The effect of partial vitrectomy on blood-ocular barrier function in the rabbit

Melanin Precursor 5,6-Dihydroxyindol: Protective Effects and Cytotoxicity on Retinal Cells in vitro and in vivo

5,6-Dihydroxyindole (DHI) is a melanin pigment precursor with antioxidant properties. In the light of a report about cytotoxicity of DHI, the aim of this study was to assess possible toxic effects of DHI on cells related to the eye, such as human ARPE-19 cells and mouse retinal explants. Moreover, DHI was tested on its effects on retinal function in vivo using electroretinography. We found cytotoxicity of DHI against ARPE-19 cells at 100 μM, but not at 10 μM. 10 μM DHI exhibited a slight, though not significant protective activity against UV-A damage in ARPE-19 cells. We found cytoprotection in cultured mouse retinas by 50 μM DHI or its diacetylated derivative 5,6-diacetoxyindole (DAI), respectively. In ERG measurements in vivo, amplitudes were decreased only slightly by 100 μM DHI compared to saline, whereas a better preservation of amplitudes was visible at 10 μM DHI, in particular with respect to cones. In histological sections, more cones were found at 10 μM DHI than at 100 μM DHI. As a conclusion, DHI shows a slight protective effect at 10 μM both in vitro and in vivo. At 100 μM, it shows a strong cytotoxicity in vitro, which is strongly reduced in vivo.

Intravitreal pharmacokinetics after posterior subtenon triamcinolone acetonide injection in vitrectomized rabbit eyes

PURPOSE

To investigate the intraocular pharmacokinetics of triamcinolone acetonide (TA) injected into the posterior subtenon of vitrectomized rabbit eyes.

METHODS

Vitrectomy was performed on the right eyes of 35 rabbits. Triamcinolone acetonide (40 mg/mL) was injected into the posterior subtenon space of both eyes. Five rabbits each were killed at days 1, 3, 7, 14, 28, 56, and 84. Both eyes were enucleated. The vitreous was isolated, and TA concentration was measured.

RESULTS

In vitrectomized eyes, the intravitreal concentrations of TA were 1763, 822.9, 321.5, 113.3, 35.5, 14.4, and 6.7 ng/mL, respectively, at the time points indicated above; the concentrations in nonvitrectomized eyes were 397.8, 360.4, 154.4, 48.5, 30.7, 15.2, and 8.0 ng/mL, respectively. Triamcinolone acetonide concentrations were significantly higher in the vitrectomized eyes at days 1, 3, 7, and 14. The terminal half-life of intravitreal TA was 23.3 days in the vitrectomized eyes and 28.9 days in the nonvitrectomized eyes.

CONCLUSION

Intravitreal absorption and excretion of TA in the posterior subtenon space are increased after vitrectomy. Although the terminal half-life of TA was shorter, higher early concentration and similar effective duration were achieved in the vitrectomized eyes.

Severe bacterial endophthalmitis: towards improving clinical outcomes

Endophthalmitis is an infection and inflammation of the interior of the eye that can result in significant vision loss. This infection occurs as a result of the seeding of organisms into the interior of the eye following surgery (postoperative), trauma (post-traumatic) or an infection in another site in the body (endogenous). The general rate of endophthalmitis has remained steady over the past several years. However, the increased use of intraocular injections to treat various degenerative and inflammatory ocular diseases, in addition to the already large and growing number of invasive ocular surgeries, may increase the opportunities in which organisms can gain access to the eye. In most cases of endophthalmitis, useful vision can be retained if proper treatment is instituted. However, in severe cases of bacterial endophthalmitis, blindness often occurs despite treatment. This article summarizes information on endophthalmitis epidemiology, treatment issues and current regimens, and recent experimental and clinical efforts to improve the outcome of severe and blinding forms of bacterial endophthalmitis.

Efficacy of vitrectomy in improving the outcome of Bacillus cereus endophthalmitis

PURPOSE

To evaluate the efficacy of vitrectomy with vancomycin for the treatment of experimental Bacillus cereus endophthalmitis.

METHODS

Endophthalmitis was initiated in rabbits via intravitreal injection of 100 colony-forming unit B. cereus. Treatment groups included 25-gauge transconjunctival sutureless vitrectomy with intravitreal vancomycin (1 mg) or vancomycin alone. Groups were treated at 4, 5, or 6 hours after infection. At 48 hours (for 4-hour and 5-hour groups) or 36 hours (for the 6-hour group) after infection, eyes were analyzed by electroretinography, histology, and inflammatory cell counts.

RESULTS

Treatment with vitrectomy/vancomycin at 4 hours resulted in significantly greater retinal function compared with that of vancomycin alone. Intraocular inflammation after treatment at 4 hours was minimal for both the treatment groups. Treatment with vitrectomy/vancomycin or vancomycin alone at 5 hours or 6 hours after infection resulted in similar levels of retinal function loss (i.e., >90%) and significant intraocular inflammation.

