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To study the risk of developing rubeosis iridis following vitrectomy, the use of preoperative iris fluorescein angiography was prospectively investigated on patients with diabetes mellitus, without any clinically detectable iris or angle neovascularization. With increasing severity of fluorescein leakage, the risk of iris neovascularization with or without glaucoma, six months after vitreous surgery, is significantly increased. It was also determined whether postoperative steroid therapy (periocular triamcinolone acetonide and topical prednisolone phosphate) reduces the risk of developing iris neovascularization after vitrectomy. Controlled and treated patient eyes did not differ significantly in the degree of rubeosis. However, neovascular glaucoma statistically occurred more frequently in the nonsteroid group.

To the Editor. —In the AugustArchives(1981;99:1371-1374), Ross concluded after examining 50 patients who underwent retinal dialysis that all retinal dialyses probably result from trauma and that genetic weakness of the retina at the ora serrata is not an important factor. In his analysis of inferotemporal dialyses, the author stated that in 15 of 36 dialyses (34 patients), the history was either forgotten or denied for social reasons. Although the number of dialyses in the remaining retinal quadrants came to 13, only one patient in this category denied a history of trauma. In support of a nonhereditary cause of inferotemporal dialyses, Ross also stated that there was no family history of dialysis in any of these 34 patients, but he does not mention if siblings or other relatives of these patients were examined by indirect ophthalmoscopy and peripheral scleral depression. Verdaguer et al1examined the families of 30

A man of 21 years and his sister aged 20 years had congenital bilateral horizontal gaze palsy. Convergence was normal but the vestibulocephalic and oculocephalic reflexes were absent. Aplasia of the paramedian zone of the pontine tegmentum, on a familial basis, is postulated as the cause.

To test the belief that blood is toxic to the retina, we developed an experimental model of vitreous hemorrhage in rabbits by injecting various amounts of autologous, uncoagulated, whole blood into their vitreous cavities, with the vitreous humor either intact or previously compressed by an expanding perfluoropropane gas bubble. Blood in the eyes with compressed vitreous cleared in half the time required for the same volume injected into eyes with intact vitreous (75.6 days vs 39.2 days). Large volumes of intravitreal blood (0.25 to 0.50 ml) were never toxic to the retina by ganzfeld and bright-flash electroretinography throughout a four-month observation period. The results indicated that massive vitreous hemorrhage has a dense filtering effect that can extinguish the ganzfeld but not the bright-flash electroretinogram. Blood caused moderate hemoglobin staining of the retina, without signficant iron staining (confirmed by X-ray microprobe analysis). Hemoglobin residues accumulated within cells of the inner retina, especially Muller's cells. Blood clot retraction after the injection of large volumes of fresh blood (1 ml) produced traction retinal detachment, hole formation, and subretinal accumulation of blood. This correlated with a complete and persistent extinction of the ganzfeld and bright-flash electroretinograms throughout the four-month observation period. A striking finding was that almost all eyes developed glial membranes on the peripheral retina. Fibrous membranes, causing local retinal contraction, were found over the medullary wings and optic disk in eyes with vitreous compression.

We have developed a simple technique in rabbit and baboon eyes that utilizes intravitreally injected perfluoropropane gas, which expands slowly to efficiently compress and displace nearly completely the vitreous body. There is cataract formation after extended contact of the gas bubble with the lens. However, it is rapidly reversible by reducing the duration of lens contact (gas-fluid exchange) and by using young animals. No long-term alterations in intraocular pressure or retinal function were observed, as determined by electroretinography, during the 4-month test period. Gross examination and scanning electron microscopy revealed that the vitreous cavity, shortly after full expansion of the gas bubble, was practically free of collagen. The vitreous body had been detached from most of the retina and compressed into a collagenous strand between the optic nerve head and lens in the rabbit eyes, and there was also a dense collagen accumulation on the inferior retinal surface and anterior vitreous base in the rabbits and the baboon. Large areas of the retina and medullary wings were stripped of overlying collagen. By the end of 4 months, the compressed vitreous body had expanded to become an irregular structure that remained separated from the retina in areas of previous detachment. Mechanized vitrectomy is a difficult procedure often needed in experimental work. We believe that the vitreous compression and gas-fluid exchange technique is a valid alterative to a mechanical approach. We also believe that we have a model that simulates the human situation of posterior vitreous detachment and vitreous syneresis.

• A case of unilateral proptosis secondary to Burkitt's lymphoma occurred in the ethmoidal sinuses. Involvement of the skull and paranasal sinuses by Burkitt's lymphoma may masquerade initially as an infectious process delaying diagnosis and treatment. The tumor's rapid growth and dramatic response to therapy with the potential for long-term remission and cure emphasize the need for prompt diagnosis and treatment.

We studied, prospectively, the incidence of emesis in 64 consecutive patients undergoing retinal and vitreous surgery performed either under local or general anesthesia. Of these patients 19% had at least one episode of emesis within 12 h after surgery. 30% of the patients who underwent general anesthesia had emesis, whereas only 4% of the patients with local anesthesia vomited. These results were statistically significant. Unless special attention is paid to minimize emesis, we recommend the use of local anesthesia, especially in patients with unstable metabolic disorders such as diabetes mellitus. Emesis and its potential ocular and systemic complications add to the postoperative malaise of general anesthesia.