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. 2021 Sep 22;16:6497–6530. doi: 10.2147/IJN.S329831

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© 2021 Zhang et al.

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Structural particularities of the eye. The eye can be divided into two parts of the anterior segment and the posterior segment. There are many barriers to drug delivery to the retina. Drugs cannot be easily delivered to the retina by topical administration, such as eye drops, because of the presence of tear drainage and peribulbar and choroidal blood flow. In contrast, systemically administered drugs rarely enter the retina because of the presence of the blood - aqueous barrier and the inner and outer blood-retinal barriers.