Infrared thermographic investigation on the ocular surface temperature of normal subjects.

OBJECTIVE: It is understood that the ability to measure ocular temperature accurately will increase understanding of ocular physiology and should be a support in decision-making in classical diagnostic procedures. The use of ocular thermography offers great opportunities for monitoring the temperature of the anterior eye and analyzing the effects of certain pathologies on ocular surface temperature (OST). The aim of the present work is to measure the OST of 220 healthy normal subjects, stratified according to gender and age, in order to obtain a normal temperature distribution to be used as reference values when comparing healthy versus pathological conditions. APPROACH: The OST is measured from five regions, located over the whole area of the anterior eye, which correspond to particular anatomic structures, through a semi-automated procedure to post-process the infrared images. The relationship between OST and independent variables (forehead skin temperature, age, gender, level of physical activity, cardiovascular risk factors including sedentary lifestyle and smoking, laboratory temperature, and laboratory humidity) was investigated through linear regression models. MAIN RESULTS: The OSTs measured from the five different ocular regions are statistically different (p -value < 0.001), even when dividing our subjects into males and females, with the nasal cantus being the hottest region and the central cornea the coolest; when considering also the effect of age, stratifying our subjects into young, middle-aged and elderly, the OST decreases when age increases significantly. Statistical analysis based on linear regression models pointed out that age, forehead skin temperature, and lab temperature are the main factors to be taken into account when exploring the OST. SIGNIFICANCE: As OST evaluation can be important in detecting different ocular pathologies, having precise details of the variation in temperature across the ocular surface and therefore a more detailed map of the OST adjusted according to subject characteristics and environment conditions could enhance early diagnosis and thus course of treatments.

A novel image processing procedure for thermographic image analysis.

The imaging procedure shown in this paper has been developed for processing thermographic images, measuring the ocular surface temperature (OST) and visualizing the ocular thermal maps in a fast, reliable, and reproducible way. The strength of this new method is that the measured OSTs do not depend on the ocular geometry; hence, it is possible to compare the ocular profiles belonging to the same subject (right and left eye) as well as to different populations. In this paper, the developed procedure is applied on two subjects' eyes: a healthy case and another affected by an ocular malignant lesion. However, the method has already been tested on a bigger group of subjects for clinical purpose. For demonstrating the potentiality of this method, both intra- and inter-examiner repeatability were investigated in terms of coefficients of repeatability (COR). All OST indices showed repeatability with small intra-examiner (%COR 0.06-0.80) and inter-examiner variability (%COR 0.03-0.94). Measured OSTs and thermal maps clearly showed the clinical condition of the eyes investigated. The subject with no ocular pathology had no significant difference (P value = 0.25) between the OSTs of the right and left eye. On the contrary, the eye affected by a malignant lesion was significantly warmer (P value < 0.0001) than the contralateral, where the lesion was located. This new procedure demonstrated its reliability; it is featured by simplicity, immediacy, modularity, and genericity. The latter point is extremely precious as thermography has been used, in the last decades, in different clinical applications. Graphical abstract Ocular thermography and normalization process.

Investigation into the elastic properties of ex vivo porcine corneas subjected to inflation test after cross-linking treatment.

BACKGROUND: The aim of this work was to evaluate the effect of cross-linking (CXL) on ex vivo porcine corneal elastic properties, using an inflation procedure. METHODS: Twelve corneas were subjected to standard CXL (370 nm, 3 mW/cm2, 30 minutes), while 12 were used as controls. Corneal thickness was measured by Visante optical coherence tomography, before and immediately after treatment, and before inflation test. Both intraocular pressure and radial apical cornea displacement were measured during inflation. Stress-strain curves were obtained by applying the linear shell theory. The elastic modulus was evaluated by calculating the slope of the stress-strain curves. RESULTS: Results showed a statistically significant increase in elastic modulus (p<0.0001), with a mean of 3,868 ± 502 kPa for cross-linked corneas and 2,727 ± 238 kPa for untreated corneas, when subjected to high pressure (40-60 kPa). CXL significantly increased porcine cornea stiffness by about 42%. Findings did not show any significant difference within the physiological range of pressure (2-4 kPa). CONCLUSIONS: The inflation test has been proven to be a valuable tool for the investigation of corneal biomechanics, maintaining both integrity and geometry of corneal tissue.

Investigating the ocular temperature rise during femtosecond laser lens fragmentation: an in vitro study.

