Delayed Ectasia Following LASIK With No Risk Factors: Is a 300-µm Stromal Bed Enough?

Ectasia After Corneal Refractive Surgery: A Systematic Review

INTRODUCTION

The incidence of ectasia following refractive surgery is unclear. This review sought to determine the worldwide rates of ectasia after photorefractive keratectomy (PRK), laser-assisted in situ keratomileusis (LASIK), and small incision lenticule extraction (SMILE) based on reports in the literature.

METHODS

A systematic review was conducted according to modified Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Publications were identified by a search of eight electronic databases for relevant terms between 1984 and 2021. Patient characteristics and preoperative values including manifest refractive spherical refractive equivalent (MRSE), central corneal thickness (CCT), anterior keratometry, postoperative residual stromal bed (RSB), and percent tissue altered (PTA) were summarized. In addition, annual rates of each refractive surgery were determined, and incidence of post-refractive ectasia for each type was calculated using the number of ectatic eyes identified in the literature.

RESULTS

In total, 57 eyes (70 eyes including those with preoperative risk factors for ectasia) were identified to have post-PRK ectasia, while 1453 eyes (1681 eyes including risk factors) had post-LASIK ectasia, and 11 eyes (19 eyes including risk factors) had post-SMILE ectasia. Cases of refractive surgery performed annually were estimated as 283,920 for PRK, 1,608,880 for LASIK, and 96,750 for SMILE. Reported post-refractive ectasia in eyes without preoperative identifiable risk factors occurred with the following incidences: 20 per 100,000 eyes in PRK, 90 per 100,000 eyes in LASIK, and 11 per 100,000 eyes in SMILE. The rate of ectasia in LASIK was found to be 4.5 times higher than that of PRK.

CONCLUSION

Post-refractive ectasia occurs at lower rates in eyes undergoing PRK than LASIK. Although SMILE appears to have the lowest rate of ectasia, the number of cases already reported since its recent approval suggests that post-SMILE ectasia may become a concern. Considering that keratoconus is a spectrum of disease, pre-existing keratoconus may play a larger role in postoperative ectasia than previously accounted for in the literature.

Evaluation of corneal topography and biomechanical parameters after use of systemic isotretinoin in acne vulgaris

Purpose. We report the effect of isotretinoin on corneal topography, corneal thickness, and biomechanical parameters in patients with acne vulgaris. Method. Fifty-four eyes of 54 patients who received oral isotretinoin for treatment of acne vulgaris were evaluated. All patients underwent a corneal topographical evaluation with a Scheimpflug camera combined with Placido-disk (Sirius), ultrasonic pachymetry measurements, and corneal biomechanical evaluation with an ocular response analyzer at baseline, in the 1st, 3rd, and 6th months of treatment, and 6 months after isotretinoin discontinuation. Results. The thinnest corneal thickness measured with Sirius differed significantly in the 1st, 3rd, and 6th months compared with the baseline measurement; there was no significant change in ultrasonic central corneal thickness measurements and biomechanical parameters (corneal hysteresis and corneal resistance factor) throughout the study. Average simulated keratometry and surface asymmetry index increased significantly only in the first month of treatment according to the baseline. All changes disappeared 6 months after the end of treatment. Conclusion. Basal tear secretion and corneal morphologic properties were significantly influenced during the systemic isotretinoin treatment and the changes were reversible after discontinuation. No statistical important biomechanical differences were found to be induced by isotretinoin.

Moderate keratoconus with thick corneas

PURPOSE

To describe two patients with moderate keratoconus and a corneal thickness exceeding 600 μm at the thinnest point.

METHODS

Case report.

RESULTS

In the first case, the steepest keratometric power was 51.50 diopters (D) in the right eye and 53.4 in the left eye and the thickness at the thinnest point was 658 and 625 μm, respectively. In the second case, the steepest keratometric power was 46.70 D in the right eye and 49.60 D in the left eye and the thickness at the thinnest point was 618 and 608 μm, respectively.

CONCLUSIONS

Keratoconus may develop despite a very thick cornea, reinforcing the idea that biomechanical changes can signify an important factor in the development and progression of this pathology.

Late onset corneal ectasia after LASIK surgery

PURPOSE

To report late onset corneal ectasia following myopic LASIK.

METHODS

A retrospective cohort case series. Nineteen patients with late onset corneal ectasia following LASIK procedure were examined at The Eye Center, Riyadh, Saudi Arabia. Patients underwent LASIK for myopia with spherical equivalent ranging from -1.4 to -13.75 diopters. Age and gender, history of systemic or local diseases, and time of onset of corneal ectasia were recorded. Eye examination and corneal topographical analyses were done before and after LASIK surgery.

RESULTS

Nineteen patients (29 eyes) with late onset corneal ectasia were identified from 1998 to 2008 in 13 male and six female patients. The mean follow-up period was 108 ± 23 months (range 72-144 months). No patient had pre-operative identifiable risk factors for corneal ectasia and the mean time of onset was 57 ± 24 months (range 24-120 months after LASIK). The pre-operative values included mean central pachymetry 553 ± 25 μm, mean keratometry reading of 42.9 ± 1.5 diopters, average oblique cylinder of 1.4 ± 1.2 diopters, posterior surface elevation of 26 ± 2.1 diopters, corneal flap thickness of 160 μm, mean spherical equivalent of -5.6 ± 3.6 diopters, and calculated residual corneal stromal bed thickness was 288 ± 35 μm. Three (5 eyes) patients developed ectasia after pregnancy. Three (4 eyes) patients developed corneal ectasia following severe adenoviral keratoconjunctivitis and had positive PCR for adenovirus type 8.

CONCLUSIONS

Corneal ectasia may develop many years after LASIK surgery and symptoms could go undetected for some time. Pregnancy and adenoviral keratoconjunctivitis occurred post-operatively in six patients.

Complications of sub-Bowman's keratomileusis with a femtosecond laser in 3009 eyes

PURPOSE

To assess the safety and complication rate of sub-Bowman's keratomileusis (SBK) in 3009 eyes.

METHODS

The flaps were created using the IntraLase femtosecond laser, and excimer ablation was performed with the Bausch & Lomb H.Eye.Tech laser system. The complications of SBK were evaluated retrospectively. The types of complications were grouped into intra- and postoperative flap related.

RESULTS

In 3009 SBK procedures, the total complication rate was 0.63%. Intra- and postoperative flap-related complication rates were 0.33% and 0.30%, respectively. Only 1 (0.033%) eye lost one line of best spectacle-corrected visual acuity from diffuse lamellar keratitis (DLK). Intraoperative complications included flap tear, free cap, bubble escape, and flap folds. Postoperative complications included DLK and epithelial ingrowth. Other flap-related complications such as uneven bed, buttonhole, short flap, flap striae, or wrinkles did not occur in this series. All intraoperative complications were managed within the same day.

CONCLUSIONS

The complication rate of SBK is low. Vision loss is also rare.