Corneal ectasia after laser vision correction

Crosslinking for post-laser-assisted in situ keratomileusis corneal ectasia: Transepithelial flap-on 30 minute and flap-lift 4 minute protocol

Purpose

To evaluate the outcomes of transepithelial corneal collagen crosslinking (CXL) for management of corneal ectasia after laser-assisted in situ keratomileusis (LASIK).

Methods

CXL was performed on 18 eyes of 16 patients either with LASIK flap lift (n = 9; 365 nm, 30 mW/cm², 4 minutes, pulse) or with transepithelial flap-on (n = 9 eyes; 365 nm, 3 mW/cm², 30 minutes) technique. Postoperative change in maximum keratometry (Kmax), anterior elevation, posterior elevation, spherical equivalent (SE), logMAR uncorrected distance visual acuity (UDVA), aberrations, and central corneal thickness (CCT) were evaluated at 12 months postoperatively.

Results

A total of 18 eyes of 16 patients (11 males, 5 females) were included. Overall, Kmax flattened more after flap-on CXL (P = 0.014) compared to flap-lift CXL. The endothelial cell density and posterior elevation were stable throughout the follow-up period. Index of vertical asymmetry (IVA), keratoconus index (KI), and central keratoconus index (CKI) decreased after flap-on CXL at 12 months, postoperatively (P < 0.05), whereas there were no statistically significant changes in these parameters after flap-off CXL group. The spherical aberrations and total root mean square decreased after flap-lift CXL at 12 months, postoperatively (P < 0.05).

Conclusion

In our study, transepithelial collagen crosslinking was successfully used to halt disease progression in post-LASIK keratectasia. We recommend flap-on surgical technique for these cases.

Comparison of Corneal Biomechanical Characteristics After Surface Ablation Refractive Surgery and Novel Lamellar Refractive Surgery

PURPOSE

To investigate and compare corneal biomechanical changes in the form of corneal hysteresis (CH) and corneal resistance factor (CRF) after small-incision lenticule extraction (SMILE) and laser-assisted subepithelial keratectomy (LASEK).

METHODS

In this retrospective observational study, patients who underwent either SMILE (36 eyes, 21 patients) or LASEK (35 eyes, 19 patients) were included. Data were collected preoperatively and at 1 and 3 months postoperatively, which included corneal topography and Ocular Response Analyzer values of CH, CRF, and intraocular pressure (IOP). Differences between both surgical groups and the relationships between variables were evaluated.

RESULTS

CH, CRF, Goldmann IOP, and corneal compensated IOP after surgery were significantly lower than the preoperative values (P < 0.05) in both surgical groups. Lenticule thickness (LT) correlated with ΔCRF (Δ = postoperative - preoperative value) in the SMILE group (r = -0.513, P = 0.001), but the ablation depth (AD) and ΔCRF showed no correlation in the LASEK group (r = -0.297, P = 0.083). In the SMILE group, ΔCRF/LT (-0.036 ± 0.01) and ΔCH/LT (-0.021 ± 0.01) values were significantly lower than ΔCRF/AD (-0.048 ± 0.02) and ΔCH/AD (-0.026 ± 0.02) values in the LASEK group (P < 0.05).

CONCLUSIONS

Both SMILE and LASEK alter corneal biomechanical strength. However, the changes induced by SMILE are more predictable than those induced by LASEK. In terms of per unit tissue removed, SMILE seems to have less effect on corneal biomechanics than LASEK, which may be due to preservation of the stiffer anterior stroma.

In vivo biocompatibility of two PEG/PAA interpenetrating polymer networks as corneal inlays following deep stromal pocket implantation

This study compared the effects of implanting two interpenetrating polymer networks (IPNs) into rabbit corneas. The first (Implant 1) was based on PEG-diacrylate, the second (Implant 2) was based on PEG-diacrylamide. There were inserted into deep stromal pockets created using a manual surgical technique for either 3 or 6 months. The implanted corneas were compared with normal and sham-operated corneas through slit lamp observation, anterior segment optical coherence tomography, in vivo confocal scanning and histological examination. Corneas with Implant 1 (based on PEG-diacrylate) developed diffuse haze, ulcers and opacities within 3 months, while corneas with Implant 2 (based on PEG-diacrylamide) remained clear at 6 months. They also exhibited normal numbers of epithelial cell layers, without any immune cell infiltration, inflammation, oedema or neovascularisation at post-operative 6 month. Morphological studies showed transient epithelial layer thinning over the hydrogel inserted area and elevated keratocyte activity at 3 months; however, the epithelium thickness and keratocyte morphology were improved at 6 months. Implant 2 exhibited superior in vivo biocompatibility and higher optical clarity than Implant 1. PEG-diacrylamide-based IPN hydrogel is therefore a potential candidate for corneal inlays to correct refractive error.

Recurrent ectasia in corneal grafts and outcomes of repeat keratoplasty for keratoconus

AIM

To analyse cases of recurrent ectasia in donor corneas after penetrating keratoplasty (PK) for keratoconus.

METHODS

Data on 25 patients (36 eyes) with recurrent ectasia were retrospectively analysed in this study. The main outcome measures were time to development of recurrent ectasia after first PK for keratoconus, change in keratometric sphere and astigmatism between final suture removal and development of recurrent ectasia, status of regrafts for recurrent ectasia, and histopathology of grafts excised for recurrent ectasia.

RESULTS

The age at first PK was 32.6 (SD 8.5) years, and ectasia developed 21.9 (7.0) years after PK. The mean keratometric sphere and cylinder increased by 4.2 D and 3.0 D, respectively, between final suture removal and diagnosis of recurrent ectasia. Ectasia was often preceded by thinning without bulging of the recipient stroma at the graft-host junction. Fifteen eyes (13 patients) were regrafted for recurrent ectasia, and histopathology of the excised grafts showed changes characteristic of keratoconus in the donor tissue in all cases. Two regrafts (two eyes of one patient) developed ectasia again, with one eye requiring a third PK to improve vision.

CONCLUSIONS

Recurrent ectasia was diagnosed on average two decades after PK. Ectatic changes were often bilateral and occasionally recurred after regrafting, suggesting that host cellular and/or biochemical factors may be responsible. Repeat PK for recurrent ectasia is successful in the intermediate term.