Ooi, E.H. and Ng, E.Y.K.

heat generation of the eye tumor produces a greater response, thus leading to a stronger signal. From a clinical viewpoint, this would mean that the detection of the eye tumor is more efficient when the eye tumor is at later stages of growth. This may not be feasible since an early detection is crucial in the treatment of the eye tumor. This aspect requires further investigations before a definite conclusion can be drawn. One of the factors that has been excluded from this study is the location of the eye tumor. As we show in Sec. 7.1.6, when an eye tumor grows at the back of the human eye, changes in the corneal surface temperature are small and may not be effectively detected using an IR camera. For such cases, it may be possible to amplify the signal from the eye tumor by using the combination of factors (shown in Table 7.8) that minimizes the effect of noise.

Owing to the lack of similar studies, neither qualitative nor quantitative comparisons of the numerical results obtained in the present statistical analysis are possible. Nevertheless, if we compare the results from the present study with those obtained from the analysis carried out on breast tumor,16 similarities in the setting of factors that minimize the effects of noise can be found. In breast tumor detection,16 the signal from the tumor can be measured effectively by setting the noise factors to levels so that the heat loss from the surface of the breast is maximized while heat sources that originate from inside the breast that are not caused by the tumor are minimized. From our analysis, a similar pattern is observed where the best setting for detecting the eye tumor involves an increased heat loss from the corneal surface while heat from the ocular blood flow is kept as low as possible.

7.8. Concluding Remarks

We have successfully developed a 3D model of the human eye to investigate the effects of an eye tumor on the temperature distribution inside it. To account for the unknown thermal properties of the eye tumor, simulations have been performed for a range of values of eye tumor thermal conductivity, blood perfusion rate, and metabolic heat generation that have been derived from the thermal properties of tumors that grow at various parts of the human body. Despite the possible differences in the cellular structure between each type of tumor, we do not expect the actual thermal properties of the eye tumor to be significantly different from the range of values used in this study.

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From the numerical results presented in this study, we have discovered that the presence of an eye tumor inside the human eye causes an increase in ocular temperature distribution. This increase in temperature distribution has been attributed to the metabolic heat generation of the tumor tissues. An increase in the corneal surface temperature and an asymmetrical thermal profile on the corneal surface has also been observed. The magnitudes of the temperature rise and the degree of thermal asymmetry have been suggested as potential indicators of an eye tumor inside the human eye.

When carrying out the parametric optimization in Sec. 7.7, we have assumed that the use of IR thermography for detecting eye tumors is a feasible choice. This assumption has not yet been fully verified although earlier experimental and numerical investigations appear to support it.47−49 The most common method in diagnosing an eye tumor is through visual inspection using an ophthalmoscope. An ophthalmologist usually performs this method. The use of IR thermography as an alternative technique for detecting eye tumor is promising since it offers a quick and intelligent diagnostic tool. It may be used as a preliminary screening tool in mass screenings and ophthalmologists using the ophthalmoscope can verify any identification of tumors. This issue requires more investigation in the future, however.

One of the major setbacks that may impede any future investigations is the rare occurrence of an eye tumor within a given population. The American Cancer Society estimates that about 2,350 new cases of primary intraocular cancer were diagnosed in 2009.57 This figure is smaller than the 180,000 cases of breast cancer diagnosed annually.16 Nevertheless, eye tumors should not be taken lightly since vision loss from cancer is the second leading health concern.58

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Chapter 8

The Study of Ocular Surface Temperature by Infrared Thermography: The Principles, Methodologies, and Applications

Jen-Hong Tan , Ng, E.Y.K. , Rajendra Acharya, U.†

and Chee, C.‡

Thermography is a technique that records the thermal pattern of a surface without in contact with the object of interest. Infrared (IR) thermography captures the thermal pattern by utilizing the IR radiation from any object. Thermal imaging is widely used today, and its role is increasingly important in biomedical field, as it can provide details on the variation and changes of temperature in vascular tissues. This technique has also been applied for the study of ocular surface temperature (OST) in ophthalmology. In this chapter, the principles, applications, methodologies, and the corresponding advantages with the use of this method in ophthalmology are elaborated and discussed. This chapter also presents several algorithms developed to acquire OST.

School of Mechanical and Aerospace Engineering, College of Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798.

†Department of Electronics and Computer Engineering, Ngee Ann Polytechnic, Singapore.

‡Medical & Surgical Retinal Centre Department of Ophthalmology, National University Hospital, Singapore 119074.

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