A-scan ultrasound biometry
Encyclopedia
A-scan is an amplitude modulation scan. It gives the information in the form of one dimensional. it is used to detect the presence of flaws in the materials.
A-scan ultrasound biometry, commonly referred to as an A-scan, is routine type of diagnostic test used in ophthalmology
. The A-scan provides data on the length of the eye
, which is a major determinant in common sight disorders. The most common use of the A-scan is to determine eye length for calculation of intraocular lens power. Briefly, the total refractive power of the emmetropic eye is approximately 60. Of this power, the cornea provides roughly 40 diopters, and the crystalline lens 20 diopters. When a cataract is removed, the lens is replaced by an artificial lens implant. By measuring both the length of the eye (A-scan) and the power of the cornea (keratometry), a simple formula can be used to calculate the power of the intraocular lens needed. There are several different formulas that can be used depending on the actual characteristics of the eye.
The other major use of the A-scan is to determine the size and ultrasound characteristics of masses in the eye, in order to determine the type of mass. This is often termed quantitative A-scan.
Instruments used in this type of test require direct contact with the cornea
, however a non-contact instrument has been reported. Disposable covers, which come in actual contact with the eye, have also been evaluated.
http://www.ndtfolks.com/index.php/component/option,com_glossary/Itemid,59/catid,40/func,view/term,A-SCAN%20(UT)/ A-Scan (Ultrasonic Test), A data presentation method by which intelligence signals from a signal object located are displayed. As generally applied to pulse echo ultrasonics, the horizontal and vertical sweeps are proportional to time or distance and amplitude or magnitude respectively. Thus the location and magnitude of acoustical interface are indicated as to depth below the transducer. The term comes from radar technology in World War II, in which it provided the same type of display.
A-scan ultrasound biometry, commonly referred to as an A-scan, is routine type of diagnostic test used in ophthalmology
Ophthalmology
Ophthalmology is the branch of medicine that deals with the anatomy, physiology and diseases of the eye. An ophthalmologist is a specialist in medical and surgical eye problems...
. The A-scan provides data on the length of the eye
Human eye
The human eye is an organ which reacts to light for several purposes. As a conscious sense organ, the eye allows vision. Rod and cone cells in the retina allow conscious light perception and vision including color differentiation and the perception of depth...
, which is a major determinant in common sight disorders. The most common use of the A-scan is to determine eye length for calculation of intraocular lens power. Briefly, the total refractive power of the emmetropic eye is approximately 60. Of this power, the cornea provides roughly 40 diopters, and the crystalline lens 20 diopters. When a cataract is removed, the lens is replaced by an artificial lens implant. By measuring both the length of the eye (A-scan) and the power of the cornea (keratometry), a simple formula can be used to calculate the power of the intraocular lens needed. There are several different formulas that can be used depending on the actual characteristics of the eye.
The other major use of the A-scan is to determine the size and ultrasound characteristics of masses in the eye, in order to determine the type of mass. This is often termed quantitative A-scan.
Instruments used in this type of test require direct contact with the cornea
Cornea
The cornea is the transparent front part of the eye that covers the iris, pupil, and anterior chamber. Together with the lens, the cornea refracts light, with the cornea accounting for approximately two-thirds of the eye's total optical power. In humans, the refractive power of the cornea is...
, however a non-contact instrument has been reported. Disposable covers, which come in actual contact with the eye, have also been evaluated.
http://www.ndtfolks.com/index.php/component/option,com_glossary/Itemid,59/catid,40/func,view/term,A-SCAN%20(UT)/ A-Scan (Ultrasonic Test), A data presentation method by which intelligence signals from a signal object located are displayed. As generally applied to pulse echo ultrasonics, the horizontal and vertical sweeps are proportional to time or distance and amplitude or magnitude respectively. Thus the location and magnitude of acoustical interface are indicated as to depth below the transducer. The term comes from radar technology in World War II, in which it provided the same type of display.