We read with great interest the article by Kato and associates presenting the results of topography-guided conductive keratoplasty in eyes with advanced keratoconus. To understand better which particular group of eyes has benefitted the most from this minimally invasive treatment method, we would like to ask the authors to clarify some points about their study.

In the Methods section, no specific case selection criteria are mentioned except that all of the subjects were candidates for corneal transplantation. The authors describe the study eyes as having advanced keratoconus and state that advanced keratoconus is characterized by severe asymmetry or astigmatism of the cornea that interferes with spectacle-corrected visual acuity. We would like to know if any objective criteria (eg, visual acuity, degree of myopia, induced astigmatism, keratometric readings, corneal thickness) were used during case selection to decide whether the eyes have advanced disease. As far as keratometric readings are concerned, 9 of the 21 eyes listed in the article have average K readings of less than 55.0 diopters, which suggests moderate rather than advanced keratoconus.

Although the authors state that the entire corneal thickness was assessed before surgery, the article does not provide any data regarding individual or mean preoperative and postoperative corneal thicknesses. Because corneal thinning is a cardinal feature of keratoconus, preoperative corneal thickness data could help us to see how thicknesses relate to the outcomes. This relation appears in the authors’ conclusion that the eyes with extreme thinning with focal protrusion as well as corneas with a scar could not be reshaped effectively by the treatment. Although no separate data or statistical analysis pertaining to this particular group of eyes is presented, it also is not possible to differentiate these eyes in the article and to compare their outcomes with those of the others. Likewise, the retreated 5 eyes are mentioned only as having regressed markedly, whereas the presented data provide only the best outcomes achieved in these eyes at sometime during the follow-up, which apparently does not coincide with the time point when regression was detected and retreatment was decided. We would like to ask the authors if they could provide us with preoperative corneal thickness data and tell us which cases had focal protrusion, scarring, or both.

Because the authors report achieving excellent results with collagen cross-linking after conductive keratoplasty in 1 case, we also would like to ask if they considered other treatment methods like collagen cross-linking or intracorneal ring segments for all of the subjects before or after conductive keratoplasty? It seems that the study group includes 14 patients younger than 40 years who could well be candidates for collagen cross-linking, depending on their corneal thicknesses.