April 2014
Volume 55, Issue 4
Free
Letters to the Editor  |   April 2014
Author Response: Ginkgo biloba Extract Improves Visual Field Damage in Some Patients Affected by Normal-Tension Glaucoma
Author Affiliations
  • Xinxing Guo
    State Key Laboratory of Ophthalmology, Zhongshan Ophthalmic Center, Sun Yat-sen University, Guangzhou, China;
  • Mingguang He
    State Key Laboratory of Ophthalmology, Zhongshan Ophthalmic Center, Sun Yat-sen University, Guangzhou, China;
  • Mehul Patel
    University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, United States; and
  • Nathan G. Congdon
    State Key Laboratory of Ophthalmology, Zhongshan Ophthalmic Center, Sun Yat-sen University, Guangzhou, China;
    ORBIS International, New York, New York, United States. E-mail: Ncongdon1@gmail.com
Investigative Ophthalmology & Visual Science April 2014, Vol.55, 2418. doi:10.1167/iovs.14-14271
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      Xinxing Guo, Mingguang He, Mehul Patel, Nathan G. Congdon; Author Response: Ginkgo biloba Extract Improves Visual Field Damage in Some Patients Affected by Normal-Tension Glaucoma. Invest. Ophthalmol. Vis. Sci. 2014;55(4):2418. doi: 10.1167/iovs.14-14271.

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      © ARVO (1962-2015); The Authors (2016-present)

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We thank Quaranta et al. 1 for their interest in our publication on the effect of Ginkgo biloba extract on visual field and contrast sensitivity in Chinese patients with normal-tension glaucoma. We agree that differences in protocol and patient selection between the 2 studies might potentially explain the different outcomes. 2,3 Racial differences must also be considered. 
Regarding the eligibility criteria for intraocular pressure (IOP) in our article, 2 we defined normal-tension glaucoma (NTG) on the basis of maximum IOP ≤ 20 mm Hg in both eyes during five consecutive diurnal measurements. Such criteria are widely adopted in clinical trials of normal-tension glaucoma 4 and are generally consistent with the description of the study by Quaranta and colleagues 3 (they report having used IOP measurements “made from 8 AM to 6 PM, every 2 hours by Goldmann applanation tonometer.” No mention is made of nighttime measurements in their original manuscript). 3  
The purpose of recruiting only newly diagnosed NTG patients in our study was to ensure that patients had not been previously treated with Ginkgo biloba extract (GBE), which is common in our setting. While NTG may be progressive, this need not be included among diagnostic criteria. Previous studies 5 have demonstrated that a substantial proportion of NTG patients show no progression in their visual fields within 5 years. 
Regarding our not having excluded patients receiving systemic medications, only 2 of the 28 patients enrolled received such treatments (antihypertensive drugs in both cases). Excluding these patients had no effect on our results. Topical pressure-lowering therapy was administered to our patients as it has been proven to be effective in slowing field progression, 5 and we considered it to be the standard of care, which could not ethically be withheld. We are aware of no evidence that concomitant topical medication use interferes with GBE's effectiveness. 
Quaranta et al. 3 mention investigating patients for Raynaud's phenomenon, but since neither of our studies used this as a criterion for enrollment or reported it as a covariate, 2 this is of uncertain relevance. 
We found no effect of GBE on either visual field or contrast sensitivity. Our study's power to have identified a difference as large as that observed by Quaranta et al. 3 was 80%. Thus, we cannot agree that our study did “not allow [us] to conclude that GBE is not effective,” 1 as in this setting GBE treatment was in fact without measurable effect on our main trial outcomes. We must further disagree with the assertion by Quaranta et al. 1 that their data “strongly support” the hypothesis that GBE improves visual field in NTG patients by improving ocular perfusion, as their original article did not in fact measure this parameter. In view of our conflicting results, further studies with longer administration of GBE appear warranted, particularly in view of its widespread use. 
References
Quaranta L Riva I Floriani I. Ginkgo biloba extract improves visual field damage in some patients affected by normal-tension glaucoma. Invest Ophthalmol Vis Sci . 2014; 55: 2417. [CrossRef] [PubMed]
Guo X Kong X Huang R Effect of Ginkgo biloba on visual field and contrast sensitivity in Chinese patients with normal tension glaucoma: a randomized, crossover clinical trial. Invest Ophthal Vis Sci . 2014; 55: 110–116. [CrossRef] [PubMed]
Quaranta L Bettelli S Uva MG Semeraro F Turano R Gandolfo E. Effect of Ginkgo biloba extract on preexisting visual field damage in normal tension glaucoma [discussion in Ophthalmology . 2003; 110: 362–364]. Ophthalmology . 2003; 110: 359–362. [CrossRef]
Krupin T Liebmann JM Greenfield DS Rosenberg LF Ritch R Yang JW. The Low-pressure Glaucoma Treatment Study (LoGTS) study design and baseline characteristics of enrolled patients. Ophthalmology . 2005; 112: 376–385. [CrossRef] [PubMed]
Anderson DR. Collaborative normal tension glaucoma study. Curr Opin Ophthalmol . 2003; 14: 86–90. [CrossRef] [PubMed]
Shields MB. Normal-tension glaucoma: is it different from primary open-angle glaucoma? Curr Opin Ophthalmol . 2008; 19: 85–88. [CrossRef] [PubMed]
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