High-index lenses are a new type of eyeglass lens made from (CR-39) plastic materials with a high refractive index, resulting in lenses that are thinner and lighter than standard ones .They are used for high-prescription corrections—typically exceeding 5 diopters—and are compatible with a wide range of stylish, lightweight frames; however, they do have some disadvantage, including: Cost: High-index lenses may be more expensive than other lenses; however, investing in them enhances comfort, lightness, and aesthetic appeal. Chromatic aberration: Some high-index lenses may exhibit slight chromatic aberration; therefore, it is advisable to consult an optician to select the appropriate type The refractive index (n)is the ratio of the speed of light in a vacuum to its speed within a material. This relationship is described by the lens maker’s equation—which relates the lens's strength (power) to the reciprocal of its focal length(f). = Power. Where: R is the radius of curvature. d is center thickness in mm. n is refractive index. University of Al-Mustaqbal – The First and Leading Private University