Evaluation of filtering bleb function by thermography

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.

[Methods of assessing the condition of filtering bleb after glaucoma surgery]

Currently, there is a need to assess the condition of structures at the surgery site after glaucoma intervention due to the necessity to decide further treatment tactics after performed operations, as well as the possibility of developing more advanced methods of surgical treatment of glaucoma. Despite the fact that there are several methods of examining the filtration bleb (FB), some of them have both clear advantages and significant disadvantages. This article reviews the possibilities of using optical coherence tomography (OCT), ultrasound biomicroscopy (UBM), thermography, confocal microscopy, and the Hyperemia-3 program for assessing the structural and functional state of the FB.

Objective evaluation of allergic conjunctival disease (with a focus on the application of artificial intelligence technology)

We have summarized the past efforts and results of objective measurement methods for conjunctival hyperemia classification. Severity classification using conjunctival blood vessel occupancy rate, ocular surface temperature analysis, and artificial intelligence have been reported to be clinically useful, as they have been found to correlate with the severity of conjunctival hyperemia by doctors. The AI method using slit lamp microscope images, whose main purpose is to be widely used in daily clinical practice, can be spread all over the world. As a result, it may lay the foundation for clinical research using large amounts of clinical data collected on the same basis without human bias.

Correlation between Corneal Endothelial Cell Density and Central Ocular Surface Temperature in Normal and Keratoconus Eyes

PURPOSE

In keratoconus (KC), an increase of the corneal back surface area may result in endothelial cell density (ECD) decrease and an increase of the corneal front surface area in ocular surface temperature (OST) decrease due to increased heat dissipation. Along with these hypotheses, we aimed to analyse the correlation between ECD and central corneal OST in patients with KC and healthy controls.

PATIENTS AND METHODS

A total of 154 eyes with KC (mean age 36.1 ± 12.5 years) and 92 healthy eyes (mean age 36.4 ± 12.8 years) were examined. Corneal front and back surface area at the central 5 mm corneal diameter (FSA and BSA) were calculated based on Pentacam measurement data:FSA or BSA = 2×3.14×R(R-√R²-D/2)²,where R referred to corneal front or back surface radius of curvature and D to the corneal front or back surface diameter (5 mm for the present study), respectively.ECD was determined by specular microscopy (EM-3000) and central corneal OST by thermography (TG-1000).

RESULTS

ECD was significantly lower in KC (2498 ± 356/mm²) patients than in controls (2638 ± 294/mm²; p < .001). FSA (20.35 ± 0.26 mm² vs. 20.17 ± 0.03 mm²) and BSA (20.84 ± 0.58 mm² vs. 20.45 ± 0.08 mm²) were significantly higher in KC patients than in controls (p = .001; p < .001), but the average central corneal OST did not differ significantly between both groups (34.2 ± 0.6°C vs.34.3 ± 0.7°C; p = .62). OST at the corneal centre correlated weakly, positively with ECD (r = 0.2; p < .05), but OST did not correlate with FSA (r = 0.045) or BSA (r = 0.064).

CONCLUSIONS

Endothelial cell density seems to have a mild impact on central ocular surface temperature in keratoconus and normal subjects. This effect is not correlated to the corneal front or back surface area.

Ocular Surface Disease Index and Ocular Thermography in Keratoconus Patients

Purpose

Keratoconus (KC) has been defined as a “noninflammatory” corneal disease, but recent studies have noted a potential inflammatory origin. We analysed the Ocular Surface Disease Index (OSDI) and ocular surface temperature (OST) in KC patients compared to controls. Patients and Methods. A total of 179 eyes in 90 patients with KC (topographic keratoconus classification 0-1 to 4, age 36.1 ± 12.5 years, 65.9% males) and 82 eyes in 41 controls (age 36.4 ± 12.8 years, 47.6% males) were examined. The participants completed the OSDI questionnaire and underwent corneal topography, tomography, and thermography. Additional outcome measures were vision- and discomfort-related OSDI subscores and mean OST  at the corneal centre during 10 seconds of sustained eye opening after blinking.

