Femtosecond Laser-Assisted Keratoplasty: Laboratory Studies in Eye Bank Eyes

Comparing the efficacy and safety of femtosecond laser-assisted vs conventional penetrating keratoplasty: a meta-analysis of comparative studies

PURPOSE

To investigate the safety and efficacy of femtosecond laser-assisted penetrating keratoplasty (FLAK) versus conventional penetrating keratoplasty (CPK).

METHODS

A literature search of PubMed, Cochrane, Embase, Web of Science, and Clinicaltrials.gov was conducted for comparative studies published from January 2007 to October 2019. Studies that involved both FLAK and CPK groups and reported on the relevant efficacy and/or safety parameters were included. The Newcastle-Ottawa quality assessment scale was used to analyse the methodological quality of these studies. Further, weighted mean differences (WMDs) with 95% confidence intervals (CIs) were calculated.

RESULTS

From the screened articles, a total of 1991 eyes from nine comparative studies were included. FLAK was not statistically superior for twelve-month postoperative best corrected visual acuity (WMD = - 0.06; 95% CI [- 0.16, 0.04]; P = 0.22), corneal astigmatism (WMD = - 0.81; 95% CI [- 1.63, 0.01]; P = 0.05) or six-month postoperative uncorrected visual acuity (WMD = - 0.11; 95% CI [- 0.27, 0.06]; P = 0.21). There were no significant differences in corneal graft rejection rate and the graft failure between FLAK and CPK at twelve months postoperative. However, best-corrected visual acuity (BCVA) and corneal astigmatism corrected with FLAK were better than those with CPK six months postoperative after elimination of data heterogeneity.

CONCLUSION

Visual outcomes improvement in FLAK was better than that in CPK at six months postoperative, but not twelve months postoperative. This review recommends selecting a technique based on patients' work demands and economic burdens.

Systematic review and meta-analysis of femtosecond laser-enabled keratoplasty versus conventional penetrating keratoplasty

PURPOSE

The aim of this meta-analysis is to compare femtosecond laser-enabled keratoplasty with conventional penetrating keratoplasty regarding postoperative astigmatism, visual functions, graft rejection, graft failure, and complications.

METHODS

Eligible studies were retrieved from five mainstream electronic databases, including PubMed, Embase, Ovid MEDLINE, Cochrane Library, and ClinicalTrial.gov. Postoperative topographic astigmatism was set as the primary outcome, and best-corrected visual acuity, spherical equivalent, endothelial cell density, graft rejection, graft failure, and complications were chosen as the secondary outcomes. Standard mean difference and risk ratio were the size effects for continuous data and binomial data, respectively. The data were pooled through either the random-effects model or the fixed-effects model based on data heterogeneity. Moreover, subgroup analyses were conducted when the heterogeneity occurred distinctly (I² > 50%).

RESULTS

A total of seven comparative studies were included. The pooled standard mean difference (-0.32, 95% confidence interval: -0.74 to 0.10) showed that femtosecond laser-enabled keratoplasty was not superior over conventional penetrating keratoplasty to decrease postoperative topographic astigmatism (p = 0.14). However, best-corrected visual acuity after femtosecond laser-enabled keratoplasty was significantly better than that after conventional penetrating keratoplasty (p = 0.00, standard mean difference: -0.23, 95% confidence interval: -0.37 to -0.10). Furthermore, endothelial cell density after femtosecond laser-enabled keratoplasty was preserved significantly better (p = 0.03, standard mean difference: 0.63, 95% confidence interval: 0.07-1.20). Moreover, spherical equivalent, graft rejection, graft failure, and complications represented no distinct differences between femtosecond laser-enabled keratoplasty and conventional penetrating keratoplasty (p > 0.05).

CONCLUSION

Femtosecond laser-enabled keratoplasty may not be superior over conventional penetrating keratoplasty in decreasing postoperative topographic astigmatism, but might have advantages to achieve best-corrected visual acuity and endothelial cell density preservation. In addition, the two techniques seem to be comparable regarding spherical equivalent, graft rejection/failure, and complications.

