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The choroidal vasculature lies between sclera and retina and supplies the majority of nutrients to the outer retina. It is necessary for normal visual function because it removes waste from photoreceptor disk shedding and supplies 90 to 100 percent of the oxygen photoreceptors require. Dysfunction of the choroidal vasculature occurs in systemic diseases such as diabetes and hypertension and in AMD.

Glossary

Age-related macular degeneration (AMD): Degeneration of chorio-capillaris, photoreceptors, and retinal pigment epithelium in macula.

Choriocapillaris: Capillary system of choroid.

Fenestrations: Apertures in the walls of choroidal capillaries that exclude molecules by size.

Acknowledgments

The authors acknowledge and are very grateful to D. Scott McLeod, Wilmer Ophthalmological Institute, who created the figures, critically evaluated this chapter, and provided many of the insights on the choroidal circulation that are mentioned herein. They also thank Stephen Wajer, Johns Hopkins Applied Physics Lab, Laurel, MD, who provided the image of the vascular cast.

References

1. Hayreh, S. S. (1990). In vivo choroidal circulation and its watershed zones. Eye 4, 273-289. This is a landmark paper describing watershed zones and their importance in choroid.

2. McLeod, D. S., and Lutty, G. A. (1994). High resolution histologic analysis of the human choroidal vasculature. Invest. Ophthalmol. Vis. Sci. 35, 3799-3811.

3. Shimizu, K., and Ujiie, K. (1978). Structure of Ocular Vessels. New York: Igaku-Shoin. This textbook has the most extraordinary vascular casts of the eye.

4. Flower, R. W., Frychowski, A. W., McLeod, D. S. (1995). Variability in choriocapillaris blood flow distribution. Invest. Ophthalmol. Vis. Sci. 36, 1247-1258.

5. Wangsa-Wirawan, N. D., and Linsenmeier, R. A. (2003). Retinal oxygen. Fundamental and clinical aspects. Arch. Ophthalmol. 121, 547-557. This is an excellent review about oxygen in retina and choroid and how to measure it. Linsenmeier is one of the pioneers in making direct measurements of oxygen in tissue.

6. Alm, A., and Bill, A. (1972). The oxygen supply to the retina, II: Effects of high intraocular pressure and of increased arterial carbon dioxide tension on uveal and retinal blood flow in cats. Acta Physiol. Scand. 84, 306-319.

7. McLeod, D. S., Taomoto, M., Otsuji, I., Green, W. R., Sunness, J. S., and Lutty G. A. (2002). Quantifying changes in RPE and choriocapil-laris in eyes with age-related macular degeneration. Invest. Ophthal-mol. Vis. Sci. 43, 1986-1993.

8. Bhutto, I. A., and Amemiya, T. (2002). Choroidal vascular changes in spontaneously hypertensive rats—transmission electron microscopy and scanning electron microscopy with casts. Ophthalm. Res. 34, 54-62.

9. Cao, J., McLeod, S., Merges, C. A., Lutty, G. A. (1998). Choriocapil-laris degeneration and related pathologic changes in human diabetic eyes. Arch. Ophthalmol. 116, 589-597. This was the first study to quantify the loss of choriocapillaris in diabetic choroid.

10. McLeod, D. S., Lefer, D. J., Merges, C., Lutty, G. A. (1995). Enhanced expression of intracellular adhesion molecule-1 and P-selectin in the diabetic human retina and choroid. Am. J. Pathol. 147, 642-653.

Capsule Biography

Dr. Imran Bhutto was awarded an M.D. degree from Sind University, Pakistan and a Ph.D. in Ophthalmology from the University of Nagasaki, Japan, and was a Research Associate in Department of Ophthalmology, University of Nagasaki, Japan, from 1996 to 2001. He was the winner of the Medical Research Award of University of Nagasaki School of Medicine in 2000. His research work primarily focused on ocular blood vessels and systemic diseases, and he has recently become a Research Fellow with Dr. Gerard Lutty at the Wilmer Ophthalmological Institute, Johns Hopkins Hospital, Baltimore, Maryland.

Dr. Gerard A. Lutty was awarded a masters of science degree from Catholic University of America, Washington, DC, and a Ph.D. from the Johns Hopkins School of Medicine Biochemistry, Cellular and Molecular Biology. The Wilmer Ophthalmological Institute is the Department of Ophthalmology but it seemed redundant to say that. He is the recipient of an American Heart Association Established Investigator and a Research to Prevent Blindness Lew Wasserman Merit Award. His research focuses on development of the retinal and choroidal vasculatures and how they change in disease states like diabetes, sickle cell disease, retinopathy of prematurity and age-related macular degeneration. He is an Professor at the Wilmer Ophthalmological Institute, Johns Hopkins Hospital, Baltimore, Maryland.

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