The benefits of ultra-thin high-index lenses include comfort and aesthetic appeal. They also provide sharper vision when treated with an antireflection coating, and they have flatter curvatures and a wider variety of smaller frames.
High-index lenses have a refraction index of at least 1.64; the higher the index, the thinner the lens. Thinner lenses require less material to produce and are lighter in weight. Ultra-thin high-index plastic lenses have thinner edges and are more comfortable to wear. They have an aspheric design making them slimmer. The design also reduces off-axis blurred vision and the magnified bug eye effect common with strong prescriptions of standard index lenses.
Ultra-thin high-index lenses with antireflection coating allow more light to pass through to the eye for better vision. They are also more transparent and allow people to see the wearer's eyes more clearly. When driving at night, the antireflection coating reduces glare.
A high refraction index means that the lens bends light at steeper angles than standard lenses. Ultra-thin high-index lenses produce the same focal power with less curvature. A flatter curve, thin lenses and the aspheric design makes them a good fit for smaller frames such as rimless and semi-rimless, and smaller frames make the eyeglasses lighter.