The evolution of scleral lenses has led to new formulations of scleral fitting concepts and designs. The diameters of modern scleral lenses have been overhauled too and they are smaller comparing to the original ones. Nowadays, prescription of mini-sclerals supposedly seems in major extension and it appears indeed the necessity of some practitioner to differentiate the smaller mini-scleral lenses from larger mini-scleral lenses empathizing that they are the “smaller” ones. Therefore, it is maybe, necessary a definition of mini-scleral lenses referring to the landing zone width in relation to the horizontal visible iris diameter (HVID) and the limbus extension. The choice of the total diameter is crucial for a successful fitting and it depends majorly on patient’s topographic patterns and anatomic factors. However, there are other important criteria for the selection of the scleral lens diameter based on oxygen supply, bubbles formation, mechanical stress on a toric sclera, ocular surface disease protection, entity of the vault over the cornea and distribution of the lens weight on the sclera. The advantages of mini-scleral lenses are various nonetheless in some cases large lenses are necessary. This paper presents a review of the benefits and disadvantages of both mini and large scleral lenses analyzing the conditions in which it may be better to prefer one diameter to another. A suggestion may be that to start fitting the smallest lens as possible, depending on the dimension of HVID and limbus width and consider larger lenses only when issues occur.