Subretinal semiconductor microphotodiode array

BACKGROUND AND OBJECTIVE

To examine the function of a semiconductor microphotodiode array (SMA) surgically implanted in the subretinal space.

MATERIALS AND METHODS

Positive-intrinsic layer-negative (PiN) or negative-intrinsic layer-positive (NiP) SMAs were surgically placed into the subretinal space of rabbits through a pars plana incision and a posterior retinotomy. The implants required no external connections for power and were sensitive to light over the visible and infrared (IR) spectrum; IR stimuli were used to isolate implant-mediated responses from the activity of native photoreceptors. A stimulator ophthalmoscope was used to superimpose IR stimuli on the implant and adjacent retinal areas, and responses were recorded during the postoperative recovery period. SMA responses were also evaluated in vitro. The animals were given lethal anesthetic overdoses, and the retinas were examined histologically.

RESULTS

The in vitro implant response consisted of an electrical spike, followed by a small-amplitude DC offset that followed the time course of the IR stimulation, and an overshoot at the stimulus offset. The SMAs placed in the subretinal space retained a stable position and continued to function throughout the postoperative period. The SMA responses recorded in vivo included additional slow-wave components that were absent from the in vitro recordings. These responses reverted to the in vitro configuration following the death of the animal. There was a significant loss of retinal cells in areas overlying the implant, and the retina appeared normal away from the implant and surgical site.

CONCLUSION

SMAs can be successfully implanted into the subretinal space and will generate current in response to light stimulation during an extended period of time.

Immunohistologic study of epiretinal membranes in proliferative vitreoretinopathy

We performed an immunohistologic study on 11 specimens of epiretinal membranes surgically obtained from patients who had rhegmatogenous retinal detachment with proliferative vitreoretinopathy. Immunostaining procedures were used to identify immunoglobulin and complement deposits, to visualize class II antigen expression by proliferating cells, and to determine eventual infiltration by cells of the immune system. Diffuse deposits of IgG, IgA, IgE, C1q, C3c, and C3d were found in epiretinal membranes, whereas numerous cells, including glial or pigmented epithelial cells, expressed HLA-DR and HLA-DQ antigens. Some macrophages and B or T8 lymphocytes were identified. These results suggest activation of the immune system during the course of proliferative vitreoretinopathy. Class II antigen expression could be dependent upon growth-promoting factors and interferon gamma and could play a crucial role in this immune reaction, which resulted in immunoglobulin deposition and activation of complement. However, the eventual role of immune phenomena in the extension of proliferative processes remains to be determined.

Mesectodermal leiomyoma of the ciliary body: new evidence for neural crest origin

An 8-year-old white boy had a mass of the ciliary body in his left eye. Both the translucent characteristics and the magnetic resonance imaging findings suggested that this lesion was cystic. Fluid aspiration biopsy and iridocyclectomy were performed. By light microscopy the neoplasm showed the characteristic appearance of a neuroid tumor; however, on electron microscopic examination, the tumor exhibited characteristic features of a smooth muscle neoplasm and was diagnosed as a mesectodermal leiomyoma. Observation of melanin granules in scattered tumor cells further confirmed that the tumor had the same origin as uveal melanocytes, which also derive from the neural crest.

Class II antigen expression in diabetic preretinal membranes

Using immunofluorescence and immunoperoxidase procedures, we found large amounts of IgG, IgA, IgM, and IgE, as well as C1q, C3c, and C3d, in the connective stroma and within the vascular walls on eight specimens of preretinal membranes obtained from diabetic patients with proliferative retinopathy. The membranes contained many isolated human leukocyte antigen (HLA) DR- and DQ-expressing cells, and vascular endothelial cells strongly expressed class II determinants. Monoclonal antibodies to immunocompetent cells disclosed only rare B lymphocytes or suppressor/cytotoxic T cells and few monocytes. These findings confirm previous evidence of immune reactions in the pars plana of patients with proliferative diabetic retinopathy, and suggest that an autoimmune reaction is a factor in this complication. It is yet not possible to determine whether this reaction is a nonspecific consequence of the vasoproliferative processes or if it plays a direct role in the development and extension of preretinal membranes.

