Big-bubble deep anterior lamellar keratoplasty using central vs peripheral air injection: a clinical trial

Ex Vivo Evaluation of a Pressure-Sensitive Device to Aid Big Bubble Intrastromal Dissection in Deep Anterior Lamellar Keratoplasty

Purpose

To develop and perform ex vivo testing for a device designed for semiquantitative determination of intracorneal dissection depth during big bubble (BB) deep anterior lamellar keratoplasty.

Methods

A prototype device connected to a syringe and cannula was designed to determine depth of intrastromal placement based on air rebound pressure emitted by a software controlled generator. Ex vivo testing of the device was conducted on human corneas mounted on an artificial anterior chamber in three experiments: (1) cannula purposely introduced at different depths measured with anterior segment optical coherence tomography, (2) cannula introduced as per the BB technique, and (3) simulation of the BB technique guided by the device.

Results

A positive pressure differential and successful BB were observed only when the cannula was positioned within 150 microns from the endothelial plane. In all successful BB cases (21/40), a repeatable increase in tissue rebound pressure was detected, which was not recorded in unsuccessful cases. The device was able to signal to the surgeon correct placement of the cannula (successful BB) in 16 of 17 cases and incorrect placement of the cannula (unsuccessful BB) in 8 of 8 cases (94.1% sensitivity, 100% specificity).

Conclusions

In our ex vivo model, this novel medical device could reliably signal cannula positioning in the deep stroma for effective pneumatic dissection and possibly aid technical execution of BB deep anterior lamellar keratoplasty.

Translational Relevance

A medical device that standardizes big bubble deep anterior lamellar keratoplasty could increase the overall success rate of the surgical procedure and aid popularization of deep anterior lamellar keratoplasty.

Approaches toward enhancing survival probability following deep anterior lamellar keratoplasty

The greatest advantage of deep anterior lamellar keratoplasty over full-thickness corneal transplantation is the elimination of graft failure caused by endothelial rejection. Despite this advantage, a deep anterior lamellar keratoplasty graft can fail because of several factors, such as complications related to the donor-recipient interface, graft epithelial abnormalities, graft vascularization, stromal graft rejection, and recurrence of herpetic keratitis. Increased deep anterior lamellar keratoplasty graft survival is mainly built upon optimization of the ocular surface to provide a hospitable environment for the graft. Any predisposing factors for graft epithelial abnormalities, corneal neovascularization, and preexisting vernal keratoconjunctivitis should be identified and treated preoperatively. Prompt recognition and appropriate treatment of interface-related complications and stromal graft rejection usually result in good anatomic outcomes, with no detrimental effects on vision.

Microbubble technique in failed deep anterior lamellar keratoplasty: 2-year outcomes

Purpose:

To compare the long-term results of big-bubble technique and microbubble techniques to complete stroma dissection after failure of achieving a big-bubble.

Methods:

A total of 35 eyes with keratoconus underwent lamellar keratoplasty with the big-bubble technique (15 eyes) or the microbubble technique (15 eyes). Conversion to penetrating keratoplasty was performed in 3 eyes of the big-bubble group and in 2 eyes of the microbubble group. Best-corrected visual acuity, corneal thickness, corneal astigmatism, and endothelial cell count were assessed preoperatively and at 12 and 24 months after surgery.

Results:

Mean preoperative visual acuity was 0.29 ± 0.18 in the big-bubble group and 0.25 ± 0.15 in the microbubble group. Postoperatively, all patients showed a regular interface between donor and recipient tissue. At 24 months, mean best-corrected visual acuity was 0.84 ± 0.16 in the big-bubble group and 0.68 ± 0.17 in the microbubble group (p = 0.013), and mean central corneal thickness was 530 ± 39 µm in the big-bubble group and 545 ± 30 µm in the microbubble group. Astigmatism was 2.41 ± 1.29 D and 3.59 ± 1.48 D (p = 0.036), respectively, while endothelial cell density was 1,671 ± 371 in the big-bubble group and 1,567 ± 275 in the microbubble group.

Conclusions:

The microbubble technique appears to be a valid alternative as it was safe and provided good functional results.

Intrastromal Corneal Ring Segments for Astigmatism Correction after Deep Anterior Lamellar Keratoplasty

Background. To evaluate the change in corneal astigmatism after intrastromal corneal ring segment (ICRS) implantation in keratoconus patients with previous deep anterior lamellar keratoplasty (DALK). Design was a longitudinal, retrospective, interventional study. The study included 25 eyes of 24 patients with keratoconus who had DALK performed at least two years prior to ICRS implantation. All patients had a clear corneal graft with up to 8.00 D of corneal astigmatism and intolerance to contact lenses. The studied parameters were age, sex, corrected distance visual acuity (CDVA), maximum keratometry (K1), minimum keratometry (K2), spherical equivalent, and astigmatism. There was a statistically significant decrease in the postintervention analysis as follows: 3.5 D reduction in K1 (p < 0.001); 1.53 D in K2 (p = 0.005); and 2.52 D (p < 0.001) in the average K. The spherical equivalent reduced from -3.67 D (±2.74) to -0.71 D (±2.35) (p < 0.001). The topographic astigmatism reduced from 3.87 D preoperatively to 1.90 D postoperatively (p < 0.001). The CDVA improved from 0.33 (±0.10) to 0.20 (±0.09, p < 0.001). ICRS implantation is a useful option for the correction of astigmatism after DALK as it yields significant visual, topographic, and refractive results.

Weighing of risk factors for penetrating keratoplasty graft failure: application of Risk Score System

AIM

To analyze the relationship between the score obtained in the Risk Score System (RSS) proposed by Hicks et al with penetrating keratoplasty (PKP) graft failure at 1y postoperatively and among each factor in the RSS with the risk of PKP graft failure using univariate and multivariate analysis.

METHODS

The retrospective cohort study had 152 PKPs from 152 patients. Eighteen cases were excluded from our study due to primary failure (10 cases), incomplete medical notes (5 cases) and follow-up less than 1y (3 cases). We included 134 PKPs from 134 patients stratified by preoperative risk score. Spearman coefficient was calculated for the relationship between the score obtained and risk of failure at 1y. Univariate and multivariate analysis were calculated for the impact of every single risk factor included in the RSS over graft failure at 1y.

RESULTS

Spearman coefficient showed statistically significant correlation between the score in the RSS and graft failure (P<0.05). Multivariate logistic regression analysis showed no statistically significant relationship (P>0.05) between diagnosis and lens status with graft failure. The relationship between the other risk factors studied and graft failure was significant (P<0.05), although the results for previous grafts and graft failure was unreliable. None of our patients had previous blood transfusion, thus, it had no impact.

CONCLUSION

After the application of multivariate analysis techniques, some risk factors do not show the expected impact over graft failure at 1y.