We thank Drs Oral and Kaya for their interest in our recently published article on conductive keratoplasty in keratoconus, a clinical trial report concerning a novel treatment for advanced keratoconus. The inclusion criteria in this study was defined as keratoconus patients who were candidates for corneal transplantation. Candidates for corneal transplantation can be defined categorically as patients who reveal typical keratoconus by corneal topography, best-corrected visual acuity of less than 10/20, and contact lens intolerance resulting from ophthalmic pain or other factors. For these patients with advanced keratoconus, other methods like corneal cross-linking alone or intracorneal ring segments are no longer applicable. As Drs Oral and Kaya indicated, some of the patients included in our investigation had relatively low K readings, such as 39.0 or 43.9 diopters. These patients had severe corneal scarring that affected the visual axis, so the K reading did not reflect accurately the severity of the disease in these cases.
We measured the corneal thickness at the thinnest point in all cases before surgery, and all of them except for 3 cases revealed thickness of less than 400 μm. In addition, pachymetry was impossible in 7 eyes because the cornea was too thin, although we also referred to pachymetric readings obtained using the Orbscan (Bausch & Lomb Japan Ltd, Tokyo, Japan). Those corneae were estimated to be less than 200 μm from observation using slit-lamp microscopy. We tried to analyze the correlation between the corneal thickness and the outcomes of topography-guided conductive keratoplasty. However, we could not observe any significant correlation between the visual acuities or refractive error and corneal thickness or existence of scarring, probably because of the small number of patients and greater variance between the cases. The detailed information is included in the Supplemental Table .
Meanwhile, we found that the corneal thickness was significantly thinner in 6 eyes that later required corneal transplantation (305.4 ± 57.5 mm) than the other eyes (398.8 ± 78.8 mm; P = .014). Five of the 6 eyes that required corneal transplantation revealed stromal scarring or extreme focal protrusion. Another eye had neither stromal scarring nor extreme focal protrusion and recovered visual function just after topography-guided conductive keratoplasty. However, this eye deteriorated thereafter and required corneal transplantation.
We recently came to believe that the indication for topography-guided conductive keratoplasty is eyes with corneal thickness of more than 450 μm and absence of dense stromal scarring, in addition to being candidates for keratoplasty, and that all should be followed up by corneal cross-linking to maintain the improved corneal configuration. Therefore, these criteria also are reasonable from a safety viewpoint, because corneal cross-linking is recommended for corneas thicker than 400 μm without the epithelium to protect corneal endothelial cell damage. However, the drawback of these criteria is that appropriate cases are limited because advanced keratoconus with corneal thickness of more than 450 μm is relatively rare. We hope that advanced methods for the treatment of thin corneas will be developed in the near future.
Appendix
| Case | Age | Gender | Previous surgery | Preop UCVA | Preop BSCVA | Preop MR | Preop Kave | Preop thinnest corneal thichness (μm) | Focal thinning or stroma opacity | Postop best achieved UCVA (time after TGCK) | Postop best achieved BSCVA (time after TGCK) | Postop Kave (same timepoint as BSCVA) | Outcome at the final examination point (time of final evaluation) |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 1 | 27 | M | 1.7 | 0.8 | −18.0 | 61.7 | 304 | − | 0.4 (1W) | 0.0 (6Mo) | 60.93 | CT (2Y) | |
| 2 | 23 | M | 1.4 | 0.4 | −12.0 | 61.1 | n.m. | − | 1.2 (1D) | 0.2 (3Mo) | 52.5 | CL (1Y) | |
| 3 | 17 | M | 0.4 | −0.1 | −12.0 | 49.8 | 500 | + | 0.5 (1W) | −0.1 (6Mo) | 46.125 | CL (1Y) | |
| 4 | 28 | M | 1.7 | 1.0 | −9.0 | 50.6 | 373 | − | 0.2 (1W) | 0.0 (1W) | 43.125 | CL (1Y) | |
| 5 | 32 | M | ICRS | 1.2 | 1.0 | −12.0 | 57.0 | 291 | − | 0.5 (1W) | 0.5 (1W) | 37.875 | (1M) |
| 6 | 42 | M | IOL | 1.3 | 1.0 | −23.0 | 68.8 | 211 | − | 1.1 (1W) | 0.8 (1W) | 54.755 | Repeated TGCK, CT (6Mo) |
| 7 | 20 | M | 1.7 | 0.7 | −10.0 | 44.0 | 359 | + | 1.0 (1W) | 0.7 (1W) | 32.155 | CT (6Mo) | |
| 8 | 27 | M | 1.7 | 0.4 | −10.87 | 56.7 | 301 | − | 0.7 (1D) | 0.0 (1Mo) | 49.215 | (6Mo) | |
| 9 | 26 | M | 2.0 | 2.0 | 0 | 58.2 | 324 | − | 0.7 (1D) | 0.4 (1Mo) | 57.5 | CL (3Mo) | |
| 10 | 44 | M | 1.7 | 0.7 | −21.75 | 43.7 | 304 | + | 1.0 (1W) | 0.7 (1Mo) | 33.6 | Repeated TGCK, CL (1Y) | |
| 11 | 53 | M | 1.4 | 0.5 | −17.0 | 47.7 | n.m. | + | 0.1 (1W) | 0.1 (1W) | 50.0 | (3Mo) | |
| 12 | 19 | F | 1.4 | 0.4 | −6.5 | 62.4 | n.m. | − | 0.1 (1W) | 0.1 (1W) | 49.25 | Repeated TGCK, CL (1Y) | |
| 13 | 45 | M | 2.0 | 1.4 | −14.0 | 62.9 | n.m. | − | 1.4 (1M) | 0.3 (6Mo) | 52.33 | CL (1Y) | |
| 14 | 45 | M | 2.0 | 1.7 | −28.5 | 52.1 | n.m. | − | 2.0 (1D) | 1.0 (1Y) | n.m. | CL (1Y) | |
| 15 | 29 | M | 1.7 | 1.4 | −6.25 | 69.0 | 443 | − | 1.2 (1D) | 1.5 (1Mo) | 53.485 | Repeated TGCK (6Mo) | |
| 16 | 35 | M | 1.0 | 0.5 | −7.5 | 47.6 | 424 | − | 0.2 (1Mo) | 0.0 (1W) | 39.25 | CXL at 2 M (1Y) | |
| 17 | 48 | M | 2.0 | 1.5 | −18.0 | 48.0 | 310 | + | 2.0 (1D) | 0.8 (3M) | 48.28 | Repeated TGCK, CT (6Mo) | |
| 18 | 37 | M | IOL | 1.5 | 1.2 | −17.0 | 56.8 | n.m. | − | 0.3 (6Mo) | 1.0 (1W) | 46.5 | CL (3Mo) |
| 19 | 28 | M | 1.7 | 1.7 | 0 | 39.0 | 343 | + | 0.8 (1D) | 0.8 (1W) | 55.455 | CL, (CT) (3Mo) | |
| 20 | 61 | M | 2.0 | 1.4 | −28.0 | 61.1 | n.m. | + | 1.5 (1D) | 1.3 (3M) | 64.24 | CT (1Y) | |
| 21 | 27 | M | n.m. | 1.7 | −16.0 | n.m. | 345 | − | 1.7 (1D) | 1.5 (1W) | 53.75 | CL (6Mo) |
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