Handbook of Nutrition, Diet, and the Eye

Victor R Preedy, Ronald Ross Watson, Victor R. Preedy

• Publisher: Academic Press
• Year: 2019
• eBook ISBN: 9780128152461
• Edition: 2
• Topic: Biological Sciences
• Subtopic: Neuroscience
• Index: Biological Sciences

Handbook of Nutrition, Diet, and the Eye, Second Edition, thoroughly addresses common features and etiological factors on how dietary and nutritional factors affect the eye. The ocular system is perhaps one of the least studied organs in diet and nutrition, yet the consequences of vision loss are devastating. There are a range of ocular defects that have either their origin in nutritional deficiencies/excess or have been shown to respond favorably to nutritional components. Featuring a new section on animal model studies where both the ocular problem and dietary remedies can be varied, there are also new chapters on dietary supplements.- Serves as a foundational collection for neuroscience, neurology and nutrition researchers, illustrating the importance of nutrition and diet in eye health and function- Provides a common language for readers to discuss how nutritional factors and related diseases and syndromes affect the eye- Features new chapters on infectious diseases of the eye where nutrition is a factor- Discusses animal model studies, dietary supplements, natural dietary extracts from around the world, and age-related changes in ocular health

Section B

Macular Degeneration

2

Overview of Risk Factors for Age-Related Macular Degeneration

R.A. Armstrong^⁎; R.P. Cubbidge^{† ⁎} Optometry School, Aston University, Birmingham, United Kingdom
^† Vision Sciences, Aston University, Birmingham, United Kingdom

Abstract

Age-related macular degeneration (AMD) is a multifactorial disorder and identification of risk factors enables individuals to make lifestyle choices that may reduce disease risk. Genetics plays a significant role in AMD especially in younger patients, with complement system genes and the age-related maculopathy susceptibility protein 2 (ARMS2) gene accounting for a significant proportion of cases. Smoking is the modifiable risk factor most consistently associated with AMD with current smokers having a two to three times higher risk than nonsmokers. There is increasing evidence that dietary factors may influence the risk of AMD, but whether the risk is increased by exposure to sunlight or associated with alcohol is controversial. Synergistic effects occur among the risk factors and therefore, cessation of smoking, dietary changes, and the regular use of dietary supplements should be considered to reduce the lifetime risk of AMD especially in those individuals carrying “at risk” genetic alleles.

Keywords

Age-related macular degeneration (AMD); Risk factors; Genes; Smoking; Sunlight; Diet; Alcohol

Chapter Outline

• Introduction
• Genetic Risk Factors
• Dietary Risk Factors
• Cardiovascular Risk Factors
• Sunlight
• Smoking
• Alcohol
• Discussion and Conclusions
• Summary Points
• References

List of Abbreviations

aAMD advanced AMD

ABCR ATP-binding cassette rim protein

ACE angiotensin-converting enzyme

AMD age-related macular degeneration

APOE apolipoprotein E

ARDES age-related eye disease study

ARM age-related maculopathy

ARMS2 age-related maculopathy susceptibility protein 2

BDES Beaver Dam Eye Study

BES Beijing Eye Study

BMES Blue Mountain Eye Study

BMI body mass index

C3 factor 3

CACNG3 voltage-dependent calcium channel 3

CBWS Chesapeake Bay Waterman Study

CC case-control study

CFB complement factor B

CFH complement factor H

CI 95% confidence interval

dGI dietary glycemic index

DHA docosahexanoic acid

EDCCSG Eye Disease Case-Control Study Group

ERCC6 DNA excision repair protein

FGF2 fibroblast growth factor 2

HDL high-density lipoprotein

HR hazard ratio

HTRA1 HTRA serum peptidase 1

LOX1 lysyl oxidase-like 1

MPCC matched pairs case-control study

OR odds ratio

PHS Physician’s Health Study

POLA Pathologies Oculaires Liées à l’Age study

PS prospective study

RR relative risk

SA survival analysis

SELP selectin-P

SERPING1 serpin peptidase inhibitor

SiMES Singapore Malay Eye Study

Introduction

Age-related macular degeneration (AMD) is the most important cause of blindness in industrialized countries in individuals over 65 years of age. In the United Kingdom, for example, overall prevalence of late stage AMD is 2.4% of the population and approximately 10% of patients 66–74 years of age exhibit some evidence of macular degeneration, prevalence increasing to 30% in patients 75–85 years of age.¹ According to the most recent estimates, there are 513,000 individuals currently in the United Kingdom with the visual impairment characteristic of AMD suitable for registration as seriously visually impaired. This figure is predicted to rise to 679,000 by 2020 as the proportion of older individuals in the population continues to increase, a phenomenon likely to be repeated in many countries.

There are two forms of AMD, viz. the “atrophic” or “dry” form and the “exudative” or “wet” form. The dry form is characterized by degeneration of the macular pigment epithelium, choriocapillaris, and photoreceptor cells. Larger areas of degeneration result from the merging of small areas of atrophy and this state is often referred to as “geographic atrophy.” By contrast, in the wet form, new choroidal vessels are formed (neovascularization) and ultimately retinal detachment, edema, and hemorrhage may occur followed by macular degeneration. Age-related maculopathy (ARM) is a further term often used to describe the early stages of AMD and is characterized by the presence of discrete drusen and increased deposition of retinal pigment in individuals over 50 years of age.

Multiple risk factors are likely to be involved in AMD including genetics, diet, cardiovascular disease, sunlight, smoking, and alcohol.^2–4 There are also likely to be synergistic effects among these risk factors, which will ultimately determine the overall risk of disease for an individual. The objective of this chapter is to review the major risk factors associated with AMD and their interactions and to assess their relative contribution to AMD risk.

Genetic Risk Factors

Genetic factors play a highly significant role in AMD, 52 individual gene associations having been detected, including common and rare variants, across 34 gene loci.⁵ The most important genes linked to AMD are involved in immune modulation and in the complement system such as complement factor H (CFH),^6–8 complement factor B (CFB),⁹ factor 3 (C3),¹⁰ and serpin peptidase inhibitor (SERPING1)¹¹ strongly suggesting that inflammatory processes are important. Hence, CFH, C3, and SERPING1 together with HTRA serum peptidase 1(HTRA1), which may regulate the availability of insulin-like growth factor, could account for 45% of the total AMD risk.¹¹ Genes associated with membrane transport such as ATP-binding cassette rim protein (ABCR),¹² and voltage-dependent calcium channel 3(CACNG3),¹² the vascular system, for example, fibroblast growth factor 2 (FGF2),¹³ Lysyl oxidase-like 1 (LOX1),¹⁴ and selectin-P (SELP),⁷ and with lipid metabolism, for example, apolipoprotein E (APOE),¹⁵ and LOX1¹⁶ may also be involved. Genes associated with the vascular system are of particular intere...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright
• Contributors
• Section A: Introductions and Overviews
• Section B: Macular Degeneration
• Section C: Glaucomas and Cataracts
• Section D: Other Eye Conditions
• Section E: Obesity and Macronutrients
• Section F: Micronutrients
• Section G: Nutraceuticals
• Index