Refractive Power Map

Modesto / Stockton LASIK Surgeon – Dr. Ash – Serving Tracy, Manteca, Merced

Refractive power map is sometimes called a "Snell's Law Map." The Refractive Power Map shows the power of the eye in its refractive state, measured in diopters. This map uses the arc step reconstruction, along with ray tracing using Snell's Law, to measure the refraction of light rays as they pass through the corneal surface. Taking into account spherical aberration, the Refractive Map more closely illustrates how light rays behave as they strike an aspheric surface such as a human cornea.

The portion of the refractive map that is of most importance relates to the central cornea lying over the patient's pupil, as this is where visual performance is assessed. Dilated pupil size can also be a factor in visual function, especially at night.

Refractive power maps may differ from axial maps in their readings of power and radius for the same patient. The biggest differences can be seen in the periphery and on eyes that have unusual or abnormal shapes. This is due to the spherical aberration effect that the refractive power maps take into account.

The refractive power map is most useful in assessing the visual performance of a postoperative patient or the result of a refractive surgical procedure. The precise power can be accurately measured using corneal topography and compared to the amount of correction that was desired. This gives the surgeon a much better idea of how the surgery affected the visual potential of the cornea.