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«Visual Impairment Geoffrey C. Tabin, M.D. Kurt H. Kelley, M.D. John A. Moran Eye Center Fletcher Allen Health Care University of Utah University of ...»

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Visual Impairment

Geoffrey C. Tabin, M.D. Kurt H. Kelley, M.D.

John A. Moran Eye Center Fletcher Allen Health Care

University of Utah University of Vermont

Burlington, VT

Salt Lake City, UT

Prepared as part of an education project of the Global Health

Education Consortium and collaborating partners

Learning objectives

1. To briefly review normal eye anatomy

2. To be able to define and appreciate the magnitude of visual impairment

3. To understand why visual impairment is an important global health issue

4. To be able to describe the major causes of visual impairment worldwide, including background, epidemiology, and management

5. To present some of the public health efforts to improve eye health worldwide Page 2 Normal eye anatomy

• Before we begin a discussion of visual impairment and its causes, let’s take a moment to review the normal structures of the eye (seen here in cross-section).

Cross-sectional diagram of the human eye. (Image:

National Eye Institute, National Institutes of Health) Page 3 Normal eye anatomy

• Cornea: the transparent front “window” of the eye, the cornea serves as an important refractive surface.

• Iris: the colored part of the eye which helps to screen out and focus incoming light.

• Pupil: the circular opening in the center of the iris.

• Lens: a transparent, biconvex structure behind the pupil and iris that aids in focusing of images.

• Retina: the neural tissue which lines the back of the eye, it converts light energy to impulses that travel to the brain via the optic nerve.

• Macula/Fovea: the area of the retina responsible for fine, central vision.

Page 4 What is visual impairment?

• Includes both low vision and blindness, as clinically

defined by the World Health Organization (WHO):

– Low vision is the inability, even with corrective lenses, to clearly see at a distance of 6 meters (20 feet) what individuals with normal vision can clearly see at a distance of 18 meters (60 feet).

– Blindness is the inability to read the largest letter on a vision chart at a distance of 3 meters (10 feet).

WHO. International statistical classification of diseases, injuries and causes of death: tenth revision. Geneva: WHO, 1992.

Page 5 The magnitude of visual impairment

• Accordingto WHO, in 2002 more than 161 million people were visually impaired. Of those individuals, an estimated 37 million were blind.

• Uncorrected refractive error (near-sightedness, farsightedness, and astigmatism) may account for an additional 82 to 117 million cases of visual impairment.

• Over 90% of all blind people live in developing countries.

–- Resnikoff S et al. Global data on visual impairment in the year 2002. Bull World Health Organ 2004;


–- Dandona L, Dandona R. What is the global burden of visual impairment? BMC Med 2006; 4:6.

–  –  –

• Blindness and low vision are important global health issues because they confer increased morbidity and mortality, decreased quality of life, and substantial economic productivity loss.

• Without additional intervention, the total number of blind people worldwide has been predicted to increase to 76 million by 2020.

• Remarkably, at least 75% of world blindness is believed to be entirely treatable or preventable. Let’s discuss the leading causes.

–- Frick KD, Foster A. The Magnitude and Cost of Global Blindness: An Increasing Problem That Can Be Eliminated. Am J Ophthalmol 2003; 135:471-476.

–- Lee DJ et al. Visual Impairment and Morbidity in Community-Residing Adults: The National Health Interview Survey 1986-1996. Ophthalm Epidemiol 2005; 12:13-17.

–- McCarty CA et al. Visual impairment predicts 5 year mortality. Br J Ophthalmol 2001; 85:322-326.

–- Lee DJ et al. Visual Acuity Impairment and Mortality in US Adults. Arch Ophthalmol 2002; 120:1544-1550.

–- Wang JJ et al. Visual Impairment, Age-Related Cataract, and Mortality. Arch Ophthalmol 2001; 119:1186- Knudtson MD et al. Age-Related Eye Disease, Visual Impairment, and Survival: The Beaver Dam Eye Study. Arch Ophthalmol 2006; 124:243-249.