Anvil-profiled penetrating keratoplasty: load resistance evaluation

The aim of this study was to qualitatively evaluate the biomechanical load resistance of different surgical wound configurations (mushroom, zig-zag, anvil and conventional trephination) in penetrating keratoplasty (PK) by designing a 2D and a 3D finite-element biomechanical model of the cornea. A mathematical model of the human cornea was developed, and different geometric configurations for PK were designed. The internal pressure was raised until the wound misaligned; wound prolapse then occurred. Better wound resistance was found in all the laser trephined profiles tested in comparison with the conventional straight one. The anvil profile was more resistant to the increasing internal pressure than was the mushroom or the zig-zag pattern. Thanks to its greater mechanical load resistance, the anvil profile made possible the apposition of a restricted number of sutures and early suture removal. These advantages can contribute to a faster visual recovery in patients undergoing penetrating keratoplasty.

Outcomes of femtosecond laser-assisted mushroom-configuration keratoplasty in advanced keratoconus

PURPOSE

To evaluate the long-term outcomes after femtosecond laser (FSL)-assisted mushroom-configuration keratoplasty in advanced keratoconus.

PATIENTS AND METHODS

Thirteen eyes with Amsler-Krumeich stage IV keratoconus underwent FSL-assisted mushroom-configuration penetrating keratoplasty (PKP) and deep anterior lamellar keratoplasty (DALK) at a tertiary referral centre. Preoperative risk factors included low orneal thickness, high keratometry measurements, previous hydrops, and central stromal scarring. Main outcome measures were visual acuity and refractive outcome.

RESULTS

The median follow-up was 33 months (range: 4-43). Preoperatively, the mean corrected distance visual acuity (CDVA) was 1.22±0.47 LogMAR (range: 0.5-1.9 LogMAR), mean minimum corneal thickness was 282±100.8 μm (range: 147-478 μm), and mean average keratometric (K) value was 63.4±7.63 dioptre (D; range: 57.0-75.7 D). Four patients underwent PKP and nine underwent DALK (two converted to PKP). Five patients subsequently underwent a modified arcuate mushroom interface dissection (AMID) procedure for astigmatic correction. At the final follow-up, the mean CDVA was 0.05±0.13 LogMAR (range: -0.10 to 0.20 LogMAR), mean spherical equivalent was -3.21±3.21D, mean cylindrical refractive error was 3.23±2.20 D, and mean average K was 43.1±1.53 D. Complications included early graft dehiscence, corneal vascularisation, stromal rejection, and sclerokeratitis. Sutures were completely removed at the mean 18.4 months for PKP and 9.1 months for DALK postoperatively.

CONCLUSION

FSL-assisted mushroom-configuration keratoplasty is feasible and safe in patients with stage IV keratoconus. AMID could further enhance the refractive outcome safely.

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.

Laser-assisted penetrating keratoplasty: 1-year results in patients using a laser-welded anvil-profiled graft

PURPOSE

To describe a new laser-assisted penetrating keratoplasty technique combining a femtosecond anvil-like trephination pattern with the laser welding procedure.

DESIGN

Cohort prospective study with 1 year of follow-up (June 2011 through January 2013).

METHODS

This study was performed at Misericordia e Dolce Public Hospital, Prato, Italy. Twenty-four eyes of 22 patients underwent penetrating keratoplasty: 4 had granular dystrophy, 12 had keratoconus in its final stages, 3 had post-herpetic leukoma, and 5 had corneal scars. A femtosecond laser was used to create anvil-profiled cuts in donor and recipient corneas. Diode laser welding was performed, supporting standard suturing. All patients were evaluated for corrected distance visual acuity, pachymetry, manifest astigmatism, and endothelial cell density after 1, 3, 6, and 12 months.

RESULTS

Mean ± standard deviation postoperative corrected visual acuity was 0.48 ± 0.23 logarithm of the minimal angle of resolution (logMAR), 0.30 ± 0.18 logMAR, 0.18 ± 0.13 logMAR, and 0.13 ± 0.16 logMAR at 1, 3, 6, and 12 months, respectively. At the same follow-up times, mean pachymetry was 537 ± 57 μm, 533 ± 74 μm, 528 ± 72 μm, and 529 ± 58 μm, respectively; and mean endothelial cell density was 1945 ± 371 cells/mm(2), 1881 ± 410 cells/mm(2), 1781 ± 401 cells/mm(2), and 1730 ± 376 cells/mm(2), respectively. Mean manifest and topographic postoperative astigmatism were: 3.6 ± 2.5 diopters (D) and 4.65 ± 2.57 D at 1 month, 2.93 ± 2.34 D and 4.79 ± 2.85 D at 3 months, 2.82 ± 1.75 D and 3.44 ± 2.28 D at 6 months, and 2.08 ± 1.25 D and 2.73 ± 2.01 D at 12 months, respectively. All surgical operations were successful and without intraoperative complications.

