Corneal Endothelial Morphology in Eyes Implanted With Anterior Chamber Aqueous Shunts

Recent advances in high-speed scanning technology have enabled a new generation of optical coherence tomographic (OCT) systems to perform imaging at video rate. Here, a handheld OCT probe capable of imaging the anterior segment of the eye at high frame rates is demonstrated for the first time. To demonstrate real-time OCT imaging of anterior segment structures. Survey of anterior segment structures in normal human subjects. Laboratory. Achieving real-time imaging of the anterior segment, satisfactory image quality, and convenience of a handheld probe. Optical coherence tomographic imaging of the anterior segment of the eyes of human subjects was performed using 1310-nm wavelength light with an image rate of 8 frames per second. Imaging trials demonstrated clear resolution of corneal epithelium and stroma, sclerocorneal junction, sclera, iris pigment epithelium and stroma, and anterior lens capsule. The anterior chamber angle was clearly visualized. Limited imaging of the ciliary body was performed. Real-time imaging of pupillary constriction in response to light stimulus was also performed. High-speed OCT at 1310-nm wavelength is a potentially useful technique for noninvasive assessment of anterior segment structures. Our results suggest that real-time OCT has potential applications in glaucoma evaluation and refractive surgery.

To observe how the treatment of glaucoma has changed over the last decade. Retrospective, observational, population-based analysis. Medicare beneficiaries between 1995 and 2004. Medicare fee-for-service data claims between 1995 and 2004 were analyzed to determine the number of penetrating surgeries and laser procedures performed for glaucoma in the decade spanning 1995 and 2004. Number of Medicare beneficiaries receiving glaucoma-related laser procedures or surgery. Trabeculectomies in eyes without previous surgery or trauma decreased 53% over the study period, from 51,690 in 1995 to 24,178 in 2004, although trabeculectomy in eyes with scarring increased 9%. The number of aqueous shunting devices placed rose 184%, from 2728 in 1995 to 7744 in 2004. Cyclophotocoagulation procedures rose 248% over the study period, from 3264 procedures in 1995 to 11,356 procedures in 2004. Between 1995 and 2001, the number of laser trabeculoplasties decreased 57%, from a high of 151,244 in 1995 to a low of 75,647 in 2001. From 2001 to 2004, the number of trabeculoplasties more than doubled, with 157,490 performed in 2004. The number of laser iridotomies showed little fluctuation, increasing 18% over the study period and ranging from 63,773 to 85,286 every year. Over the study period, surgical iridectomies, including peripheral and sector iridectomies, decreased 66%, from a total of 4842 in 1995 to 1654 in 2004. Fistulization procedures other than trabeculectomy (including the Scheie and Holt procedures and iridencleisis) dropped 83% over the study period, decreasing from 2833 in 1995 to 478 in 2004. Medicare recipients with glaucoma are more likely to be treated with aqueous shunting procedures or cyclophotocoagulation and less likely to be treated with trabeculectomy, compared with past years. After a decline in use between 1995 and 2001, laser trabeculoplasty increased substantially from 2001 to 2004. Fistulization procedures other than trabeculectomy and surgical iridectomy have become very uncommon.

Corneal endothelium is the single layer of cells forming a boundary between the corneal stroma and anterior chamber. The barrier and "pump" functions of the endothelium are responsible for maintaining corneal transparency by regulating stromal hydration. Morphological studies have demonstrated an age-related decrease in endothelial cell density and indicate that the endothelium in vivo either does not proliferate at all or proliferates at a rate that does not keep pace with the rate of cell loss. Lack of a robust proliferative response to cell loss makes the endothelium, at best, a fragile tissue. As a result of excessive cell loss due to accidental or surgical trauma, dystrophy, or disease, the endothelium may no longer effectively act as a barrier to fluid flow from the aqueous humor to the stroma. This loss of function can cause corneal edema, decreased corneal clarity, and loss of visual acuity, thus requiring corneal transplantation to restore normal vision. Studies from this and other laboratories indicate that corneal endothelium in vivo DOES possess proliferative capacity, but is arrested in G1-phase of the cell cycle. It appears that several intrinsic and extrinsic factors together contribute to maintain the endothelium in a non-replicative state. Ex vivo studies comparing cell cycle kinetics in wounded endothelium of young ( 50 years old) provide evidence that cells from older donors can enter and complete the cell cycle; however, the length of G1-phase appears to be longer and the cells require stronger mitogenic stimulation than cells from younger donors. In vivo conditions per se also contribute to maintenance of a non-replicative monolayer. Endothelial cells are apparently unable to respond to autocrine or paracrine stimulation even though they express mRNA and protein for a number of growth factors and their receptors. Exogenous transforming growth factor-beta (TGF-beta) and TGF-beta in aqueous humor suppress S-phase entry in cultured endothelial cells, suggesting that this cytokine could inhibit proliferation in vivo. In addition, cell-cell contact appears to inhibit endothelial cell proliferation during corneal development and to help maintain the mature endothelial monolayer in a non-proliferative state, in part, via the activity of p27kip1, a known G1-phase inhibitor. The fact that human corneal endothelium retains proliferative capacity has led to recent efforts to induce division and increase the density of these important cells. For example, recent studies have demonstrated that adult human corneal endothelial cells can be induced to grow in culture and then transplanted to recipient corneas ex vivo. The laboratory work that has been conducted up to now opens an exciting new door to the future. The time is right to apply the knowledge that has been gained regarding corneal endothelial cell proliferative capacity and regulation of its cell cycle to develop new therapies to treat patients at risk for vision loss due to low endothelial cells counts.