Cataract is the opacification of the lens. Usually cataract occurs slowly, causing progressive vision loss over several months or years. In ophthalmic clinical practice, repeated objective quantitative measurements of lens opacity may be necessary to document its progression and support a surgical indication. The subjective methods of evaluating the opacification of the lens have limitations, in particular due to the lack of reproducibility between observers. Thus, innovative objective techniques with precise and reproducible cataract classification results have been developed, such as the Objective Scatter Index (OSI) on the Optical Quality Analysis System (OQAS), Visiometrics SL in 2010 and, more recently, Average Lens Density (ALD) on the IOLMaster® 700 device. Cataract is diagnosed as mature when the OSI is ≥ 2 and / or when the ALD is ≥ 74 pixel units. Vitrectomy is a surgery of the posterior segment of the eye indicated for retinal detachment, epimacular membranes, macular holes, vitreous hemorrhage. The incidence of post-vitrectomy cataract varies among studies, and the methodology is often retrospective. Age has already been identified as a risk factor for progression since in a study of 28 eyes of patients under 50 years old, only 7% developed cataracts secondarily, compared to 79% in the 'over 50' group. To date, there is no prospective study describing the progression kinetics of lens opacification according to precise and reproducible quantitative objective criteria in patients treated by vitrectomy. It also involves confirming the age and preoperative lens status as a risk factor for postoperative cataract progression.