Feasibility of blood flow measurement by externally controlled dye delivery

We are developing a new method of delivering substances locally and repeatedly in the retinal vasculature under external control. This delivery system is based on encapsulating the substance in heat-sensitive lipsomes, which are injected intravenously and lysed by a heat pulse delivered by a laser. The feasibility of using this system with dyes and creating a sharp dye front was tested in vitro and in vivo. The results indicate that the background fluorescence of intact liposomes is minimal but in contrast a dramatic increase in fluorescence is achieved where the dye is released. In vivo tests indicated that only the selected vascular branch fluoresced. Moreover, a sharp dye front could be obtained repeatedly and preserved over significant distances. The presence of a sharp dye front allowed measurements, in vitro, of blood velocity which correlated well (r = 0.985, P less than 0.001) with the average blood velocity values calculated from the known flow rate.

Internal sclerostomy with the Nd: YAG contact laser versus thermal sclerostomy in rabbits

The authors undertook an investigation to evaluate the efficacy and complications of performing internal sclerostomy with the synthetic sapphire contact neodymium:YAG (Nd:YAG) laser compared with standard external thermal sclerostomy. Fifteen rabbits underwent internal laser sclerostomy in one eye; 12 additional rabbits underwent a standard external thermal sclerostomy in one eye. The fellow eyes served as controls. The differences between the groups in duration of functional blebs and pressure reduction were statistically significant (P = 0.034 and 0.0013, respectively). The evaluation of success (as determined by a pressure reduction greater than 3 mmHg between both eyes after digital pressure) using life-survival analysis indicated that the success rate of the laser-treated group was significantly different from the standard surgical group (P = 0.002). Histologically, there was less inflammation in the laser-treated group 2 days postoperatively. The complications of the laser treatment include focal injury to the overlying cornea, adjacent iris stroma, and lens.

Toxicity of intravitreal injection of fluconazole in the rabbit

Fluconazole is a new bis-triazole derivative proven highly effective against Candida in various animal models. To determine its potential use in exogenous fungal endophthalmitis, 13 New Zealand white rabbits were given intravitreal injections of up to 100 micrograms/0.1 mL of the antifungal. All eyes underwent biomicroscopy, ophthalmoscopy and electroretinography before and after the procedure. No evidence of toxic intraocular effects was detected with these techniques or on light microscopy, performed 8 days after injection. The results suggest that fluconazole has potential application in the treatment of exogenous fungal endophthalmitis.

Dextran 40-containing incubation media: effect on lens electrolyte and water balance

The effect of dextran 40 on lens swelling and electrolyte balance in lenses stressed by incubation in Ca++-free media was studied. Dextran 40 substantially inhibited lens swelling, Na+ gain, and K+ loss caused by six-hour incubation in Ca++-free media. After an additional 12-hour incubation in Ca++-enriched media, the water and electrolyte balance in the dextran 40-incubated group was essentially the same as that of lenses that were never exposed to a Ca++-free media. Those lenses that were not incubated in dextran 40 demonstrated significant residual lens swelling and electrolyte imbalance. It is concluded that dextran 40, by virtue of its oncotic effect, inhibits colloidal osmotic swelling and exerts a protective effect on lens function under a stress situation.

Intraocular lens fixation with Dacron mesh: Part I

Rabbits were used to demonstrate the feasibility of using Dacron fibers to fix intraocular lenses. Adhesion occurred five days after insertion and was confirmed by histologic examination to consist of fibroblastic ingrowth into the Dacron fibers. This cellular response was consistent and remained localized. Anterior and posterior placement of the acrylic portion of the lens was compared. It is our clinical impression that the risk of pupillary block is increased with posterior placement of the lens.