Elevated urine formaldehyde in elderly patients with primary open angle glaucoma

Abstract

Aim: To investigate the risk factor of primary open angle glaucoma (POAG), which is the leading cause of irreversible blindness worldwide. An abnormally high level of endogenous formaldehyde (FA) has recently been found correlated with cell death and neurodegenerative disease, raising the possibility of a putative correlation of abnormal endogenous FA with POAG.

Methods: Thirty-four elderly patients with POAG and sixteen healthy controls were enrolled. Glaucomatous visual defects were present at both the functional (visual field) and structural [retinal nerve fiber layer (RNFL) thickness] levels. Morning urine samples were obtained and were analyzed by high-performance liquid chromatography (HPLC) to detect the endogenous FA level in a double blind manner.

Results: Patients with POAG (P<0.05) had significantly higher urine FA levels. The urine FA level of patients with severe visual field defects [mean deviation (MD)≥12 dB] was significantly (P<0.001) greater than that of patients with mild to moderate defects (MD<12 dB). By optical coherence tomography (OCT), the superior and inferior RNFL thickness of POAG group was significantly (P<0.001) thinner than in controls. Furthermore, the superior and inferior thinning of the RNFL was correlated with the elevation of urine FA concentration.

Conclusion: Endogenous FA level is positively correlated with the neuronal defects of POAG.

Keywords: Alzheimer's disease; primary open angle glaucoma; urine formaldehyde.

Figure 1. Elevated FA level of patients with POAG and visual field defect

A: Urine FA levels in POAG and control group; B: The distribution of urine FA levels in the control, mild to moderate and severe POAG groups. POAG patients were divided into mild to moderate and severe groups according to the visual field defects (mild to moderate defect, MD<12dB; severe defect, MD≥12 dB). Data was expressed as means±SEM. ^aP<0.05, ^bP<0.01, ^cP<0.001 by t-test and ANOVA.

Figure 2. RNFL thickness of POAG and control groups detected by optical coherence tomography at superior, inferior, nasal and temporal quadrants of optic disc

Total numbers of enrolled people were 50, including control group (n=16), mild to moderate POAG (n=18) and severe POAG (n=16). ^aP<0.05, ^bP<0.01, ^cP<0.001 by ANOVA.

Figure 3. Defect of RNFL correlated with MD value and FA concentration

Scattergrams showing linear regression analysis between MD value and RNFL thickness of superior quadrant (A) and inferior quadrant (B), respectively. Scattergrams showing linear regression analysis between urine FA concentration and RNFL thickness of superior quadrant (C) and inferior quadrant (D), respectively.