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increased in both types of surgeries (deep sclerectomy and trabeculectomy) three month after operations, and postoperative changes in ophthalmic artery resistivity index were negatively correlated to corneal surface temperature for both types of surgeries.37
In addition to the studies on procedures for open-angle glaucoma, several cataract surgery procedures were compared and analyzed based on the phacoemulsification system in used. In these studies, the amount of heat generated during surgery,57 the thermal impact on eye,58 and the intraoperative thermal levels at the wound site59 produced by different phacoemulsification systems were determined by the IR thermal imager.
8.5. Discussion
Thermometry was pioneered as a noninvasive method by Zeiss to measure ocular temperature.60 However, Mapstone and Wachtmeister in fact brought IR thermal imaging to the field of ophthalmology. Since then, diagnostic criteria made on the observed asymmetry and anomalies were developed. However, these criteria were proved incorrect. The resolution of ocular thermogram was poor in the beginning, and the eye was not clearly discernible.
The rapid advancement in technology improved the resolution and, thus, provided a more detailed ocular thermogram. Such movement has enabled investigators to focus their concern on the thermographic pattern illustrated at anterior surface rather than at the orbito-ocular region. Besides, the horizontal temperature profile and the vertical profile have also been illustrated.
Investigations in the OST of ocular diseases by IR thermal imaging have been fruitful. Ocular diseases such as exophthalmos, dry eye, cataract, and glaucoma were investigated. Besides, the issues such as the OST in postherpetic neuralgia,61 and the thermal impact by photorefractive keratectomy treatment62 were also studied. However, for most of the investigations in ocular diseases, only mean temperatures on one or several sites (in this context, a site refers to a point or an area) over the anterior eye of both eyes were analyzed and compared.
In literature, investigators often employed first-order textural spatial statistics such as mean, standard deviation, or median over temperatures of a region to study ocular thermogram. These first-order spatial statistics
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alone are insufficient to delineate ocular thermographic pattern clearly. Other techniques in texture analysis, such as second-order spatial statistics, may do a better job.
Ocular thermal image does not have discernible corneal boundary, hence cornea is not easily located. This issue has been addressed in several investigations, as discussed in previous section. For the manual OST acquisition, the obtained values often do not represent the actual OST, and the corresponding accuracy is highly dependent on the area or the region covered. The semi-automated method requires human intervention to crop the eye. The fully automated method does not require human intervention and locate the eye and cornea automatically.
IR thermography does not emit ionizing radiation. It passively receives IR radiation. Unlike other ophthalmic imaging techniques, IR thermography poses no harm or induces no discomfort, as subject has no contact with the instrument and his/her eyes are not exposed to any electromagnetic and acoustic wave. It is capable of spotting pathological changes that are obscured under many other examinations, for example, mild inflammation can be overlooked under slit lamp biomicroscope examination as the changes are so subtle, however, enough to induce a measurable increase in OST.34 These characteristics make it an excellent diagnostic tool, especially for the delicate human eye.
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Chapter 9
Automated Microaneurysm Detection in Fluorescein Angiograms for Diabetic Retinopathy
Prerna Sethi and Hilary W. Thompson†
Diabetic retinopathy (DR), an ocular complication of diabetes, is a leading cause of blindness in the Western world. DR is a progressive disease that has stages of severity, which are characterized by the number and types of lesions it produces on the retina. The symptoms of DR can drastically change the texture and appearance of the retina. Microaneurysms (MAs) are visible early and continue their presence as DR progresses. After the venous filling phase, fluorescein angiograms depict MAs as small, round, hyperfluorescent objects. Following this phase, manual MA counting can quantify the progress and stage of the disease. Computed MA detection can potentially be more rational than the manual process, which is prone to be tedious and time consuming, and introduces the potential for an inaccurate diagnosis. Hence, automated MA detection aids the early detection of DR, as it assists in quantifying MAs and differentiating them from other features.
Our objective in this chapter is to describe a comprehensive study on the current automated MA detection techniques. Several methods have
Department of Health Informatics and Information Management, Adjunct Assistant Professor of Research, School of Biological Sciences, Louisiana Tech University, Ruston LA 71272.
†Professor of Biometry, LSUHSC School of Public Health, Adjunct Associate Professor of Ophthalmology, Biometry, and Neuroscience, Director, Clinical Trials and Biometry Unit, LSU Eye New Orleans, LA 70112.
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