Results

The OSDI score (31.4 ± 22.4 vs. 17.5 ± 17.9) and vision- (17.7 ± 14.6 vs. 10.5 ± 13.2) and discomfort-related (14.3 ± 10.7 vs. 9.4 ± 10.5) OSDI subscores were significantly higher in KC patients than in controls (p < 0.001). We found no significant difference in the central corneal OST (34.2 ± 0.6°C vs. 34.2 ± 0.7°C; p < 0.001). We found no significant difference in the central corneal OST (34.2 ± 0.6°C vs. 34.2 ± 0.7°C; p < 0.001). We found no significant difference in the central corneal OST (34.2 ± 0.6°C vs. 34.2 ± 0.7°C; r > 0.174, p < 0.001). We found no significant difference in the central corneal OST (34.2 ± 0.6°C vs. 34.2 ± 0.7°C; r > 0.174, r > 0.174,

Conclusion

KC patients had increased OSDI scores and vision- and discomfort-related OSDI subscores without an increase in the OST compared to a normal population. OSDI score/subscores weakly correlate with SAI and SRI but do not correlate with OST in KC patients or controls. Vision- and discomfort-related symptoms of KC have to be managed in parallel in ophthalmological practice, but the necessity of anti-inflammatory treatment cannot be verified through ocular thermography.

Association among Blink Rate, Changes in Ocular Surface Temperature, Tear Film Stability, and Functional Visual Acuity in Patients after Cataract Surgery

Purpose

To investigate the association among the ocular surface temperature (OST), tear film stability, functional visual acuity (FVA), and blink rate in patients after cataract surgery.

Methods

We recruited 98 eyes of 69 patients (mean age, 73.7 ± 5.2 years) 1 month after phacoemulsification with implantation of acrylic intraocular lenses and assessed slit-lamp microscopy, corrected distance VA, FVA, noninvasive tear breakup time (NIBUT), and OST. We defined the changes in the OST from 0 to 10 seconds after eye opening as the ΔOST. We measured the FVA and blink rate using the FVA measurement system. We divided the patients into two groups based on tear film stability: stable tear film (NIBUT, >5.0 seconds) and unstable tear film (NIBUT, ≤5.0 seconds). We evaluated the differences between the two groups and the association between the blink rate and other clinical parameters.

Results

The unstable tear film group (56 eyes) had significantly (p < 0.0001, unpaired t-test) shorter NIBUTs than the stable tear film group (42 eyes). The ΔOSTs and blink rates were significantly (p < 0.0001) higher in the unstable tear film group than in the stable group. Linear single regression analysis showed that the ΔOST (r = −0.430, p < 0.0001), NIBUT (r = −0.392, p < 0.0001), and gender (r = −0.370, p=0.0002) were correlated significantly with the blink rate. Multiple regression analysis showed that the ΔOST independently contributed to the blink rate.

Conclusions

The frequency of blinks is associated with tear film stability in patients after cataract surgery. The blink rate may be useful for evaluating the tear film stability in clinical practice. The ΔOST should be an important contributing factor to the blink rate. [This trial is registered with UMIN000026970].

[Optical coherence tomography for examination of glaucoma surgery site]

The article reviews the results of using optical coherence tomography (OCT) - a non-invasive non-contact examination method for obtaining a tomographic slice image of the site of glaucoma surgery. The method helped reveal the functional relationships between the newly created outflow pathways and various parameters of the filtering bleb such as its linear dimensions, wall structure, presence of microcysts, position of drainage, etc. Due to its high resolution and noninvasiveness, OCT can be reliably used to examine the structure of aqueous outflow pathways in different postoperative periods with accuracy close to morphometric. The amount of data that had been obtained with the method has allowed the creation of new classifications and clarification of OCT-relevant prognostic signs for glaucoma surgery site.

LC-MS analysis to determine the biodistribution of a polymer coated ilomastat ocular implant

Ilomastat is a matrix metalloproteinase inhibitor (MMPi) that has shown the potential to inhibit scarring (fibrosis) by mediating healing after injury or surgery. A long lasting ocular implantable pharmaceutical formulation of ilomastat is being developed to mediate the healing process to prevent scarring after glaucoma filtration surgery. The ilomastat implant was coated with water permeable and biocompatible phosphoryl choline polymer (PC1059) displayed extended slow release of ilomastat in vitro and in vivo. The ocular distribution of ilomastat from the implant in rabbits at day 30 post surgery was determined by the extraction of ilomastat and its internal standard marimastat from the ocular tissues, plasma, aqueous humour and vitreous fluid followed by capillary-flow liquid chromatography (cap-LC), the column effluent was directed into a triple quadrupole mass spectrometer operating in product scan mode. The lower limits of quantification (LLOQs) were 0.3 pg/μL for ocular fluids and plasma, and 3 pg/mg for ocular tissues. The extraction recoveries were 90-95% for ilomastat and its internal standard from ocular tissues. Ilomastat was found in ocular fluids and tissues at day 30 after surgery. The level of ilomastat was 18 times higher in the aqueous humour than vitreous humour. The concentration ranking of ilomastat in the ocular tissues was sclera > bleb conjunctiva > conjunctiva (rest of the eye) > cornea. Mass spectrometry analysis to confirm the presence of ilomastat in the ocular tissues and fluids at day 30 post-surgery establishes the extended release of ilomastat can be achieved in vivo, which is crucial information for optimisation of the ilomastat coated implant.

