الفهرس 
Posterior segment drug deliveryOnly 14 pages are availabe for public view
 |  | from | 202 |  |  |
| | | from | 202 | | |
Abstract
The vitreous body makes up approximately 80% of the volume of the eye and thus is the largest single structure of the eye.
The vitreous support function for the retina and filling up function of the vitreous body cavity, a diffusion barrier between the anterior and the posterior segment of the eye, has metabolic buffer function , and establishment of an unhindered path of light.
Drug delivery to the eye can be in the form of topical DROPs or long-acting, slow-release conjunctival inserts, periocular injections, direct intracameral or intravitreal injections, or a surgically implanted intravitreal slow-release device. Systemic delivery is usually via oral, intramuscular, or intravenous routes.
Direct intravitreal injection has the obvious advantage of being able to achieve immediate therapeutic concentrations in the eye while largely avoiding systemic exposure. However, following injection, drugs are rapidly eliminated from the vitreous, typically by either passive or active first order processes.
Prior to the 1980s, the conventional treatment for infectious endophthalmitis consisted of intravenous, subconjunctival, and topical antibiotics. The results of such treatment were dismal with approximately 75 % of cases progressing to visual acuities of hand motions or worse. Failure of therapy was at least in part due to poor penetration of antibiotics into the vitreal cavity. The major diffusional barrier to antibiotics appears to be located at the vitreoretinal interface.
Studies related to the intravitreal administration of antibiotics are open to criticism for many reasons, including : Dosage and dose schedule of antibiotic, Interval to examination, Adequacy of histopathologic studies and Examinations, Control of mitigating variables, such as status of lens, the presence of vitreous, and the extent of intraocular inflammation.
In candidal endophthalmitis, if there is no sign of disseminated infection, treatment with intravitreal amphotericin B and oral ketoconazole or f1ucytosine can be effective. Therefore, for significant vitreous involvement, intravitreal amphotericin B combined with vitrectomy should be considered.
Intravitreal injections of either ganciclovir or foscarnet have been used successfully to control CMV retinitis in some patients, especially those with recurrent or refractory disease. Multiple injections are required due to the short intraocular drug half-life. About 30% of immunocompromised patients will develop recurrent disease if only treated intravitreal injection. The ganciclovir intraocular implant is used to deliver this drug in a sustained release fashion directly to the posterior segment .
Complications associated with the ganciclovir intraocular implant are uncommon Complications may be related to the surgical procedure, the implant device or the medication contained within the implant.
Corticosteroids have antiangiogenic, antifibrotic, and antipermeability properties. The principle effects of steroids are stabilization of the blood retinal barrier , resorption of exudation, and down regulation of inflammatory stimuli.
Intravitreal TA as a treatment for conditions including refractory macular edema and choroidal neovascularization.
TA is an effective for intravitreal injection in conditions , such as uveitis , macular edema secondary to ocular trauma or retinal vascular disease proliferative diabetic retinopathy , intraocular proliferation such as proliferative vitreoretinopathy, and choroidal neovascularization from AMD.
The fluocinolone acetonide intravitreal implant is an intravitreal drug implant approved for the treatment of chronic uveitis by the FDA.
A biodegradable implant with a sustained-release formulation of dexamethasone was used after cataract surgery to treat postsurgical inflammation.
The bevacizumab is currently approved by the FDA for the treatment of metastatic colorectal cancer, metastatic breast cancer, and non-small cell lung cancer, it is widely used as an off-label treatment for neovascular age-related macular degeneration and retinal vascular disorders including retinal vein occlusion and diabetic macular edema.
Other anti-VEGF drugs, pegaptanib and ranibizumab, are currently approved by the FDA for the treatment of age-related macular degeneration.
Intravitreal MTX is a form of local therapy for intraocular lymphoma in patients, affected eyes by intravitreal injections of MTX.
There are many other drugs used by intravitreal injection for treatment of ocular diseases such as denufosol tetrasodium used in RD treatment, erythropoietin used in retinal vascular diseases , ciliary neurotrophic factor analogue used in hereditary retinal degeneration , tissue plasminogen activator used in recent onset central retinal vein occlusion, intravitreal tacrolimus injection and encapsulated cell technology.
The patient should be aware that further intervention may be needed, the problem may not be rectified, and that vision or even the eye could conceivably be lost as a result of the procedure. The patient should be warned to contact the ophthalmologist with any concerns and definitely for symptoms of worsening pain, worsening vision, increasing redness, flashes, and symptoms of retinal detachment.
complications such as retinal detachment, retinal tears, vitreous hemorrhage, endophthalmitis, increased IOP, cataract formation, and, with repeated use (required for successful treatment), fibrosis and ptosis. The most common side effect is increased IOP, which has been found on rare occasion to increase drastically (up to 50mmHg).Close IOP monitoring is crucial following intravitreal injection .