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A. Demetriades, S. D'Anna, A. Eghrari, D. Emmert, E. McCartney, M. P. Grant, S. L. Merbs; Intraglandular Injection of Botulinum Toxin-A Reduces Tear Production in Rabbits. Invest. Ophthalmol. Vis. Sci. 2008;49(13):2448.
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Many patients suffer with intractable tearing, even after lacrimal and eyelid surgery. A few papers report the use of Botulinum Toxin type A injected into the lacrimal gland in a limited number of tearing patients. The aim of this study is to use an animal model to systematically study the effect of an intraglandular injection of Botulinum Toxin A on tear production.
New Zealand White sexually mature female rabbits weighing about 3 kg were used. Prior to anesthesia, photographs were taken to document the pre-operative eyelid position in each animal. The rabbits were anesthetized and fluorescein and Rose Bengal were used to evaluate the corneal surface. A Schirmer’s test after topical anesthesia was performed. In a volume of 0.1 ml, either 2.5, 1.25 or 0.625 units of Botulinum Toxin A (Botox, Allergan, Irvine, CA) were injected transconjunctivally into the superolateral lobe of the right lacrimal gland of 4 rabbits. As a control, 0.1ml volume of 0.9% sodium chloride was injected into the left lacrimal gland of each animal. One week following injection, photographs were taken to document the post-operative eyelid positions. The animals were anesthetized, and the corneas were evaluated with fluorescein and Rose Bengal. A post-injection Schirmer’s test with anesthesia was performed.
Right rabbit eyes injected with the highest dose (2.5 U) of Botulinum Toxin A displayed a statistically significant decrease in tear production (Schirmer’s 6.25±1.65mm) as compared to the corresponding saline injected left eyes (Schirmer’s 12±2.68mm; n=4; p=0.02). No evidence of corneal pathology from excessive dryness following injection was observed, as demonstrated by a lack of fluorescein and Rose Bengal staining. At one week following injection, ptosis was present in the right eye of one rabbit in each of the three dosage groups.
Intraglandular injection of Botulinum Toxin A resulted in decreased tear production in rabbits at one week. Despite suppression of baseline tear production, no evidence of dry eye was observed. We did observe ptosis in three of twelve rabbits, which has also been seen in patients. Further studies are needed to optimize the reduction in tear production while minimizing the risk of ptosis. Intraglandular injection of Botulinum Toxin A may eventually be a treatment option in patients with intractable tearing.
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