Nystagmus characteristics and their impact on pattern-reversal VEP in patients with albinism.

PURPOSE

To describe the association between nystagmus characteristics and pattern-reversal VEP (prVEP) P100 amplitude and peak time in patients with albinism.

METHODS

We analyzed the prVEP (60' and 15' checksize) and nystagmus recordings from 47 patients with albinism, 17 with a relatively good visual acuity (≤ 0.3 logMAR), and 30 with a relatively poor visual acuity (≥ 0.6 logMAR). The nystagmus waveforms were classified into two types: dominantly pendular and dominantly jerk. We correlated the nystagmus type, amplitude, frequency, and percentage of low velocity (PLOV) to P100 amplitude and peak time.

RESULTS

For most patients (87%), reproducible responses were observed for the large checks (60'). Among patients with good visual acuity, 94% had reproducible responses of which the majority (82%) of P100 amplitudes fell within the normal reference range. In contrast, although 83% of patients with poor visual acuity showed reproducible responses, only a minority (17%) of P100 amplitudes were within the normal range. The P100 amplitude to 60'check sizes was statistically correlated with PLOV (r = 0.58, p < 0.0001), nystagmus type (r = -0.55, p < 0.0001), and nystagmus amplitude (r = -0.39, p = 0.0092). Patients with relatively good visual acuity and jerk nystagmus exhibited the highest PLOV and the largest P100 amplitude (p < 0.0001). In contrast, there was no significant correlation between P100 peak time and any nystagmus parameters in patients with good or poor visual acuity.93% normal peak time. For the small checks (15'), 76% of patients with good visual acuity, still showed reproducible responses, with the majority (71%) of P100 amplitudes falling within the normal reference range. In contrast, among patients with poor visual acuity, only 3% (1 patient) showed reproducible responses, but with amplitudes below the normal range. For the patients with good visual acuity, PLOV showed a significant correlation with P100 amplitude. P100 peak time was normal for 77% (10/13) of these patients.

CONCLUSIONS

For the prVEP with 60' checks, nystagmus in patients with albinism predominantly affects the P100 amplitude but not the P100 peak time. For 15' checks the amplitude is often so small that clear responses are no longer discernable, especially in patients with poor visual acuity.