Evaluation of ocular surface temperature and retrobulbar haemodynamics by infrared thermography and colour Doppler imaging in patients with glaucoma

Thermal mapping the eye: A critical review of advances in infrared imaging for disease detection

Infrared thermography (IRT) has become more accessible due to technological advancements, making thermal cameras more affordable. Infrared thermal cameras capture the infrared rays emitted by objects and convert it into temperature representations. IRT has emerged as a promising and non-invasive approach for examining the human eye. Ocular surface temperature assessment based on IRT is vital for the diagnosis and monitoring of various eye conditions like dry eye, diabetic retinopathy, glaucoma, allergic conjunctivitis, and inflammatory diseases. A collective sum of 192 articles was sourced from various databases, and through adherence to the PRISMA guidelines, 29 articles were ultimately chosen for systematic analysis. This systematic review article seeks to provide readers with a thorough understanding of IRT's applications, advantages, limitations, and recent developments in the context of eye examinations. It covers various aspects of IRT-based eye analysis, including image acquisition, processing techniques, ocular surface temperature measurement, three different approaches to identifying abnormalities, and different evaluation metrics used. Our review also delves into recent advancements, particularly the integration of machine learning and deep learning algorithms into IRT-based eye examinations. Our systematic review not only sheds light on the current state of research but also outlines promising future prospects for the integration of infrared thermography in advancing eye health diagnostics and care.

Glaucoma Surgery and Ocular Blood Flow in Colour Doppler Imaging: Is There a Link?

Glaucoma is a common cause of blindness worldwide. This disease is characterised by increased intraocular pressure (IOP) and the concomitant disruption of ocular haemodynamic. Several studies have demonstrated that trabeculectomy is associated with changes in extraocular blood flow. In this study, we reviewed the available evidence on the use of colour Doppler imaging to evaluate and manage patients with open-angle glaucoma. We present the detailed anatomy of ocular blood flow to provide a background for the research findings. We also discuss the physiological foundations of ocular blood flow and detailed flow characteristics of specific extraocular vessels. Finally, we reviewed published studies that analysed the effects of glaucoma surgery on the blood flow parameters of the eye.

[Study of the growth temperature of ocular surface microorganisms in norm and in infectious keratitis]

Standard bacteriological examinations, which involve culturing microorganisms at 37 °C, are commonly used in clinical practice for diagnosing infectious diseases. However, the growth temperature of microorganisms on the ocular surface (OS) during infectious keratitis (IK) may not coincide with the laboratory standard, which is due to the characteristic features of heat exchange in the eye.

PURPOSE

This exploratory study examines the distribution and properties of OS microorganisms isolated under different temperature cultivation conditions in patients with IK and healthy volunteers without ophthalmic pathology.

MATERIAL AND METHODS

Fifteen participants were divided into two groups. Group 1 (n=10) consisted of patients with signs of unilateral infectious keratitis, while group 2 (n=5) served as the control group. A novel microbiological method was employed to isolate pure cultures of microorganisms. This method involved cultivating microorganisms at two temperature regimes (37 °C and 24 °C) and subsequently identifying them using biochemical, immunological, and physicochemical techniques, including mass spectrometry. Scanning electron microscopy (SEM) with lanthanide staining used as the reference method. The temperature status of the ocular surface was assessed using non-contact infrared thermography.

RESULTS

The study demonstrated the presence of psychrotolerant microorganisms on the ocular surface, which exhibited growth at a relatively low temperature of 24 °C. These psychrotolerant microorganisms were found to be isolated from the ocular surface displaying signs of temperature dysregulation. Among such microorganisms are Acinetobacter lwoffii, Achromobacter xylosoxidans, Bacillus licheniformis, Enterococcus faecalis, Klebsiella oxytoca, Klebsiella pneumoniae, Micrococcus luteus, Pseudomonas luteola, Streptococcus spp.

CONCLUSION

When identifying the causative agent of infectious keratitis, it is crucial to consider the divergence of growth temperature of ocular surface microorganisms. The presence of psychrotolerant microorganisms on the ocular surface, which can effectively grow at room temperature, should be taken into account, especially in cases of temperature dysregulation.

