Localized Evaporative Cooling Explains Observed Ocular Surface-Temperature Patterns.

Purpose: We determined interblink corneal surface-temperature decline and tear-film evaporation rates of localized tear breakup cold regions (LCRs) and localized tear unbroken warm regions (LWRs) of the corneal surface, as well as that of the overall average corneal surface. Methods: Each subject underwent 4 inter-day visits where the interblink corneal surface-temperature history of the right eye was measured using a FLIR A655sc infrared thermographer. Corneal surface temperature history was analyzed to determine the overall, LCR, and LWR temperature-decline rates. Evaporation rates of LCR and LWR regions were determined from the measured LCR and LWR temperature data using the physical model of Dursch et al. Results: Twenty subjects completed the study. Mean (SD) difference of LCR temperature-decline rate was -0.08 (0.07)°C/s faster than LWR (P < 0.0001). Similarly, evaporation rates of LCR and LWR were statistically different (P < 0.0001). At ambient temperature, mean LCR and LWR evaporation rates were 76% and 27% of pure water evaporation flux, respectively. There was no statistically significant difference between the inter-day measured temperature-decline rates and the interblink starting temperature. Conclusions: Significant differences in corneal temperature-decline rate and evaporation rate between LCR and LWR were quantified using infrared thermography. In agreement with literature, LCRs and LWRs correlate directly with fluorescein break-up areas and unbroken tear areas, respectively. Because lipid-evaporation protection is diminished in breakup areas, higher local evaporation rates and faster local cooling rates occur in LCRs relative to LWRs. Our results confirm this phenomenon clinically for the first time.

Evaluation of Antibiotic Allergy in the Ambulatory Setting Using a Standardized Questionnaire.

Patients are sometimes mislabeled as having an immune-mediated antibiotic allergy in their medical records. Therefore, the aim of this study was to investigate the prevalence of subjects with non-immune mediated reactions to antibiotics using a standardized questionnaire. Subjects aged 18 years and older with a documented antibiotic allergy were identified and recruited from 2 outpatient clinics in the greater Chicago area. Subjects completed a standardized questionnaire during a single visit regarding their previous adverse reaction to an antibiotic. For subjects with multiple documented antibiotic allergies, 1 questionnaire was filled out for each antibiotic allergy. Investigators subsequently evaluated the questionnaire responses to determine whether the adverse reaction was a true immune-mediated allergic reaction or an adverse drug reaction. A total of 98 subjects were recruited with completion of 159 questionnaires. Eighteen subjects (18.37%, 95% CI: 10.7%, 26.3%) had antibiotic allergy labels with no corresponding immune-mediated reaction history. There were 35 allergy labels (22.0%, 95% CI: 14.7%, 29.4%) that were unlikely to be immune-mediated. Antibiotics with the highest percentage of clinical histories that were unlikely to be immune-mediated were macrolides (8 of 11 subjects), nitrofurantoin (1 of 2 subjects), and amoxicillin/clavulanate (2 of 8 subjects). The most common antibiotic allergy labels were penicillin (43 of 159 subjects), sulfonamides (25 of 159 subjects), and fluoroquinolones (21 of 159 subjects). Identification of adverse reactions to antibiotics that are unlikely to be immune-mediated can be accomplished using a standardized questionnaire in the outpatient setting. Improved identification of low-risk antibiotic allergy labels can guide de-labeling initiatives to improve antibiotic prescribing.

Ocular surface cooling rate associated with tear film characteristics and the maximum interblink period.

The surface of the human eye is covered with a protective tear film that refreshes with each blink. Natural blinking occurs involuntarily, but one can also voluntarily blink or refrain from blinking. The maximum time one can refrain from blinking until the onset of discomfort is the maximum interblink period (MIBP). During the interblink period the tear film evaporates and thins from the ocular surface. Infrared thermography provides a non-invasive measure of the ocular surface temperature (OST). Due to evaporation, ocular surface cooling (OSC) generally occurs when the eyes are open and exposed to the environment. The purpose of our study was to investigate the effect of OSC rate on the MIBP, and to investigate the association of the MIBP with tear film characteristics in subjects who do and do not exhibit OSC. The MIBP was measured simultaneously with OST over time. Non-invasive tear breakup time, tear meniscus height, tear lipid layer thickness, and Schirmer I test strip wetted lengths were measured on a day prior to the thermography visit. Subjects were divided into cooling and non-cooling groups based on OSC rate, and demographic and tear film characteristics were tested for inter-group differences. A faster OSC rate was associated with an exponentially shorter duration of the MIBP overall and within the cooling group alone. Faster non-invasive tear breakup time was significantly associated with a shorter MIBP in both groups. These results suggest that tear film evaporation initiates a pathway that results in the onset of ocular discomfort and the stimulus to blinking. The presence of a subset of subjects with no or minimal OSC who nevertheless have a short MIBP indicates that evaporative cooling is not the only mechanism responsible for the onset of ocular discomfort.