Positively charged particles are thought to form bonds with the negatively charged proteoglycans found in scleral tissue. Another variable to take into account would be with regards to charged particles, where negatively charged particles are more permeable than positively charged particles. These proteoglycans allow easier passage of hydrophilic compounds when compared to lipophilic compounds. Permeability of scleral tissue decreases as the lipophilicty increases which is thought to be the result of proteoglycans found in the tissue. This matrix allows for the presence of pores that may be of variable size in regional areas of the sclera ( i.e., looser fiber matrix in the posterior sclera compared to anterior). Scleral tissue is composed of collagen and elastin fibers arranged in a matrix array. These effects could be explained by the structure of the sclera. Further research in this area has proven that as molecular radius increases there is an exponential decrease in permeability. In studies conducted on rabbits, globular proteins of the same molecular weight as linear dextrans proved to be more permeable. Interestingly, molecular radius has a more profound impact on permeability than molecular weight. Permeability of scleral tissue for large and small molecules is low and high, respectively. Such influencing factors are molecular weight/molecular radius, lipophilicty, and charge. Ex-vivo studies have been conducted extensively with respect to factors pertinent to the permeability of scleral tissue. The static barriers found within the eye are composed of different segments-the cornea, sclera, retina, and the blood-retina barriers. Static barriers are those that provide a physical impediment to foreign substances. Barriers Affecting Drug Delivery and Metabolism Therefore, given the widespread use of these injections and infusions in patients with ME, we will conduct a thorough review of the two most extensively studied intraocular steroid delivery modalities-intravitreal injection and sub-Tenon’s infusions-and appraise the efficacy and safety of each in an attempt to better understand factors affecting the treatment of ME and reveal a preferred steroid delivery method in the management of this process.

This difference in efficacy is attributed to the fact that corticosteroids are more likely to achieve therapeutic concentrations and their effects are sustainable for a greater duration of time when administered intraocularly. However, oftentimes in clinical practice, intraocular injections and infusions have proven to be more efficacious than topical or systemic steroids in the management of certain ocular pathologies, of which ME is included.

Various routes of corticosteroid administration exist in the treatment of ME, including topical application, oral intake, and intraocular injection or infusion of steroids. Additionally, corticosteroids contain certain anti-angiogenic properties that provide further benefit to patients suffering from ME. Treatment with corticosteroids has been shown to be effective in reducing ME associated with diabetic retinopathy, vein occlusions, and other pathologies by inhibiting the formation of prostaglandins, which are potent regulators of inflammatory mediation.

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