Correlation of Handheld Infrared Skin Thermometer and Infrared Videothermography Device for Measurement of Corneal Temperature

PURPOSE

In our study, we aimed to investigate the correlation of handheld infrared skin thermometer and videothermography device for the measurement of corneal temperature.

METHODS

Forty healthy individuals (80 eyes) were enrolled to the study. Participants underwent a detailed ophthalmologic examination and medical history review for excluding any ocular and systemic diseases. The measurements of the central corneal temperature were performed in a room having constant temperature, humidity, and brightness levels. To avoid any variability, all the temperature measurements were performed in the same examination room by a single examiner. The temperature was measured with a handheld infrared skin thermometer (MEDISANA, FTN) from the corneal surface. The same instrument was also used to measure the subjects' body temperature. Moreover, the subjects underwent the corneal temperature measurement by a noncontact videothermography device (Optris PI 450; Optris GmbH).

RESULTS

The male to female ratio was 19:21 among the subjects. The mean age was 25.1±4.7 years. The mean body temperature was 36.93±0.33°C. The mean corneal temperatures measured by the handheld infrared skin thermometer and the ocular videothermography device were 36.94±0.28°C and 35.61±0.61°C, respectively (P<0.01). The mean temperature difference was 1.34±0.57°C, with a 95% confidence interval. There was a moderate correlation between the corneal temperatures measured by the 2 devices in the right, the left eyes, and both eyes, respectively (P=0.450, 0.539, 0.490).

CONCLUSIONS

Handheld infrared skin thermometers can be used for the evaluation of the corneal temperature. These devices may provide a simple, practical, and cheaper way to detect the corneal temperature, and the widely performed corneal temperature measurements may afford us to understand the temperature variability in numerous ocular conditions in a better way.

[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.

Bipolaris oryzae, a novel fungal opportunist causing keratitis

We report a case of mycotic keratitis caused by Bipolaris oryzae with predisposing trauma from a foreign body. The fungus was identified by sequencing the internal transcribed spacer region, translation elongation factor 1α (TEF1) gene, and partial glyceraldehyde-3-phosphate dehydrogenase (GPDH) gene, and the species identity was confirmed on the basis of its characteristic conidial phenotype. The patient was treated with surgical intervention and antifungal agents, including intravenous fluconazole (FLC), oral itraconazole, topical 0.15% amphotericin B eye drops, and 0.5% FLC eye drops. To our knowledge, this is the first report of mycotic keratitis caused by B. oryzae worldwide.

Thermography: a new option to monitor filtering bleb function?

PURPOSE

To evaluate the filtering bleb function after trabeculectomy using a new ocular surface thermography device.

METHODS

Thirty-five eyes of 35 patients after trabeculectomy were included in this prospective study. The filtering bleb function was tested with a new ocular surface-oriented, infrared radiation thermographic device in a noncontact manner (TG 1000). The eyes were classified into poorly controlled and well-controlled intraocular pressure (IOP) groups according to the patients' postoperative IOP. According to Kawasaki and colleagues, the mean temperature decrease in the filtering bleb (TDB) for evaluating bleb function was used, where TDB=(mean temperature of the temporal and nasal bulbar conjunctiva)-(mean temperature of the filtering bleb). Furthermore, the filtering bleb was evaluated during 10 seconds of eye opening and a new parameter was introduced, the TB10sec. TDB and TB10sec were analyzed statistically.

RESULTS

The TDB was 0.911°C (±0.467) and the TB10sec was -1.027°C (±0.312) in the well-controlled IOP group. The TDB was 0.599°C (±0.499), and the TB10sec was -0.623°C (±0.265) in the poorly controlled IOP group, respectively. The difference in TDB (P=0.045), as well as that of TB10sec (P<0.001), between the well-controlled and poorly controlled IOP groups was significant.