Multifunctional transition and temperature-responsive contact lenses

Smart contact lenses have recently gained traction due to their functionalization as noninvasive diagnostic and therapeutic wearables that can address several ocular diseases. Herein, multifunctional contact lenses exhibiting UV-transition and temperature-responsive capabilities were developed utilizing chromogenic materials that were integrated simultaneously into poly(2-hydroxyethyl methacrylate) (pHEMA) contact lenses. The functionalities of the contact lenses were optically evaluated in both their activated and non-activated states. Transition contact lenses offered excellent UV and blue light blocking capabilities (~45%) at their inactive states. When activated via UV exposure, the transparent lenses darkened instantaneously and absorbed portions of the visible light spectrum. The absorption intensity and transient discoloration of the transition lenses relied primarily on the utilized photochromic material. Likewise, the temperature-responsive contact lenses exhibited distinct colorimetric variations in response to temperature changes within the physiological range (33-38 °C). The maximum sensitivity of the thermochromic lens was 8% transmitted light per Celsius degree shift. Physiochemical and morphological analysis indicated the adequacy of the contact lenses. Hence, the multifunctional contact lenses can be deployed as smart wearables to manage ophthalmic deficiencies that are deterred by UV radiations and variations in ocular surface temperature.

Applications of Infrared Thermography in Ophthalmology

Body temperature is one of the key vital signs for determining a disease’s severity, as it reflects the thermal energy generated by an individual’s metabolism. Since the first study on the relationship between body temperature and diseases by Carl Reinhold August Wunderlich at the end of the 19th century, various forms of thermometers have been developed to measure body temperature. Traditionally, methods for measuring temperature can be invasive, semi-invasive, and non-invasive. In recent years, great technological advances have reduced the cost of thermographic cameras, which allowed extending their use. Thermal cameras capture the infrared radiation of the electromagnetic spectrum and process the images to represent the temperature of the object under study through a range of colors, where each color and its hue indicate a previously established temperature. Currently, cameras have a sensitivity that allows them to detect changes in temperature as small as 0.01 °C. Along with its use in other areas of medicine, thermography has been used at the ocular level for more than 50 years. In healthy subjects, the literature reports that the average corneal temperature ranges from 32.9 to 36 °C. One of the possible sources of variability in normal values is age, and other possible sources of variation are gender and external temperature. In addition to the evaluation of healthy subjects, thermography has been used to evaluate its usefulness in various eye diseases, such as Graves’ orbitopathy, and tear duct obstruction for orbital diseases. The ocular surface is the most studied area. Ocular surface temperature is influenced by multiple conditions, one of the most studied being dry eye; other diseases studied include allergic conjunctivitis and pterygium as well as systemic diseases such as carotid artery stenosis. Among the corneal diseases studied are keratoconus, infectious keratitis, corneal graft rejection, the use of scleral or soft contact lenses, and the response to refractive or cataract surgery. Other diseases where thermographic features have been reported are glaucoma, diabetic retinopathy, age-related macular degeneration, retinal vascular occlusions, intraocular tumors as well as scleritis, and other inflammatory eye diseases.

Measurement of intraocular temperature in glaucoma: week-day and seasonal fluctuations

PURPOSE

To evaluate long-term intraocular temperature (IOT) variations in eyes with primary open-angle glaucoma (POAG) using an intraocular telemetric sensor.

METHODS

This prospective, open-label, multicentre observational study analysed the IOT variations in 22 eyes of 22 patients with POAG. All enrolled patients underwent implantation of an intraocular pressure (IOP) sensor during cataract surgery. The telemetric system uses a built-in temperature sensor to control measured IOP for temperature. Each time a patient measures their IOP, both the IOP and IOT are recorded in the reader device. Patients were instructed to self-measure their IOP as often as desired, but at least four times daily. Recorded readings were retrieved and analysed using mixed effect models and pairwise comparisons using Bonferroni correction to assess the statistical significance of average IOT variations between each individual weekday and calendar month.

RESULTS

The mean age of patients was 67.8±6.8 years and 36.4% were women. A total of 132 745 readings over 21 102 measurement-days were obtained. On average, IOT was significantly higher on Sundays (34.57°C; 95% CI 34.37 to 34.78) than on any other day of the week (p<0.001). Mean IOT on other weekdays ranged from 34.48°C to 34.51°C. Over the year, IOT followed a clear seasonal pattern, reaching its maximum in July (34.8°C; 95% CI 34.56 to 34.97) and its minimum in January (34.4°C; 95% CI 34.15 to 34.56; p<0.001).

