The purpose of this review is to summarise a literature survey on thermal thresholds for tissue damage. This review covers published literature for the consecutive years from 2002-2009. The first review on this subject was published in 2003. It included an extensive discussion of how to use thermal dosimetric principles to normalise all time-temperature data histories to a common format. This review utilises those same principles to address sensitivity of a variety of tissues, but with particular emphasis on brain and testis. The review includes new data on tissues that were not included in the original review. Several important observations have come from this review. First, a large proportion of the papers examined for this review were discarded because time-temperature history at the site of thermal damage assessment was not recorded. It is strongly recommended that future research on this subject include such data. Second, very little data is available examining chronic consequences of thermal exposure. On a related point, the time of assessment of damage after exposure is critically important for assessing whether damage is transient or permanent. Additionally, virtually no data are available for repeated thermal exposures which may occur in certain recreational or occupational activities. For purposes of regulatory guidelines, both acute and lasting effects of thermal damage should be considered.

/pdf/thresholds-for-thermal-damage-to-normal-tissues-an-update-5d2iyey5rv.pdf

Thresholds for thermal damage to normal tissues: An update

http://studioelenaalbe.it/pdf-pubblicazioni/013-CXL%20Ophthalmology%202009.pdf

Refractive, Topographic, Tomographic, and Aberrometric Analysis of Keratoconic Eyes Undergoing Corneal Cross-Linking

The last 2 years has seen a marked increase in the prominence of corneal collagen cross-linking as a treatment strategy for progressive keratoconus. This interest has arisen from a body of laboratory evidence documenting the biomechanical and cellular changes induced by cross-linking. The findings of this research provide a plausible rationale for its use in keratoconus to retard the progression of this common disease. The rapidly growing number of clinical reports suggests, not only a consistent stabilizing effect of cross-linking, but that a variable improvement in corneal shape and visual function may also occur in some patients. However, the marked variation in the clinical course of keratoconus, together with the challenges of accurately evaluating refractive error, visual acuity and even corneal shape in this condition, demands further evidence from randomized controlled clinical trials. The aim of this review is to summarize the theoretical basis and risks of corneal collagen cross-linking, along with the available evidence for its use in keratoconus and other corneal disease states.

Collagen cross-linking: a new treatment paradigm in corneal disease - a review.

Corneal healing after riboflavin ultraviolet-A collagen cross-linking determined by confocal laser scanning microscopy in vivo: early and late modifications.

Changes in the biomechanical properties of the human cornea play an important role in the pathogenesis of corneal ectatic diseases. Biomechanical investigation shows significant differences between human ectatic corneas and normal corneas, including decreased stiffness and reduction of collagen crosslinks in the ectatic cornea. Induction of crosslinks is a well-established procedure in polymer chemistry to increase the elastic modulus of materials. Crosslinking (CXL) in connective tissue can occur during aging and as a side effect of diabetes mellitus. CXL has been used medically to increase stability and reduce the biodegradation of collagen-based biomaterials for bioprostheses. CXL of the cornea using riboflavin and UVA light with a wavelength of 370 nm and a dosage of 5.4 J/cm² is a new approach that increases the mechanical and biochemical stability of stromal tissue. This technique combines the principles of CXL (chemical and nonenzymatic) and the biochemical mechanisms of photo-oxidative CXL with riboflavin as a photosensitizer. In this review, the enrichment of riboflavin in the stroma by standard (epi-off) and transepithelial (epi-on) CXL is discussed. The theoretical and experimental measurements of the absorption of UV light explain the stronger CXL effect in the anterior stroma and its importance for the prevention of damage to the endothelial cells. UV devices are described. Changes of the physical properties after CXL, as well as the cellular changes, are discussed. From these basic investigations, treatment parameters for effective and safe CXL are identified.

/pdf/corneal-crosslinking-with-riboflavin-and-ultraviolet-a-i-qd4z6f5gfc.pdf

Corneal Crosslinking with Riboflavin and Ultraviolet A. I. Principles

Purpose To compare corneal endothelial changes after phacoemulsification performed with a standard technique versus a bimanual microincision cataract surgery (MICS) technique. Setting University ophthalmology department. Methods Eighty patients scheduled for routine cataract surgery were randomized into 2 groups; 40 eyes had standard stop-and-chop phacoemulsification (standard group) and 40 eyes had stop-and-chop phacoemulsification with microincision surgery (MICS group). Central corneal endothelial cell counts, coefficient of variation in cell size, hexagonality, and pachymetry were assessed preoperatively and 1 and 3 months postoperatively. Results The mean preoperative cell count in the entire sample was 2245 cells/mm2 ± 37 (SE). The mean decreased by 102 cells at 1 month (95% confidence interval [CI], −133 to −71; P Conclusion No significant differences in corneal endothelial cell loss or endothelial morphology were found between MICS and standard incision techniques.

