Histopathology and immunocytochemistry of the neurosensory retina in fundus flavimaculatus.

BACKGROUND: Fundus flavimaculatus (Stargardt disease) is a group of inherited macular dystrophies in which central vision usually decreases in the first two decades of life. Previous histopathologic studies used light, scanning, and transmission electron microscopy to characterize the retinal pigment epithelium (RPE) in fundus flavimaculatus. The authors describe in detail the pathologic changes in the neurosensory retina, including use of specific immunocytochemical markers. METHODS: The eyes of a patient with fundus flavimaculatus were processed using Medcast and JB-4 plastic for light and electron microscopy, and cryomicrotomy and LR-white resin for immunocytochemistry. RESULTS: Changes in the RPE occurred in a peripheral/central gradient and included increased lipofuscin content and cell loss toward the macula. The changes in the retina paralleled those in the RPE, including accumulation of lipofuscin in photoreceptor inner segments, loss of photoreceptors, and reactive Müller cell hypertrophy. Immunocytochemistry using rod- and cone-specific markers showed abnormal photoreceptor morphology but qualitatively normal immunoreactivity, and there was strong reactivity for glial fibrillary acid protein in reactive Müller cells. Labeling for cellular retinaldehyde-binding protein was qualitatively normal in Müller cells, but was reduced in RPE cells that were engorged with lipofuscin. CONCLUSIONS: The histopathologic changes in the retina correlate with clinical progression of the disease process. Although abnormal lipofuscin metabolism has been implicated in the loss of vision in fundus flavimaculatus and other macular diseases, the mechanism is not understood. Based on the authors' observations and a review of recent literature on lipofuscin, the authors propose that all-trans-retinol dehydrogenase, a photoreceptor outer segment enzyme, may be defective in fundus flavimaculatus.

A cryodamage model for studying corneal nerve regeneration.

This study used a transcorneal freezing technique to produce a 2-mm circular, central wound in the rabbit cornea for investigating corneal nerve regeneration. All the corneal cells, nerves, and associated Schwann cells were dead inside the wound, but the extracellular matrix components remained intact. The destroyed epithelium and endothelium were replaced in 1 and 5-7 days, respectively. The necrotic keratocytes and stromal and subepithelial nerves were removed completely in 1-3 days by invading macrophage-like cells. The wounded stroma was repopulated centripetally by migrating keratocytes between days 1-5. Two types of nerve growth were identified in the stroma. The first type was novel sprouting of straight, long neurites between days 2-21, initially from the undamaged, periwound nerves and later from regenerated stromal nerves inside the wound. These small-caliber neurites proliferated in a random and disorderly pattern both inside and outside the wound and sometimes terminated on stationary, stellate keratocytes. The second type was genuine regrowth of stromal and subepithelial nerves in a centripetal direction between days 3-7. Schwann cells appeared on the newly formed nerves starting on day 4 or 5. A near-normal pattern and size of the nerves were established in the wound as early as day 10. In the epithelium, transient, wound-oriented neurites (days 1-3), single nerves, and semileashes (days 4-10) appeared. A near-normal leash pattern was restored between days 10-21 only at the wound periphery. Thus, in this model, the major groundwork of nerve regeneration occurred between days 3-10, simultaneously, at all three levels of nerve organization. These data suggest that nerve-Schwann cell interaction contributes to the restoration of stromal and subepithelial nerves, whereas a reparative epithelium deficient in trophic activity may account for the incomplete regrowth of epithelial nerves. The cryodamage model offers an efficient and multifaceted system for the experimental study of corneal nerve regeneration.