MEDS or “double elevator” palsy is a descriptive term denoting a congenital deficiency of monocular elevation that is equal in abduction and adduction [5, 6].Luo et al reported the mean pre- and postoperative deviation is 32.0±8.0 PD and 3.8±8.0 PD (P<0.001), respectively. In the current study, these values were 15.31±11.03 PD and 3.22±1.2 PD (P=0.00), respectively . Luo et al. also reported similar findings .
The genetic basis of MED is yet unclear. Previously, it was speculated to arise due to a supranuclear abnormality [7, 8].In the current study, paediatric (64.5%) revealed phenomena similar to those in the study by Luo et al. .We also reported a jaw winking phenomena in 14 (22%) cases, which has not been shown previously.
The Bell phenomenon reported in identical twins  was not observed in the current study.Khan et al. reported a case with double elevator weakening for unilateral congenital superior oblique palsy with ipsilateral superior rectus contracture and lax superior oblique tendon .
Nagpal et al. reported congenital double elevator palsy with sensory exotropia. . Verma et al. reported a rare case of golden harr syndrome associated with MEDS . Khawam et al. demonstrated coexistence of MEDS with Duane’s retraction syndrome . Munoz et al. reported acquired MEDS in association with pineocytoma .
Typically, the choice of surgery in the management of MED depends on the FDT results. In patients with a positive FDT, inferior rectus recession is the first choice of management. If there is no restriction, the transposition of the medial and lateral rectus muscles to the superior rectus muscle could be performed (Knapp procedure). Other options include resection of the ipsilateral superior rectus muscle or recession of the contralateral superior rectus muscle [1, 14, 15].
The surgery for double elevator palsy must be customised according to FDT, FGT, and Bell’s reflex. The outcomes are favourable with appropriate surgical planning, as reported by Bagheri et al. .
According to Metz et al., superior rectus muscle and inferior oblique muscle insufficiency are the primary factors in the aetiology of congenital double ocular elevator palsy. Vertical rectus recession and superior oblique tenectomy on paretic eyes are effective surgical procedures for the treatment of the disease .Burke et al. reported that vertical transposition of the horizontal recti (Knapp procedure) could be applied to treat double elevator palsy due to its effectiveness and long-term stability .
The Knapp procedure had an increasing effect in a time-dependent manner, but the amount of vertical correction was not correlated with the size of the preoperative vertical deviation and was less predictable when a prior IR had been performed. The current study had similar findings (P=0.06).
Caldeira et al. studied a similar technique (Knapp) in early-age acquired cases. This transposition procedure could reduce or eliminate the distal and proximal vertical deviation; similar findings with increased effects were observed in the current study in a time-dependent manner .
Kocak-Altintas et al. and Yurdakul et al. also studied Knapp procedure or inferior rectus recession without any comparison. We proposed that the surgical intervention should be selected according to DEP clinical features. The surgical effect of transposition surgery may be enhanced by IR recession; a similar finding was reported previously [19, 20].
Li et al. tried Knapp and modified Knapp procedure with Foster sutures for this condition . Snir combined rectus muscle transposition and posterior fixation suture for MEDS .Luo et al. compared Knapp and Froster procedures and revealed that the surgery selection is based on the angle of vertical deviation.