## 4 Discussion
[PERSON] and [PERSON] reported immediate swelling in 15% of patients in whom the needle technique was chosen [9]. [PERSON] et al. reported an incidence of 8% out of a total of 150 patients using the needle technique [26]. [PERSON] et al., [PERSON] et al., and [PERSON] et al. did not report any cases of post-procedure swelling [22; 23; 24; 25]. [PERSON] et al. did not report swelling in any of their patients at 4 weeks following injections with cannula [27]. It is important for this aspect to take into consideration the characteristics of the hyaluronic acid used [48; 49]. It is possible to show a higher incidence of swelling when an HA filler with a lower G\({}^{\prime}\) and a lower degree of cross-linking is used (Teosyal, Teoxane) [9; 27]. When a product with a high G\({}^{\prime}\) is used, the affinity for water is reduced, and the incidence of swelling is lower (Restylane, Galderma) [22; 23]. The needle technique is more associated with the development of swelling, particularly when performed on a more superficial tissue layer [1; 10; 24; 50]. Blue-gray dyschromia, also known as the Tyndall effect, is commonly reported in this area after filler injections [51; 52]. The Tyndall effect is a phenomenon that occurs more commonly in patients with thin, poorly pigmented skin, but the exact cause of the discoloration is poorly understood. In order to minimize the occurrence of this complication, injections of HA should not be performed too superficially [50]. The ideal plane of the positioning of small quantities of filler is below the orbicularis muscle of the eye or at the pre-periosteal level 1. Our studies show that the onset of this effect is not related to the type of filler used or to the delivery system chosen, but it is strictly dependent on the depth of deposition of the HA. When this is deposited at the epi-periosteal level, the incidence is practically nil [6; 9; 26; 27]; instead, when it is placed on a more superficial layer, the occurrence of blue-gray discolorations is higher than 30% [24]. It is also important to specify that the administration of volumes of HA that is too high and the deposition of the filler on superficial planes are to be avoided, as these determine a greater compression of the lymphatic vessels and a greater incidence of the Tyndall effect [10]. Contour irregularities can occur both as early or late manifestations and are observed more frequently above the inferior orbital border [24]. Contour irregularities are most commonly related to injections of excessive volumes, which are often performed too superficially [53; 54]. As highlighted in our review, no major surface irregularities were reported in the treated areas when the filler was injected deeply [26; 27], while they were seen in a higher percentage of the cases when the filler was injected more superficially [24; 25]. Gently massaging the area immediately after the injection can help minimize the presence of surface irregularities; in any case, the gradual dispersion of the filler over time will improve any irregularities. Persistent complications can be resolved by dissolution with hyaluronidase, as in the case of persistent edema or swelling or with the addition of fillers [9; 24; 25]. It should be pointed out, from what was reported by [PERSON] et al., that the use of a modified protocol used in group B of patients enrolled in their study, which includes pre-injection and post-injection cooling of the periorbital area, incision with the displacement of malar fat 10 mm below the orbital border, some gentle back and forth movements during injection, and oral corticosteroid therapy 48 h after surgery, was found to be more effective and safe, with significantly lower complication rates [23].