In this retrospective review, we examined patients with unilateral mild-to-moderate ptosis undergoing MMCR with two different tarsus resection lengths. For unilateral ptosis surgery, the symmetry of the outcome was especially important. From an aesthetic point of view, the symmetry of MRD1 and TPS were both pivotal. This study aimed to highlight the role of tarsal platform show (TPS) in optimizing the aesthetic outcome of MMCR for unilateral mild-to-moderate ptosis. Compared to external approach such as levator muscle resection which was adjustable during procedure, it is difficult to perform graded adjustment of lid height during MMCR procedure. This makes the predictability and symmetry of the outcome even more important. As we can see in the results, the postoperative symmetry of the surgery was satisfactory when the length of tarsectomy was well-adjusted. The rate of symmetry in this study (88.3%) is comparable with those in other reports that used different techniques and algorithms (10, 12–17).
The internal approach for the correction of blepharoptosis was first mentioned in 1961 by Fasanella and Servat (18). MMCR was designed by Putterman and Urist soon after (1), suggesting resection length ranged from 8 to 9 mm. The resection amount depends on the response to phenylephrine testing. Since then, MMCR has come with a lot of modified surgical designs (2–4). Later on, Perry et al. defined a modified algorithm which included tarsectomy into his procedure (7). They recommended a 9-mm resection of Muller's muscle and conjunctiva with additional tarsectomy which contributed a 1:1 elevation to eyelid position. A recent study also found that MMCR with tarsectomy could be a safe and effective procedure for treating congenital ptosis (19). It is worth noting that previous studies had revealed a 4:1 ratio of Muller's muscle resection length to eyelid elevation (17, 20). However, according to our clinical observations, this 4:1 algorithm could not be applied properly in most of our Asian patients. This may be due to the greater volume and weight of preseptal fat in the Asian population. Thus, we applied additional tarsectomy to achieve better clinical outcome.
The exact mechanism by which MMCR works for ptosis remains to be elucidated (5). As for the results of our study, the mechanism and efficacy of this surgical design can be discussed from two different perspectives: MMCR and tarsectomy. Regarding MMCR, the mechanism may be related to plication or scarring of the posterior lamella. Zauberman et al. believed that resecting more Müller muscle did not associate with a higher MRD1 elevation (11). As for tarsectomy, it was reasonable to assume that each 1 mm of tarsus resected could lead to an approximate 1-mm MRD1 elevation since the tarsus serves as a skeleton for eyelid tissue rather than a contractile tissue. Our data showed that mean changes in MRD1 for 8-mm MMCR with 1-mm tarsectomy and 2-mm tarsectomy were 1.66 and 2.72 mm respectively. This result revealed that an extra 1 mm tarsus resected was equivalent to 1.06 mm of change in MRD1 which was compatible to our conjecture. In conclusion, the mechanism for MMCR with tarsectomy to correct lid position include not only shortening of the posterior lamella (21) but also plication of the levator aponeurosis.
Reducing variability and improving predictability have always been important issues for a surgical design. However, as mentioned above, MMCR surgery does not appear to have a purely mechanical mechanism, causing difficulty in titrating Müller muscle resection length to predict outcomes. On the other hand, tarsus works as a scaffold for eyelid tissue, indicating a potential possibility to control outcome by adjusting tarsus resection length under a 1:1 ratio.
Our results may have implications for understanding the predictability of this procedure. As shown in Fig. 3, analysis after adjustment revealed concentrated distributions for both groups and more importantly, there was no overlapping of value ranges between the two gorups. These results suggested that 1- and 2-mm tarsectomies could lead to significantly different ranges of eyelid elevation, making it possible for surgeons to decide the amount of tarsectomy according to the target value. It would be reasonable to set a cut point at approximately 2.1 mm between the two groups. If the patient has a preoperative difference of MRD1 greater than 2.1 mm between his two eyes, MMCR with at least 2-mm tarsectomy would be recommended. On the contrary, if the patient has a difference of MRD1 less than 2.1 mm between his two eyes, MMCR with 1-mm tarsectomy would be the treatment of choice to achieve a symmetrical outcome. By and large, the underlying condition of the patient, levator muscle function, and comprehensive consideration of the surgeon should as well be important factors for final decision making.
In our study, we used 9 mm reference markers to set the measurement scale, which makes our data even more accurate and reliable. However, limitations of this study include its retrospective nature of data analysis, lack of a masked observer, and the limited sample size. In addition, we did not include severe cases. If we do so, we may have more than two different tarsus resection lengths, making it even more likely to clarify the efficacy of tarsectomy. Further investigation would include an expanded case series with different tarsus resection lengths to further demonstrate its efficacy and potential predictability, hoping to build a comprehensive algorithm for tarsectomy length and expected MRD1 elevation.