Faculty Bibliography

PURPOSE/OBJECTIVE:To evaluate the impact of varying treatment time on the efficacy of iontophoresis-assisted transepithelial corneal cross-linking (I-CXL) in ex vivo porcine corneas. METHODS:, or were not irradiated (controls). Elastic modulus and stress after relaxation of 5-mm wide corneal strips were analyzed. RESULTS:for 60 minutes setting (group 4) showed a significant stiffening effect. All epithelium-off groups provided a stiffening effect significantly stronger than I-CXL: with a stiffening effect of 149% and 112%, groups 1 and 4 were the groups with greater elastic modulus between the S-CXL and I-CXL groups, respectively. CONCLUSIONS:The biomechanical effect of I-CXL increased significantly when using a low irradiance/long irradiation setting. Oxygen diffusion thus represents a limiting factor even when riboflavin penetration is improved via iontophoresis. Still less effective than S-CXL, this modification may help establish transepithelial CXL as a treatment option in selected cases. [J Refract Surg. 2018;34(11):768-774.].

BACKGROUND/AIM:Keratoconus (KC) is a ectatic corneal disorder with marked progression during childhood and puberty that may lead to severe visual loss. In addition to KC prevalence, estimate shows major geographical variations; recent studies using Scheimpflug technology are in contrast to the 1980s and 1990s literature. The present study aims to determine the prevalence of KC in paediatric patients in Riyadh, Saudi Arabia (KSA). METHODS:This prospective, cross-sectional, observational, multicentre study collected data from paediatric patients from 6 years and 21 years of age who were seen at multiple non-ophthalmic emergency departments within KSA. Bilateral corneal measurements were performed using a rotational Scheimpflug corneal tomography system. Two masked examiners established the diagnosis of KC using both objective and subjective screening criteria. Cohen's kappa coefficient (κ) was used to qualitatively analyse the interexaminer agreement. RESULTS:There were 522 patients (1044 eyes) evaluated, with an average age of 16.8±4.2 years (range 6-21 years). KC prevalence was 5.56% for examiner 1 and 3.83% for examiner 2. The κ was 0.81 (almost perfect agreement), with discrepancy in nine cases, which were jointly evaluated and consensus obtained. Final KC prevalence was 4.79% (95% CI 2.96 to 6.62) or 1:21 patients. CONCLUSIONS:The prevalence of KC among paediatric patients in the KSA is considerably higher than numbers reported from earlier studies and from similar studies in other countries. This increase might be due to geographical variations in disease prevalence or due to the ability of screening technology to detect undiagnosed KC with greater accuracy.

The initial published clinical report on riboflavin/ultraviolet A corneal cross-linking (CXL) for treatment of progressive keratoconus dates back to 2003. CXL has since then been widely used outside the United States for treatment of progressive keratoconus and post-laser in situ keratomileusis ectasia. The Food and Drug Administration (FDA) approved Avedro Inc.'s corneal cross-linking system (KXL) for treatment of patients with progressive keratoconus and post-laser in situ keratomileusis ectasia in April 2016. The procedure is not currently approved for stable keratoconus. There are 2 FDA-approved topical ophthalmic solutions for use in CXL. Riboflavin 5'-phosphate in 20% dextran ophthalmic solution 0.146% (Photrexa Viscous) and Riboflavin 5'-phosphate ophthalmic solution 0.146% (Photrexa) are intended for use with the KXL system. Photrexa Viscous is used in all CXL procedures, whereas Photrexa is indicated for use when the corneal stroma is thinner than 400 µm after completion of the Photrexa Viscous induction period. The FDA-approved procedure using the Dresden protocol (UV-A, 3 mW/cm for 30 min) induces cytologic and morphologic changes in the anterior 250 to 300 µm of the corneal stroma. It has been believed that a minimum thickness of 400 μm was necessary to protect the corneal endothelium from potential damage. The CXL procedure using the standard Dresden protocol is established as the gold standard for treatment of progressive keratoconus. CXL treatment is indicated for a list of conditions ranging from corneal ectasia to infectious keratitis. Newer protocols, treatment regimens, and expanded indications will require further refinements, investigations, and long-term studies.

PURPOSE:To evaluate the correlation between anterior axial curvature difference maps following corneal cross-linking (CXL) for progressive keratoconus obtained from Scheimpflug-based tomography and Placido-based topography. DESIGN:Between-devices reliability analysis of randomized clinical trial data. METHODS:for 30 minutes). Regularization index (RI), absolute maximum keratometry (K Max), and change in K Max (ΔK Max) were compared between the 2 devices at each time point. RESULTS:Fifty-one eyes from 36 patients were evaluated at all time points. Values were significantly different at all time points (56.01 ± 5.3 diopters [D] Scheimpflug vs 55.04 ± 5.1 D scanning-slit preoperatively [P = .003]; 54.58 ± 5.3 D Scheimpflug vs 53.12 ± 4.9 D scanning-slit at 12 months [P < .0001]) but strongly correlated between devices (r = 0.90-0.93) at all time points. The devices were not significantly different at any time point for either ΔK Max or RI but were poorly correlated at all time points (r = 0.41-0.53 for ΔK Max, r = 0.29-0.48 for RI). At 12 months, 95% limits of agreement were 7.51 D for absolute K Max, 8.61 D for ΔK Max, and 19.86 D for RI. CONCLUSIONS:Measurements using Scheimpflug and scanning-slit Placido-based technology are correlated but not interchangeable. Both devices appear reasonable for separately monitoring the cornea's response to CXL; however, caution should be used when comparing results obtained with one measuring technology to the other.

PURPOSE/OBJECTIVE:To investigate the biomechanical properties of the ex vivo human cornea after flap-based versus cap-based laser refractive surgery in the same donor. METHODS:In this experimental study, 11 pairs of human corneas unsuitable for transplantation were equally divided into two groups. Corneas from the right eye were treated with femtosecond laser-assisted LASIK (FSLASIK) and corneas from the left eye with small incision lenticule extraction (SMILE). Pachymetry was measured in each eye directly before laser refractive surgery. All corneas were subjected to a refractive correction of -10.00 diopters (D) sphere and -0.75 D cylinder at 0° with a 7-mm zone, using either a 110-μm flap (FS-LASIK) or 130-μm cap (SMILE). For two-dimensional biomechanical measurements, corneoscleral buttons underwent two testing cycles (preconditioning stress-strain curve from 0.03 to 9.0 N and stress-relaxation at 9.0 N during 120 sec) to analyze the elastic and viscoelastic material properties. The effective elastic modulus was calculated. Statistical analysis was performed with a confidence interval of 95%. RESULTS:In stress-strain measurements, the effective elastic modulus was 1.47 times higher (P = .003) after SMILE (median = 8.22 [interquartile range = 4.76] MPa) compared to FS-LASIK (median = 5.59 [inter-quartile range = 2.77] MPa). The effect size was large (r = 0.83). No significant differences (P = .658) were observed among stress-relaxation measurements, with a mean remaining stress of 181 ± 31 kPa after SMILE and 177 ± 26 kPa after FS-LASIK after relaxation. CONCLUSIONS:Compared to a flap-based procedure such as FS-LASIK, the SMILE technique can be considered superior in terms of biomechanical stability, when measured experimentally in ex vivo human fellow eye corneas. [J Refract Surg. 2018;34(6):419-423.].