Ultrastructure of the microvessels of the iris in mammals with special reference to their permeability

The anterior chamber of the eye technology and its anatomical, optical, and immunological bases

The anterior chamber of the eye (ACE) is distinct in its anatomy, optics, and immunology. This guarantees that the eye perceives visual information in the context of physiology even when encountering adverse incidents like inflammation. In addition, this endows the ACE with the special nursery bed iris enriched in vasculatures and nerves. The ACE constitutes a confined space enclosing an oxygen/nutrient-rich, immune-privileged, and less stressful milieu as well as an optically transparent medium. Therefore, aside from visual perception, the ACE unexpectedly serves as an excellent transplantation site for different body parts and a unique platform for noninvasive, longitudinal, and intravital microimaging of different grafts. On the basis of these merits, the ACE technology has evolved from the prototypical through the conventional to the advanced version. Studies using this technology as a versatile biomedical research platform have led to a diverse range of basic knowledge and in-depth understanding of a variety of cells, tissues, and organs as well as artificial biomaterials, pharmaceuticals, and abiotic substances. Remarkably, the technology turns in vivo dynamic imaging of the morphological characteristics, organotypic features, developmental fates, and specific functions of intracameral grafts into reality under physiological and pathological conditions. Here we review the anatomical, optical, and immunological bases as well as technical details of the ACE technology. Moreover, we discuss major achievements obtained and potential prospective avenues for this technology.

Lipemic uveitis and its etiologies in dogs: 75 cases

OBJECTIVE

To describe clinical features of dogs with lipemic uveitis (LU).

ANIMALS STUDIED

Seventy-five dogs (114 eyes) with LU.

PROCEDURES

Medical records of dogs examined by the Cornell University ophthalmology service with a clinical diagnosis of LU between 2008 and 2017 were analyzed. Signalment and clinical case aspects, including concurrent ocular disease, systemic disease, and previous ophthalmic surgery, were recorded.

RESULTS

Lipemic uveitis was diagnosed in 114 eyes of 75 dogs. The mean (±standard deviation) age of dogs was 9.0 years (±2.7 years). Miniature Schnauzers and Yorkshire Terriers were statistically overrepresented compared to the ophthalmology canine referral population. Lipemic flare varied in severity with loss of menace response due to markedly opaque flare seen in 15/114 eyes (13%). Two dogs developed LU after dietary indiscretion. Forty-nine eyes (43%) had concurrent ocular disease, most commonly keratoconjunctivitis sicca, ulcerative keratitis, and cataracts. Pseudophakia was present in 75/114 eyes (66%) and LU developed within 30 days of an intraocular surgical procedure in 63/114 eyes (55%). Hypertriglyceridemia was noted in 52 dogs of the 55 dogs tested (95%). Systemic disease affected 54/75 dogs (72%), of which diabetes mellitus, hyperadrenocorticism, and hypothyroidism were overrepresented compared to the referral population. Primary hyperlipidemia was identified in 12 dogs. Lipemic uveitis resolved at first reevaluation in 92/110 eyes (84%) and recurred in 6/114 eyes (5%) after complete resolution.

CONCLUSIONS

Development of lipemic uveitis in dogs appears to require the combination of hyperlipidemia and uveitis. Systemic disease is commonly associated with LU in dogs.

A contemporary concept of the blood-aqueous barrier

This review traces the evolution of the concept of the blood-aqueous barrier (BAB) during the past 20 years. The Classical model simply stipulated that the tight junctions of the iris vasculature and ciliary epithelium excluded plasma proteins from the aqueous humor (AH). It failed to reconcile the presence of AH protein levels equal to 1% of that found in plasma. Moreover, models of barrier kinetics assumed that the processes of AH secretion and plasma protein entry were directly linked. Thus, elevations of AH protein levels could only be explained by a pathological breakdown of the BAB. Over the last 20 years it has been shown that the plasma proteins in normal AH by-pass the posterior chamber entirely. Instead, these proteins diffuse from the capillaries of ciliary body stroma, into the iris stroma and then into the anterior chamber. This creates a reservoir of plasma-proteins in the iris stroma that is not derived from the iris vessels. This reservoir is prevented from diffusing posteriorly by tight junctions in the posterior iris epithelium. The one-way valve created by the pupil resting on the anterior lens capsule, combined with the continuous, forward flow of AH through the pupil, prevents protein reflux into the posterior chamber. Importantly, in the new paradigm, secretion of AH and the entry of plasma proteins into AH, are semi-independent events. This opens the possibility that AH protein levels could increase in the absence of breakdown of the BAB. Clinical consequences of this new paradigm of the BAB are discussed.

Quantitative determination of aqueous flare and cells in healthy eyes

We studied 263 eyes of 141 normal subjects, 33 men and 108 women, including 129 Finns and 12 Ibero-Americans, with the age ranging between 12 and 89 (mean 43.0 +/- 20.4) years using the Kowa FC-1000 laser flare cell meter. The mean photon count/ms was 4.5, it was 3.1 in the age groups of 10-19 years and 11.5 in the age group of 80 years or over; the increase with age was statistically significant (p = 0.0001). There were no significant differences in the photon count/ms between right and left eyes (p = 0.75), between sexes (p = 0.61), or between Ibero-Americans and age-matched Finns (p = 0.62). The mean cell count was 1.1 and there were no significant changes between the right and left eyes (p = 0.56) or between different age (p = 0.38), sex (p = 0.32) and race (p = 0.64) groups. There were no significant differences in the mean photon count/ms (p = 0.97) and cell counts (p = 0.35) between the first and second measurements 5 min later. There was no subject-within variability after 24 h and 7 days in the flare (p = 0.95) and cell counts (p = 0.89).

Comparison of lectin reactivity in the vessel beds of the rat eye

The capillary beds of the eye are lined by two types of endothelia, fenestrated in the choriocapillaris and ciliary body, and continuous in the retina and iris. In this study, we wished to find a marker for each of these types of vessel beds using lectin histochemistry. Sections of glutaraldehyde fixed rat eyes embedded in epoxy resin were extracted with sodium ethoxide and rehydrated. Binding of 15 different lectins was visualized using the avidin-biotin peroxidase technique. We found WGA, WGA-s, LFA and PHA-E to strongly bind retinal vessels. In addition to the above lectins, iris vessels bound GSL-I. Choriocapillaris reacted variably only with WGA and not at all with other lectins tested. Vessels of ciliary body processes did not react with any lectin studied. The less fenestrated vessels of the base of the ciliary process bound lectins similar to the retina. We speculate that the differential lectin staining of the various vessel beds of the eye may reflect the degree of fenestration of the endothelium. This reactivity may be influenced by variations in the surrounding milieu including cells and extracellular matrix.

Rubeosis iridis and glaucoma associated with sickle cell retinopathy: a light and electron microscopic study

The ultrastructure of rubeosis iridis in sickle cell-hemoglobin C disease is described for the first time. Findings included open interendothelial cell junctions, intraendothelial cytoplasmic attenuations (fenestrations), and pericyte formation. The ultrastructural appearance of rubeosis iridis gives no clue to the underlying etiology and is similar to that reported in rubeosis associated with diabetes mellitus, central retinal vein occlusion, and uveitis. The electron microscopic findings explain the functional incompetence of rubeotic vessels that are manifested by transmural leakage of fluorescein.