Astigmatism causes persistent blurry vision due to irregular corneal curvature. Affects approximately 40% of adults worldwide. Most commonly congenital, with genetic causes. Can develop later in life from injury or other conditions
Barrett Universal II forms foundation for all other formulae. Barrett Toric calculator predicts toric lens power for astigmatism. True K formula handles patients with previous refractive surgery. Barrett Rx formula provides solutions for unexpected cataract outcomes
Aberration causes light rays to deviate through lenses, creating blurred images. Unlike mirrors, lenses produce imperfect images, becoming ideal only for parallel rays. Equations for spherical lenses deal only with paraxial rays