A standardized classification of corneal topography after laser refractive surgery.

ith the expanding literature and discourse at professional meetings regarding the influence of corneal topography on outcomes following laser refractive surgery, the need for a universal, standardized classification system has become increasingly apparent. We have previously reported a seven-category topography classification schema for eyes following excimer laser pho-torefractive keratectomy (PRK). 1,2 We propose this original system with minor changes as a standard for evaluating corneal topography after laser refrac-tive surgery. The rigorous classification of topography patterns is important for a number of reasons: (1) To facilitate comparison of clinical studies and clarify professional communication. For instance, is a " central island " in Study A designated a " keyhole " in Study B? (2) To better understand the source of postopera-tive optical aberrations such as glare, halo, and monocular multiplopia. Do specific topography patterns cause specific optical side effects? (3) To facilitate studies focusing on the potentially unique eti-ologies of different patterns. Are hydration shifts, beam inhomogeneity, plume effects, wound healing, and other as yet undiscovered causes related to specific topography patterns? Are some patterns elevations whereas others are depressions? (4) To allow natural history studies of topography patterns after laser procedures. Is the keyhole pattern a resolving central island, a forme fruste of the latter, or is it unrelated? Will visually significant patterns resolve on their own? (5) To suggest initial surgical strategies to avoid less desirable patterns. Should treatments be continuous or interrupted? Should the cornea be dried? Are pretreatments, multizone, mul-tipass, or other techniques advisable? (6) To suggest postoperative medical and surgical treatment interventions. What patterns should be treated? How should they be treated? When should intervention be considered? These and other such questions remain unan-swered and call for rigorous clinical investigation. An appropriate topography classification schema would comprise distinct and clinically useful patterns to maximize our ability to address these issues. A number of investigators have identified a variety of patterns following PRK. Lin and coworkers 3,4 , using differential maps, originally classified topography into one of four patterns—central uniform, keyhole, semicircular, and central bump (known in the literature as a central island). In their system, the semicircular pattern comprised a non-uniform crescentic pattern with a power difference of 1.50 diopters (D) or more across any meridian, extending for 90° or more. The keyhole pattern was defined as a non-uniform pattern with a power difference of 1.50 D or more between equidistant points on any meridian …