Comparison of corneal densitometry between big-bubble and visco-bubble deep anterior lamellar keratoplasty

Aims To evaluate deep corneal densitometry and visual outcomes after big-bubble (BB-DALK) and visco-bubble (VB-DALK) deep anterior lamellar keratoplasty performed in patients with keratoconus. Methods Prospective comparative study of 50 advanced keratoconic patients who underwent DALK surgery; 25 eyes (group I) were completed with BB-DALK and 25 eyes (group II) with VB-DALK after the failure of pneumatic dissection. Best spectacle-corrected visual acuity (BSCVA), corneal tomographic parameters and endothelial cell count were recorded 1, 3, 6, 12 and 24 months after surgery. Densitometric analysis of the deep corneal interface was obtained using Scheimpflug tomography at each visit; values recorded were compared between the two groups and statistically analysed. Results BSCVA was significantly better in the BB-DALK group than the VB-DALK group (0.39 +/- 0.29 vs 0.65 +/- 0.23 logarithm of the minimum angle of resolution, respectively) for the first 3 months; and in the same time period, densitometry was significantly higher in the VB-DALK group than those recorded in the BB-DALK group (23.97 +/- 5.34 vs 17.13 +/- 4.44 grayscale units). However, densitometric values and visual acuity did not differ significantly in the two groups at 1 year. No statistically significant difference for the other variables analysed at any time frame was found. Conclusion The use of viscoelastic substance in the VB-DALK technique may induce modification of interface stromal reflectivity resulting in reduced visual acuity up to 3 months postoperatively. However, this initial negative effect on the interface quality does not affect the long-term visual outcome, with densitometric values and visual outcomes similar in the two groups from 6 months postoperatively.