Pattern visual evoked potential and foveal sensitivity in amblyopia

Amblyopic eyes show impaired visual functions such as poor visual acuity and reduced foveal sensitivity. The purpose of this study was to determine the association between foveal threshold and visual evoked potentials (VEP) in strabismic and anisometropic amblyopia.

Forty-five subjects (age range: 7-28 years, 43.3% female) including 15 strabismic and 15 anisometropic amblyopes, and 15 age-similar control subjects participated in this study. Each subject had pattern visual evoked potentials and foveal threshold recorded in each eye using RetiScan (Roland Consult, Germany) and Humphrey Visual Field Analyzer II (HFA II; Carl Zeiss Meditec Inc., Dublin, CA), respectively. These outcomes were compared among the amblyopic eyes, their fellow eyes, and the control eyes.

Compared to the amblyopic eyes (Mean ± SD: 33.4 ± 3.48 dB), the foveal threshold was higher in fellow eyes (37.0 ± 2.04 dB, p = 0.0002) and in control eyes (38.7 ± 0.96 dB, p < 0.0001). Strabismic amblyopes had a lower foveal threshold than anisometropic amblyopes (31.8 ± 3.86 vs. 35.0 ± 2.17 dB, p = 0.005). Relative to the P100 peak time in fellow eyes (1° checks:116.1 ± 9.00 ms; 0.25° checks:118.8 ± 5.67 ms), amblyopic eyes had delayed P100 peak times for both 1° (122.7 ± 11.4 ms, p < 0.0001) and 0.25° (130.4 ± 11.2 ms, p < 0.0001) check sizes. There were also significant differences in P100 peak time between amblyopic and control eyes (1°:122.7 ± 11.4 vs.112.4 ± 5.01 ms, p = 0.15; 0.25°:130.4 ± 11.2 vs.113.9 ± 5.71 ms, p < 0.0001) and between fellow and control eyes (0.25°:118.8 ± 5.67 vs.113.9 ± 5.71 ms, p = 0.009). Amblyopic eyes exhibited lower N75-P100 amplitudes than fellow eyes (1°:12.6 ± 7.96 vs.15.9 ± 8.82 µV, p = 0.01; 0.25°:10.6 ± 6.11 vs. 15.8 ± 10.6 µV, p = 0.001) and control eyes (0.25°: p = 0.0008). Foveal threshold correlated negatively with P100 peak time (1°: r = -0.45, p = 0.002 and 0.25°: r = -0.58, p < 0.0001) and positively with N75-P100 amplitude responses (1°: r = 0.42, p = 0.004 and 0.25°: r = 0.52, p = 0.002).

Amblyopic eyes showed reduced pattern VEP amplitudes and delayed peak times with significant associations with the foveal sensitivity. However, the VEP measures overlapped extensively between amblyopic and control eyes with no apparent criterion value for optimal discrimination, suggesting that foveal sensitivity might be a better discriminator of amblyopia than pattern VEP.