Etiology of Keratoconus: proposed biomechanical pathogenesis

Abstract Background The etiology of keratoconus most likely involves substantial biomechanical interactions. The goal of this study was to characterize corneal biomechanics using computer modeling techniques in order to elucidate the pathogenesis of keratoconus in biomechanical terms. Methods Finite element models of the cornea that are based on anatomical dimensions were developed. Cases comprising of thinned regions as well as regions with degraded isotropic mechanical properties and a case of gradual stiffening towards the limbus were subjected to normal intraocular pressures. The resulting deformations and dioptric power maps were analyzed and compared. Three additional cases that are based on a model of a thin plate were used to demonstrate the effect a transition from orthotropic to isotropic mechanical properties would have in terms of deformations and diopteric power maps. Results Results show that under 10mmHg intraocular pressure, decreasing the modulus of elasticity and thinning have opposite effects on the dioptric power maps of a homogenous isotropic cornea. When the thickness was maintained at 500 microns and the stiffness was decreased from 0.4 MPa to 0.04 MPa there was an increase of more than 40 diopters. For a cornea with a constant modulus of elasticity value of 0.4 MPa, 350 microns decrease in thickness resulted in a decrease of approximately 25 diopters. The anisotropic non-homogenous characteristics of the cornea have shown to be critical for maintaining the morphology of a healthy corneal. Conclusions Degradation of the circumferential fibers may very well be an initiating factor of a biomechanical process in which a bulge is gradually created from a presumably healthy cornea under normal underlying pressures and therefore, the identification of the early stages of keratoconus might be achievable by monitoring the in-vivo corneal fiber distribution. </jats:sec

Conjunctival Inflammatory Nodule in a Patient with Pityriasis Lichenoides et Varioliformis Acuta

Aim: To report a case of a patient with pityriasis lichenoides et varioliformis acuta (PLEVA) who developed a conjunctival inflammatory nodule. Case Report: a 13-year-old boy with a diffuse papulovesicular rash diagnosed as PLEVA presented to our clinic complaining of irritation in his right eye. Slitlamp examination revealed a conjunctival inflammatory nodule. His symptoms resolved under topical steroid treatment. Discussion: Pityriasis lichenoides (PL) is a rare condition, diagnosed by a combination of a typical clinical presentation and histopathology. Mucous membrane involvement has been described in severe cases. Ocular involvement in PL has seldom been reported. We suggest that conjunctival inflammatory nodules may be part of the clinical spectrum of this condition and should be looked for and treated in these patients

Corneal Collagen Crosslinking: A Systematic Review

Keratoconus (KCN) is an ectatic disorder with progressive corneal thinning and a clinical picture of corneal protrusion, progressive irregular astigmatism, corneal fibrosis and visual deterioration. Other ectatic corneal disorders include: post-LASIK ectasia (PLE) and pellucid marginal degeneration (PMD). Corneal crosslinking (CXL) is a procedure whereby riboflavin sensitization with ultraviolet A radiation induces stromal crosslinks. This alters corneal biomechanics, causing an increase in corneal stiffness. In recent years, CXL has been an established treatment for the arrest of KCN, PLE and PMD progression. CXL has also been shown to be effective in the treatment of corneal infections, chemical burns, bullous keratopathy and other forms of corneal edema. This is a current review of CXL - its biomechanical principles, the evolution of CXL protocols in the past, present and future, indications for treatment, treatment efficacy and safety.</jats:p

Toxic Anterior Segment Syndrome following a Triple Descemet’s Stripping Automated Endothelial Keratoplasty Procedure

Purpose: To present a unique case of a 58-year-old female with toxic anterior segment syndrome (TASS), following a triple procedure: Descemet’s stripping automated endothelial keratoplasty (DSAEK), phacoemulsification and posterior chamber intraocular lens implantation. Methods: The patient was treated with topical dexamethasone sodium phosphate 0.1% and topical atropine sulfate 1%. Due to a slow improvement in her clinical status, oral prednisone 1 mg/kg/day was added. Results: The anterior chamber reaction improved gradually, with tapering down of topical and oral treatment, until a complete resolution of the anterior chamber reaction was observed. Conclusions: Taking into account the estimated volume of DSAEK triple procedures performed worldwide, we would expect an annual incidence of several TASS cases, following triple DSAEK procedures. However, we were unable to find any such previous reports in the literature. This fact raises questions regarding the cause of reduced TASS incidence following triple DSAEK procedures