CONCLUSION

These results demonstrate that vitrectomy may be of therapeutic benefit in the treatment of B. cereus endophthalmitis but only during the early stages of infection.

Effects of vitrectomy on age-related macular degeneration

PURPOSE

To determine whether vitrectomy alters the long-term progression of age-related macular degeneration (AMD).

DESIGN

Retrospective case-control study.

PARTICIPANTS

Forty-four eyes of 22 patients with AMD who underwent vitrectomy in 1 eye were included in the study. The progression of AMD at follow-up in the 22 eyes that underwent vitrectomy was compared with the 22 fellow, nonvitrectomized eyes.

METHODS

The charts and photographs of subjects with Age-Related Eye Disease Study category 3 AMD in both eyes who previously underwent vitrectomy surgery for an epiretinal membrane or macular hole were reviewed. Subjects were excluded if they had had a vitrectomy in both eyes, had <2 years of follow-up, had previous choroidal neovascularization (CNV), retinal detachment, diabetic retinopathy, angioid streaks, high myopia, vascular occlusions, or extensive macular scarring in either eye, or insufficient hospital records or photographs to determine the extent of AMD. Clinical notes throughout the follow-up interval were reviewed. Two vitreoretinal specialists independently graded pre- and postvitrectomy fundus photographs of all eyes in a masked fashion.

MAIN OUTCOME MEASURES

The development or progression of geographic atrophy of the retinal pigment epithelium and the development of CNV.

RESULTS

Twenty-two patients were included. The average follow up interval was 5.5 years (range, 2-15). Choroidal neovascularization developed in 5 control eyes and in 2 vitrectomized eyes, and atrophy developed in 7 control and 4 vitrectomized eyes. The difference between vitrectomized eyes and fellow eyes for the combined end points of RPE geographic atrophy or CNV was significant (P = 0.02).

CONCLUSIONS

In this pilot study, we did not detect that vitrectomy increased the progression of AMD. In fact, it was associated with a reduced progression to geographic atrophy or CNV. Additional studies are needed to confirm or refute this association.

FINANCIAL DISCLOSURE(S)

The authors have no proprietary or commercial interest in any of the materials discussed in this article.

Recurrent anterior uveitis after trabeculectomy with mitomycin C

OBJECTIVE

To report 4 cases of recurrent anterior uveitis occurring 1-11 months after trabeculectomy with mitomycin C.

DESIGN

Observational case series.

PARTICIPANTS

Four patients in whom recurrent uveitis developed after trabeculectomy with mitomycin C, followed at Maisonneuve-Rosemont Hospital in Montreal, Quebec.

METHODS

Retrospective review of the medical records.

RESULTS

One to 11 months after trabeculectomy with mitomycin C, noninfectious, recurrent anterior uveitis developed in 4 patients with no prior history of uveitis. Topical and intravitreal corticosteroids were effective in reducing acute inflammation, yet 2 patients went on to have chronic anterior uveitis.

CONCLUSIONS

Recurrent anterior uveitis presenting later than 3 weeks postoperatively may be associated with trabeculectomy with mitomycin C. It should be included in the differential diagnosis of a nonresolving blebitis.

MRI in ocular drug delivery

Conventional pharmacokinetic methods for studying ocular drug delivery are invasive and cannot be conveniently applied to humans. The advancement of MRI technology has provided new opportunities in ocular drug-delivery research. MRI provides a means to non-invasively and continuously monitor ocular drug-delivery systems with a contrast agent or compound labeled with a contrast agent. It is a useful technique in pharmacokinetic studies, evaluation of drug-delivery methods, and drug-delivery device testing. Although the current status of the technology presents some major challenges to pharmaceutical research using MRI, it has a lot of potential. In the past decade, MRI has been used to examine ocular drug delivery via the subconjunctival route, intravitreal injection, intrascleral injection to the suprachoroidal space, episcleral and intravitreal implants, periocular injections, and ocular iontophoresis. In this review, the advantages and limitations of MRI in the study of ocular drug delivery are discussed. Different MR contrast agents and MRI techniques for ocular drug-delivery research are compared. Ocular drug-delivery studies using MRI are reviewed.

Bevacizumab (avastin) does not harm retinal function after intravitreal injection as shown by electroretinography in adult mice

PURPOSE

Scavenging of VEGF by specific antibodies is a promising way to treat ocular conditions connected with neovascularization. Intravitreal injections of Avastin (bevacizumab) are performed frequently as a treatment of such conditions. In this study, the authors examine whether the retinal function in wild-type mice is affected by an intravitreal injection of Avastin.

METHODS

Electroretinography was performed in four different experimental groups of wild-type C57BL/6 mice before treatment and 1, 4, 12, and 25 days afterwards. The first group was injected intravitreally with BSS, the second one received injections of a vehicle solution, and the third group was injected with the commercial Avastin solution. In a fourth group, sham surgery was performed. Immunohistochemistry was performed in some eyes to evaluate penetration of the bevacizumab molecule through the retina.

