Nutritional and Environmental Influences on the Eye Allen Taylor. Boca Raton, FL: CRC Press. Pages: 285. Price: $129.95. ISBN: 0-8493-8565-2
Allen Taylor, Ph.D., is the Director of the Laboratory for Nutrition and Vision Research at the United States Department of Agriculture’s Jean Mayer Human Nutrition Research Center on Aging at Tufts University. The CRC Series in Modern Nutrition explain, review, and explore present knowledge and recent trends, developments, and advances in nutrition. Dr. Taylor has done a remarkable job in assembling myriad disciplines and professions to create, for the first time, an organized compendium text that can be used by both eye clinicians and basic science researchers. Dr. Taylor states in chapter 1: “The inspiration for putting this book together was my conviction that we are on the verge of achieving a means to diminish the risk for cataract and AMD.” This text explicitly reviews undeniable scientific evidence—the biochemical, cell biological, physiological, and epidemiological association of cataract and AMD, with each other and with nutrition and other environmental influences. The text also discusses uniform means to evaluate eye tissue damage—perhaps the most crucial element in successful therapeutic intervention. Taken together, the implications to eye care in the coming millennium are both evolutionary and revolutionary.
The text is divided into two parts. The first part covers the lens—a slow-metabolizing tissue—and the second covers the retina, a fast-metabolizing tissue. In both cases, nutrients provide potent antioxidative influences that may be exploited to delay age-related or environmental tissue stress.
Chapter 2, written by Shambhu Varma, Ph.D., et al., of the University of Maryland, discusses reactive oxygen species (ROS) in the pathogenesis of cataract, with a relevant historical discussion of the discovery and biologic reactivity of oxygen by Priestley in 1775. The reader is introduced to the concepts of oxygen free radicals, gene-derived antioxidant enzymes, photochemical reactions, and endogenous and exogenous photosensitizers. The central importance of the nutrient ascorbate (vitamin C), which is substantially higher in concentration in the ocular fluids of diurnal animals (including humans), is given ample coverage. The chapter concludes with Dr. Varma’s discovery that pyruvate, an α-keto acid end product of glycolysis, is a potent anticataractogenic agent when administered as a 10% eyedrop to rats fed a cataract-forming galactose diet.
Chapter 3 follows with a logical discussion on the evolution of measuring lens opacification (i.e., cataract) written from a historical perspective by Leo Chylack, M.D., of the Brigham and Women’s Hospital in Boston. It is now possible to quantify the type, severity, and rate of growth of age-related cataracts. Dr. Chylack notes the contributions of Drs. Ian Bailey and Mark Bullimore and states “we are prepared to move into prospective, randomized, placebo controlled, double masked clinical trials of anti-cataract medications or nutritional supplements.”
Taylor authored chapter 4, which concerns environmental and nutritional influences on risk for cataract. Dr. Taylor has a long record of accomplishment in basic science publications on the etiopathogenesis of cataract with specific attention to the association with ascorbic acid. As a scientist, Dr. Taylor takes a critical and measured perspective of all of the data, some of which is negative, concerning nutrient intakes and serum levels and the risk of age related cataract. The chapter contains a series of very useful cataract risk ratio diagrams of historical studies for vitamin C, vitamin E, and carotenoids as well as composite measures of antioxidant intake. The conclusion of this chapter is similar to that of chapter 3: “… since cost-benefit analysis regarding remediation clearly indicates that cataract prevention is preferable (and essential where there is a dearth of surgeons) to surgery, it is not premature to contemplate the value of interventions for populations at risk.”
Chapter 5, authored by William D. Christen, Sc.D., of Brigham and Women’s Hospitals, Boston discusses the critical elements required to evaluate the heft of a cataract nutritional epidemiologic study with respect to the limitations of the study design employed. He reminds us that confounding is a significant issue in cataract studies because “persons with favorable diets are likely to differ from persons with less-favorable diets on a range of factors that may be related to the risk of developing cataracts.”
