Development of non-invasive treatments for cataract calls for a sensitive diagnostic assay. We conducted a study to test whether the ratio of folded tryptophan to non-tryptophan fluorescence emission (F-factor) may be used for grading cataracts in human lenses. The F-factor was measured on aspirated lens material from eyes undergoing femtosecond laser assisted cataract surgery (FLACS) and was compared to a preoperative optical grading of cataract using Scheimpflug imaging. The preoperative optical grading allocated the cataracts to 1 of 4 categories according to the density of the cataract. All cataracts were age-related. Lens material from 16 eyes of 14 patients was included in the study. Cataracts were preoperatively graded in categories 1, 2 and 3. No lenses were category 4. For nuclear cataracts mean values of F-factor were 52.9 (SD 12.2), 61.7 (SD 5.3) and 75.7 (SD 8.9) for categories 1, 2 and 3 respectively. Linear regression on F-factor as a function of preoperative grading category showed increasing values of F-factor with increasing preoperative grading category, R2 = 0.515. Our experiment showed that preoperative optical grading of cataracts by Scheimpflug imaging may correlate to measures of tryptophan and non-tryptophan fluorescence in human lenses. Based on our results we find that measuring the ratio between tryptophan- and non-tryptophan fluorescence may be a future tool for grading cataracts, but further research is needed.