Molecular sieve properties of the blood-aqueous barrier in uveitis

Infectious Uveitis in Horses and New Insights in Its Leptospiral Biofilm-Related Pathogenesis

Uveitis is a sight-threatening eye disease in equids known worldwide that leads to considerable pain and suffering. By far the most common type of uveitis in Germany and neighboring countries is classical equine recurrent uveitis (ERU), which is caused by chronic intraocular leptospiral infection and is the main cause of infectious uveitis in horses. Other infectious causes are extremely rare and are usually clinically distinguishable from ERU. ERU can be treated very effectively by vitreous cavity lavage (vitrectomy). For proper indications of this demanding surgery, it is necessary to differentiate ERU from other types of uveitis in which vitrectomy is not helpful. This can be conducted on the basis of anamnesis in combination with ophthalmologic findings and by aqueous humor examination. During vitrectomy, vitreous material is obtained. These vitreous samples have historically been used for numerous etiologic studies. In this way, a chronic intraocular leptospiral infection has been shown to be the cause of typical ERU and, among other findings, ERU has also been recognized as a biofilm infection, providing new insights into the pathogenesis of ERU and explaining some thus far unexplainable phenomena of ERU. ERU may not only have transmissible aspects to some types of uveitis in humans but may also serve as a model for a spontaneously occurring biofilm infection. Vitreous material obtained during therapeutically indicated vitrectomy can be used for further studies on in vivo biofilm formation, biofilm composition and possible therapeutic approaches.

Paraneoplastic aqueous flare intensity in patients with esophagogastric carcinoma

A study was conducted of anterior chamber aqueous flare intensity in patients with esophagogastric malignancies. The subjects included 79 patients with upper alimentary tract malignancies (69 scheduled for surgery for the underlining cancer and 10 with metastases), 47 patients with stable ocular sarcoidosis, and 46 age-matched healthy volunteers. A laser cell-flare meter was used to measure flare intensity in patients and healthy controls. The average flare intensity before surgery in patients with cancer was 10.7 +/- 4.9 photon counts/millisecond (pc/ms), which was not statistically significantly different from that in patients with sarcoidosis (11.9 +/- 8.3 pc/ms) but was significantly higher (p < 0.0001) than that in healthy volunteers (4.3 +/- 1.3 pc/ms). The average flare intensity after surgery in patients with carcinomas was 7.5 +/- 2.5 pc/ms, which was significantly (p < 0.0001) lower than the preoperative value. These results suggest that alterations in aqueous flare intensity might represent a paraneoplastic syndrome in patients with esophagogastric carcinoma. If so, measurements of flare intensity may be helpful in the differential diagnosis and evaluation of the disease course of digestive tract cancer.

Quantitative assessment of aqueous flare intensity in diabetes

Aqueous flare intensity was measured with the laser flare-cell meter in 231 eyes of diabetic patients and 31 eyes of normal age-matched controls. Diabetic patients were divided into four groups based on the degree of retinopathy: (1) non-retinopathy, 42 eyes; (2) background retinopathy, 72; (3) preproliferative retinopathy, 23; and (4) proliferative retinopathy, 94. There was no significant difference between the normal controls and the non-retinopathy group, whereas the rest of the diabetic groups showed significantly higher flare values than did normal controls (P less than 0.001). Flare intensity increased with the progression of retinopathy. Our results demonstrate that clinical use of the flare-cell meter enables the quantitative assessment of blood-aqueous barrier function in diabetics and suggest that diabetic iridopathy, as one of the manifestations of diabetes in the anterior part of the eye, exists even in the early stages of this disease and progresses in parallel with retinopathy.

Age-related differences in ophthalmic drug disposition II: drug-protein interactions of pilocarpine and chloramphenicol

Although drug-protein interactions have been shown to be important in the transport of drugs into and through the eye, age-related differences in ocular drug-protein binding have not been explored. This study was designed to investigate protein binding characteristics of pilocarpine and chloramphenicol in aqueous humour and plasma from rabbits of different ages. The method of equilibrium dialysis was used to quantitate drug-protein interactions. Younger animals showed decreased binding of chloramphenicol in plasma when compared to older rabbits. On the other hand, the interactions of both drugs with aqueous humour proteins were more extensive in younger rabbits. Age-related differences in drug-protein binding were not directly related to the total protein contents of the respective biological fluids. These findings suggest possible age-related differences in the relative protein fractions contained in aqueous humour and plasma, or qualitative differences in the binding capacity of the proteins involved.

Mediation of the ocular response to cyclocryocoagulation

The possible roles of prostaglandins and a neural pathway in the disruption of the blood-aqueous barrier in the rabbit eye after cyclocryocoagulation were studied. Both the preoperative IV administration of the prostaglandin inhibitor acetylsalicylic acid and the application of retrobulbar and topical anesthesia reduced IOP and decreased breakdown of the blood-aqueous barrier, as measured by protein in the aqueous humour. These results imply that the acute response of the animal eye to cyclocryocoagulation is mediated partly by prostaglandins and partly by a neural component resistent an inhibitor of prostaglandin synthesis. When administered together, acetylsalicylic acid and ocular anesthesia yielded a further reduction in postoperative reactions and protein concentrations in the aqueous humour, but were unable to abolish the ocular response completely. The dual ocular mediation to cyclocryocoagulation is apparently due to the combined thermal and mechanical injury caused to ocular structures which synthesize prostaglandins and receive sensory innervation from the trigeminal nerve. The considerable breakdown of the blood-aqueous barrier in cyclocryocoagulation allows leakage of different molecular weight proteins, in equal ratio, into the aqueous humour.