Background <p>The infraorbital region is one of the most complex and esthetically critical areas of the face. Age-related changes, such as infraorbital groove and infraorbital fat bulging, frequently coexist and vary significantly among individuals. Although hyaluronic acid (HA) filler injection is a common nonsurgical treatment for infraorbital hollows, improper placement, particularly into the infraorbital fat, can result in suboptimal outcomes and complications such as bulging. Clinical evaluation alone is often insufficient to identify anatomical variations beneath the skin. This study aimed to classify infraorbital grooves and fat patterns using ultrasound imaging and to propose practical guidelines that enhance the safety and precision of filler injections in this region.</p> Methods <p>Thirty one patients aged &gt; 40 years underwent ultrasonographic evaluation of the lower eyelid. Based on the relationship among the infraorbital fat, inferior orbital rim, and visible grooves, five anatomical types (A–E) were identified.</p> Results <p>Each anatomical type reflects different degrees of infraorbital fat descent and groove depth. In Types D and E, infraorbital fat extends to or beyond the orbital rim, increasing the risk of 1 filler misplacement during deep injections.</p> Conclusions <p>Pre-injection ultrasound evaluation provides critical insights into fat positioning and vascular structures, supporting safer and more individualized injection strategies. The proposed classification offers a clinically useful framework for personalized infraorbital filler treatments.</p> Level of Evidence III <p> This journal requires that authors assign a level of evidence to each article. For a full description of these Evidence-Based Medicine ratings, please refer to the Table of Contents or the online Instructions to Authors www.springer.com/00266</p>