PURPOSE: To investigate the trend of temperature variation during lens fragmentation simulated by a femtosecond laser on an in vitro eye model. METHODS: In our experimental study, a convex cylinder of gelatinous material, usually employed in femtosecond laser calibration, was used to simulate both an anterior segment and a crystalline lens during fragmentation performed with the Victus femtosecond laser (Technolas Perfect Vision GmbH, Germany; Bausch + Lomb Incorporated, USA). Two radiated energies (7000 nJ and 9000 nJ) and three cutting patterns (crosses, circles and cross + circle) were applied. Trends of temperature variation as a function of time were obtained using a T-type thermocouple. RESULTS: The maximum value of temperature rise during lens fragmentation ranged from 3.53 to 5.13 °C; the rise was directly proportional to the intensity of the radiated energy (7000 nJ or 9000 nJ) and the cutting pattern performed. This behavior was experimentally represented by an asymmetric function with a characteristic bell curve shape, whereas it was mathematically described by a transport diffusive model. CONCLUSIONS: Since the temperature rise at the fragmentation volume base resulted to be around 5 °C in our in vitro study, lens fragmentation performed using the Victus femtosecond laser might be considered safe form a thermal point of view.

In vivo thermographic analysis of the corneal surface in keratoconic patients undergoing riboflavin-UV-A accelerated cross-linking.

PURPOSE: To assess corneal thermal profile during combined riboflavin and accelerated UV corneal collagen cross-linking (A-CXL) using in vivo surface thermographic analysis. METHODS: In this open-label, nonrandomized, prospective pilot study, 28 eyes of 28 patients were included. The study was conduced at the Department of Surgery and Translational Medicine, University of Florence, Italy, in collaboration with the Ophthalmic Operative Unit of Siena University, Italy. All patients underwent high-fluence A-CXL in pulsed light and continuous light UV-A exposure at 30 and 18 mW/cm. Patients were divided into 4 groups: 7 for continuous light A-CXL, 7 for pulsed light A-CXL at 30 mW/cm with 7.2 J energy, 7 for continuous light A-CXL, and 7 for pulsed light A-CXL at 18 mW/cm with 5.4 J energy. Corneal surface temperature measurements were recorded using an infrared FLIR thermocamera (FLIR 320A; FLIR Systems). Corneal temperature values were detected in the surface area exposed to UV-A light irradiation, selecting it in the acquired thermographic image. The maximum temperature value detected in the area studied was recorded and considered for comparative analysis. RESULTS: Infrared thermocamera measurements of the corneal surface during A-CXL treatments showed an average temperature of 31.5°C during the entire procedure in all groups and UV-A powers (30 mW/cm at 7.2 J/cm and 18 mW/cm at 5.4 J/cm) and light exposure modality remained under the threshold of collagen thermal injury. CONCLUSIONS: Accelerated corneal collagen cross-linking did not cause thermal rise over the threshold of thermal injury to the corneal surface, demonstrating a safe thermal profile both at 30 mW/cm with 7.2 J and 18 mW/cm with 5.4 J energy dose.

Ocular surface temperature in age-related macular degeneration.

Background. The aim of this study is to investigate the ocular thermographic profiles in age-related macular degeneration (AMD) eyes and age-matched controls to detect possible hemodynamic abnormalities, which could be involved in the pathogenesis of the disease. Methods. 32 eyes with early AMD, 37 eyes with atrophic AMD, 30 eyes affected by untreated neovascular AMD, and 43 eyes with fibrotic AMD were included. The control group consisted of 44 healthy eyes. Exclusion criteria were represented by any other ocular diseases other than AMD, tear film abnormalities, systemic cardiovascular abnormalities, diabetes mellitus, and a body temperature higher than 37.5°C. A total of 186 eyes without pupil dilation were investigated by infrared thermography (FLIR A320). The ocular surface temperature (OST) of three ocular points was calculated by means of an image processing technique from the infrared images. Two-sample t-test and one-way analysis of variance (ANOVA) test were used for statistical analyses. Results. ANOVA analyses showed no significant differences among AMD groups (P value >0.272). OST in AMD patients was significantly lower than in controls (P > 0.05). Conclusions. Considering the possible relationship between ocular blood flow and OST, these findings might support the central role of ischemia in the pathogenesis of AMD.

Analysis and comparison of clutch techniques of two dental implants.

From the clinical point of view, primary implant stability is a fundamental requirement. The aim of the present work was to investigate the primary stability of two types of dental implants, with truncated cone (TC) and cylindrical (CL) geometry, by evaluating their performance by means of pull-out tests. Moreover, several samples were tested by varying surgical preparation method as well as the material where the implant was housed in order to assess whether primary stability could be affected by these factors. A critical load which corresponds to a displacement of 0.2mm in pull-out test was chosen as indicator of the implant primary stability. CL implants had the advantage of requiring lower torques during the installation phase, and thus, applying less local stresses on the bone. Among the housing preparation methods investigated in the present study, the housings realized by using two mill cutters of different diameters for different depths implied higher primary stability for TC implant.

Relationship between ocular surface temperature and peripheral vasoconstriction in healthy subjects: a thermographic study.

