### Results of Individual Studies  
[PERSON] et al. [6], in 2010, treated 25 patients with a serial puncture technique through the 30-gauge needle in the pre-periosteal tissues (total injection volume of filler \"Restylane\" (Galderma, Fort Worth, TX, USA) for each side was 0.1 to 1.1 mL on the right side and 0.2 to 1.2 mL on the left side) for the tear trough treatment. At the first follow-up (seven  
Figure 3: ROBINS-I Weighted Summary Plot bias assessment. Figure 2: ROBINS-I Traffic Light Plot bias assessment. days), they observed bruising in 13 patients (52%), erythema in 10 patients (40%), and local swelling in two patients (8%). [PERSON], in a study conducted from December 2008 to July 2009, treated 26 patients with contour abnormalities in the periorbital region [22]. The hyaluronic acid gel in each case was Restylane. A cannula was used to perform the injection was performed parallel to the periosteum, and, on average, 0.8 to 1.0 mL oh HA was injected. At the follow-up, 7 patients showed hematomas (13%), one patient showed the Tyndall effect (3%), 12 patients showed edema (21%), and 2 patients showed surface irregularities (14%). [PERSON] et al., in a retrospective study from January 2009 until January 2013, treated 176 patients with tear trough abnormalities [23]. The authors used two methods on two patient collectives. Group A was treated using hyaluronic acid gel (Restylane; Q-Med, Uppsala, Sweden) and a reinforced 25-gauge Pix?1+ micro cannula. The authors developed a modified method for group B that included a combination of cooling of the periorbital area, no local anesthesia, pre-incision displacement of malar fat 10 mm below the orbital border, and postintervention corticoid therapy for 48 h. The quantity of HA injected was 0.6 to 1.0 mL per side, parallel to the periosteum. The complication of edema and swollen reactions were observed in 51.2 percent (21 of 41) of group A. Eleven of 41 patients (26.8 percent) complained about lump or surface irregularities after treatment with protocol A. Alteration of pigmentation was observed in 17.1 percent (seven of 41) in group A. Migration of the injected hyaluronic acid was observed in 16 of 41 patients in group A (39.0 percent). A hyaluronidase injection to minimize complications was necessary for 48.8 percent (20 of 41 patients) in group A. Only group A was evaluated, as group B, in which pre-dressings are used before the injection of HA, did not meet the inclusion criteria of our study. [PERSON] et al., in 2017, treated 151 patients with the use of a semi-cross-linked hyaluronic acid filler \"Teosyal\" PureSense Redensity (TEOXANE SA, Geneva, Switzerland)\" for the tear trough deformity [9]. The procedure was performed using a standard 30-gauge needle in 58% of cases and a cannula in 42% of cases. Injections were administered in the pre-periosteal tissues with a mean volume of 0.48 mL for each side (range, 0.1-1.0 mL). No serious complications were recorded. At the first visit, immediately after the treatment, the 151 patients showed: swelling in 22 patients, bruising in 17 patients, redness in 32 patients, pain in only 1 patient, and blue discoloration in 4 patients. At the 1 month follow-up (visit 2) of 112 patients: swelling occurred in 13 patients, bruising in 12 patients, redness in 7 patients, and blue discoloration in only one patient were recorded. In a retrospective review of 2017, [PERSON] et al. evaluated the efficacy and safety of filler injection \"Restylane\" in 147 patients performed for the rejuvenation of the periorbital tissues, which were followed for at least 5 years since 2014 [24]. All patients underwent injection into the periorbital area using a fanning technique in the suborbicular plane using a 30-gauge needle. The mean number of injections for a patient was 6.88 (\(\pm\)1.72), and the mean total volume injected was 3.19 mL (\(\pm\)0.42). Seventeen patients developed malar edema, three blue-gray dyschromia, and three contour irregularity/orbital ridge.