Estimate and measure of the region of view and myopia resulting from vitreous gas.

PURPOSE: After vitreous gas injection, patients notice better acuity in downward gaze than in horizontal gaze. The authors evaluated the refractive error and the size of the region within which vision improves. METHODS: For the vitreous fluid-gas interface, the authors calculated the angle of total internal reflection and the expected myopic shift and then measured them in nine consecutive patients. The volume of gas, declination angle at which perception of small targets occurred, and preoperative and postoperative refractive error in downward gaze were measured. RESULTS: Total internal reflection occurs at 41.5 degrees declination. Patients perceived a region of improved acuity below 41 degrees (+/-5 degrees) declination. The difference between the calculated and clinically measured gas-induced myopia was less than 25% for five of nine patients. The largest measured induced myopia was -23.9 diopters (60% gas volume). In eight eyes, patients read 5-point type or smaller. CONCLUSIONS: Patients accurately perceive that their acuity improves in downward gaze; the boundary of this region corresponds with the angle of total internal reflection. Calculations predict that vitreous gas produces a myopic shift and aberration. These data support the notion that ocular positioning by patients with vitreous gas can be enhanced by instructing them to regard near targets in downward gaze.

Clinical features and pathogenesis of Alport retinopathy.

BACKGROUND: Alport syndrome refers to the clinical triad of hereditary nephritis, sensorineural deafness, and ocular abnormalities. Ultrastructural findings in the lens capsule and in the renal glomeruli have provided evidence that abnormal basement membranes are elaborated in affected tissues of patients with this disorder. Recently, the results of several linkage studies have allowed the genetic defect in Alport syndrome to be mapped to a locus that codes for a subtype of type IV collagen (alpha 5) known to be present in glomerular basement membranes. In spite of these advances, the nature of the retinal flecks in Alport syndrome and the visual consequences of the flecks remain controversial. METHODS: Detailed psychophysical and electrophysiologic testing was performed in a young man with Alport syndrome. The concurrence of an unusually extensive fleck retinopathy and unilateral pseudophakia afforded a unique opportunity to assess the effect of the flecks on retinal function. RESULTS: No sensory deficits were present in the eye with clear media. CONCLUSION: Macular flecks in Alport syndrome are not associated with demonstrable retinal dysfunction. The authors address questions about the nature and pathogenesis of the flecks in light of new clinical and genetic information.

Transmission electron microscopic study of a subretinal choroidal neovascular membrane due to age-related macular degeneration.

From a patient with age-related macular degeneration we studied ultrastructurally a disciform scar that was removed from an eye with a vitreous hemorrhage. In cross section, the scar was divided by a retinal pigment epithelial (RPE) cell layer. The choroidal side consisted of fibrovascular tissue with active neovascular buds and inflammatory cells, including macrophages attached to the RPE basement membrane. Apart from the RPE, no components of Bruch's membrane could be identified. The retinal side contained organizing hemorrhage and a collagenous matrix with fibroblastlike cells probably of RPE and choroidal origin. The anatomy and the clinical findings at surgery suggest that such scars lie on (rather than within) the inner collagenous layer of Bruch's membrane and contain two components divided by the original RPE layer. The choroidal side is fibrovascular, including active neovascularization, and the retinal side is fibrous and formed by metaplastic RPE cells and choroidal fibrovascular ingrowth.