|Cataract type||Grade 1||Grade 2||Grade 3||Grade 4|
|Cortical (by degree of intrapupillary space obscured)||10%||10%-50%||50%-90%||> 90%|
|Posterior subcapsular (by degree of posterior capsule obscured)||3%
Nuclear cataracts are graded according to their color and opacification using slit lamp examination. Cortical and posterior subcapsular cataracts are graded instead using retroillumination to evaluate the degree to which the intrapupillary space or posterior capsule are obscured.
Many types of grading systems have been used to describe cataract severity. Commonly used systems in epidemiological studies include the Lens Opacity Classification System (LOCS, LOCS II, and LOCS III), the Oxford Clinical Cataract Classification and Grading System, and the Johns Hopkins system. The simpler, LOCS II four-point grading system is also commonly used in clinical settings (see below from Chylack et al. 1989).
Mature cataracts can prevent evaluation of the posterior segment by slit lamp exam. In these cases, imaging such as by ultrasound can be used to assess the retina and other posterior structures.