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 microns. 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.

Melanocytes and iris color. Electron microscopic findings.

OBJECTIVE: To quantitatively associate iris color with melanocyte pigment content. METHODS: Autopsy eyes were classified as uniform-blue, uniform-hazel, or uniform-brown or showing a darker peripupillary ring. Using electron microscopic images and computerized image analysis, area, number, and size of mature melanosomes within the perinuclear cytoplasmic area only or within perinuclear and peripheral cytoplasmic areas of the superficial stromal melanocytes combined were measured. RESULTS: Average melanosomal area per perinuclear cytoplasmic area (AMAC) and average number of melanosomes per perinuclear area (AMNC) significantly differed across iris color groups (overall P<.001). This result reflects the large difference between blue-uniform and all other color groups. A marginally significant (nominal) trend from blue-ring through brown-ring was also detected (P=.06 for AMAC and P=.07 for AMNC). The average perinuclear cytoplasmic area was larger in the central iris zone (within 1 mm around the pupillary margin) than in the intermediate iris zone (between 1 and 2 mm around the pupillary margin) (P=.002), but AMAC and AMNC did not significantly differ between zones. The average melanosome size did not differ significantly across color groups (P=.11). CONCLUSION: Differences in iris colors are at least partially attributed to variable AMNC and AMAC within superficial melanocytes.

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.

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.

Systemic hypertension produces pericyte changes in retinal capillaries.

PURPOSE: The purpose of this study was to examine retinal capillaries and their pericytes that previous research suggests to be contractile. A contractile role regulating capillary blood flow may be more apparent when the vasculature is subjected to the stress of systemic hypertension. METHODS: Using ultrastructural morphometry and the myosin subfragment-1 technique, retinal capillaries of normal and hypertensive rats were measured at three different time points, early, intermediate, and late (24, 44, and 68 wk). RESULTS: Hypertensive capillaries seemed to dilate at the early time point (P = 0.002), were constricted at the intermediate time point (P < 0.001), and did not redilate later. Wall thickness was enlarged at all times, pericyte coverage (the ratio of plasma membrane length in contact with the vascular circumference to the outer circumference of the endothelial tube) was greater at early and intermediate time points, and the total area of viable cytoplasm relative to the vessel wall area was increased at the intermediate time (all P < 0.001). Also, at the intermediate time, the circumferential coverage of the endothelial tube by actin filament bundles within pericytes and the actin area relative to the vessel wall area had increased (P < 0.001). CONCLUSIONS: These data indicate that the effects of systemic hypertension extend into the retinal capillary bed, causing pericyte change with actin increase and capillary constriction. They represent the first in vivo indirect evidence by morphologic criteria for pericyte contractility in retinal vascular disease.

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.

Pericyte changes in branch retinal vein occlusion.

The model of experimental branch vein occlusion (BVO) in the monkey offers the opportunity to examine retinal capillaries under stress. Electron microscopic morphometry was done on 812 capillaries of 13 eyes of cynomolgus monkeys, comparing 579 capillary collaterals of 9 BVO eyes with 233 normal capillaries of 4 control eyes. The tissue underwent the myosin subfragment-1 technique to decorate and quantify bundles of actin filaments in capillary pericytes. The duration of BVO was 2-48 months. Capillary collaterals of BVO eyes had an enlarged caliber, endothelial hyperplasia, and pericyte hypertrophy, but no proportional increase in basement membrane area. Collaterals near the inner plexiform layer (IPL) had a greater wall thickness, pericyte coverage, and actin coverage than collaterals near the outer plexiform layer (OPL). Pericyte hypertrophy was proportionate to caliber increase in OPL vessels and exceeded caliber increase only in IPL vessels. Actin coverage was proportional with the vessel dilation and size of pericyte cytoplasm in all vessels. These findings indicate that capillary collaterals in BVO are not equipped morphologically for an increased regulatory role in microvascular flow beyond their normal function.

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.