CONCLUSIONS

Temperature decrease in the filtering bleb provides information about its function. Because of the easy handling and reproducible measurements, thermography using Tomey TG 1000 may be a useful tool in the evaluation of filtering bleb function.

Fungal keratitis caused by Beauveria bassiana: drug and temperature sensitivity profiles: a case report

BACKGROUND

Beauveria bassiana is an entomopathogenic fungus and is a rare cause of keratitis. We present a case of fungal keratitis caused by B. bassiana that was diagnosed by in vivo confocal microscopy and in vitro corneal cultures. In addition, we determined the temperature- and drug-sensitivities of the isolated strain of B. bassiana.

CASE PRESENTATION

A 59-year-old Japanese man with a 2-month history of keratitis was examined by slit-lamp biomicroscopy, in vivo confocal microscopy, and histology and cultures of corneal scrapings. The corneal scrapings were used to determine the minimal inhibitory concentrations of different antifungal drugs and also to determine the temperature-sensitivity. In vivo confocal microscopy and histological examinations showed filamentous fungal keratitis. The characteristics of the fungal growth indicated that the keratitis was caused by B. bassiana. The keratitis responded poorly to systemic and topical voriconazole and to natamycin ointment. However, it was resolved after changing the natamycin to micafungin combined with surgical debridement. The isolated strain was sensitive to itraconazole, miconazole, micafungin, voriconazole, and resistant to flucytosine and fluconazole. It was moderately sensitive to amphotericin B, and natamycin. After 7 days in culture, the isolate grew small white colonies at 25 °C, very small colonies at 35 °C and 37 °C.

CONCLUSION

The drug-sensitivity and temperature-sensitivity profiles of B. bassiana should be helpful in the treatment of B. bassiana keratitis. Therapeutic surgery may be helpful for mycotic keratitis poorly responsive to medical therapy alone.

Characterisation of ilomastat for prolonged ocular drug release

We are developing tablet dosage forms for implantation directly into the subconjunctival space of the eye. The matrix metalloproteinase inhibitor, ilomastat, has previously been shown to be efficacious at suppressing scarring following glaucoma filtration surgery (GFS). We report on the physical characterisation of ilomastat which is being developed for ocular implantation. Since ilomastat is being considered for implantation it is necessary to examine its polymorphs and their influence on aspects of the in vitro drug release profile. X-ray powder diffraction identified two polymorphs of ilomastat from different commercial batches of the compound. Tablets were prepared from the two different polymorphs. Isothermal perfusion calorimetry was used to show that amorphous content is not increased during tablet formulation. The melting points of the two polymorphs are 188 and 208°C as determined by differential scanning calorimetry. Utilising single crystal X-ray diffraction, the structural conformations and packing arrangements of the different polymorphs were determined. The orthorhombic crystal crystallised as a monohydrate while the second monoclinic crystal form is non-solvated. Ilomastat tablets prepared from the two different solid forms exhibited similar drug release profiles in vitro under conditions mimicking the aqueous composition, volume and flow of the subconjunctival space after GFS. This suggests that a reproducible dose at each time point during release after implantation should be achievable in vivo with ilomastat tablets prepared from the two polymorphs identified.

Measurement of dynamic ocular surface temperature in healthy subjects using a new thermography device

PURPOSE

To investigate the routine use and applicability of a new ocular thermography device (TG 1000; Tomey Corp, Nagoya, Japan) in healthy individuals.

METHODS

Sixty eyes of 30 healthy subjects were included in this prospective study. Intraobserver reproducibility was tested with an ocular surface-oriented infrared radiation thermographic device in a non-contact manner. Using a standard examination protocol, the ocular surface temperature was assessed by dynamic thermal imaging over a time period of 10 s. The procedure was repeated three times during a single session by one examiner. Intraclass correlation coefficients (ICC) were calculated.

RESULTS

Ocular surface temperature measurements were highly reproducible. The mean ocular surface temperature was 34.02°C ± 0.22. The ICC was 0.947%, 0.949%, and 0.955% for minimum, maximum, and mean temperatures, respectively.

CONCLUSION

Ocular surface temperature measurements made using the Tomey TG 1000 in healthy subjects showed excellent intraobserver reproducibility. This novel non-invasive technique offers new options for increased understanding of the physiology of the ocular surface.