CONCLUSIONS

This study demonstrates the feasibility of continual and long-term measurement of IOT using intraocular sensors. The results show significant short-term and long-term fluctuations of IOT. Research is warranted to understand the impact of IOT variations on IOP, ocular perfusion and glaucoma progression.

Intraocular Temperature Distribution in Eyes Undergoing Different Types of Surgical Procedures during Vitreous Surgery

Vitreous temperature has been reported to vary during intraocular surgery. We measured the temperature at three intraocular sites, just posterior to the crystalline lens (BL), mid-vitreous (MV), and just anterior to the optic disc (OD), and investigated temperature changes before and after different types of surgical procedures in 78 eyes. The mean temperature at the beginning was 30.1 ± 1.70 °C in the anterior chamber, 32.4 ± 1.41 °C at the BL, 33.8 ± 0.95 °C at the MV, and 34.7 ± 0.95 °C at the OD. It was lowest at the BL, and highest at the OD. The mean temperature after cataract surgery was slightly lower especially at an anterior location. Thus, the temperature gradient became slightly flatter. The mean temperature after core vitrectomy was even lower at all sites and a gradient of the temperature was not present. The mean temperature after membrane peeling was significantly higher than that after core vitrectomy, and there was no gradient. The mean temperature after fluid/air exchange was lower at the BL and higher at the MV and at the OD. Thus, a gradient of higher temperatures at the OD appeared. The intraocular temperature distribution is different depending on the surgical procedure which can then change the temperature gradient. The temperature changes at the different intraocular sites and the gradients should be further investigated because they may affect the physiology of the retina and the recovery process.

Ocular Surface Temperature: Characterization in a Large Cohort of Healthy Human Eyes and Correlations to Systemic Cardiovascular Risk Factors

Purpose: To characterize ocular surface temperature (OST) in healthy eyes and its association with systemic risk factors of cardiovascular and ischemic heart disease. Methods: This prospective cross-sectional study included consenting subjects who were examined at the Institute for Medical Screening in Sheba Medical Center. A Therm-App™ thermal imaging camera (Opgal LTD, Israel) was used for OST acquisition, and the mean OST of the medial canthal, lateral canthal, and central cornea regions were measured. Room and body temperatures were also recorded. Past medical and ocular history as well as data from various clinical examinations performed at the same visit were obtained. Results: Thermographic images were obtained from 186 subjects, 150 of which were included in the final analysis. OST was significantly higher in the medial canthal, central cornea, and lateral canthal regions in people with a history of ischemic heart disease (p = 0.02, p = 0.02, and p = 0.03, respectively). There were no significant OST differences (ANOVA test) associated with the presence of hypertension, diabetes mellitus, or active smoking status. Conclusions: OST correlated positively with the presence of ischemic heart disease. This correlation, its pathophysiological base, and its clinical application warrants further investigation.

Intraocular Temperature at Different Sites in Eye Measured at the Beginning of Vitreous Surgery

The temperature of the vitreous has been reported to vary during cataract and vitreous surgery. We measured intraocular temperature at four intraocular sites; the anterior chamber (AC), just behind the crystalline lens, mid-vitreous, and just anterior to the optic disc (OD) at the beginning of vitrectomy with a thermoprobe in 48 eyes. The temperatures were compared in three groups; eyes that underwent vitrectomy for the first time (Group V, n = 30), eyes that had previous vitrectomy and the vitreous cavity had been filled with balanced salt solution (BSS; Group A, n = 12), and eyes that had previous vitrectomy and the vitreous cavity was filled with silicone oil (Group S, n = 6). There was a gradient in the temperature in all groups, i.e., it was lowest in the AC, and it increased at points closer to the retina. The intraocular temperature was significantly correlated with the type of fluid in the vitreous cavity. The mean intraocular temperatures were not significantly different in Groups V and A, but they were significantly higher in Group S. Clinicians should be aware of the differences in the temperature at the different intraocular sites because the temperatures may affect the physiology of the retina and the recovery process.

Ocular surface temperature differences in glaucoma

PURPOSE

Accumulating evidence suggests that neuroinflammation and immune response are part of the sequence of pathological events leading to optic nerve damage in glaucoma. Changes in tissue temperature due to inflammation can be measured by thermographic imaging. We investigated the ocular surface temperature (OST) profile of glaucomatous eyes to better understand the pathophysiology of these conditions.