RESULTS

In all four groups, a similar behavior of the ERG parameters could be detected. One day after the injections, the amplitudes showed a clear decrease. Later on, they recovered gradually. No difference could be seen between eyes injected with Avastin or vehicle solution. Bevacizumab immunoreactivity was already present in the whole retina half an hour after the intravitreal injection and was not detectable 25 days later. Moreover, binding of bevacizumab to endogenous mouse VEGF could be shown.

CONCLUSIONS

Based on the electroretinographic findings, the authors conclude that bevacizumab does not have any toxic effects on the mouse retina and its function. The bevacizumab molecule penetrates the retina quickly. Therefore, it can act safely and very quickly, also in deeper retinal layers after its injection.

Anti-inflammatory effects of topical ocular MAXIDEX® administration to rabbits following vitrectomy or lensectomy

We conducted a series of surgical studies (n=155) to find out the possible utility of the Dutch Belted rabbits as an ocular test model. Following either vitrectomy (n=59) or lensectomy (n=96) studies using either BSS or BSS Plus, we characterized the corresponding magnitude and duration of inflammatory response of selected endpoints over a one-week period. Preoperative Dutch Belted rabbits served as controls for baseline determination (n=27). Inflammatory endpoints included clinical inflammation, blood aqueous barrier (BAB) changes measured by particle-scatter and fluorophotometry, corneal edema, and prostaglandin-E2 (PGE2). Topical ocular 0.1% dexamethasone (MAXIDEX) served as a positive treatment group. We compared the inflammatory features (treated and untreated) to determine significance. Using either irrigating solution, the endpoints (n=101) were shown increased in both models. While the clinical scores were similar following both types of surgery (ns; p=0.51), the lensectomy study caused a more marked effect on corneal edema (p=0.0004) and PGE2 production (p=0.002) compared with the vitrectomy study. After the lensectomy procedure, BSS Plus (n=52) compared with BSS (n=24) showed a significant improvement (p=0.004) of clinical score during the recovery phase. Further improvement was gained over BSS Plus (n=52) using MAXIDEX treatment. Topical MAXIDEX (lensectomy, n=20/group; vitrectomy, n=12/group) reduced clinical score (p<0.001), decreased BAB breakdown to fluorescein (p<0.01), lessened particle flare (p<0.05), inhibited aqueous PGE2 levels (p<0.001), and reduced corneal edema (p=0.01) in the lensectomy group. The use of the rabbit model offers a convenient test to identify therapeutic agents that could lessen ocular complications after these common ocular surgeries.

Differential protein expression in lens epithelial whole-mounts and lens epithelial cell cultures

PURPOSE

Lens fibergenesis is a problem in several types of cataract and in the posterior capsular opacification following cataract surgery. To correct improper fiber differentiation or to prevent unwanted growth on the posterior capsule following cataract surgery requires a thorough understanding of normal and abnormal fiber formation. To this end, studies were initiated to characterize fiber differentiation in the bovine lens and in lens epithelial cell cultures.

METHODS

Indirect immunofluorescence and immunoblot analysis were employed to study the expression of vimentin, beta-crystallin, gamma-crystallin, filensin, aquaporin 0 and the Na, K-ATPase catalytic subunit isoforms (alpha1, alpha2, alpha3) in bovine lens epithelium whole-mounts as well as lens epithelial cell cultures propagated in medium containing 10% bovine serum or in medium supplemented with bovine serum concentrations < or =4%.

RESULTS

Three distinct cell types were observed in the bovine lens epithelium. The cells of the central zone were identified by a polarized distribution of two distinct Na, K-ATPase catalytic subunit isoforms, alpha1 to the apical (fiber side) and alpha3 to the basal (aqueous humor side) membranes. Lateral to the polarized central zone, was the germinative zone of cells, best characterized by perinuclear vimentin basket-like structures and the loss of polarized Na, K-ATPase catalytic subunit isoforms. Lateral to the germinative zone were the cells of the transition zone (meridinal rows) where expression of the lens specific proteins beta-crystallin, gamma-crystallin, filensin and aquaporin 0 as well as the lens fiber-, adipocyte- and brain glia-specific Na, K-ATPase catalytic subunit, alpha2 are expressed. The cultured cells propagated in medium supplemented with 10% serum bore no resemblance to any of the cells of the bovine lens epithelium whole-mounts. The cells propagated in the medium supplemented with the lower bovine serum levels resembled the differentiating fibers of the transition zone of the bovine lens epithelium whole-mounts as well as superficial cortical fibers.

CONCLUSIONS

Since the low-serum lens epithelial cell cultures bear a remarkable resemblance to early differentiating fibers, they are reasonable models for the study of early fiber differentiation or prevention of differentiation. The culture conditions employed do not yield the polarized cells of the central zone. Nor has the function of these polarized cells in lens fluid, nutrient and ion homeostasis been determined.