Temperature Distribution Inside the Human Eye with Tumor Growth

7.6.3. Case 2

The thermal effects of categories T1, T2, and T3 eye tumors on the temperature increases along the pupillary axis in Case 2 are plotted in Figs. 7.9, 7.10, and 7.11, respectively. Unlike the “bell-shaped” curves seen in Figs. 7.6, 7.7, and 7.8, in Case 1, the profiles observed in Figs. 7.9, 7.10, and 7.11 show a warmer temperature distribution at the posterior region of the eye. This warmer region is a consequence of the eye tumor being oriented along the pupillary axis. Variations of the temperature at the anterior regions of

Fig. 7.10. Temperature variations along the pupillary axis of an eye with a category T2 eye tumor in Case 2.

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Fig. 7.11. Temperature variations along the pupillary axis of an eye with a category T3 eye tumor in Case 2.

the human eye are small due to the location of the eye tumor, which is positioned at the back of the eye. As distance from the eye tumor increases, the warming effect of the metabolic heat generated by the tumor diminishes.

Table 7.4 tabulates the magnitude of the temperature rise on the corneal surface due to the growth of the eye tumor in Case 2. As in Case 1, the results presented in Table 7.4 are obtained as control values of eye tumor thermal conductivity, blood perfusion rate, and metabolic heat generation. Contrary to the results obtained in Case 1, the largest increase in temperature in Case 2 occurs in the center of the corneal surface. This result is not surprising,

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Temperature Distribution Inside the Human Eye with Tumor Growth

Table 7.4. Increase in temperature on the corneal surface in Case 2.

since the center of the corneal surface is now closer to the eye tumor than the superior, inferior, nasal, and temporal points.

While the increase in temperature at the center of the corneal surface is the largest, no significant differences in the temperatures at the periphery of the corneal surface are found. This lack of varying temperatures indicates a lack of thermal asymmetry, which is to be expected, since the eye tumor is positioned in such a way that it is symmetrical about the pupillary axis. Consequently, the warming effects of the eye tumor are evenly dispersed into adjacent regions of the human eye, thus leading to a uniform increase in temperature at the corneal periphery.

Comparing the results in Table 7.3 with those in Table 7.4, we find that the eye tumor in Case 1 produces a temperature increase that is, on average, 2.4 times greater than the temperature increase in Case 2. This may be attributed to the greater distance between the eye tumor and the corneal surface in Case 2 when compared with the location of the eye tumor in Case 1 (see Fig. 7.4).

7.6.4. Discussion

From the numerical results presented in Secs. 7.6.2 and 7.6.3, we can see that the growth of a tumor inside the human eye produces a warmer ocular temperature distribution. For the location of the eye tumor in Case 1, a

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thermal asymmetry on the corneal surface is detected. Although simulations have not been carried out for the locations of an eye tumor that are at the negative y region of the human eye, results from our present study suggest that a temperature increase at the inferior of the corneal surface is expected to be the largest when the eye tumor grows at the negative y region of the human eye. Future studies may include the investigations of the ocular temperature changes for the locations of an eye tumor that are different from the two cases considered here.

In the present study, the model of the eye tumor is assumed to be a homogeneous region. This assumption, however, does not accurately depict the actual structure of tumors. In reality, a tumor may be divided into two zones, a necrotic zone at the center of the tumor and a regionally vascularized zone at the periphery.46 Because of the tissue heterogeneity, the thermal properties of the tumor, particularly blood perfusion rate and metabolic heat generation may not be uniform throughout the entire tumor region. Instead, the vascularized periphery is expected to have a larger blood perfusion rate and metabolic heat generation than the necrotic center. Although it is not known whether such heterogeneity may cause any significant difference to the simulated results, the present model may be reworked in the future to address these problems, if sufficient information is available.

Investigations in the present study have been limited to choroidal melanoma. For eye tumors that grow on the iris (iris melanoma) and ciliary body (ciliary body melanoma), similar investigations may be performed by making minor modifications to the model developed in the present study. These areas are open for future studies.

To verify the accuracy of the model developed in this study, the numerical results are compared to the experimental observations reported by other researchers that can be found in the literature. Bourjat and Gautherie, who used IR thermography to observe the temperature profile of the corneal surface in patients with unilateral exophthalmos, found a marked orbital hyperthermy in the infected eye.47 Bogdasarov et al. found that IR thermography is a feasible choice for the diagnosis of retinoblastoma in children.48 Furthermore, they discovered that the intensity and the extent of the temperature increase inside the eye are related to the stages of tumor growth. Wittig et al.49 observed warmer corneal surfaces and slight thermal asymmetries in patients with malignant uveal and conjunctival melanomas. The numerical

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