Laboratory model of bursting pressures of femtosecond laser-assisted penetrating keratoplasty wounds using novel pattern designs

Correlation Between Corneal Button Size and Intraocular Pressure During Femtosecond Laser-Assisted Keratoplasty

PURPOSE

To evaluate changes in intraocular pressure (IOP) in recipient and donor eyes during femtosecond laser-assisted keratoplasty (FLAK) and to assess for differences in the diameter of trephinated corneal buttons according to changes in pressure.

MATERIALS AND METHODS

Twenty porcine whole eyes (recipient model) and 20 porcine-corneoscleral rims (donor model) were prepared, and anterior chamber pressures were measured using a fiberoptic sensing device (Opsens, Quebec, Canada) during the femtosecond laser corneal cutting process. To determine the diameter of corneal buttons, 10 porcine whole eyes (recipient model) and 12 corneoscleral rims (donor model) of each baseline IOP were cut with the femtosecond laser programmed to the following pattern: "vertical side cut"; 1200 μm (depth), 8 mm (diameter). Digital photographs were obtained using microscopy and subsequently analyzed.

RESULTS

The IOP (mean ± SD) for the recipient model was 10.2 (±0.9) mm Hg at baseline and ranged from 96.6 (±4.5) to ∼138.4 (±3.8) mm Hg during the corneal cutting process. This shows that the maximum IOP during FLAK increased 13.5 times compared with baseline. In the donor model, the mean pressure elevation from baseline artificial anterior chamber (AAC) pressure to corneal cutting was 15.8 (±5.4) mm Hg. This showed a positive correlation with baseline IOP [correlation coefficient (CC) = 0.827, P = 0.006]. As the baseline IOP in the recipient eye increased, trephinated corneal button size was reduced by up to 3.9% in diameter (CC = -0.945, P = 0.015). In addition, in donor eyes, the diameter was decreased by up to 11.7% as the baseline AAC pressure increased (CC = -0.934, P = 0.006).

CONCLUSIONS

During the FLAK procedure, the IOP increases in both recipient and donor eyes. The diameter of the trephinated donor and recipient corneal buttons was decreased as the initial baseline IOP increased. Ophthalmic surgeons can determine the AAC pressure based on the baseline IOP in the recipient patient.

Outcome of "mushroom" pattern femtosecond laser-assisted keratoplasty versus conventional penetrating keratoplasty in patients with keratoconus

PURPOSE

The aim of this study was to compare the outcomes of "mushroom" femtosecond laser-enabled keratoplasty (M-FLEK) with those of conventional penetrating keratoplasty (PKP) in eyes with keratoconus. The femtosecond laser-enabled "mushroom" pattern keratoplasty technique results in less postoperative astigmatism and higher endothelial cell counts compared with conventional PKP in patients with keratoconus.

METHODS

This was a nonrandomized retrospective, single private center clinical study. Between March 2010 and April 2012, 26 eyes underwent M-FLEK and 33 eyes underwent conventional PKP. Data on preoperative and postoperative manifest refraction, uncorrected visual acuity and best-corrected visual acuity (BCVA), endothelial cell counts, vector analysis, and complications were retrieved and analyzed.

RESULTS

At 12 months of follow-up, the mean logMAR BCVA was 0.31 ± 0.55 in the M-FLEK group and 0.32 ± 0.21 in the PKP group (P = 0.91). The mean spherical equivalent was similar between the groups. The mean manifest cylinder was significantly lower in the M-FLEK group (-2.84 ± 1.08 diopters) than in the PKP group (-3.93 ± 2.26 diopters; P = 0.03). There was a smaller mean endothelial cell loss in the M-FLEK group compared with the PKP group (32.1% vs 38.7%, respectively, P = 0.17) 1 year postoperatively. The complication rates were similar for both groups.

CONCLUSIONS

M-FLEK appears to be a safe procedure that results in less astigmatism and a trend toward higher endothelial cell counts compared with conventional PKP, with similar postoperative BCVA.

Femtosecond laser-assisted keratoplasty: full and partial-thickness cut wound strength and endothelial cell loss across a variety of wound patterns

PURPOSE

To evaluate wound strength for patient safety during transport and endothelial viability when partial and complete femtosecond laser-assisted keratoplasty (FLAK) incisions are made in cadaveric corneas.

METHODS

19 human corneoscleral rims were divided into six groups, mounted on an anterior chamber maintainer and cut with a femtosecond laser programmed to the following patterns: 'zigzag' (A), 'mushroom' (B) and 'top hat' (C) in both full (1) and partial (2) thicknesses. The pressure required to produce leakage from the corneal incision was then measured. Eight additional corneas were cut with the 'zigzag' pattern: four full and four partial thickness, prepared and transported per standard eye bank protocol, and analysed for endothelial cell loss with trypan blue staining and digital image analysis.

RESULTS

Mean leakage pressure in mm Hg for group A1 was 110 (SD 94); group A2, 1180 (SD 468); group B1, 978 (SD 445); group B2, 987 (SD 576); group C1, 710 (SD 474); group C2, 1290 (SD 231). There was a significant difference in leakage pressure between groups A1 and A2 (p=0.05), groups A1 and B1 (p=0.05), and groups A1 and C1 (p=0.05). Mean percentage endothelial damage after full-thickness cuts was 8.40 (SD 2.34) and 5.30 (SD 1.33) in partial-thickness cuts (p=0.11).

CONCLUSIONS

Partial thickness zigzag, top hat and mushroom-style partial FLAK incisions left an intact tissue wall with high resistance to rupture, whereas full-thickness cuts were more variable. Laser trephination and eye bank handling protocol for donor FLAK buttons leads to moderate peripheral endothelial cell loss in tissue with both complete and partial cuts.