Abstract
Abstract: :
Purpose:Optic disc drusen is a common cause of pseudopapilloedema and is an important differential diagnosis of disc swelling. Ultrasound is a successful means of identifying the calcified areas within the disc, which establishes the presence of drusen. However, when there is surface drusen only, or the calcified areas are small, conventional 10 MHz imaging may not identify the calcification. Recent advances in B scan echography have introduced the 20 MHz probe which gives high resolution images of the posterior segment. This study evaluates the use of the 20 MHz probe in the diagnosis of optic disc drusen. Methods:Thirty patients (60 eyes) with suspected optic disc drusen, underwent 10 and 20 MHz B scan and vector A Scan ultrasound using a QuantelTM CineScan standardised Ultrasound system. The scans were performed axially in order to image the optic disc. The Vector A Scan was positioned through the disc in order to quantify the disc reflectivity. Vertical images of the retroscleral optic nerve were also obtained with the 10 MHz probe held at the lateral canthus. Results:The 10 MHz probe identified buried drusen in 17 patients (30 eyes), and surface drusen in 3 patients (5 eyes). The 20 MHz probe identified buried drusen in 21 patients (41 eyes) and surface drusen in 7 patients (14 eyes). Two patients (4 eyes) were found to have no drusen to10 or 20 MHz examination, but uniform disc swelling (20 MHz), and fluid distension of the optic nerve sheaths (10 MHz), and were therefore diagnosed as papilloedema. Conclusions:In this study the use of 20 MHz USG increased the sensitivity of buried disc drusen by 37%, and surface disc drusen by nearly 3 times. Using the 10 MHz probe alone the false negative error for disc drusen was 36%. The ability to readily differentiate between the dome shaped disc in papilloedema, and the irregular shaped disc in surface drusen using 20 MHz imaging is the main reason for the improved diagnostic rate, particularly in cases of surface drusen.
Keywords: drusen • imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound) • optic disc