Corneal endothelial damage after cataract surgery : Microincision versus standard technique

Purpose To determine rabbit cornea thermal tolerance and evaluate the effects of ultrasound (US) on this tissue after applying defined US heat doses. Setting Eye Clinic; Anatomy Histology and Forensic Medicine, University of Florence, Florence, Italy. Methods Hyperthermia was induced in rabbit corneas using US, simulating a phacoemulsification procedure. The US power was set at 100% in continuous mode, and temperature values were reached within 10 seconds of the onset of US treatment. Corneal surface temperatures were continuously monitored and recorded by thermographic registration. The eyes of 16 rabbits were examined: 4 controls, 8 treated at 40°C for 10 seconds, 8 treated at 50°C for 10 seconds, and 12 treated at 60°C for 10 seconds. All 32 corneal buttons were removed and prepared for light microscopic evaluation with hematoxylin and eosin staining, trichromic staining, and zinc iodide–osmium tetroxide solution. The 12 corneas treated at 60°C for 10 seconds were also processed for immunohistochemical analysis. Results Corneas at 40°C for 10 seconds were grossly and histologically normal and were not different from control corneas. Corneas at 50°C for 10 seconds showed initial stromal damage with collagen disorganization, mild stromal edema, and initial signs of keratocyte damage. Half of the corneas at 60°C for 10 seconds were examined at time 0 and the other half after 1 week. At time 0, massive corneal damage with epithelial cell edema, collagen disorganization, severe stromal edema, intrastromal vacuole formation, plump keratocyte nuclei, and endothelial cell detachment were found, as was a severely impaired nerve plexus. At 1-week follow-up, corneas showed persistent stromal and endothelial cell edema with an increase activated keratocytes and mitotic features in the stroma and the epithelial layer. Conclusions Rabbit corneas showed a considerable tolerance to US damage up to 50°C. Higher thermal doses produced severe histological damage, even though corneas showed a considerable plasticity due to their regenerative capacity.

Ultrasound thermal damage to rabbit corneas after simulated phacoemulsification.

Purpose To assess the possible thermal damage to the cornea during combined riboflavin and ultraviolet-A crosslinking using in vivo surface thermographic analysis. Setting Department of Oto-Neuro-Ophthalmological Surgical Sciences, Eye Clinic, University of Florence, Florence, Italy. Methods Collagen crosslinking was performed on a day-surgery basis under aseptic conditions with traditional techniques. During the procedure, temperature measurements on the corneal surface were taken using an infrared thermocamera. The temperature values were detected in the area directly exposed to light irradiation, selecting it in the acquired thermographic image. Because the aim of the study was to consider the thermal damage that may be induced during the procedure, the maximum temperature value detected in the area studied was recorded and considered for successive analysis. Results Infrared thermocamera measurements of the corneal surface during crosslinking treatment showed that the temperature was constant during the entire procedure and remains under the threshold of thermal injury to corneal collagen. Conclusion Corneal collagen crosslinking was a safe procedure that did not cause thermal injury to the corneal surface.

Riboflavin and ultraviolet A collagen crosslinking: in vivo thermographic analysis of the corneal surface.

Purpose To analyze the surface quality before and after folding of 2 intraocular lens (IOL) models designed for microincision cataract surgery. Setting Eye Clinic and Department of Human Pathology and Oncology, University of Florence, Florence, Italy. Methods Two IOL models now available for sub-2.0 mm microincision were studied: UltraChoice 1.0 Rollable ThinLens (ultrathin lens by ThinOptX) and AcriSmart (foldable lens by AcriTec). Eight IOLs of each model were examined. Scanning electron microscopy (SEM) was performed before and after IOL folding with a dedicated injector. Special attention was given to the optic surface and edges, the optic–haptic junction, and the haptic itself. Results Initially, the surface quality of IOLs was evaluated before folding. On SEM, smooth and homogeneous optic and haptic surfaces were revealed in both IOL models with no surplus material or molding flashes; edge finish of all optics showed no evidence of ridges. The IOL surfaces were evaluated after insertion into their injectors and after ejection at room temperature. After folding, the microincision IOLs showed no sign of surface alteration, probably because of their high water content, which makes these IOLs soft and flexible. Conclusions Visual results and long-term biocompatibility of the IOLs are influenced by surface properties. In recent years, there has been a trend toward microincision cataract surgery. Our study shows that the 2 IOL models now available for sub-2.0 mm microincision have acceptable surface properties.

Claudia Ponchietti

Papers

Corneal endothelial damage after cataract surgery : Microincision versus standard technique

Ultrasound thermal damage to rabbit corneas after simulated phacoemulsification.

Riboflavin and ultraviolet A collagen crosslinking: in vivo thermographic analysis of the corneal surface.

Scanning electron microscopic analysis of acrylic intraocular lenses for microincision cataract surgery.