Purpose: The purpose of the study is to investigate diagnostic criteria and treatment methods for patients with congenital periodic alternating nystagmus (PAN). Methods: A retrospective analysis was performed of clinical findings and serial eye movement recordings of patients with congenital PAN. Eighteen patients observed from 1983 through 1996 and diagnosed with congenital PAN are included. Five of these have ocular or oculocutaneous albinism. Nine of the 18 patients were treated. Three had Kestenbaum operations before referral to the authors, one was treated with baclofen, and five had large recessions of the four horizontal recti. The studied parameters included visual acuity (VA) and abnormal head posture (AHP); temporal aspects of PAN cycle, nystagmus waveforms, frequency, amplitude, and velocity; as well as mean foveation fraction, a mean percentage of the nystagmus cycle spent at retinal slip velocities less than 10°per second. Results: The authors diagnosed PAN in 9% of patients with congenital nystagmus, although most had not been diagnosed with PAN before referral, despite changing nystagmus. Sixteen patients had AHP, typically shifting. The PAN cycle was of variable duration, often with asymmetric right- and left- beating components. Although horizontal jerk nystagmus with accelerating slow phase was predominant, other waveforms were encountered in the active phase of PAN. In the quiet phase (close to null zone), similar, but less intense, oscillations than those in the active phase were characteristic. Half of the patients showed a combination of waveforms in both phases. Baclofen treatment was unsuccessful. Patients who had Kestenbaum procedures remained with AHP in the original or opposite direction, without change in nystagmus or VA. Large recessions of four horizontal recti proved uncomplicated. This treatment improved, at least for several years, AHP and VA and caused favorable changes in nystagmus parameters in all patients. Mean foveation fractions increased significantly after surgery. Conclusions: Congenital PAN often is underdiagnosed. Differing waveforms may indicate PAN. Evaluation of nystagmus, especially before surgery, for at least 3 minutes, preferably with eye movement recordings, is necessary to diagnose PAN and perhaps prevent Kestenbaum procedures, which seem inappropriate. Large horizontal recti recessions seem to provide safe and promising treatment.
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