Ginkgo May Slow Visual Field Loss in Normal Tension Glaucoma

Glaucoma and Altered Ocular Blood Flow

There are two leading theories to explain the mechanisms underlying glaucoma. The first, a mechanical theory, postulates that increased intraocular pressure (IOP) stretches the lamina cribrosa and damages retinal ganglion cell axons. The second theory suggests that an inadequate vascular supply, such as reduced blood flow to the optic nerve, results in ganglion cell damage.

Although there’s agreement that IOP reduction is a beneficial treatment in both high and normal tension glaucoma (NTG), the vascular theory may be more relevant in explaining NTG pathogenesis. In support of this idea is the observation that glaucoma continues to progress in many patients despite IOP reductions, and the fact that a reduction in blood flow often precedes optic nerve damage. Additionally, risk factors for NTG – such as low blood pressure, orthostatic hypotension, nighttime hypotension, migraine and sleep apnea – result in reduced blood flow to the brain.

Ginkgo biloba: Mechanisms & Research Findings

Ginkgo biloba leaf extracts have been used in Chinese traditional medicine for 5000 years. In recent times, Ginkgo has been reported to be neuroprotective for retinal ganglion cells in animal models of chronic glaucoma, and clinically shown to increase ocular blood flow and reduce visual field damage in NTG patients in the short term. Ginkgo has demonstrated antioxidant activity, and may increase blood flow by changes in blood viscosity and inhibition of platelet activating factor.

The current study (1) was conducted to evaluate the long-term effects of G. biloba extract on progression of visual field defects in patients with NTG.

Study Design

In this retrospective study, 42 eyes of 42 NTG patients were evaluated for more than a 4-year period before and 4 years after receiving 80 mg of Gingko biloba extract twice daily (total of 160 mg per day). Patients had at least 5 visual field (VF) tests in the 4 years prior to and after supplementation. The VF tests were routinely preformed at diagnosis, 3 months later, and every 6-12 months thereafter with the Humphrey VF Analyzer. The change of progression rate was evaluated using mean deviation, pattern standard deviation, and visual field index. The time course of mean total deviation in 10 zones corresponding to the glaucoma hemifield test was analyzed using a linear mixed effects model with unequal random effects variance.

Results

The mean follow-up period was 12.3 years. After Ginkgo treatment, the regression coefficients of the mean deviation (MD), pattern standard deviation (PSD) and visual field index (VFI) change improved significantly (p<0.001). Before and after treatment regression coefficient values were as follows:

• MD,  -0.619 and –0.379 dB/yr
• PSD, -0.626 and 0.342 dB/yr
• VFI change, -2.351 and -1.212 %

In zone 1, after Ginkgo biloba administration, visual field damage was significantly slowed (rate of the regression coefficient of mean total deviation change significantly increased; p<0.05).

Comment

The authors conclude that Ginkgo biloba extract slowed the progression of visual field damage in patients with NTG, especially in zone 1 which corresponds to the superior central field. A number of studies have shown that the superior central field is the main location of visual field defects in NTG, whereas high tension glaucoma defects tend to be more diffuse (2,3).

No ocular or systemic adverse effects were reported among patients during follow-up in this retrospective study cohort. This appears to be the first study to compare visual field progression in the same patients after Ginkgo supplementation, and the results suggest that Ginkgo biloba may be useful as a complementary treatment for glaucoma.

References

1. Lee J et al. Effect of Ginkgo biloba extract on visual field progression in normal tension glaucoma. J Glaucoma [Epub May 12, 2012].  
2. Ahrlich KG et al. Visual Field progression differences between normal-tension and exfoliative high-tension glaucoma.  Invest Ophthalmol Vis Sci 51:1458-63, 2010.
3. Araie M et al. Visual field defects in normal-tension and high-tension glaucoma. Ophthalmol 100:1808-14, 1993.