Clear lenses refers to lens that does not have a tint or does not change with the sunlight such as transitions lens or sunglass lenses.
Clear lenses are available in many types of materials.
CR-39 Plastic A plastic lenses which is a good choice for a person that has a mild prescription.
Polycarbonate material has a higher index of refraction than plastic and is thinner and more impact resistant with a built in UV blocker. Since it is impact resistant, it can protect the eye against sudden impacts and is the safest lenses material, especially recommended for children and for sports.
1.67 High index material has a higher index of refraction than polycarbonate and is recommended for prescriptions between 3.00 diopters and 4.50 diopters. Hi index lenses reduce light transmission and require an anti reflective coating.
1.74 High Index material is the thinnest lens material available. Recommended for prescriptions starting at 4.75 diopters and above. An anti reflective coating is required due to reduced light transmissions.