Biomechanical corneal changes induced by different flap thickness created by femtosecond laser

OBJECTIVE: To evaluate the impact of the creation of corneal flaps at different thicknesses on the biomechanical properties of swine corneas. METHOD: Twelve swine eyes were obtained to form two groups: 100 μm flap thickness and 300 μm flap thickness. Each eye was submitted to the following examinations: raster topography to investigate corneal curvature alterations, ocular response analyzer to investigate corneal hysteresis change, optical coherence tomography to measure central corneal and flap thickness and sonic wave propagation velocity as a measure of stiffness, before and immediately after flap creation. After flap amputation, surface wave velocity measurements were repeated. RESULTS: Measured flap thicknesses were statistically different for thin and thick flap groups, with an average of 108.5 + 6.9 and 307.8 + 11.5 μm respectively. Hysteresis and corneal resistance factor did not change significantly after flap creation in the thin flap group. With thicker flaps, both parameters decreased significantly from 8.0 +1.0 to 5.1 +1.5 mmHg and from 8.2 + 1.6 to 4.1 +2.5 mmHg respectively. Simulated keratometry values increased in the thick flap group (from 39.5 + 1 D to 45.9+1.2 D) after flap creation but not in the thin flap group (from 40.6 + 0.6 D to 41.4+ 1.0 D). Regarding surface wave velocity analysis, the surgical procedures induced statistically lower results in some positions. CONCLUSION: In the experimental conditions established by this model, thicker flaps presented a greater biomechanical impact on the cornea.National Institutes of Health (NIH)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES

A Review of Structural and Biomechanical Changes in the Cornea in Aging, Disease, and Photochemical Crosslinking

The study of corneal biomechanics is motivated by the tight relationship between biomechanical properties and visual function within the ocular system. For instance, variation in collagen fibril alignment and non-enzymatic crosslinks rank high among structural factors which give rise to the cornea's particular shape and ability to properly focus light. Gradation in these and other factors engender biomechanical changes which can be quantified by a wide variety of techniques. This review summarizes what is known about both the changes in corneal structure and associated changes in corneal biomechanical properties in aging, keratoconic, and photochemically crosslinked corneas. In addition, methods for measuring corneal biomechanics are discussed and the topics are related to both clinical studies and biomechanical modeling simulations

Patient-Specific Computational Modeling of Keratoconus Progression and Differential Responses to Collagen Cross-linking

A whole-eye computational model of keratoconus based on patient-specific biometry can replicate topographic features of disease progression using progressive decreases in focal corneal elastic strength as the primary disease-driving mechanism. Simulations of standard and novel collagen cross-linking patterns illustrate the utility of patient-specific modeling in treatment planning and suggest that a smaller diameter treatment centered on the cone may have optical advantages over standard exposure patterns

Patient-Specific Modeling of Corneal Refractive Surgery Outcomes and Inverse Estimation of Elastic Property Changes

The purpose of this study is to develop a 3D patient-specific finite element model (FEM

Method for optical coherence elastography of the cornea

The material properties of the cornea are important determinants of corneal shape and refractive power. Corneal ectatic diseases, such as keratoconus, are characterized by material property abnormalities, are associated with progressive thinning and distortion of the cornea, and represent a leading indication for corneal transplantation. We describe a corneal elastography technique based on optical coherence tomography (OCT) imaging, in which displacement of intracorneal optical features is tracked with a 2-D cross-correlation algorithm as a step toward nondestructive estimation of local and directional corneal material properties. Phantom experiments are performed to measure the effects of image noise and out-of-plane displacement on effectiveness of displacement tracking and demonstrated accuracy within the tolerance of a micromechanical translation stage. Tissue experiments demonstrate the ability to produce 2-D maps of heterogeneous intracorneal displacement with OCT. The ability of a nondestructive optical method to assess tissue under in situ mechanical conditions with physiologic-range stress levels provides a framework for in vivo quantification of 3-D corneal elastic and viscoelastic resistance, including analogs of shear deformation and Poisson’s ratio that may be relevant in the early diagnosis of corneal ectatic disease

Toric Topographically Customized Transepithelial, Pulsed, Very High-Fluence, Higher Energy and Higher Riboflavin Concentration Collagen Cross-Linking in Keratoconus

Purpose: To report a novel application of toric topographically customized transepithelial collagen cross-linking (CXL) aiming to achieve refractive astigmatic changes in a keratoconic cornea. Methods: Specially formulated riboflavin transepithelial administration and delivery of high-fluence UVA in a topographically customized pattern was applied in an eye with progressive keratoconus. Visual acuity, cornea clarity, keratometry, topography, and pachymetry with a multitude of modalities, as well as endothelial cell counts were evaluated for >6 months. Results: Uncorrected distance visual acuity changed from preoperative 20/40 to 20/25 at 6 months. A mean astigmatic reduction of 0.8 D, and significant cornea surface normalization was achieved 6 months postoperatively. There was some mild change in the epithelial distribution, with the treated area having a slight normalization in the average epithelial thickness. Conclusions: We introduce herein the novel application of a topographically customizable transepithelial CXL in progressive keratoconus in order to achieve an astigmatic refractive effect and ectasia stabilization. This novel technique offers a nonablative and nonincisional approach to treat irregular astigmatism in ectatic cornea with rapid visual rehabilitation

Etanercept (Enbrel)-Associated Inflammatory Eye Disease: Case Report and Review of the Literature

Purpose: To report a case of severe anterior uveitis flare following the administration of etanercept (Enbrel) for ankylosing spondylitis and to review the literature pertaining to inflammatory eye disease associated with the use of etanercept. Methods: Clinical data were collected from a 52-year-old female with chronic symptomatic ankylosing spondylitis. The relationship between etanercept administration and the patient's systemic and ocular inflammation was assessed. A review of the literature was conducted to identify additional reports. Results: A patient with a history of ankylosing spondylitis exhibited acute exacerbations of uveitis that were temporally related to etanercept injections. Re-challenge was associated temporally with a worsening of symptoms, and drug withdrawal, in concert with aggressive systemic steroid treatment, resulted in rapid resolution. Seventeen cases of inflammatory eye disease (uveitis, scleritis, orbital myositis) believed to be associated with etanercept therapy were found in the recent literature. Conclusions: Ocular inflammation is paradoxically a potential adverse event following the use of etanercept in both previously uninvolved and inflamed eyes. Careful surveillance of patients on etanercept is warranted to assure that flares in ocular inflammation are not secondary to etanercept therapy

A Multicenter Study of Ocular Response Analyzer Custom Variables in Disqualified and Candidate Refractive Surgery Screening Patients

CAPESOhio Third Frontier Innovation Platform AwardRPBCleveland Clin, Cole Eye Inst, Cleveland, OH 44106 USAUniv Fed Sao Paulo, Ophthalmol, Sao Paulo, BrazilEmory Univ, Emory Eye Ctr, Atlanta, GA 30322 USAUniv Fed Sao Paulo, Ophthalmol, Sao Paulo, BrazilCAPES: PDSE - 99999.007333/2015-03, R01 EY023381TECH: 13-059Web of Scienc