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1096 SECTION XIV Ophthalmology Table 63-1

Some Characteristics of Ocular Routes of Drug Administration*

Route

Absorption Pattern

Special Utility

Limitations and Precautions

Topical

Subconjunctival, sub-Tenon's, and retrobulbar injections

Intraocular (intracameral) injections Intravitreal injection or device

Prompt, depending on formulation

Prompt or sustained, depending on formulation

Prompt

Absorption circumvented, immediate local effect, potential sustained effect

Convenient, economical, relatively safe

Anterior segment infections, posterior uveitis, cystoid macular edema

Anterior segment surgery, infections

Endophthalmitis, retinitis

Compliance, corneal and conjunctival toxicity, nasal mucosal toxicity, systemic side effects from nasolacrimal absorption Local toxicity, tissue injury, globe perforation, optic nerve trauma, central retinal artery and/or vein occlusion, direct retinal drug toxicity with inadvertent globe perforation, ocular muscle trauma, prolonged drug effect Corneal toxicity, intraocular toxicity, relatively short duration of action Retinal toxicity

*See text for more complete discussion of individual routes.

Drug penetration into the eye is approximately linearly related to its concentration in the tear film. Certain disease states, such as corneal ulcers and other corneal epithelial defects, may increase drug penetration when anatomic barriers are compromised or removed. Experimentally, drugs may be screened for their potential clinical utility by assessing their corneal permeability coefficients. These pharmacokinetic data combined with the drug's octanol/water partition coefficient (for lipophilic drugs) or distribution coefficient (for ionizable drugs) yield a parabolic

FIGURE 63-1 Anatomy of the globe in relationship to the orbit and eyelids. Various routes of administration of anesthesia are demonstrated by the needle pathways numbered in blue.

figure 63-2 Anatomy of the lacrimal system.

Interior lacrimal papilla and puncta figure 63-2 Anatomy of the lacrimal system.

relationship that is a useful parameter for predicting ocular absorption. Of course, other factors also affect corneal absorption in vivo, such as epithelial integrity, blink rate, dilution by tear flow, nasolacrimal drainage, drug binding to proteins and tissue, and transconjunctival absorption.

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