If a patient has had refractive surgery, a direct keratometry reading will be?

A direct keratometry reading will be inaccurate in a patient who has had refractive surgery, such as LASIK or PRK. This is because refractive surgery alters the shape of the cornea to improve visual acuity. The keratometry measurement relies on the curvature of the cornea to provide information about its refractive power. When the cornea is reshaped through surgical intervention, the normal assumptions that keratometry makes about the corneal surface may no longer apply.

As a result, the values obtained from keratometry do not reflect the true corneal curvature needed for accurate calculations for intraocular lens power in cataract surgery or for fitting contact lenses. Clinicians must often rely on additional diagnostic tools, such as corneal topography or specular microscopy, to get a more accurate understanding of the corneal shape and characteristics post-surgery. This makes the direct keratometry reading not only inaccurate but also less clinically useful for decision-making regarding further vision correction or surgical procedures.