–- Vu HTV et al. Impact of unilateral and bilateral vision loss on quality of life. Br J Ophthalmol 2005; 89:360

–  –  –

Major causes of blindness as a proportion of total blindness. (Data: Resnikoff S et al. Global data on visual impairment in the year 2002. Bull World Health Organ 2004; 82(11):844-851.)

–  –  –

• Epidemiology – The most common cause of world blindness, accounting for almost 50% of cases (18 million people) – Risk factors: cigarette smoking, UV-B light exposure, diabetes mellitus, and corticosteroid use; possibly dehydration (e.g. from severe diarrhea), malnutrition, and heavy alcohol use

–  –  –

shown to have excellent visual outcomes –- Baltussen R et al. Cost-effectiveness analysis of cataract surgery: a global and regional analysis. Bull World Health Organ 2004; 82:338-345 –- Ruit S et al. A Prospective Randomized Clinical Trial of Phacoemulsification vs Manual Sutureless SmallIncision Extracapsular Cataract Surgery in Nepal. Am J Ophthalmol 2007; 143:32-38

Page 11Causes of visual impairment:Glaucoma• Background

– A group of diseases characterized by optic nerve cupping and irreversible vision loss, usually associated with elevated intraocular pressure (IOP) – Two most common forms are primary open-angle glaucoma (POAG) and angle-closure Optic nerve cupping consistent with glaucoma. (Image:

glaucoma (ACG) National Eye Institute, National Institutes of Health)

–  –  –

• Epidemiology – The 2nd most common cause of world blindness, accounting for 12.3% of cases (4.4 million people) – Risk factors: increasing age, African ethnicity (POAG), Asian ethnicity (ACG), increasing IOP, and genetic predisposition; possibly diabetes mellitus

–  –  –

• Management – Goal is to maintain normal IOP through the use of a variety of pharmacologic therapies – Refractory cases may be treated with laser therapy or surgically – Regular eye examinations assessing IOP, visual fields, and changes in the appearance of the optic nerve are essential

–  –  –

• Background – A chronic, degenerative condition common in older individuals that affects the part of the eye responsible for central vision – Classified into two types, dry and wet:

• Dry form accounts for 80% of all AMD

• Wet form involves proliferation of blood vessels (neovascularization) and accounts for the nearly 80% of blindness caused by AMD

–  –  –

A. Dry age-related macular degeneration. The multiple small, yellow deposits in the macula are called drusen. B. Wet age-related macular degeneration demonstrating neovascular changes and hemorrhage. (Images: National Eye Institute, National Institutes of Health)

–  –  –

• Epidemiology – The third leading cause of blindness worldwide, accounting for 8.7% of cases (3.2 million people), and the primary cause of blindness in developed countries, particularly in elderly individuals – Risk factors: increasing age, cigarette smoking, family history, low dietary intake of antioxidants and zinc, white ethnicity, and hypertension; possibly female gender, cardiovascular disease, and cataract surgery

–  –  –

– Studies have shown a possible benefit from antioxidants such as vitamins C and E, beta-carotene, and zinc – Laser therapy, intravitreally injected medications, and photodynamic therapy are options for treatment of the wet form –- Klein R et al. The Epidemiology of Age-Related Macular Degeneration. Am J Ophthalmol 2004; 137:486Fine SL et al. Age-Related Macular Degeneration. New Engl J Med 2000; 342:483-492.

–- Age-Related Eye Disease Study Research Group. A Randomized, Placebo-Controlled, Clinical Trial of High-Dose Supplementation With Vitamins C and E, Beta Carotene, and Zinc for Age-Related Macular Degeneration and Vision Loss: AREDS Report No. 8. Arch Ophthalmol 2001;119:1417-1436.

–  –  –

• Epidemiology – The 4th most common cause of blindness worldwide, accounting for 5.1% of cases in 2002 – Prevalence varies significantly by region and age, with some studies showing corneal opacity as the most common cause of blindness in certain populations

–  –  –

– Corneal transplantation is the treatment of choice for blinding corneal opacity but is not cost-effective in most developing countries due to limited resources (corneal surgeons, eye banks) and availability of long-term care – Many causes of corneal opacity in developing countries are preventable or treatable, thus emphasizing the importance of establishing effective public health programs • - Whitcher JP et al. Corneal blindness: a global perspective. Bull World Health Organ 2001; 79:214-221.

