Head-down Posture Induces PERG Alterations in Early Glaucoma

Purpose: To probe susceptibility of retinal ganglion cells (RGC) to physiological stressors associated with moderate head-down body tilt in patients with suspicion of glaucoma or early manifest glaucoma (EMG). Methods: One hundred nine subjects with best corrected visual acuity (BCVA) >= 20/20 and no disease other than glaucoma [glaucoma suspects (GS) = 79, EMG = 14, normal controls (NC) = 16 and comparable age range were tested. Noncontact intraocular pressure (IOP), pattern electroretinogram (PERG), and brachial blood pressure/heart rate measurements were performed in 3 consecutive conditions (similar to 0038 min apart): seated (baseline), - 10-degree whole body head-down tilt (HDT), and seated again (recovery). PERG amplitude and latency, IOP, and systolic/diastolic blood pressures, heart rate, calculated mean central retinal artery pressure, ocular perfusion pressure, and systolic/diastolic perfusion pressures were evaluated. Results: During HDT, IOP significantly (P < 0.001) increased in all groups approximately to the same extent (approximately 20%). PERG amplitude did not change in NC but decreased significantly (P < 0.001) in patients (GS, -25%, EMG -23%). PERG phase become delayed in NC (-1.6%, P = 0.04) but more so in patients (GS, -2.7%, P < 0.001; EMG, -6.0%, P < 0.001). The proportion of patients with PERG alterations significantly (P < 0.05) exceeding those occurring in age-adjusted and baseline-adjusted NC were, GS: amplitude 20%, phase 15%; EMG: amplitude 14%, phase 50%. All measures recovered baseline values after HDT. Conclusions: Moderate HDT induces temporary worsening of RGC function in a subpopulation of GS and EMG patients. This noninvasive protocol may help disclose abnormal susceptibility of RGCs in a subset of the patients at risk of glaucoma.