CONCLUSIONS

The use of the anvil trephination profile was effective for performing laser-assisted penetrating keratoplasty. The large donor-recipient interface enables the laser welding procedure and good preservation of the recipient's endothelial cell pool.

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.

Application of the femtosecond laser LASIK microkeratome in eye banking

PURPOSE OF REVIEW

To review the literature for recent advancements in the femtosecond laser technology with regard to its applications in corneal transplantation and eye banking.

RECENT FINDINGS

Advancements in corneal surgery have encouraged the use of disease-specific corneal subcomponents, utilized in procedures such as anterior-lamellar keratoplasty and endothelial keratoplasty, instead of traditional transplant procedures to minimize adverse effects of penetrating keratoplasty. Femtosecond laser microkeratomes can precisely create flaps for such transplant procedures, achieve better wound stability, and promote healing by shaped wound configurations. Laser microkeratomes have been compared to traditional mechanical microkeratomes for keratoplasty procedures from various aspects and are superior in some aspects and offer unique capabilities.

SUMMARY

Femtosecond laser applications in eye banking include preparation of donor and recipient corneas for use in penetrating keratoplasty, anterior-lamellar keratoplasty, and endothelial keratoplasty. Advantages of femtosecond laser microkeratomes include higher precision of the cut, ability to achieve thinner flaps, and wound configurations that allow greater wound stability, shorter recovery time, and less postoperative pain. However, cost and availability at the eye-bank level may hinder widespread and immediate application.

Quality of corneal lamellar cuts quantified using atomic force microscopy

PURPOSE

To quantify the cut quality of lamellar dissections made with the femtosecond laser using atomic force microscopy (AFM).

SETTING

Bascom Palmer Eye Institute, University of Miami Miller School of Medicine, Miami, Florida, USA.

DESIGN

Experimental study.

METHODS

Experiments were performed on 3 pairs of human cadaver eyes. The cornea was thinned to physiologic levels by placing the globe, cornea side down, in 25% dextran for 24 hours. The eyes were reinflated to normal pressures by injecting a balanced salt solution into the vitreous cavity. The eyes were placed in a holder, the epithelium was removed, and the eyes were cut with a Visumax femtosecond laser. The energy level was 180 nJ for the right eye and 340 nJ for the left eye of each pair. The cut depths were 200 μm, 300 μm, and 400 μm, with the cut depth maintained for both eyes of each pair. A 12.0 mm trephination was then performed. The anterior portion of the lamellar surface was placed in a balanced salt solution and imaged with AFM. As a control, the posterior surface was placed in 2% formalin and imaged with environmental scanning electron microscopy (SEM). Four quantitative parameters (root-mean-square deviation, average deviation, skewness, kurtosis) were calculated from the AFM images.

RESULTS

From AFM, the 300 μm low-energy cuts were the smoothest. Similar results were seen qualitatively in the environmental SEM images.

CONCLUSION

Atomic force microscopy provided quantitative information on the quality of lamellar dissections made using a femtosecond laser, which is useful in optimizing patient outcomes in refractive and lamellar keratoplasty surgeries.

Optimal parameters to improve the interface quality of the flap bed in femtosecond laser-assisted laser in situ keratomileusis

PURPOSE

To analyze the interface quality of the anterior stroma after femtosecond laser flap creation using atomic force microscopy.

SETTING

IRCCS Fondazione G.B. Bietti, Rome, Italy.

DESIGN

Experimental study.

