Understanding the potential of the suprachoroidal space

A novel approach to drug delivery into the back of the eye1

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Eye

Suprachoroidal-Space

The suprachoroidal space is a potential pathway that traverses the circumference of the eye’s posterior region1

The suprachoroidal space lies internal to the sclera and external to the choroid.2

The innermost layer of the choroid, known as Bruch’s membrane, is compact. The outermost border is more a zone of transition, consisting of several lamellae with variable thickness.3 Because of its proximity to the choroid, drug delivery through the suprachoroidal space has the potential to reach the retina and the retinal pigment epithelium via the choroid.1

Expandable Suprachoroidal Space

The suprachoroidal space is expandable, allowing fluids to enter and exit without disruption1

The suprachoroidal space is primarily in a collapsed state under typical physiological conditions, primarily due to intraocular pressure (IOP). The suprachoroidal space plays a role in maintaining IOP via uveoscleral outflow, which is an alternative drainage route for the aqueous humor, and is a natural flow path from the front to the back of the eye.1,2

Due to its role in maintaining IOP, the suprachoroidal space has the potential to expand and contract in response to the presence of fluid.1 In animal models,* the suprachoroidal space has been reported to expand to accommodate different volumes.4 The maximal thickness ranged from 1.7-2.8 mm, depending on injection volumes.1 On injection, the suprachoroidal space expands locally, then rapidly empties into the posterior region of the eye.4 Within an hour postinjection, IOP returns to baseline and the suprachoroidal space contracts.1,4

*Based on studies of adult porcine and canine ex vivo eyes.4

Treatments that target retina disease through the vitreous space have the potential to diffuse toward nontarget regions of the eye, such as the lens and ciliary body.1

Imaging the size of the suprachoroidal space may help diagnose and monitor ocular conditions3

Optical coherence tomography (OCT) scan showing the suprachoroidal space3

OCT Scan showing the Suprachoroidal Space

Enhanced depth imaging (EDI)—OCT made it possible to clearly image not only the retina but the layers underneath it.3

Initially, it was thought that the inner border of the sclera is the outer boundary of the choroid. However, recent imaging studies have shown that the suprachoroidal space increases with age and the presence of certain ocular conditions. Although the exact relationship between the size of the suprachoroidal space and retinal diseases has not been fully elucidated, it may become another parameter that will be useful for their diagnosis and follow-up.3

The suprachoroidal space provides a novel approach with possible treatment opportunities3

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Targeted

The back of the eye is the location of many irreversible and debilitating visual impairments2

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Expandable

The suprachoroidal space can extend in a volume-dependent manner, diffusing fluid into the back of the eye, then naturally return to its original thickness

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Bioavailable

Fluid spreads circumferentially and posteriorly when injected within the suprachoroidal space, bathing the choroid and adjacent areas with drug1

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Compartmentalized

Drug is compartmentalized in the suprachoroidal space, which helps keep it away from nondiseased tissues1

References: 1. Chiang B, Jung JH, Prausnitz MR. The suprachoroidal space as a route of administration to the posterior segment of the eye. Adv Drug Deliv Rev. 2018;126:58-66. 2. Rai UDJ, Young SA, Thrimawithana TR, et al. The suprachoroidal pathway: a new drug delivery route to the back of the eye. Drug Discov Today. 2015;20(4):491-495. 3. Moisseiev E, Loewenstein A, Yiu G. The suprachoroidal space: from potential space to a space with potential. Clin Ophthalmol. 2016;10:173-178. 4. Seiler GS, Salmon JH, Mantuo R, Feingold S, Dayton PA, Gilger BC. Effect and distribution of contrast medium after injection into the anterior suprachoroidal space in ex vivo eyes. Invest Ophthalmol Vis Sci. 2011;52(8):5730-5736.

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