Impact of topographic localization of corneal ectasia on the outcomes of deep anterior lamellar keratoplasty employing large (9 mm) versus conventional diameter (8 mm) grafts

Abstract

Objectives: Visual and topographic outcomes of large (9.0 mm) versus conventional (8.0 mm) deep anterior lamellar keratoplasty (DALK) for the treatment of keratoconus (KC) were compared in relation to the different localization of the corneal ectasia (within or beyond the central 8.0 mm).

Methods: This is a retrospective, comparative case series. Preoperatively, the topographic extension of the conus was calculated by measuring the distance from the geometric center of the cornea and the outermost point of the corneal ectasia (ectasia <8.0 mm, group A; ectasia ≥8.0 mm, group B). DALK was performed using both small grafts (8.0 mm, group 1) and large grafts (9.0 mm, group 2). Best-corrected visual acuity and topographic astigmatism were evaluated preoperatively (T0) and postoperatively after complete suture removal (1 year, T1).

Results: Data from 224 eyes of 196 patients (mean age 37.6 ± 15.1 years) were evaluated. Topographic astigmatism improved from T0 to T1 (4.94 ± 2.92 diopters (D) [95% CI, 4.56-5.33] vs 4.19 ± 2.45 D [95% CI, 3.87-4.51], p = 0.001). There was no significant difference in postoperative topographic cylinder between group 1 and group 2 when considering eyes with corneal ectasia <8.0 mm (group 1 A, 4.15 ± 2.19 D [95% CI, 3.64-4.66] vs group 2 A, 3.65 ± 2.13 D [95% CI, 2.92-4.38], p = 0.14); conversely, the difference was significant considering eyes with corneal ectasia ≥8.0 mm (group 1B, 4.74 ± 2.90 D [95% CI, 4.09-5.38] vs group 2B, 3.68 ± 1.94 D [95% CI, 3.10-4.26], p = 0.02).

Conclusions: Large 9.0-mm DALK provided better anatomical outcomes compared to conventional 8.0-mm DALK, particularly in eyes with corneal ectasia extending beyond the central 8.0 mm.

Fig. 1. Preoperative assessment of the topographic localization of corneal ectasia.

Left: the distance between the geometric center of the cornea and the outermost point of the corneal ectasia (with keratometric axial power ≥ 50.5 diopters [D]) was 2.93 mm (radius) (ectasia < 8.0 mm, group A). Right: the distance between the geometric center of the cornea and the outermost point of the corneal ectasia (with keratometric axial power ≥ 50.5 D) was 4.22 mm (ectasia ≥ 8.0 mm, group B).

Fig. 2. Number of eyes belonging to each study group, according to both graft size and topographic localization of the conus.

Top left: 8.0-mm graft diameter and ectasia < 8.0 mm (group 1A). Top right: 8.0-mm graft diameter and ectasia ≥ 8.0 mm (group 1B). Bottom left: 9.0-mm graft diameter and ectasia < 8.0 mm (group 2A). Bottom right: 9.0-mm graft diameter and ectasia ≥ 8.0 mm (group 2B).

Fig. 3. Postoperative topographic cylinder (diopters [D]), group 1A vs 2A and group 1B vs 2B.

Graph showing the difference detected in postoperative topographic cylinder between group 1A and group 2A (p = 0.14) and between group 1B and group 2B (p = 0.02).

Fig. 4. Both corneal maps show a corneal ectasia extending beyond 8.0 mm.

The black circle marks the dimensions of the graft employed for deep anterior lamellar keratoplasty (DALK). Left: employing a conventional 8.0-mm graft corneal ectasia extending beyond 8.0 mm is not completely removed. Right: employing large 9.0-mm graft it is possible to remove the entire amount of the conus.