METHODS

Subjects diagnosed with glaucoma (primary open angle glaucoma [POAG] or pseudo exfoliation glaucoma [PXFG]) treated at the Sam Rothberg Glaucoma Center (11/2019-11/2020.) were recruited. Healthy subjects with no ocular disease served as controls. The Therm-App thermal imaging camera was used for OST acquisition. Room and body temperatures were recorded, and the mean temperatures of the medial cantus, lateral cantus, and cornea were calculated with image processing software.

RESULTS

Thermographic images were obtained from 52 subjects (52 eyes: 25 POAG and 27 PXFG) and 66 controls (66 eyes). Eyes with glaucoma had a significantly higher OST compared to controls (mean 0.9 ± 0.3°C, p < 0.005). The difference between the two groups remained significant after adjustment for age, sex, intraocular pressure (IOP) and room and body temperatures. Lens status and topical IOP-lowering medication did not significantly affect OST. A subgroup analysis revealed that the OST was higher among eyes with POAG compared to eyes with PXFG, but not significantly.

CONCLUSIONS

Differences in the OST between glaucomatous and normal eyes strengthens current thinking that inflammation affects the pathophysiology of glaucoma. Longitudinal studies are warranted to establish the prognostic value of thermographic evaluations in these patients.

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.

Characterization of the ocular surface temperature dynamics in glaucoma subjects using long-wave infrared thermal imaging

We evaluated the dynamics of ocular surface temperature using thermal imaging in 21 glaucoma subjects and 19 healthy subjects. On opening of the eye, subjects with glaucoma showed significantly cooler temperatures in the central cornea compared to the control group. The upper eyelid was also significantly cooler just before the eye opened. Immediately after opening the eye, the dynamic of temperature change was different in the two groups. In subjects with glaucoma, the eyes cooled significantly faster, with an average decrease of 0.49°C during the first second compared to 0.24°C in the control group. Our results support the hypothesis that both the stability of the tear film and changes in the ocular blood supply in subjects with glaucoma play an important role in thermal dynamics of the ocular surface.

Eye Surface Temperature as a Potential Indicator of Physical Fitness in Ranch Horses

This study aimed to investigate the use of maximum eye surface temperature (EST_max), recorded by infrared thermography, as an indicator of physical fitness in ranch horses. Data collection was carried out with 16 horses by recording six physical fitness biomarkers (EST_max, respiratory rate, creatine kinase activity [CK], and concentrations of total serum protein, plasmatic cortisol, and lactate) before and after a regular working day. We also recorded heart rate during the exercise, exercise duration, average velocity, distance traveled, and air temperature and humidity. The variation between the sampling times was compared by using repeated measures ANOVA or Wilcoxon paired test. The t-test was used to compare EST_max means of dehydrated and nondehydrated horses. The differences (DIF-) between each variable's sampling times were calculated, and the Spearman's correlation coefficients between DIF-EST_max and DIF- of other variables were estimated. A hierarchical cluster analysis was used to classify the horses according to their physical fitness. All biomarkers increased after the workday, and the EST_max means of dehydrated and nondehydrated horses did not differ (P < .05). DIF-CK and DIF-EST_max were positively correlated (rs = 0.56, P < .05). The cluster analysis defined two groups of horses (LOW and HIGH), with DIF-EST_max and DIF-CK differing statistically between them. HIGH horses showed CK higher than 350 U/L, indicating some degree of muscle damage. These results suggest that EST_max has potential to predict changes in CK and, thus could be a useful indicator of physical fitness in ranch horses; although, its effectiveness has to be confirmed in future studies.

Ambient Air Currents Activate Corneal Nerves During Ocular Desiccation in Rats: Simultaneous Recordings of Neural Activity and Corneal Temperature

Purpose

Previously we found two types of corneal neurons that we hypothesized to play an important role in tearing. One type is called low threshold–cold sensitive plus dry sensitive (LT-CS + DS), and the other is termed high threshold–cold sensitive plus dry sensitive (HT-CS + DS). The present study examined critical stimuli influencing the activity of these neurons to elucidate environmental factors that may trigger this ocular reflex.

