Ocular surface temperature in patients with evaporative and aqueous-deficient dry eyes: a thermographic approach.

OBJECTIVE: In recent decades infrared thermography (IRT) has facilitated accurate quantitative measurements of the ocular surface temperature (OST), applying a non-invasive procedure. The objective of this work was to develop a procedure based on IRT, which allows characterizing of the cooling of the ocular surface of patients suffering from dry eye syndrome, and distinguishing among patients suffering from aqueous deficient dry eye (ADDE) and evaporative dry eyes (EDE). APPROACH: All patients examined (34 females and 4 males, 23-84 years) were divided into two groups according to their Schirmer I result (⩽ 7 mm for ADDE and > 7 mm for EDE), and the OST was recorded for 7 s at 30 Hz. For each acquisition, the temperatures of the central cornea (CC) as well as those of both temporal and nasal canthi were investigated. MAIN RESULTS: Findings showed that the maximum temperature variation (up to 0.75 ± 0.29 °C) was at the CC for both groups. Furthermore, patients suffering from EDE tended to have a higher initial OST than those with ADDE, explained by the greater quantity of the tear film, evenly distributed over the entire ocular surface, keeping the OST higher initially. Results also showed that EDE patients had an average cooling rate higher than those suffering from ADDE, confirming the excessive evaporation of the tear film. SIGNIFICANCE: Ocular thermography paves the way to become an effective tool for differentiating between the two different etiologies of dry eye syndrome.

Investigation on the load-displacement curves of a human healthy heel pad: In vivo compression data compared to numerical results.

The aims of the present work were to build a 3D subject-specific heel pad model based on the anatomy revealed by MR imaging of a subject's heel pad, and to compare the load-displacement responses obtained from this model with those obtained from a compression device used on the subject's heel pad. A 30 year-old European healthy female (mass=54kg, height=165cm) was enrolled in this study. Her left foot underwent both MRI and compression tests. A numerical model of the heel region was developed based on a 3D CAD solid model obtained by MR images. The calcaneal fat pad tissue was described with a visco-hyperelastic model, while a fiber-reinforced hyperelastic model was formulated for the skin. Numerical analyses were performed to interpret the mechanical response of heel tissues. Different loading conditions were assumed according to experimental tests. The heel tissues showed a non-linear visco-elastic behavior and the load-displacement curves followed a characteristic hysteresis form. The energy dissipation ratios measured by experimental tests (0.25±0.02 at low strain rate and 0.26±0.03 at high strain rate) were comparable with those evaluated by finite element analyses (0.23±0.01 at low strain rate and 0.25±0.01 at high strain rate). The validity and efficacy of the investigation performed was confirmed by the interpretation of the mechanical response of the heel tissues under different strain rates. The mean absolute percentage error between experimental data and model results was 0.39% at low strain rate and 0.28% at high strain rate.

A comparison between internal and surface temperature measurement techniques during phacoemulsification cataract surgery: thermocamera versus thermocouple.

PURPOSE: Corneal and scleral burns, one of the main complications that can occur during a cataract operation, are produced by overheating due to the use of the phacoemulsifier. The temperature of the anterior chamber of the eye can be measured both invasively using thermocouples and non-invasively, but only superficially, using a thermocamera. METHODS: To compare the measures obtained from both techniques an in vitro experimental analysis was conducted on pigs' eyes. During a simulated phacoemulsification cataract operation both the surface temperature with a thermocamera and the temperature inside the anterior chamber with a thermocouple were recorded. For each procedure, the maximum temperature values measured by each technique were compared. RESULTS: The results of this research show that the difference between the maximum values measured with the two techniques is on average 0.5 degrees C. CONCLUSIONS: It is possible to employ a thermocamera technique instead of a thermocouple technique to provide an indication of the temperature inside the anterior chamber.

Ocular surface temperature in central retinal vein occlusion: preliminary data.

PURPOSE: To compare ocular surface temperature (OST) measures in patients with central retinal vein occlusion (CRVO) and controls. METHODS: Thirty-six patients with unilateral CRVO and 54 healthy volunteers were included in the study. OST was evaluated by infrared thermography. RESULTS: In CRVO eyes and in fellow, nonaffected eyes, OST values were lower than in controls (p<0.05). Ischemic CRVO eyes showed lower temperatures than nonischemic ones. CONCLUSIONS: Infrared thermography may be helpful in the management of patients with CRVO.

Functional analysis of bioprosthetic heart valves.

Glutaraldehyde-treated bovine pericardium is used successfully as bioprosthetic material in the manufacturing of heart valves leaflets. The mechanical properties of bovine pericardial aortic valve leaflets seem to influence its mechanical behaviour and the failure mechanisms. In this study the effect of orthotropy on tricuspid bioprosthetic aortic valve was analysed, using a three-dimensional finite element model, during the entire cardiac cycle. Multiaxial tensile tests were also performed to determine the anisotropy of pericardium. Seven different models of the same valve were analysed using different values of mechanical characteristics from one leaflet to another, considering pericardium as an orthotropic material. The results showed that even a small difference between values along the two axes of orthotropy can negatively influence leaflets performance as regard both displacement and stress distribution. Leaflets of bovine pericardium bioprostheses could be manufactured to be similar to natural human heart valves reproducing their well-known anisotropy. In this way it could be possible to improve the manufacturing process, durability and function of pericardial bioprosthetic valves.

[The method of finite elements in evaluation of the mechanical behavior of the Ilizarov apparatus]. / Il metodo degli elementi finiti nella valuazione del comportamento meccanico dell'apparato di Ilizarov.

An accurate, rapid response technique for ascertaining the mechanical behavior of the Ilizarov apparatus has been developed. A widely-adopted numerical method (finite elements), is used to achieve simulation of the apparatus configuration, whereby the orthopedic surgeon is able to custom tailor the apparatus to the clinical situation. Experimental activity verifies the validity of the finite element simulation and provides information on the magnitude and type of loads affecting the apparatus during implantation. From this information it is possible to inocuously derive objective parameters characterizing the evolution of patient rehabilitation.