METHODS

A 110 μm depth flap was created in 20 human corneal tissues using a femtosecond laser platform (Intralase iFS). Tissues were divided into 4 groups of various cutting parameters: pulse energy and spot separation of 0.75 μJ and 6 μm (Group 1), 0.65 μJ and 5 μm (Group 2), 0.55 μJ and 4 μm (Group 3), and 0.45 μJ and 4 μm (Group 4). Four additional tissue sections were cut using a motorized microkeratome (Hansatome). Atomic force microscopy (Autoprobe CP) analysis was performed on the stromal bed of each sample.

RESULTS

The corneal tissues treated with higher pulse energies and wider spot separations (Groups 1 and 2) showed a rougher stromal bed interface (root mean square [RMS] rough = 0.23 μm ± 0.008 (SD) and 0.24 ± 0.009 μm, respectively) than tissues in Groups 3 and 4 (RMS rough = 0.18 ± 0.006 μm and 0.18 ± 0.008 μm, respectively; P<.001, 1-way analysis of variance). The stromal surface quality of tissues treated with pulse energies of 0.55 μJ or lower and 4 μm spot separation compared favorably with that of tissues cut by the microkeratome (RMS rough = 0.17 ± 0.006 μm; P>.05, Tukey).

CONCLUSIONS

The femtosecond stromal interface quality was improved with pulse energy lower and spot separations narrower than those currently used in the clinical setting. The flap interface smoothness created by the femtosecond laser was comparable to that created by the microkeratome.

FINANCIAL DISCLOSURE

No author has a financial or proprietary interest in any material or method mentioned.

In vivo confocal microscopic evaluation of corneal wound healing after femtosecond laser-assisted keratoplasty

BACKGROUND AND OBJECTIVE

To evaluate corneal wound healing after femtosecond laser-assisted keratoplasty (FLAK) using in vivo confocal microscopy (IVCM).

PATIENTS AND METHODS

Prospective, interventional, consecutive case series of 17 eyes after mushroom-shaped FLAK. IVCM was performed preoperatively and at 1, 3, 6, and 12 months postoperatively to assess wound healing.

RESULTS

Mean keratocyte activation grade increased from preoperative levels to 1 month postoperatively in both the central (0.41 ± 0.62 to 1.73 ± 1.03) and peripheral (0.47 ± 0.52 to 1.57 ± 1.09) cornea, then gradually decreased through 12 months. Dendritic cells increased from preoperatively to 1 month postoperatively in both the central (0.71 ± 0.83 to 1.33 ± 0.98) and peripheral (0.79 ± 0.70 to 1.42 ± 0.90) cornea, then gradually decreased until 6 months postoperatively. Stromal reinnervation was 1 month postoperatively in 8 patients (50%). By 12 months, sub-epithelial nerves were observed centrally in 5 patients (45.5%).

CONCLUSION

IVCM after FLAK shows an initial increase in keratocyte activation and dendritic cells that decrease over time. Corneal reinnervation is seen as early as 1 month postoperatively.

Investigation of femtosecond laser--enabled keratoplasty wound geometry using optical coherence tomography

PURPOSE

To measure the wound geometry after femtosecond laser-enabled keratoplasty (FLEK) using optical coherence tomography (OCT).

DESIGN

Prospective nonrandomized clinical study and laboratory study.

PARTICIPANTS

Patients who were candidates for penetrating keratoplasty at an academic referral center.

METHODS

Wound architecture was measured and analyzed by OCT in 8 eyes of 8 consecutive patients who underwent FLEK. Femtosecond laser lamellar cuts were performed on 3 eye bank corneas, and the wound diameters were measured by OCT.

RESULTS

Sutures were completely removed on average at 1 month per decade of age after surgery. No cases of wound dehiscence were noted, and graft-host tissue apposition appeared excellent on OCT. The mean spectacle-corrected visual acuity 1 month after suture removal was 20/35, and mean astigmatism was 5.0 diopters by manifest refraction and 8.7 diopters by computerized topography. The measured graft diameter was smaller than the laser setting by 2.5% (P = 0.007). The cut diameters of the eye bank corneas were also slightly smaller than the laser setting.

CONCLUSIONS

FLEK offers benefits of rapid wound healing and predictable wound geometry. The measured wound geometry agreed well with laser setting other than a small systematic deviation that could be explained by the mechanics of corneal applanation during the laser cut. OCT is a useful tool to measure the actual graft diameter after FLEK.