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Mundt and Hughes ( 5 ) found in 1956 and Oksala and Lehtinen (6) in 1957, that an ultrasonic equipment was of benefit in the diagnosis of tumours within the eye. Oksala and Lehtinen (6, 7, 8) established moreover that ultrasound can be used e.g. in the diagnosing and localisation of foreign bodies within the eye, in detachment of the retina and in rupture of the sclera. The ultrasound apparatus is evidently exceedingly suitable for examinations of the eye, because the eye is a fairly regular ball of fluid, because its numerous parts are separated from each other by clear and regular demarcating surfaces, and because several parts of the eye are normally fairly homogeneous acoustically.The segregation of various parts of the eye from each other is based on the circumstance that they have a sufficiently different velocity of sound. In an earlier paper of ours (6) we carried out determinations of the velocity of sound in various parts of the eye by means of an interferometer. In the present paper we have made these measurements with greater accuracy than before. The knowledge of the velocity of sound in different parts of the eye is of fundamental importance for the diagnostic use of ultrasound in ophthalmology.

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BackgroundThe goal of this Geographic Information System (GIS) study was to obtain accurate information on the locations of study subjects, road network and services for research purposes so that the clinical outcomes of interest (e.g., vaccine efficacy, burden of disease, nasopharyngeal colonization and its reduction) could be linked and analyzed at a distance from health centers, hospitals, doctors and other important services. The information on locations can be used to investigate more accurate crowdedness, herd immunity and/or transmission patterns.MethodA randomized, placebo-controlled, double-blind trial of an 11-valent pneumococcal conjugate vaccine (11PCV) was conducted in Bohol Province in central Philippines, from July 2000 to December 2004. We collected the information on the geographic location of the households (N = 13,208) of study subjects. We also collected a total of 1982 locations of health and other services in the six municipalities and a comprehensive GIS data over the road network in the area.ResultsWe calculated the numbers of other study subjects (vaccine and placebo recipients, respectively) within the neighborhood of each study subject. We calculated distances to different services and identified the subjects sharing the same services (calculated by distance). This article shows how to collect a complete GIS data set for human to human transmitted vaccine study in developing country settings in an efficient and economical way.ConclusionsThe collection of geographic locations in intervention trials should become a routine task. The results of public health research may highly depend on spatial relationships among the study subjects and between the study subjects and the environment, both natural and infrastructural.Trial registration numberISRCTN: ISRCTN62323832