An impairment of ocular blood flow regulation is commonly considered one of the main pathogenetic mechanisms involved in the development of several eye diseases, like glaucoma. The aim of this study was to investigate whether an alteration of ocular blood supply induced by peripheral vasoconstriction might be detected by measuring the ocular surface temperature. The ocular surface temperature was evaluated in a group of 38 healthy young subjects (28 males and 10 females; mean age: 25.4 ± 4.1 years) by infrared thermography. For each subject, the experimental procedure consisted of two thermographic acquisitions both lasting 10 s, recorded before and during the immersion of both hands in a mixture of ice and water (1.6 °C ± 0.4 °C). Specifically, the second acquisition began 20 s after the hand immersion. Analysis of variance was used to compare the ocular surface temperature of the two profiles. The analysis of infrared images was carried out every 2 s: at the eye opening (t(0)) until 10 s (t(5)), for both profiles. Data showed that ocular surface temperature increased significantly (p-value < 0.05), especially near the sources of ocular blood supply, that is, temporal and nasal areas (mean increasing temperature at t(0) for P(1) = 0.12 °C ± 0.13 °C). Therefore, these results suggest a response of the ocular hemodynamic to the peripheral vasoconstriction. The ocular surface temperature may represent a cheap, non-invasive and non-time-consuming test to evaluate ocular vaso-regulation.

Investigations on the viscoelastic behaviour of a human healthy heel pad: in vivo compression tests and numerical analysis.

The aim of this study was to investigate the viscoelastic behaviour of the human heel pad by comparing the stress-relaxation curves obtained from a compression device used on an in vivo heel pad with those obtained from a three-dimensional computer-based subject-specific heel pad model subjected to external compression. The three-dimensional model was based on the anatomy revealed by magnetic resonance imaging of a 31-year-old healthy female. The calcaneal fat pad tissue was described with a viscohyperelastic model, while a fibre-reinforced hyperelastic model was formulated for the skin. All numerical analyses were performed to interpret the mechanical response of heel tissues, with loading conditions and displacement rate in agreement with experimental tests. The heel tissues showed a non-linear, viscoelastic behaviour described by characteristic hysteretic curves, stress-relaxation and viscous recovery phenomena. The reliability of the investigations was validated by the interpretation of the mechanical response of heel tissues under the application of three pistons with diameter of 15, 20 and 40 mm, at the same displacement rate of about 1.7 mm/s. The maximum and minimum relative errors were found to be less than 0.95 and 0.064, respectively.

Clinical performance diagnosing alleged exposure to falanga--a phantom study.

BACKGROUND: Falanga torture involves repetitive blunt trauma to the soles of the feet and typically leaves few detectable changes. Reduced elasticity in the heel pads has been reported as characteristic sequelae and palpatory testing of heel pad elasticity is therefore part of medicolegal assessment of alleged torture victims. OBJECTIVE: The goal was to test the accuracy of two experienced investigators in determining whether a heel pad model was soft, medium or hard. The skin-to-bone distance in the models varied within the human range. METHOD: Two blinded investigators independently palpated nine different heel pad models with three different elasticities combined with three different skin-to-bone distances in five consecutive trials and categorized the models as soft, medium or hard. RESULTS: Two experienced investigators were able to identify three known elasticities correctly in approximately two thirds of the cases. The skin-to-bone distance affected the accuracy. CONCLUSION: The use of clinical examination in documenting alleged exposure to torture warrants a high diagnostic accuracy of the applied tests. The study implies that palpatory testing of the human heel pad may not meet this demand. It is therefore recommended that a device able to perform an accurate measurement of the viscous-elastic properties of the heel pad be developed.

Diagnostic accuracy of heel pad palpation - a phantom study.

UNLABELLED: Falanga torture involves repetitive blunt trauma to the soles of the feet and typically leaves few detectable changes. Reduced elasticity in the heel pads has been reported as characteristic sequelae and palpatory testing of heel pad elasticity is therefore part of medicolegal assessment of alleged torture victims. The goal was to test the accuracy of two experienced investigators in determining whether a heel pad model was soft, medium or hard. The skin-to-bone distance in the models varied within the human range. METHOD: Two blinded investigators independently palpated nine different heel pad models with three different elasticities combined with three different skin-to-bone distances in five consecutive trials and categorized the models as soft, medium or hard. RESULTS: Two experienced investigators were able to identify three known elasticities correctly in approximately two thirds of the cases. The skin-to-bone distance affected the accuracy. CONCLUSION: The use of clinical examination in documenting alleged exposure to torture warrants a high diagnostic accuracy of the applied tests. The study implies that palpatory testing of the human heel pad may not meet this demand. It is therefore recommended that a device able to perform an accurate measurement of the viscous-elastic properties of the heel pad be developed.