Colleen D. Bindley

Identification of orbital lymphatics: enzyme histochemical light microscopic and electron microscopic studies.

The presence of orbital lymphatics in the primate model is demonstrated using light and electron microscopic enzyme histochemistry. In addition, strictly morphological definitions of lymphatics, such as discontinuous basal lamina, thin and irregular walls, anchoring filaments, and attenuated endothelial cell cytoplasm, were applied. This study confirmed the presence of conjunctival lymphatics reported by others. It also clearly demonstrated the presence of orbital arachnoid and lacrimal gland lymphatics that have not been previously described. A few areas of the extraocular muscles and connective tissue at the orbital apex also showed evidence of the presence of lymphatic vessels. Additional work is needed to define the nature and extent of orbital lymphatics as well as their connection to the extraorbital lymphatic system.

Cystoid Macular Degeneration in Experimental Branch Retinal Vein Occlusion

Macular edema and collateral vessels were examined clinically and histopathologically up to 48 months after branch retinal vein occlusion in six eyes of five cynomolgus monkeys. In all six, central macular swelling and fluorescein leakage from the retinal vasculature were confined to the acute stage. However, histopathologically, at the chronic stage, only two maculas were completely recovered and unremarkable, whereas the other four showed variable degrees of cystoid degeneration and photoreceptor cell loss. In the two recovered maculas, six to eight normal-sized capillaries separated the fovea from the nearest cluster of capillary collaterals. In three maculas with cystic degeneration, collaterals incorporated the circumfoveal capillaries. In the fourth macula with cystic degeneration, collaterals were separated from the center by two normal-sized capillaries but were also associated with large areas of capillary nonperfusion partially due to occlusion of the macular arteriole.

Renin mRNA is synthesized locally in rat ocular tissues.

Components of the Renin Angiotensin System (RAS) have been detected in ocular tissues and fluids. The source of the ocular RAS proteins is unknown but possibilities include diffusion or leakage from the systemic circulation, specific uptake from the blood, or local synthesis. We have used RT-PCR and in situ hybridization (ISH) to show that renin mRNA is present in ocular tissues from 3 strains of rats. By RT-PCR, we found 10 of 15 ciliary body samples, 13 of 16 iris samples, and 1 of 3 retina samples were positive for renin mRNA. Also, 6 of 6 brain and 7 of 8 kidney samples were positive. Using ISH, we found renin mRNA in the ciliary muscle adjacent to the sclera extending into the choroid. Tissue near the outflow channels of the anterior chamber angle also labeled. Retinal labeling was weak but present in the nerve fiber layer. Clusters of grains, possibly representing blood vessels, were also seen in the ciliary body, iris, and retina using ISH. These results suggest the presence of a local ocular RAS.

CLINICOPATHOLOGIC CORRELATION OF INTRARETINAL MICROVASCULAR ABNORMALITIES

Purpose: To define the cross‐sectional morphology of intraretinal microvascular abnormalities, which previously have been described only in terms of trypsin digestion. Material/Methods: Fourteen vascular lesions of five patients with diabetic retinopathy were identified on fundus photographs and/or fluorescein angiograms and classified as intraretinal microvascular abnormalities. Eyes of these patients were obtained after the patients’ deaths. The period between the time at which the photographs were taken and that at which enucleation was performed was 3‐20 months. The duration of autolysis before fixation was 5 hours or less. The embedded tissue was evaluated by light and electron microscopy, and these findings were correlated with the clinical appearance. Results: The lesions consisted of multiple, closely spaced, thin‐walled vascular lumina with a caliber of 20‐70 &mgr;m. They were located in the inner retina and surrounded by a wide cuff containing randomly oriented collagen fibers. Endothelial cell nuclei were numerous. Pericyte degeneration and multiplication of the endothelial and pericyte basement membrane had occurred. Endothelial junctions were short, and gaping of junctions was not seen. However, occasional fenestrations were present. Conclusion: The cross‐sectional morphology of intraretinal microvascular abnormalities is consistent with vascular pathology typical for intraretinal diabetic microangiopathy, but also includes features usually seen in new vessels. This supports the concept that intraretinal microvascular abnormalities have the particular potential for neovascularization.

Ocular renin angiotensin: EM immunocytochemical localization of prorenin

Prorenin (PR) was localized by electron microscopic (EM) immunostaining of cryo-ultramicrotomy sections of human ciliary body and correlated with light microscopic immunostaining. Both layers of the ciliary epithelium contained the prohormone. However, density was much higher in the adjacent extracellular spaces, particularly in the vitreous cortex. This observation adds further evidence to a role of the ciliary epithelium in the transfer, storage or synthesis of components of a putative ocular renin angiotensin system.

FOCAL PHOTOCOAGULATION OF DIABETIC MACULAR EDEMA: A Clinicopathologic Case Report

This is the first reported clinicopathologic correlation of focal photocoagulation treatment in a diabetic patient treated as part of the Early Treatment of Diabetic Retinopathy Study (ETDRS). Twenty focal argon laser burns were evaluated clinically in their acute and chronic stages, and histopathologically more than 3 years after exposure. Damage profiles of the lesions were reconstructed from serial tissue sections. In single burns the outer nuclear layer defect measured 78 +/- 31 microns, in confluent burns 257 +/- 73 microns. Inner nuclear layer defects were present only in lesions that clinically, during their acute stage, showed a white center or a white collar around the treated target. Fibrous subretinal and subpigment epithelial membranes extended from the burn centers for a distance of up to 900 microns and contained Müller cell processes as identified by immunostaining. These findings confirm the empirical rationale of current focal treatment, but also, because of the apparent risk of membrane formation, urge caution when treating close to the fovea.

Chorioretinal and Choriovitreal Neovascularization After Photocoagulation for Proliferative Diabetic Retinopathy: A Clinicopathologic Correlation

A patient with proliferative diabetic retinopathy was treated by panretinal and focal photocoagulation. Later, he developed one area of clinically diagnosed chorioretinal and choriovitreal neovascularization (CNV), neovascular glaucoma, and a blind painful eye necessitating enucleation. Clinicopathologic correlations of this eye including fundus photography, fluorescein angiography, light and electron microscopy are reported. Histopathologic examination revealed three areas of CNV, suggesting that some CNV may go undetected clinically also in other cases and thus may occur more frequently than evident from the literature. Our CNV occurred at sites of focal treatment. Retreatment of one area was unsuccessful. Choriovitreal neovascularization passed through discontinuities of Bruchs membrane into the retina and showed fenestrae of the endothelial cells. Endothelial fenestrae may account for the profuse fluorescein leakage seen clinically in CNV.