Methods

Single corneal neurons were extracellularly recorded from the trigeminal ganglia in response to ocular stimuli that mimic environmental conditions one encounters in daily life. They included an ocular desiccation and slight air currents and were presented while simultaneously monitoring the ocular surface temperatures (OST) in rats.

Results

The results showed that the changes in steady state (SS) activity of the neurons closely followed the changes in SS OST: during the sustained ocular desiccation, neural firing displayed numerous small sudden increases in activities (“spiking”); these “spiking” activities of LT-CS + DS neurons were replicated by a minute air current that induced slight ocular surface cooling of approximately 0.2–0.1°C; and the responses of HT-CS + DS neurons showed an inconsistent relationship to the changes in SS OST or exhibited little evidence for “spiking” activities.

Conclusions

These results suggest that LT-CS + DS neurons play a role in the afferent trigger of tearing as we face the environment, exposing the cornea to prevailing air currents that produce a slight cooling of the ocular surface. By contrast, HT-CS + DS neurons may serve to protect the eyes from extreme dryness by eliciting nociception-evoked tearing when the OST or osmolarity of tears becomes injurious.

Contact lenses for continuous corneal temperature monitoring

Temperature variation is a ubiquitous medical sign to monitor ocular conditions including dry eye disease (DED), glaucoma, carotid artery stenosis, diabetic retinopathy, and vascular neuritis. The ability to measure OST in real time is desirable in point-of-care diagnostics. Here, we developed minimally invasive contact lens temperature sensors for continuous monitoring of the corneal temperature. The contact lens sensor consisted of a laser patterned commercial contact lens embedding temperature-sensitive Cholesteric Liquid Crystals (CLCs), which exhibited a fully reversible temperature-dependent color change in the visible spectrum. The contact lens allowed the corneal temperature to be mapped in four key areas, at distances of 0.0, 1.0, 3.0, and 5.0 mm from the pupil's edge. Liquid crystals exhibited a wavelength shift from 738 ± 4 nm to 474 ± 4 nm upon increasing the temperature from 29.0 °C to 40.0 °C, with a time responsivity of 490 ms and a negligible hysteresis. Readouts were performed using a smartphone, which output RGB triplets associated to temperature values. Contact lens sensors based on CLCs were fitted and tested on an ex vivo porcine eye and readouts were compared with infrared thermal measurements, resulting in an average difference of 0.3 °C.

Temperature variation is a ubiquitous medical sign to monitor ocular conditions including dry eye disease (DED), glaucoma, carotid artery stenosis, diabetic retinopathy, and vascular neuritis.

Ocular Image and Haemodynamic Features Associated with Different Gradings of Ipsilateral Internal Carotid Artery Stenosis

OBJECTIVES

To analyse the changes of ocular haemodynamics and morphology in Chinese patients with internal carotid artery (ICA) stenosis in the current study.

METHODS

A retrospective case-control study was conducted with 219 patients. The haemodynamic characteristics, the calibre of retinal vessels, and the subfoveal choroidal thickness (SFChT) were compared. We analysed the correlations with the degree of ipsilateral ICA stenosis.

RESULTS

There were no significant differences among the groups in the central retinal artery equivalent (CRAE), central retinal vein equivalent (CRVE), and AVR (p = 0.073, p = 0.188, and p = 0.738, resp.). The peak systolic velocity (PSV) and end diastolic velocity (EDV) in the central retinal artery (CRA) and the posterior ciliary artery (PCA) were significantly lower than normal eyes (p < 0.001). The outer retinal layer thickness and SFChT values of the ICA stenosis groups were significantly lower than normal eyes (p = 0.030 and p < 0.001, resp.).

CONCLUSION

The PSV and EDV in CRA and PCA and the SFChT and outer retinal layer thickness of ICA eyes were significantly lower than normal eyes. ICA stenosis may impact choroidal haemodynamics, and decreased choroidal circulation might affect the discordance of the SFChT and the outer retinal layer thickness.

[Use of infrared thermography in ophthalmology]

Thermoregulation disorders are associated with Body temperature fluctuation. Both hyper- and hypothermia are evidence of an ongoing pathological process. Contralateral symmetry in the Body heat spread is considered normal, while asymmetry, if above a certain level, implies an underlying pathology. Infrared thermography (IRT) is employed in many medical fields including ophthalmology. The earliest attempts of eye surface temperature evaluation were made in the 19^th century. Over the last 50 years, different authors have been using this method to assess ocular adnexa, however, the technique remains insufficiently studied. The reported IRT data is often contradictory, which may be due to heterogeneity (in terms of severity) of patient groups and disparities between research parameters.

