To calculate the lens power for a refractive cataract surgery, measurements are taken of the eye’s axial length, corneal power, the estimated lens position and the anterior chamber constant, according to Dr. Bing Qin and David Huang of EyeWiki. These measurements are fed into one of several commonly used formulas that calculate the intraocular lens power. Most widely known formulas include the Haigis, Holladay and SRK-T.
The intraocular lens is a corrective lens that is implanted to replace a cataract after the cataract is removed, notes NV Eye Surgery. Although these lenses can significantly improve vision, they cannot be tested out beforehand in the way that eyeglasses can. This leads to significant errors in estimating the appropriate lens needed.
Eye measurements determine the appropriate lens power by accounting for the current and anticipated position of the lens after surgery, according to EyeWiki. The most important measurement is the eye's axial length, which measures the distance from the front to the back of the eye. The axial length influences the position where light is bent or refracted as it comes into the eye.
Lenses that are too strong for a given axial length result in axial myopia, characterized by blurry vision and nearsightedness, states the journal Review of Ophthalmology. Farsightedness or axial hyperopia occurs when lenses are too weak for a given axial length.