A Scan Ultrasound

Ultrasonido de exploración A
Synonyms Ultrasound, A-Scan; IOL Measurement; Pseudophakos Measurement
Applies to Diagnostic Preoperative Cataract and Intraocular Lens Implant Surgical Assessment; Intraocular Lens Calculation Procedure Commonly Includes Keratometry readings, intraocular lens power calculation for various lens types Indications Provide measurement of axial length of eye, identify abnormalities in globe length. Measurement is used in preoperative intraocular lens (IOL) power calculation. Helps in differential diagnosis of intraocular pathology (ie, tumors, membranes). Patient Preparation Patient should bring spectacles to the testing area. If glaucoma patient, delete routine glaucoma drops one dose just prior to appointment, with ophthalmologist's approval. Pupils may be dilated. Aftercare Patient will be cautioned not to rub or touch around eyes for 30 minutes after testing because of local anesthesia. May have eyes dilated, dark glasses are helpful. Patient should arrange for a ride home from testing site. Special Instructions Type of intraocular lens to be implanted must be known for proper power calculation. Simultaneous B-scan ultrasound may be needed for proper orientation and interpretation of intraocular pathology. Equipment Changes in acoustic density of ocular tissue are displayed on an oscilloscope. Technique Digital biometric ruler uses A-scan ultrasound to accurately measure axial length of globe. Various calculation formulas (of either theoretical or regression types) are used to determine power of IOL to be implanted. Ultrasound probe is applied to the surface of anesthetized eye. Probe may be handheld or fixed in apparatus such as a mounted tonometer. Patient is usually in sitting position. Data Acquired Axial length of the eye is the distance from the stationary transducer to the retinal echo spike. Turnaround Time Immediately if indicated Limitations Results may be variable in patients with poor central visual fixation. Patient cooperation is required. Additional Information Axial length and keratometry measurements are used in various formulas for calculation of intraocular lens power. The acoustical density (height of echo spikes) helps to differentiate between intraocular tumor types or causes of intraocular membranes.