Association of Tear Film Stability and Corneal Surface Temperature in Pudong Patients

OBJECTIVE

To investigate the association between corneal temperature on ocular surface and stability of tear film, and define the normal reference range of corneal surface temperature in the population of Pudong New Area, Shanghai, China.

METHODS

Temperature of cornea (TOC) and tear film break-up time (BUT) were measured among 515 volunteers with or without dry eye. The association between TOC and tear film stability was analyzed, and the normal reference range of TOC was determined.

RESULTS

TOC was 32.6 ± 0.97°C among the 318 subjects without dry eye including 147 males (TOC = 32.6 ± 0.70°C) and 171 females (TOC = 32.64 ± 1.16°C). Significant differences existed in TOC on ocular surface among three separated groups according to BUT measurement. Age was positively related to TOC, whereas BUT was negatively correlated with TOC.

CONCLUSION

It is recommended to consider 32.6 ± 0.70°C as the normal reference value for human central corneal temperature. Instability of tear film is concomitant with elevated TOC in the population of Pudong New Area, Shanghai.

[Interobserver and intraobserver reliability of corneal surface temperature measurements with the TG-1000 thermograph in normal eyes]

PURPOSE

The aim of this study was to analyze the reliability of temperature measurements with the ocular TG-1000 thermograph in a setup of sequential measurements performed by one observer (intraobserver) and a sequence of measurements performed by different observers (interobserver) in normal subjects without pathologies of the anterior segment of the eye.

PATIENTS AND METHODS

A total of 50 right eyes from 50 individuals (mean age 29.1 ± 7.9 years) without ocular pathologies or history of ocular surgery were enrolled in this prospective monocentric clinical case series. Eyes with signs of dry eye syndrome (based on a positive McMonnies questionnaire) were excluded from the study. Corneal surface temperature measurements were performed by three examiners to assess interobserver reliability. In addition, in a subgroup of 22 individuals, a sequence of 3 measurements were performed by 1 of the examiners to examine intraobserver reliability. Corneal surface temperature was measured within an interval of 10 s (11 frames) on a region of interest of 16 ± 12 mm (320 ± 240 pixels). Central and mid-peripheral local temperatures at 3 mm (3, 6, 9 and 12 o'clock) were extracted and analyzed from the raw data.

RESULTS

The ocular TG-1000 thermograph yielded consistent results for the interobserver as well as intraobserver conditions in measuring corneal surface temperature in the center as well as mid-periphery of the cornea. Cronbach's alpha was 0.9 or higher at all corneal locations, which proves a high consistency of results for the interobserver and intraobserver measurements. The average corneal surface temperature ranged between 34.0 °C and 34.7 °C with a slight decrease from the upper temporal (9 and 12 o'clock) to the lower nasal (3 and 6 o'clock) quadrants.

CONCLUSION

The TG-1000 thermograph yielded consistent results of corneal surface temperature in individuals without anterior segment pathologies or history of ocular surgery. With the option of raw data export (11 frames within 10 s with a lateral resolution of 320 × 240 pixels) the thermograph offers a wide range of new diagnostic options for a spatiotemporal analysis of corneal surface temperature.

Constructal approach to bio-engineering: the ocular anterior chamber temperature

The aim of this work was to analyse the pressure inside the eyes anterior chamber, namedintraocular pressure (IOP), in relation to the biomechanical properties of corneas. The approach used was based on the constructal law, recently introduced in vision analysis. Results were expressed as the relation between the temperature of the ocular anterior chamber and the biomechanical properties of the cornea. The IOP, the elastic properties of the cornea, and the related refractive properties of the eye were demonstrated to be dependent on the temperature of the ocular anterior chamber. These results could lead to new perspectives for experimental analysis of the IOP in relation to the properties of the cornea.

