Misinnervation in third nerve palsy: Vertical synergistic divergence

A 10-year-old child presented with complaints of drooping of upper lid since birth with squint. The child had a best corrected visual acuity of 20/60 in right eye (RE) and 20/20 in left eye (LE). Both the eyes were anatomically normal with normal fundus and no signifi cant ocular torsion. The pupils in both the eyes were normal in size and reacting to light. On ocular motility examination, patient had right hypotropia in primary position with ptosis. On levoversion, he had large left hypertropia with marked superior oblique overaction in RE; underaction of inferior oblique in ductions was noted. On dextroversion, patient had right hypertropia with LE showing superior oblique overaction, a limitation of RE depression [Fig. 1]. Patient showed both eyes superior oblique overaction in dextro and levo depression. The elevation which was restricted in RE was apparently normal in dextroversion. Patient had moderate ptosis (MRD1= 2.5 mm) in RE with poor levator function (4 mm) and frontalis overaction. A lid retraction was noted in downgaze. Also, an A patt ern was noted. However, on att empted elevation of LE, there was a downshoot of RE [Fig. 1]. The head tilt test was done but did not reveal any signifi cant change [Fig. 2]. Patient was advised surgery but was lost to follow-up. A forced duction test could not be performed because the child was uncooperative.

A 10-year-old child presented with complaints of drooping of upper lid since birth with squint. The child had a best corrected visual acuity of 20/60 in right eye (RE) and 20/20 in left eye (LE). Both the eyes were anatomically normal with normal fundus and no signifi cant ocular torsion. The pupils in both the eyes were normal in size and reacting to light. On ocular motility examination, patient had right hypotropia in primary position with ptosis. On levoversion, he had large left hypertropia with marked superior oblique overaction in RE; underaction of inferior oblique in ductions was noted. On dextroversion, patient had right hypertropia with LE showing superior oblique overaction, a limitation of RE depression [ Fig.  1]. Patient showed both eyes superior oblique overaction in dextro and levo depression. The elevation which was restricted in RE was apparently normal in dextroversion. Patient had moderate ptosis (MRD 1 = 2.5 mm) in RE with poor levator function (4 mm) and frontalis overaction. A lid retraction was noted in downgaze. Also, an A patt ern was noted. However, on att empted elevation of LE, there was a downshoot of RE [ Fig. 1]. The head tilt test was done but did not reveal any signifi cant change [ Fig. 2]. Patient was advised surgery but was lost to follow-up. A forced duction test could not be performed because the child was uncooperative.
Aberrant regeneration is found in congenital third nerve palsies. [1] Wilcox et al., [2] performed electromyography in a boy with congenital adduction palsy and synergistic divergence. They concluded that the bizarre movements were secondary to a misinnervation by a branch of the third nerve with nil or minimal nerve supply by the sixth nerve. Cases with vertical retraction syndrome have also been reported where there is retraction during att empted depression.
The most common acquired eye muscle misdirection syndrome involves the structures innervated by a single cranial nerve, the oculomotor nerve, and is manifested by abnormal patt erns of pupillary, lid, and ocular movements. [3] An important alternative to the misdirection hypothesis involves ephaptic transmission or side-to-side interaxonal cross stimulation. However, ephaptic transmission has not been demonstrated in the third nerve. [3] A third theory states that peripheral nerve injury induces retrograde changes that result in central nervous system (CNS) reorganization. [3] This central reorganization presumably produces synkinesis by unmasking previously encoded connections in the brainstem or higher control center areas.
Currently, congenital cranial dysinnervation disorders (CCDDs) is the term given to such disorders. [4] The CCDDs result from aberrant innervation of the ocular and facial Our case shows a bilateral superior oblique overaction secondary to third nerve paresis. The downshoot can be explained by the aberrant regeneration of the third nerve with paresis of superior rectus. This prevents any retraction in att empted downgaze. Our case therefore represents a case of vertical synergistic divergence; a variant of vertical Duane's retraction syndrome or similar to horizontal synergistic divergence with no retraction.

Minimally invasive Knapp's procedure: Modifi ed fornix incision approach
Dear Editor, Minimally invasive surgical procedures reduce tissue trauma, postoperative patient discomfort, hospital stay, working disability, and the economic impact of surgery. [1,2] The majority of surgeons use the limbal approach incision in squint surgery, fi rst described by Harms [3] in 1949 and later popularized by von Noorden. [4] A lot of incisions have been described for simple recession and resection of muscles. Small and micro incisions have been advocated in strabismus surgery too. [5][6] Traditional incision for Knapp's procedure is a large limbal U-shaped incision [5] similar to the limbal incision but slightly larger. [1,2] We describe Knapp's procedure via fornix incisions to make it a minimally invasive conjunctival approach. The incisions may be left unsutured too since they would be in the cul de sac.
The patient was prepared for the surgery under general anesthesia. Aft er putt ing the speculum in place, a 6-0 vicryl stay suture was passed at 10.30 o' clock in right eye and the eyeball was pulled at an angle. Around 8 mm from the limbus in the superotemporal quadrant a conjunctival incision concentric to the limbus was placed [ Fig. 1]. The conjunctiva and Tenon's was separated and the lateral rectus muscle was hooked. The muscle was freed from its att achments with the conjunctiva, intermuscular ligament and 6-0 vicryl sutures were passed at the insertion. The muscle was cut at the insertion and resutured back near the superior rectus concentric to the limbus. A similar incision was put in the superonasal quadrant and the medial rectus was hooked, sutured, separated and reinserted parallel to the superior rectus on the nasal side concentric to the limbus A large range of incisions, limbal, cul de sac and more recently minimally invasive incisions have been described in strabismus surgery. [5][6] Minimally invasive strabismus surgery (MISS) is becoming popular. The purpose of these smaller and  smaller incisions is to reduce the hyperemia, for bett er healing and earlier patient rehabilitation. [6] In a study of comparison of limbal incision with the minimally invasive incision, Mojon et al., [6] found that the MISS technique was bett er than the limbal approach as the former had less dissection, less chances of limbal ischemia and therefore less postoperative tissue scar. However, with a fornix incision all the merits of MISS are available as pointed out by Kushner. [7] We, therefore used the fornix incision for the classic Knapp's procedure and called it minimally invasive Knapp's procedure. Such a possibility has also been hinted at by Coats et al., who have told about both the larger incision and small butt onhole incisions for transposition surgeries. [8]