A Novel Method of Measuring Tear Evaporation Rates using Infrared Thermography

A Novel Method of Measuring Tear Evaporation Rates using Infrared Thermography

Andrea Petznick¹, Samantha Sze Yee Lee¹, Jen Hong Tan², U. Rajendra Acharya^2,3,4, Eddie Ng⁵, Louis Tong^1,6,7,8

¹Singapore Eye Research Institute, Singapore

²School of Engineering, Ngee Ann Polytechnic, Singapore

³SIM University, Singapore

⁴Singapore Institute of Technology – University of Glasgow, Singapore

⁵School of Mechanical and Aerospace Engineering, Nanyang Technological University, Singapore

⁶National Eye Centre, Singapore

⁷Duke-NUS Graduate Medical School, Singapore

⁸Yoon Loo Lin School of Medicine, National University of Singapore

PURPOSE: Dry eye is a very common medical problem and meibomian gland dysfunction (MGD) may be an aggravating factor. There is no single reliable diagnostic tool to determine the presence and severity of dry eye and MGD. The measurement of dynamic tear evaporation rates would allow for a more objective diagnosis. In this study, we present a novel non-invasive method of measuring tear evaporation rates using infrared thermography that is reliable and able to detect changes after heat therapy.

METHODS: Infrared thermographic sequential images of ocular surface temperature were recorded from healthy participants (mean age ± SD: 24±7 years) while remaining in a consulting room with a temperature of 22.08±0.77°C and humidity of 63.82±0.02%. 1) Repeatability of the equipment was tested by taking 2 measurements 20 min apart (n=16). 2) Measurements were taken before and 60 min after 5-min heated eye mask wear (Eyegiene^®, US) (n=10) to test for changes in ocular surface temperature and tear evaporation. Tear evaporation rates were calculated based on ocular surface temperature profiles and controlled for body and room temperature as well as room humidity using principles of thermodynamics. Statistical comparisons were performed using paired t-test with p<0.05.

RESULTS: 1) There were significant correlations between the first and second measurements of ocular surface temperature (r=0.94) and tear evaporation rates (r=0.98) (p<0.01). The coefficients of repeatability were 0.42˚C for ocular surface temperature and 6.78 Wm^-2 for tear evaporation rates. 2) Ocular surface temperature before heat therapy was 33.66±0.53˚C which significantly decreased to 32.50±0.97˚C after heat application (p<0.01). Tear evaporation rates significantly increased from 65.64±12.51 to 78.72±21.53 Wm^-2 following heat treatment (p<0.01). 

CONCLUSIONS: We established that ocular thermography has a good repeatability in measuring ocular surface temperatures and tear evaporation rates under constant conditions and may therefore present a valuable tool for diagnosing dry eye and MGD. Findings also suggest a drop in ocular surface temperature and an increase in tear evaporation 60 min after heating, but it is possible that vasodilation in ocular tissues may have affected calculations of tear evaporation rates after heating.

The application of temperature measurement of the eyes by digital infrared thermal imaging as a prognostic factor of methylprednisolone pulse therapy for Graves' ophthalmopathy.

The application of temperature measurement of the eyes by digital infrared thermal imaging as a prognostic factor of methylprednisolone pulse therapy for Graves' ophthalmopathy.
Shih SR, Li HY, Hsiao YL, Chang TC.

Source
Department of Internal Medicine, National Taiwan University Hospital and National Taiwan University College of Medicine, Taipei, Taiwan.

Abstract
PURPOSE:
Graves' ophthalmopathy (GO) involves autoimmune process resulting in proptosis, congestion, oedema and diplopia. Werner's NOSPECS classification and clinical activity score (CAS) of GO cannot objectively describe the inflammatory status. Digital infrared thermal imaging (DITI) detects local temperature and may reflect the degree of orbital inflammation. The aim of this study was to evaluate the clinical application of the eye temperature measured by DITI.

METHODS:
Forty-six patients with GO receiving intravenously methylprednisolone pulse therapy (MPT) were included in this study. Local temperatures of the lateral orbit, upper eyelid, inner caruncle, medial conjunctiva, lateral conjunctiva, lower eyelid and cornea were measured with DITI before and after MPT. CAS, proptosis, eye movement (EOM) and diplopia were also recorded. Improvement of CAS was defined as at least one point decrease at either side of the eye, which was 0.5 score decrease as to the average of bilateral CAS.

RESULTS:
Local temperatures of the eyes decreased after MPT. The mean value of temperature (MT) of 12 points including the lateral orbit, upper eyelid, inner caruncle, medial conjunctiva, lateral conjunctiva and lower eyelid of both eyes before MPT was 32.65 degrees . The mean change of MT after MPT (DeltaT) was -0.22 degrees. DeltaT significantly negative-correlated with basal MT (correlation coefficient=-0.54, p=0.004). Higher baseline MT and CAS before MPT correlated with higher possibility of improvement of CAS after MPT (p=0.013 and 0.012, respectively). Baseline MT and CAS together correlated with improvement of CAS after MPT
better than baseline CAS alone could do (area under the receiver operating characteristic curve: 82.81% and 66.63%, respectively).

CONCLUSIONS:
Basal temperature of the eyes measured by DITI was an objective indicator of inflammation of GO. Combining CAS and MT could better predict the outcome of MPT than CAS alone.

Ocular surface temperature gradient is increased in eyes with bacterial corneal ulcers.

Ocular surface temperature gradient is increased in eyes with bacterial corneal ulcers.

Klamann MK, Maier AK, Gonnermann J, Klein JP, Bertelmann E, Pleyer U.

Source

Department of Ophthalmology, Charité-University Medicine Berlin, Berlin, Germany. matthias.klamann@charite.de

Abstract

AIMS:

To investigate the ocular surface temperature gradient in eyes with bacterial corneal ulcers.

METHODS:

Prospective examination of 12 eyes with bacterial corneal ulcers (group 1) and 12 control eyes (group 2). Infrared thermal imaging (Tomey TG 1000) was used to study the temperature of the ocular surface. The mean, minimum and maximum temperature of the ocular surface and temperature course over a time period of 10 s of sustained eye opening were evaluated. Furthermore, a correlation between the overall corneal temperature and the temperature at the base of the corneal ulcers was determined.

RESULTS:

A significant difference between both groups was present. Mean corneal temperature was 35.6°C ± 0.9 in group 1 and 34.8°C ± 0.8 in group 2 (p = 0.033). The temperature course over 10 s of sustained eye opening was -0.6°C ± 0.4 in group 1 and -0.3°C ± 0.2 in group 2 (p = 0.045). There was a close correlation between the mean temperature at the base of the corneal ulcer and the overall corneal temperature (r = 0.92, p < 0.001).

CONCLUSION:

Infrared thermal imaging can be used to objectively determine the increased ocular surface temperature in patients with bacterial corneal ulcers. The use of dynamic thermography may offer new options to monitor ocular surface alterations.

Copyright © 2012 S. Karger AG, Basel.