Relationship between Corneal Temperature and Intraocular Pressure in Healthy Individuals: A Clinical Thermographic Analysis

Purpose. To study the geographical distribution of corneal temperature (CT) and its influence on the intraocular pressure (IOP) of healthy human volunteers. Materials and Methods. Fifteen subjects (7 M, 8 F), 33.8 ± 17.4 years old, were enrolled in this pilot, cross-sectional study. Measurements of CT were taken after one hour with closed eyelids (CET) or closed eyelids with a cooling mask (cm-CET) and compared to baseline. Results. If compared to baseline, after CET, average CT significantly increased by 0.56°C in the RE and by 0.48°C in the LE (p < 0.001) and IOP concomitantly significantly increased by 1.13 mmHg and 1.46 mmHg, respectively, in each eye (p < 0.001). After cm-CET, average CT significantly decreased by 0.11°C and 0.20°C, respectively, in the RE and LE (RE p = 0.04; LE p = 0.024), followed by a significant IOP decrease of 2.19 mmHg and 1.54 mmHg, respectively, in each eye (RE p < 0.001; LE p = 0.0019). Conclusion. Significant variations of CT occurred after CET and cm-CET and were directly correlated with significant differences of IOP. It can be speculated that both oxidative stress and sympathetic nerve fiber stimulation by temperature oscillations may affect the regulation of AH vortex flow and turnover, thus influencing IOP values.

Difference in ocular surface temperature by infrared thermography in phakic and pseudophakic patients

Purpose

To assess the change in ocular surface temperature between healthy phakic and pseudophakic patients.

Methods

We included patients with no history of ocular disease other than cataract. Patients were divided into three groups: clear lens, cataract, and pseudophakic. All patients had two ocular surface digital thermal scans. An average of five surface points was used as the mean ocular surface temperature. Results were analyzed with a one-way analysis of variance and a Tukey’s least significance difference test. The patients were further divided into phakic and pseudophakic groups. Correlation coefficients between several variables were done in order to assess dependencies.

Results

Fifty-six eyes (28 cataracts, 12 clear lenses, 16 pseudophakic) were enrolled. The mean ocular surface temperature in the cataract group was 34.14°C±1.51°C; clear lens: 34.43°C±2.27°C; and pseudophakic: 34.97°C±1.57°C. There were no statistical differences among the study groups (P=0.3). There was a nonsignificant negative correlation trend between age and surface temperature in the phakic group. The trend inverted in the pseudophakic group but without statistical significance.

Conclusion

Although cataract extraction and intraocular lens implantation seem to induce a mild increase in ocular surface temperature, the effect is not clear and not significant.

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.

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 (t0) until 10 s (t5), 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 t0 for P1 = 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.

Repeatability of a new method for measuring tear evaporation rates

PURPOSE

The purpose of this study was to evaluate the repeatability of tear evaporimetry based on infrared thermography in a clinical room setting and to test the effect of changing environmental humidity on ocular surface temperature (OST) and tear evaporation rates (TERs) in a controlled adverse environmental (CAE) chamber.

METHODS

Twenty-six healthy participants were enrolled, of whom 16 underwent repeatability measurements in a clinical room and 10 were exposed to a constant temperature of 30°C with a humidity of 45 and 65% in a CAE. Participants were acclimatized to each condition for at least 20 minutes before OSTs were taken. Tear film breakup time was assessed in the CAE only. Number of blinks and OSTs were continuously measured for 20 seconds for the cornea, conjunctiva, and overall ocular surface with an infrared camera; corresponding TERs were calculated.

RESULTS

The OSTs and TERs showed acceptable strength of agreement between the first and second measurements. The coefficients of repeatability were 0.4°C for OST and 6.0 W m for TER. An increase in chamber humidity (from 45 to 65%) increased OST (p < 0.05). The TER was not changed significantly (p > 0.05). The tear film breakup time and number of blinks were not significantly affected by different humidity conditions.

CONCLUSIONS

This technique has acceptable repeatability and has potential to document individual tear evaporation changes with time where humidity may differ by less than 20%.

OCULAR TEMPERATURE DISTRIBUTION: A MATHEMATICAL PERSPECTIVE

Mathematical modeling has proven to be a viable alternative for investigating the temperature distribution inside the human eye. This is due to its ability to overcome the limitations infrared (IR) thermography; the leading method in ocular temperature measurement. A wide range of mathematical studies on the ocular temperature distribution during various conditions have been published in the literature. In this paper, we carry out an in-depth review of the various mathematical models of the eye that have been developed in the past. Various problems and the implications from the mathematical predictions of these studies are discussed. The future directions of studies in ocular temperature distribution are deliberated.