The electrical stimulation of the retina by indwelling electrodes.

Chronically implanted intraocular electrodes were used to stimulate visual cortical responses to current passage through the retina. Electrical current threshold for the light-adapted cat retina lies in the region of 30 to 100 X 10(-6) amps. for the conditions used. Dark adaptation caused a large threshold increase. Retinal excitability also decreased when electrical stimuli were delivered more often than one per 5 seconds. Effective charge-density threshold was moderately greater than reported for frogs and humans.

Preliminary report: indications of improved visual function after retinal sheet transplantation in retinitis pigmentosa patients.

PURPOSE: To report indications of new visual function after retinal transplantation in two blind patients with retinitis pigmentosa. METHODS: Intact sheets of fetal retina (15 and 17 weeks gestational age) were transplanted subretinally (between the neurosensory retina and the retinal pigment epithelium) near the fovea in the left eye of a 23-year-old white man (Patient A) and in the left eye of a 72-year-old white woman (Patient B), both with autosomal-recessive retinitis pigmentosa. RESULTS: Postoperatively, at 6 and 5 months, respectively, both patients reported new visual sensation in the visual field corresponding to the transplant. In both patients, the visual sensation continued to be present after transplantation, at 12 and 8 months, respectively. In Patient A, a transient multifocal electroretinography (mfERG) response was observed in the transplant area 4 months postoperatively but was not detectable in Patient A at 6.0 and 9.5 months post-retinal transplantation. In Patient B, no positive mfERG responses were seen up to 5 months postoperatively. No rejection (presenting as cystoid macular edema, macular pucker, and extensive intraretinal edema with disrupted retinal pigment epithelium) to the transplanted tissue was seen up to 13 months in Patient A and 9 months in Patient B by fluorescein angiography. CONCLUSION: Transplantation of intact sheets of fetal human retina in two patients with retinitis pigmentosa was not associated with evidence of transplant rejection. Subjective improvement and an indication of objective improvement 4 months postoperatively were seen in Patient A, and subjective improvement only was seen in Patient B.

Simulation of massive periretinal proliferation by autotransplantation of retinal pigment epithelial cells in rabbits.

We compared the clinical pattern, the histologic findings, and the electron microscopic appearance of lesions produced by the autotransplantation into rabbit vitreous of freshly harvested and tissue-cultured (250,000) retinal pigment epithelial cells. Both harvested and cultured cells formed intravitreal strands, traction detachments, and retinal puckers, resembling the most prominent features of massive periretinal proliferation in humans. Strands produced by both types of retinal pigment epithelial cells contained cells resembling myofibroblasts which may explain the contractability of the strand. The clinical, histologic, and electron microscopic observations were similar to those found in eyes injected with tissue-cultured skin fibroblasts.

Pharmacological therapy for proliferative vitreoretinopathy.

We developed an animal model in the rabbit eye with intravitreally injected heterotransplanted bovine retinal pigment epithelial cells to test a pharmacological agent which would reduce extracellular matrix formation. Results with 20 and 60 micrograms of cis-hydroxyproline showed a 48% decrease in the rate of traction retinal detachments.

Isolated, perfused bovine eye a model for acute retinal toxicity screening.

Excorporal bovine eye has been resuscitated and sustained with an aim of its development as an alternative to whole animal in evaluating acute retinal toxicity of xenobiotics. As indicated by the stable ERG response, such preparation is functionally reactive to photic stimuli over a span of 6-12 h. Moreover, after experienced a 20 min hypoxia the reperfused eyes recovered fully. This functionally responsive preparation was used to evaluate the influence of a highly purified bacterial collagenase (Nucleolysin) on the integrity of vitreoretinal junction. Nucleolysin at concentrations between 120-600 U/ml was injected into the posterior chamber for 15 min. Retinal surfaces were irrigated and eyes were perfusion fixed with glutaraldehyde. Ultrastructural analysis indicated that thinning of the internal limiting membrane occurred when enzyme exceeded 480 U. At 600 U concentration, the principle subcellular change involved the end-foot region of the Muller cells. These studies suggest that the isolated, perfused bovine eye is a suitable model for evaluating acute retinal toxicity of xenobiotics.

Bovine RPE heterotransplants simulate proliferative vitreoretinopathy (PVR) in rabbits.

A model of proliferative vitreoretinopathy (PVR) is described. This is the first reported model based on the transplantation of heterologous retinal pigment epithelium cells into the vitreous cavity of rabbits. Freshly isolated cells or short-term primary cultures of bovine pigment epithelium are employed. Strands develop in the vitreous cavity and, with a frequency now approaching 100%, traction retinal detachments develop by 3-4 weeks. Light and electron microscopic features of this model parallel those found for transplanted autologous RPE cells; there are no overt signs of rejection. Examination of the strands should prove useful in identifying strategies of therapeutic value. This model permits such studies, since retinal detachments in adequate numbers are readily produced. The model resembles human PVR.

Anterior proliferative vitreoretinopathy in the silicone study. Silicone Study Report Number 10.

BACKGROUND: As part of the design of the Silicone Study, a new classification of proliferative vitreoretinopathy (PVR) was developed that distinguishes the different types of contraction found in PVR. In contrast to the original Retina Society system that emphasized the post-equatorial retinal pathology (posterior PVR), the Silicone Study classification system included the characteristic types of contraction found in both the equatorial region and the pre-equatorial retina and vitreous base (anterior PVR). METHODS: The authors contrast (1) preoperative and intraoperative findings and (2) vision and anatomic outcomes in the cohort of anterior PVR eyes with the cohort of posterior-only PVR eyes. For the cohort of eyes randomized to perfluoropropane gas (C3F8) or silicone oil, the authors carry out univariate and multivariate analyses to assess the predictive value of baseline and intraoperative parameters on vision and anatomic outcome. RESULTS: Anterior PVR was present in 321 eyes (79%) and was more prevalent in eyes that had undergone an unsuccessful vitrectomy before study entry than in eyes that underwent a primary vitrectomy for PVR (88% versus 73%; P < 0.001). Compared with eyes that had posterior PVR at the preoperative examination, eyes that had anterior PVR tended to (1) be graded (Retina Society classification system) as D-1 or worse (86% versus 49%; P < 0.0001), (2) have worse (< 2/200) visual acuity (93% versus 86%; P = 0.003), (3) have more hypotony (24% versus 11%; P = 0.03), more edema (8% versus 2%; P = 0.04), more aqueous flare (P = 0.02), more macular pucker (69% versus 52%; P = 0.005), and more intravitreal contraction (21% versus 6%; P = 0.002). When compared with eyes that had anterior PVR, eyes with posterior PVR had a better outcome at the 6-month postoperative examination: complete attachment of the retina (76% versus 62%; P = 0.04), visual acuity of 5/200 or better (64% versus 45%; P = 0.006), and normal intraocular pressure (86% versus 71%; P = 0.04). For eyes with anterior PVR, significant predictors of poor (< 5/200) visual acuity were a preoperative PVR grade D-1 or worse and the use of C3F8 gas as the intraocular tamponade. CONCLUSION: The Silicone Study classification of anterior PVR permits greater specificity in characterizing PVR and is prognostic of anatomic and vision outcome. Eyes with anterior PVR and clinically significant posterior PVR changes had a better visual prognosis if silicone oil was used. With the current understanding of the pathoanatomy of anterior PVR and the recent development of new surgical techniques, the incidence of anterior PVR in eyes that previously underwent vitrectomy may decline, and the prognosis in eyes with anterior PVR may improve.