• - Garg P et al. The value of corneal transplantation in reducing blindness. Eye 2005; 19:1106-1114.

• - Bowman RJC et al. Non-trachomatous corneal opacities in the Gambia—aetiology and visual burden. Eye 2002;


–  –  –

• Background – A common complication of diabetes mellitus, there are two main types, nonproliferative and proliferative,

distinguished by retinal examination:

• Nonproliferative findings include hemorrhage, microaneurysms, cotton-wool spots, and macular edema with visual impairment

• Proliferative findings include formation of new blood vessels (neovascularization) and scarring which may cause retinal detachment and profound visual loss

–  –  –

Proliferative diabetic retinopathy demonstrating marked neovascularization. (Image: National Eye Institute, National Institutes of Health)

–  –  –

• Epidemiology – In 2002 accounted for almost 5% of blindness worldwide – Particularly prevalent among working age people in developed countries – Duration of diabetes mellitus, particularly after puberty, is the most important predictor of diabetic retinopathy

–  –  –

– Annual eye examinations are recommended to assess for progression of disease – Strict blood glucose control slows the progression of retinopathy – Laser therapy may be helpful for selected patients with neovascularization – A surgical procedure called vitrectomy may be helpful in patients with severe complications of the disease –- Diabetes Control and Complications Trial Research Group. The effect of intensive diabetes treatment on the progression of diabetic retinopathy in insulin-dependent diabetes mellitus. N Engl J Med 1993; 329:977-986.

–- United Kingdom Prospective Diabetes Study Group. Intensive blood-glucose control with sulfonylureas or insulin compared with conventional treatment and risk of complications in patients with type 2 diabetes (UKPDS 33). Lancet 1998; 352:837-853.

–  –  –

• Background – Vitamin A is necessary for retinal function and ocular epithelial cell development – Vitamin A deficiency (VAD) can cause xerophthalmia, or dry eye, with a spectrum of severity ranging from night blindness to corneal ulceration and irreversible scarring – VAD also increases the risk and severity of infections such as measles

–  –  –

• Epidemiology – Considered the leading cause of preventable blindness in children worldwide – It is estimated that 127 million preschool-aged children have VAD, with 4.4 million associated cases of xerophthalmia – Mortality estimates in preschool-aged children range from 1.3-2.5 million deaths annually

–  –  –

–- Sommer A. Vitamin A deficiency and its consequences: a field guide to detection and control. Geneva: WHO, 1995.

–- Hussey GD, Klein M. A randomized, controlled trial of vitamin A in children with severe measles. N Engl J Med 1990; 323:160–4.

–- West KP Jr. Extent of vitamin A deficiency among preschool children and women of reproductive age. J Nutr 2002; 132:2857S-2866S.

–- Humphrey JH et al. Vitamin A deficiency and attributable mortality among under-5-year-olds. Bull World Health Organ 1992; 70:225-232.

–  –  –

Bailey R, Lietman T. The SAFE strategy for the elimination of trachoma by 2020:

will it work? Bull World Health Organ 2001; 79:233-236.

–  –  –

• Management – Effectively treated with the anti-parasitic agent ivermectin, typically given every 6 to 12 months in endemic regions – Additional efforts include vector control through insecticidal spraying, avoidance of blackfly-infested areas, and the use of insect repellant and protective clothing WHO. Onchocerciasis and its control. Report of a WHO Expert Committee on Onchocerciasis Control. WHO Technical Report Series 852, Geneva: WHO, 1995.

–  –  –

– Occurs when an image is not focused clearly on the retina due to some problem with one of the optical components of the eye – Includes myopia (near-sightedness), hyperopia (farsightedness), presbyopia (age-related loss of near focusing), and astigmatism – Also includes inadequate correction of refractive error in aphakic patients (i.e. those who have undergone lens removal for cataract without implantation of a synthetic intraocular lens)

–  –  –

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