Jen-Hong Tan et al.

8.1. Introduction to IR Thermography

IR thermography is a temperature-measuring technique that is neither intrusive nor contact required. Moreover, it does not alter surface temperature. Lawson brought this technology to modern medicine in 1956 and found that the temperature of the skin around breast carcinoma elevated compared to normal breast,1 and hence determined the feasibility of using thermography to study breast lesions.2 This thermography has undoubtedly revolutionized the way we measure temperature over the past 50 years.

This thermal imaging technique has numerous applications, for example, to investigate fluxes of convective heat, to comprehend fluid dynamics on complicated shapes,3 and to monitor environmental issues.4 In the medical field, this technology has been applied to manage neuropathic pain,5,6 diagnose diseases such as breast cancer,7,8 rheumatism,9 fever,10 skin lesion,11 and impotence.12 In ophthalmology, this thermal imaging technique currently are used to study and diagnose ocular diseases.13

Today, several ophthalmic imaging techniques are available to investigate ocular anterior anatomy and physiology such as confocal microscopy, slit lamp biomicroscopy, optical coherence tomography, etc. These techniques often provide detailed anatomical description, enable scientists to better understand and determine ocular diseases. Nevertheless, they are unable to detect certain pathological, physiological changes, especially those changes that are obscured or regions that are unreachable under anatomical examination but possible for thermography to capture.

Figure 8.1 shows an ocular thermal image of a normal subject. This form of a two-dimensional (2D) medical signal has brought in much research on ocular diseases such as unilateral exophthalmos,14 dry eye,15 glaucoma,16 etc. Ocular thermography have also been applied in the diagnosis of vascular neuritis17 and retinoblastoma in children.18 Hence, it is possible for the OST to help diagnose ocular diseases.

Before the introduction of this technology to the field of ophthalmology, workers measured ocular temperature by invasive measuring techniques, such as needle probes. During measurement, OST is often lowered due to the application of topical anesthesia. The needle probe cools the ocular surface during its insertion into the eye.19 This cooling leads to measurement error, especially when the penetration depth is below 40 mm. Furthermore,

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The Study of Ocular Surface Temperature by Infrared Thermography

Fig. 8.1. Typical thermogram of normal eye.

this penetration can be traumatic, inducing greater ocular blood flow and thus altering OST.

With thermography, OST can be captured without the above drawbacks. It remotely measures temperature data of some surfaces and does not alter surface temperature. The acquired thermal data is of higher quality, and, hence, enables investigators to study the ocular surface with greater convenience, control, and accuracy.

8.2. Infrared Thermography and the Measured OST

Generally, IR thermography refers to the temperature measurement of some areas by capturing IR radiated from some surfaces. In ophthalmology, the temperature of the ocular surface is of the great interest. Acquisition of OST through an IR thermal imager is widely practiced, because it is noninvasive. However, as a thermal imager determines a surface temperature according to the amount of IR radiation detected, the opacity and the transmissive properties of various ocular tissues are important. It is possible for a thermal imager to receive radiation of an ocular tissue posterior to the ocular surface if tissues around anterior chamber are transparent to IR.

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