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12 Management of Congenital Nystagmus with and without Strabismus |
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Anomalous Head Posture in Idiopathic |
Correction of Anomalous Head Posture in |
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Infantile Nystagmus |
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Idiopathic Infantile Nystagmus with Anderson- |
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Kesternbaum Surgery |
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Horizontal head turn |
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With visual effort |
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After surgery |
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Adult |
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Vertical and horizontal head turn with esotropia |
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Bi-directional Alternating Head Turn in MLN |
Measurement of head turn using Harms wall |
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Left head turn |
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Fig. 12.5 Abnormal head posture (AHP) of a child with idiopathic congenital nystagmus (a) without visual e ort and (b) with increased head turn while pointing at pictures on the Lang stereo test. Panel (c) shows a patient with idiopathic congenital nystagmus without head posture when there is no visual e ort and (d) a prominent abnormal head posture when reading at distance. Spontaneous alternating head turn to the right (e) and left (f) in a patient with MLN. Panel (g) shows a patient with idiopathic congenital nystagmus with approximately 45° head turn to the left before surgery and with straight head position (h) after Anderson– Kestenbaum procedure.A patient with oculo-cutaneous albinism and chin depression, face turn to the right and left esotropia before surgery (i) and after surgery (j). An accurate method of measuring AHP is achieved by using the Harms Wall (k) where the degree of head turn is measured by the amount of displacement of the cross observed on the tangent screen. The cross is projected from a light source fixed on the head
■Eye movement recordings have a characteristic slow phase with exponentially decreasing or linear velocity
■Amplitude of nystagmus decreases in adduction and increases in abduction, with the fast phase of nystagmus toward the side of fixating eye
12.1.3Congenital Periodic Alternating Nystagmus (PAN)
Congenital PAN is classified as a variant of congenital nystagmus according to the CEMAS classification. Congenital PAN is discussed as a separate entity because
12.1 Overview 159
it has specific implications for management which are di erent from other forms of nystagmus.
The frequency of congenital PAN is variably reported in the literature. Gradstein et al. [3] in a retrospective analysis of approximately 200 congenital nystagmus patients with and without sensory deficits found 18 patients (9%) with a diagnosis of PAN. Five of these 18 patients had albinism. AHP was seen in 16 of the 18 patients. Shallo-Ho man et al. [4] in a prospective study involving 18 patients with congenital nystagmus without sensory deficits found that seven patients (39%) had PAN. Abadi and Pascal [5] found 12 patients with PAN in 32 patients with oculocutaneous albinism (37.5%). These 12 patients did not exhibit AHP nor had dampening of nystagmus on convergence (Fig. 12.6).
Congenital PAN is most often missed or misdiagnosed if not properly investigated. The main reasons for di culties in recognizing PAN are:
PAN. Absence of alternating AHP in congenital PAN is possibly due to the asymmetry of the PAN cycle, nystagmus beating longer in one direction than the other, and also the unequal intensities of nystagmus in the two phases.
12.1.3.1Clinical characteristics of congenital periodic alternating nystagmus
■Onset in infancy.
■Nystagmus horizontal and conjugate.
■Eye movement recording shows a characteristic active phase with right/left beating nystagmus followed by a quite transition phase and then an active left/right beating nystagmus.
■The AHP is usually bidirectional.
■Long cycle duration: The cycle duration of the congenital PAN is variable lasting mostly between 2 and 7 min. Thus, ocular motility examination (clinical or with eye movement recordings) must extend over a prolonged time period.
■The absence of alternating head turn: Classically, a clinical sign assisting in the diagnosis of congenital PAN is the alternating or bidirectional head turn. Gradstein et al. [3], on the contrary, have reported that the majority of patients with congenital PAN used a predominant head posture rather than an alternating head posture.Abadi and Pascal [5] also reported the absence of AHP in all the 12 patients diagnosed with congenital
Summary for the Clinician
■Familiarity with the clinical characteristics of congenital nystagmus, MLN, and congenital PAN will minimize the chances of misdiagnosing these conditions and plan proper management of these conditions.
■Electrodiagnostics: both ERG and VEP should be done in all patients with congenital nystagmus to find a cause for the congenital nystagmus.
■Eye movement recording aids in di erentiating congenital nystagmus from MLN and congenital PAN.
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RIGHT BEATING |
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Fig. 12.6 Original eye movement recordings of a patient with idiopathic congenital periodic alternating nystagmus (PAN) of the right and left eye showing left beating nystagmus, a quiet phase and right beating nystagmus. Eye movements to the right are represented by an upward deflection, and eye movements to the left by a downward deflection. Arrows indicate blinks