Purpose: To evaluate a new nuclear cataract grading system which is intended as a surgical guidance system to predict lens hardness before cataract surgery. Methods: The new BCN 10 grading system consists of frontal and cross-sectional slit-lamp images of human eye lenses, ranging from a completely transparent lens nucleus to a totally black nuclear cataract. Validation was done with 9 observers for 110 cases. Two modalities were applied, and observers were asked to use only whole digits and then half digits for grading. Results: Repeatability with regard to test-retest differences showed a mean limit of agreement of 1.70 for whole digits and 1.32 for half digits. The absolute test-retest difference was close to zero for low as well high degrees of cataracts. Reliability for the entire group of 9 observers yielded an intraclass correlation coefficient which was within the same confidence interval, i.e., 0.991-0.995, for whole digits and half digits. Conclusions: BCN 10 grading repeatability was not affected by the severity of the cataract. It showed very good repeatability. Repeatability was significantly higher when the observers used half digits compared to whole digits. Reliability was found to be very good as well, independently of the use of whole or half digits.