George Bunce, Ph.D., of Virginia Polytechnic, authored chapter 8, which reviews the animal studies exploring associations between nutrients and the development and preservation of function of the mammalian lens. This includes the role of micronutrients: carbohydrates, protein and amino acids, vitamins—riboflavin, vitamins C and E—and the minerals zinc, copper, manganese, iron (an oxidant), and selenium. The nutritional measures that defend against cataract are the same as those endorsed to promote longevity, namely optimization of oxidant defenses, minimization of oxidant stress, and avoidance of obesity. It is interesting that reduction of calories to 79% of ad libitum levels alone lowered the incidence of spontaneous cataract to 41% in Emory mice. On the other hand, Dr. Bunce, a biochemist, reminds us that “there is clear evidence that diabetes enhances cataract (by 3 to five-fold)… . it is therefore our responsibility to inform the public of these facts and to encourage a healthy lifestyle that includes avoidance of caloric excess.”
Chapter 7, by John Clark, Ph.D., and Toshihiko Hiraoka, M.D., Ph.D., both from the University of Washington School of Medicine in Seattle, present cataract formation as a biophysical protein aggregation (crystalline lens) phase separation problem. The authors state “there is reason to be optimistic about the potential for development of anti-cataract therapies that can inhibit or delay protein aggregation during cataract formation.” Pantethine, a natural metabolite of pantothenic acid found in all cells and tissues, as well as other “multifunctional” natural compounds (ATP, glutathione, and ascorbic acid), are suggested as potential anticataractogenic agents.
Chapter 8, written by Cathy McCarty, Ph.D., M.P.H., R.D., and Hugh Taylor, M.D., of The Royal Victorian Eye Hospital in Melborne, Australia, discusses the evidence for “light” as a risk for age-related eye diseases in general. I was impressed with the terse 12-page historical review of the ocular radiation literature. In the authors’ words, “the data support a role for sunlight in the development of cataract, pterygium and possibly AMD… . it is therefore prudent to recommend that people protect their eyes from the sun, both visible light and UV B, through the avoidance of the midday sun and the use of brimmed hats and sunglasses.”
Chapter 9, written by Sheila West, Ph.D., of the Wilmer Eye Institute of the Johns Hopkins Medical Institutions, leaves little doubt that smoking is related to the two main causes of visual loss in the world today, cataract and exudative AMD. In addition, it is significant that smoking resembles premature senescence in terms of cataracts, cardiovascular disease, dermatologic and immunologic changes—all are features of the aging process. Although Dr. West makes an impassioned plea to convince our young and old alike to avoid smoking, she avoids suggesting the use of diet or supplementation to offset cigarette damage in recalcitrant smokers. One could argue, after reviewing the scientific evidence presented in the first half of this text, that this advice should also be our responsibility.
The second half of the text actually consists of only three chapters, but they are all well done. Chapter 10, by Moshe Lavav, M.D., of the NEEL Boston VA Medical Center, reviews attempts at creating a classification systems for AMD. Systems for classification, whether visual or computerized, “should be constructed based on known clinical histopathological correlation… rather than obvious manifestations such as drusen.” Chapter 11, concerning diet and AMD, was written by J. A. Mares-Perlman, Ph.D., and R. Klein, M.D., of the University of Wisconsin Medical School. They present a succinct discussion of the pathophysiology of AMD using simplified anatomic diagrams. The oxidative stress, impairment of choroidal circulation, and degradation of Bruch’s membrane theories are discussed. They make the important point that although epidemiologic evidence is inconsistent between diet and AMD, this may actually result from study design limitations or measurement/classification errors. Chapter 12, by Wolfgang Schalch, Ph.D., of Hoffman-La Roche, and Dr. Barker, of Pennsylvania College of Optometry, reviews the very exciting topic of carotenoids in the retina and the fact that, with dietary modification, macular pigment density can be enhanced within months in most people. The concluding chapter of this CRC text, authored by D. Max Snodderly, Ph.D., of the Schepens Eye Research Institute, and Billy Hammond Jr., Ph.D., of Arizona State University, reviews the in vivo assessment of macular pigment and lens density, which should certainly be of interest to those optometrists who wonder what the next century holds in terms of the intertwined effects of genes and environment on aging.
In conclusion, Nutritional and Environmental Influences on the Eye offers up-to-date and practical information on nutrition as related to eye disease written by internationally renowned experts in their respective fields. These significant advances concerning nutrition’s impact on the eye are certainly of value to all optometrists with an interest in preventive medicine of the eye. FIGURE