revised by increasing the recession of medial rectus muscles in case of esotropia, and recession of lateral rectus muscles in case of exotropia. Similar adjustments can be made to correct the AHP for example in patients with left face turn, the right lateral rectus and left medial rectus is recessed more than the right medial rectus and left lateral rectus.

The Tenotomy Procedure

Advancements in understanding secondary mechanisms involved in the reducing nystagmus amplitude in patients who underwent recession−resection surgery for congenital nystagmus mainly to correct the AHP has led to a new surgical procedure “tenotomy” of extraocular muscle. This procedure has been reported to be beneficial in patients without compensatory mechanisms, also in patients with a null region at or near primary position and in patients with a non-stationary null region (PAN) [61].The tenotomy procedure can be done on both horizontal and vertical rectus muscles based on the dominant plane of the nystagmus.

Following the initial success of the tenotomy procedure in an animal model [62], clinical trials [63, 64] were performed on patients with congenital nystagmus with and without sensory deficits including asymmetric congenital PAN. In the first trial, involving ten patients, binocular visual acuity increased in five patients and remained unchanged in the remaining patients. The eye movement recording data showed an increase in the average foveation times in all nine patients’ fixating eyes. In the second trial, tenotomy was performed on five patients with congenital nystagmus. Visual acuity improved in four of the five patients, but did not improve in a patient with retinal dystrophy.

Summary for the Clinician

■Various surgical procedures are used to treat both the AHP and strabismus seen in patients with congenital nystagmus. Surgical consists mostly of recessions alone or the combination of recessions and resections depending on the amount of head turn and strabismus.

■The surgical plan depends on whether patient has horizontal or vertical AHP or head tilt and the presence or absence of strabismus.Other compensatory need to be taken into consideration before deciding on the type of surgery. For example, if there is dampening of nystagmus mechanisms on convergence, artificial divergence surgery alone can be performed, or it can be combined with Anderson−Kestenbaum like procedures.

References 169

Acknowledgments We acknowledge support from Shery Thomas, Chris Degg, Nagini Sarvananthan, Rebecca McLean, Mervyn Thomas, Mylvaganam Surendran, and Shegufta Farooq. We thank the Nystagmus Network for their continued interest in and support for nystagmus research. We acknowledge the financial support of Ulverscroft Foundation, Medisearch, National Eye Research Centre, and Nystagmus Network.

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■Dissociated deviation (DD) manifests as a slow, intermittent, and variable vertical (DVD), horizontal (DHD), and torsional (DTD) movement. It is usually found in patients with early onset strabismus and profound sensorial anomalies.

■The treatment for patients with DD requires a specific surgical approach to improve the vertical, horizontal, and torsional misalignment simultaneously.

■DVD neither disappears nor improves over time; the aim of treatment is to obtain a latent deviation.

■Symmetric dissociated vertical deviation (DVD), with good bilateral visual acuity (VA), without oblique muscle dysfunction: four surgical alternatives: (1) Bilateral large superior rectus (SR) recession. (2) Bilateral retroequatorial myopexy (posterior fixation) of the SR combined with or without recession of these muscles. (3) Four oblique muscles weakening procedure.(4) Bilateral inferior rectus (IR) resection.

■Bilateral DVD with deep unilateral amblyopia: three available procedures: (1) Unilateral SR recession, (2) Unilateral inferior oblique anterior transposition (IOAT), and (3) Unilateral IR resection or tucking.

■DVD with inferior oblique overaction (IOOA) and V pattern: (1) Bilateral IOAT. (2) Bilateral SR recession added to bilateral inferior oblique (IO) recession.

■DVD with superior oblique overaction (SOOA) and A pattern: (1) Bilateral SR recession, (2) Bilateral SR recession + superior oblique (SO) posterior tenectomy, or (3) Four oblique muscles weakening procedure.

■Symmetric vs. Asymmetric surgeries for DVD: Bilateral symmetric procedures are performed

for cases with bilaterally symmetric DVD. Cases with asymmetric DVD are more common. These cases require asymmetrical techniques.

■Dissociated horizontal deviation (DHD): The main diagnostic sign of DHD is the presence of a horizontal deviation, esotropia (ET), or exotropia (XT) that changes with fixation of each eye, unrelated to di erent accommodation, muscle weakness, or restriction. The technique most used for DHD is unilateral lateral rectus (LR) recession. Retroequatorial myopexy (posterior fixation) of the LR with recession of this muscle is recommended by certain authors. Bilateral LR recession is indicated when XT is bilateral; unilateral or bilateral medial rectus (MR) recession when the patient exhibits ET instead of XT. Performing an LR recession added to MR advancement is a valid alternative in cases with previous surgery on the medials.

■Dissociated torsional deviation (DTD): Children with DD frequently have head turn but they also have head tilt. The head tilt can be toward the shoulder of the fixing eye (direct tilt) or toward the contralateral side (inverse tilt). We have to take into account the head tilt to attempt to improve the head position when performing surgery.

■Obtaining long-term control of the deviation in patient with DD is di cult; a successful outcome in the postoperative period does not guarantee the final alignment. In treated patients with DD, some kind of movement is always detected when performing the cover test. DVD never disappears completely and the dissociated behavior in DHD also persists when testing under slow cover test.