of Yourself 8.8 h 
Bennett and Rabbetts' Clinical Visual Optics 8.3 h 
The Art of Seeing 2.7 h 
Primary Care Optometry 11.6 h 
Bennett and Rabbett's Clinical Visual Optics 9.0 h 
Last Minute Optics 2.4 h Bar height shows length. Estimated at 250 words a minute.