Blood-Retinal Barrier

Abstract

The blood-ocular barrier system is formed by 2 main barriers: the blood-aqueous barrier and the blood-retinal barrier (BRB). The BRB is particularly tight and restrictive and is a physiologic barrier that regulates ion, protein, and water flux into and out of the retina. The BRB consists of inner and outer components, the inner BRB being formed of tight junctions between retinal capillary endothelial cells and the outer BRB of tight junctions between retinal pigment epithelial cells. The BRB is essential to maintaining the eye as a privileged site and is essential for normal visual function. Methods of clinical evaluation of the BRB are reviewed and new directions using optical coherence tomography are presented. Alterations of the BRB play a crucial role in the development of retinal diseases. The 2 most frequent and relevant retinal diseases, diabetic retinopathy and age-related macular degeneration (AMD), are directly associated with alterations of the BRB. Diabetic retinopathy is initiated by an alteration of the inner BRB and neovascular AMD is a result of an alteration of the outer BRB. Macular edema is a direct result of alterations of the BRB.

Subclinical Macular Edema as a Predictor of Progression to Clinically Significant Macular Edema in Type 2 Diabetes

“…This is in agreement with prior evidence from trials of ruboxistaurin, an orally administered inhibitor of protein kinase C-β, in DME patients, which showed that the most probable cause of sustained moderate vision loss in the eyes in their study was the presence of increased retinal thickening involving the center of the macula [11,12]. It is generally accepted that, in the initial stages of clinical DR, increased retinal thickness is associated with an early alteration of the inner blood-retinal barrier [13,14]. The resultant accumulation of fluid in the retinal layers around the fovea may lead to vision loss by altering the functional cell relationship in the retina and/or by promoting an inflammatory reparative response [14].…”

“…It is generally accepted that, in the initial stages of clinical DR, increased retinal thickness is associated with an early alteration of the inner blood-retinal barrier [13,14]. The resultant accumulation of fluid in the retinal layers around the fovea may lead to vision loss by altering the functional cell relationship in the retina and/or by promoting an inflammatory reparative response [14]. …”

Macular Thickness Measured by Stratus Optical Coherence Tomography in Patients with Diabetes Type 2 and Mild Nonproliferative Retinopathy without Clinical Evidence of Macular Edema

“…Increased RT in diabetes, in the initial stages of clinical DR, has been associated with the presence of an early alteration of the inner blood-retina barrier and resultant fluid accumulation in the retina [38]. There have also been reports of retinal ganglion cell death and axonal degeneration occurring in the initial stages of DR, particularly in diabetes type 1 patients [39,40].…”

Role of Inflammation in Diabetic Retinopathy:Therapeutic Targets

“…The inner BRB is formed by tight junctions between retinal capillary endothelial cells, and its integrity is maintained by adhesive interactions between endothelial cells and associated pericytes 8,9 . The outer BRB consists of the retinal pigment epithelium cells, located between the fenestrated choriocapillaris and the outer retina 10 .…”