Because its ultrasound beam cannot penetrate beyond a radius of 2 cm, HRES is limited in evaluating abnormalities within or adjacent to the esophageal wall. To date, however, it has provided new diagnostic capabilities in evaluating patients with several different esophageal disorders. EUS at lower frequencies has shown inconsistent results in evaluating the thickness of esophageal muscle layers in patients with achalasia. HRES has been able to more accurately measure the individual CSM, LSM, and TM layers of the muscularis propria and the mean measurements have been noted to increase in achalasia patients when compared with normals. HRES has been found to be clinically useful in assessing histologic damage following pneumatic dilatation and in localizing the LES during the administration of intrasphincter botulinum toxin injection in the treatment of achalasia.