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D. Yang, C. Xin, H. Wang, N. Wang; Ascorbic Acid Concentration in Tear Is Increased in Post-Filtering Surgery Glaucoma Patients With Thin-Wall Blebs. Invest. Ophthalmol. Vis. Sci. 2010;51(13):591.
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The use of anti-metabolites improved the success rate of trabeculectomy remarkably. However, it also increased the incidence of thin-wall blebs. We suppose that the aqueous humor may egress from the thin-wall blebs into the tear. Since the concentration of ascorbic acid in aqueous humor is ten times greater than that in tears. We evaluated the changes of ascorbic acid concentration in tear by ultraviolet spectrophotometer in patients with thin-wall blebs, thick wall blebs and normal subjects to testify our hypothesis.
21 patients (21 eyes) with successful filtering surgery prior to the study and 15 controls (15eyes) were enrolled in this study. The 21 patients were divided into a thin-wall group (N=10) and a thick-wall group (N=11) according to the morphology and UBM image of the filtering blebs. The ascorbic acid concentrations in tear of all the subjects were evaluated by ultraviolet spectrophotometer. An ANOVA with post-hoc LSD multiple comparisons were used to analyze the data among the three groups. A P<0.05 was required for results to be considered statistically significant.
The ascorbic acid concentration of the thin-wall bleb group (mean±SEM, 713.53±132.32µg/ml) was significantly increased as compared with the thick-wall bleb group and control group (541.43±81.36µg/ml and 470.95±86.85µg/ml, p<0.001). The ascorbic acid concentration of the thick-wall bleb group and control group were not significantly different (p=0.085).
This study shows that aqueous humor is able to pass through the thin-wall blebs, penetrate into the tear and change the tear composition. Changes of ascorbic acid concentration in tear in thin-wall bleb patients may be the cause of some side effects of glaucoma filtering surgery. These data should be taken into consideration of long-term care of glaucoma patients post-filtering surgery.
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