ABSTRACT
BACKGROUND: The slitlamp can be used to estimate the anterior chamber depth (ACD). The length of a slit object is increased until the corneal and iris/lens images appear to just touch. Multiplying the just-touching-slit-length (JTSL) by a conversion factor gives an estimate of the ACD as measured by ultrasonography. The purpose of this study was to determine if central corneal thickness (CCT) affects the accuracy of this technique. METHODS: The ACD of 50 subjects was measured by A-scan ultrasonography and estimated by the slitlamp technique. CCT was measured by ultrasonic pachometry. The refractive error was determined subjectively. RESULTS: The average ultrasonographic ACD for all subjects was 3.32 +/- 0.65 mm. The average JTSL was 2.46 +/- 0.38 mm. The conversion ratio between the ultrasonographic ACD and the average JTSL was 1.35. The predicted ACD using the regression equation of JTSL on the ultrasound anterior chamber depth (USACD) was 3.32 +/- 0.54 mm. The corresponding value using the regression equation of JTSL and CCT on USACD was exactly the same, that is, 3.32 +/- 0.54 mm. CONCLUSION: Incorporation of CCT into a regression equation does not improve the accuracy of the Smith technique.
Subject(s)
Anterior Chamber/diagnostic imaging , Cornea/diagnostic imaging , Hyperopia/diagnostic imaging , Hyperopia/pathology , Myopia/diagnostic imaging , Myopia/pathology , Adult , Case-Control Studies , Female , Humans , Male , Models, Theoretical , Regression Analysis , UltrasonographyABSTRACT
BACKGROUND: There are no previous reports on the velocity of ultrasound through the aqueous and vitreous humours of the one-humped camel. This information is required for determination of the depth of the aqueous and vitreous chambers and therefore the axial length. This knowledge together with other, yet to be determined, ocular dimensions will ultimately be used in drawing up a schematic eye for the camel. This will provide a tool for studying the visual capability of this animal. METHOD: A-mode ultrasonography was used to determine the velocity of sound through the aqueous and vitreous fluids of the one-humped camel. The fluids were obtained from freshly enucleated eyes. RESULTS: The average velocity of ultrasound through 20 aqueous and 22 vitreous humour samples kept at 20 degrees Celsius was 1,499 +/- 23 m/s and 1,497 +/- 24 m/s, respectively. CONCLUSION: We recommend that at 20 degrees Celsius a common value of 1,498 m/s should be adopted as the velocity of ultrasound through the aqueous and vitreous humours of the one-humped camel. This value is slower than in humans but similar to that of the cow and pig.
