PurposeTo examine the effect of riboflavin/UVA corneal crosslinking on stromal ultrastructure and hydrodynamic behaviour.MethodsOne hundred and seventeen enucleated ungulate eyes (112 pig and 5 sheep) and 3 pairs of rabbit eyes, with corneal epithelium removed, were divided into four treatment groups: Group 1 (28 pig, 2 sheep and 3 rabbits) were untreated; Group 2 (24 pig) were exposed to UVA light (3.04 mW/cm2) for 30 minutes and Group 3 (29 pig) and Group 4 (31 pig, 3 sheep and 3 rabbits) had riboflavin eye drops applied to the corneal surface every 5 minutes for 35 minutes. Five minutes after the initial riboflavin instillation, the corneas in Group 4 experienced a 30 minute exposure to UVA light (3.04 mW/cm2). X-ray scattering was used to obtain measurements of collagen interfibrillar spacing, spatial order, fibril diameter, D-periodicity and intermolecular spacing throughout the whole tissue thickness and as a function of tissue depth in the treated and untreated corneas. The effect of each treatment on the hydrodynamic behaviour of the cornea (its ability to swell in saline solution) and its resistance to enzymatic digestion were assessed using in vitro laboratory techniques.ResultsCorneal thickness decreased significantly following riboflavin application (p<0.01) and also to a lesser extent after UVA exposure (p<0.05). With the exception of the spatial order factor, which was higher in Group 4 than Group 1 (p<0.01), all other measured collagen parameters were unaltered by cross-linking, even within the most anterior 300 microns of the cornea. The cross-linking treatment had no effect on the hydrodynamic behaviour of the cornea but did cause a significant increase in its resistance to enzymatic digestion.ConclusionsIt seems likely that cross-links formed during riboflavin/UVA therapy occur predominantly at the collagen fibril surface and in the protein network surrounding the collagen.

Corneal topography proved to be useful in the follow-up for CXL because of significant changes in the keratometry. Increasing posterior elevation values, despite a stabilized anterior corneal surface, might be a sign of ongoing ectatic changes in the posterior corneal surface.

To validate and evaluate the use of a new biomechanical index known as the Corvis biomechanical index-laser vision correction (CBI-LVC) as a method for separating stable post-LVC eyes from post-LVC eyes with ectasia.

Purpose: To evaluate the intraexaminer repeatability and the interobserver reproducibility of manifest refraction. Setting: Tertiary referral center. Design: Retrospective study. Methods: Patients attending at least 2 preoperative refractions before undergoing subsequent refractive surgery were included. All manifest refractions were performed by 1 of 4 experienced optometrists using an automated phoropter according to a standard protocol. The first manifest refraction was performed after obtaining automated refraction and measuring the spectacles of the patient. The second refraction was typically refined from the first also considering wavefront refraction and tomography/topography. Results: The latest 2 manifest refractions of 1000 eyes obtained at 2 separate visits showed a mean pairwise absolute difference of 0.16 ± 0.19 diopter (D) (range 0 to 1.38 D) in spherical equivalent (SE). This SD was better than 0.25 D (the minimum measurement increment of refraction itself). The 95% limit of agreement (LoA) was within 0.50 D for sphere, cylinder, and SE. The SD of the astigmatism axis was approximately 10 degrees, and the 95% LoA was within 22 degrees (the difference in axis decreasing significantly with the measured cylinder magnitude). The SD for corrected distance visual acuity (CDVA) was half a Snellen line and the 95% LoA was within 1.5 lines (with increasing deviation with worse vision). There were no clinically meaningful differences in reproducibility (2 optometrists) compared with repeatability (same optometrist) in sphere, axis, and CDVA. Conclusions: Reproducibility was 0.16 D irrespective whether refractions were performed by 1 or 2 different optometrists. Obtaining multiple refractions preoperatively might increase the predictability of surgery and decrease the enhancement rate.

No abstract

This report illustrates that the currently used prophylactic CXL protocol in combination with LASIK may not be effectively preventing corneal ectasia in every case. [J Refract Surg. 2017;33(1):50-52.].

Purpose: To evaluate the influence of a thin cap in small-incision lenticule extraction (SMILE) for the correction of myopia or myopic astigmatism. Setting: Tertiary care private practice. Methods: A chart review of 102 eyes of 51 patients was performed. The effect of 120 µm vs 100 μm cap thickness on postoperative spherical equivalent refraction (SEQ), cylinder, corrected and uncorrected visual acuities, and ease of lenticule separation was assessed in a contralateral manner, whereas all other parameters were identical between eyes (including optical zone, minimum lenticule thickness, incision size, and energy and spot settings) using paired t test. Results: At 3 months postoperatively, SMILE with 120 μm cap thickness was undercorrected in SEQ relative to SMILE with 100 μm cap thickness in a cohort of 102 eyes of 51 consecutive patients. The difference of 0.06 ± 0.39 diopter (or 0.7% ± 5.7%) did not reach statistical significance. Postoperative cylinder was not statistically different in both groups. Visual acuity was similar in both groups. Ease of lenticule separation was identical in both groups. Suction time was shorter with a 100 μm cap (P < .005). Postoperative central residual stromal thickness was 20 ± 15 μm thicker with a 100 μm cap (P < .0001). Adverse events were comparable. Conclusions Postoperative refraction, visual acuity, ease of lenticule separation, and incidence of adverse events were not significantly affected by cap thickness. Surgeons might safely use 100 μm instead of 120 μm caps without nomogram adjustment. Alternatively, after suction loss during the lenticule cut, a second docking with a programmed cap thickness of 100 μm (and a larger optical zone) might be a rescue technique enabling surgeons to still perform the intended SMILE procedure.

Small Incision Lenticule Extraction (SMILE) is a relatively new surgical method to correct myopia and myopic astigmatism. Although considered to be safe and effective, it is not yet popular. Potential reasons for its limited use could be that surgeons fear inferior results and a higher complication rate in the learning phase. Therefore we present our experiences with the treatment of our first 200 eyes, with special attention to refraction results, complications, and learning curve. 200 myopic or myopic astigmatic eyes of 102 patients were treated with SMILE. The analysis was separated into two phases: Phase I (first 100 treatments) with large variation of laser parameters and surgical technique, phase II (second 100 treatments) with mostly constant laser parameters and identical surgical technique. Phase I showed the following 3-month results after a mean attempted correction of - 5.70 ± 2.54 D (range: - 1.25 to - 10.00 D): spherical equivalent - 0.03 ± 0.46 D, astigmatism - 0.34 ± 0.35 D, uncorrected distance visual acuity 1.02, corrected distance visual acuity (CDVA) 1.22. Postoperative and preoperative CDVA did not differ (p = 0.71). Mean refraction reached the targeted value after 5 days. Efficacy index was 0.55 ± 0.19 at day 1, 0.67 ± 0.22 at day 5, and 0.87 ± 0.23 at 3 months. In Phase II, the efficacy index improved to 0.63 ± 0.25 (p = 0.039) at day 1 and to 0.75 ± 0.26 (p = 0,02) at day 5. The most frequent complications were intraoperative abrasions and epithelial cells in the interface. Almost all complications occurred less frequently in Phase II. Our first SMILE treatments showed very good refractive predictability, very good safety and rapid visual recovery. Results after high myopic corrections were equivalent to or better than our first Femto-LASIK treatments. We had a much higher complication rate than with our LASIK treatments - that have been established over several years. All complications could be managed without loss of visual acuity. Visual recovery was faster and complications less frequent with experience gained. SMILE has replaced LASIK as our preferred treatment modality for the correction of myopic astigmatic eyes.