Common Visual Problems: Symptoms and Treatment, Part I

THE CHALLENGE

In the year 2000, nearly one million Americans over age 40 years were deemed “blind,” and 2.4 million had “low vision.” The incidence of both blindness and low vision in Americans is projected to increase dramatically by the year 2020. Persons over age 80 years accounted for more than two-thirds of the observed blindness, and, as we know, this more elderly group is the fastest-growing segment of the U.S. population.¹

In a 2-year study of individuals age 65-84 years, 25% suffered “significant vision loss” over that interval (visual acuity diminished in 25%; contrast sensitivity and visual field loss occurred in 10%). In a cohort of individuals over age 85 years, one-half had better than 20/40 acuity, but with low contrast and “veiling glare,” 75% had their acuity diminished to less than 20/200; 50% of these individuals had no stereopsis. “Glare recovery” took longer than 2 minutes versus 15 seconds for those under age 65 years, and visual fields tested with “divided attention” (ie, a central distracting task) is about one-half the expanse of that for individuals younger than age 65 years.² In addition, this loss of visual function is often compounded by other age-related disabilities. Of special note is the fact that high-contrast visual acuity, the most commonly used measure of visual function, is the slowest and probably the least sensitive measure of visual function to decline with age.^3-5

Poor visual function has deleterious effects on vocation and avocations, driving ability (especially at night), and routine activities of daily living. Positive correlations have been documented between vision loss and auto accidents, loss of employment, increasing dependence on others, social isolation, depression, personal accidents, hip fractures, and ultimately, mortality.^6-12

THE NATURE OF “VISION”

Obviously, from the foregoing discussion, vision and visual functioning is more than a simple measure of central, high-contrast acuity. Central visual acuity, as measured on the common eye charts, is certainly a critical aspect of overall visual functioning. But it is actually more important for our activities of daily living to have an adequate visual field—the panorama through which we are able to see—than it is to have central keen acuity. While our central acuity allows us to perform fine-detailed tasks, such as reading and identifying small objects at a distance, the visual field is critical for our orientation and mobility. Thus, individuals with significantly impaired visual fields are far more disabled visually than those with dramatically reduced central acuity. They cannot navigate and get about without assistance⁸ (Figures 1A and 1B). Binocularity and stereopsis represent other parameters of overall visual function, which are critical if we are to recognize our position in space, and the relative positions and distances of other people and objects in our environment.

Contrast sensitivity is the term applied to the quality of our vision that allows us to detect contours, shades of gray-on-gray, and various saturations of color. Contrast sensitivity is probably the best present means of assessing overall visual function, as it most closely represents the world as we see it—in shades of grays and colors, rather than in high-contrast black-and-white. Contrast sensitivity declines “normally” with aging, dramatically moreso in certain eye diseases (Figure 2). While there are numerous tests available to evaluate contrast sensitivity clinically, they are most commonly used as investigational tools, they vary in design, and unfortunately, they have achieved neither consensus nor widespread use.^13-20

Our color perception not only provides us with beauty and aesthetic appreciation, but it also allows us to distinguish objects because of characteristic color, and to appreciate contours and boundaries.^21,22

Lastly, no discussion of the quality of vision and overall visual function would be complete without mention of glare and light sensitivity. While these two symptoms are not inherent characteristics of our vision, they dramatically impact how well we see and function. Numerous ocular disorders such as keratitis (dry eye disease), certain types of cataracts, and reduced vision of many etiologies, result in significant photophobia, with varying but often disabling ocular discomfort and further reduction in vision.

As a generalization, “normal” changes in vision as one ages often require new, and possibly stronger, eyeglasses, but most people maintain good correctable vision.²³ Nonetheless, certain sight-threatening ocular diseases increase with almost exponential frequency in the elderly. The good news is that more than two-thirds of the causes of visual loss in the elderly are treatable or preventable. One-third of the patients simply need new glasses, and one-third can be helped significantly by cataract surgery, a highly successful procedure. While the remaining third may not be restorable to normal vision, most can have the loss of vision arrested with treatment. Of those elderly patients whose vision cannot be restored to normal, low-vision aids and rehabilitation measures often help to enable them to perform many of the tasks of daily living and regain a large measure of independence. Simple measures for these patients with low vision include a wide variety of magnification devices and adaptive techniques. Partial-vision and low-vision clinics are available in almost all the large metropolitan areas of the United States to assist the visually disabled with simple as well as sophisticated devices and rehabilitation.^2,11,24-27

From the foregoing discussion, it is obvious that the elderly need to pay attention to lighting and contrast in their surroundings. They should not rely on stereopsis. They should highlight steps and curbs with a white or highly contrasted border, for example, and should take similar precautions with other changes in contour and boundaries that could result in falls or injury (Figure 3).

COMMON CAUSES OF VISION LOSS IN THE ELDERLY

With a better understanding of the normal and abnormal changes that occur in vision, we can now examine the most common problems threatening the visual functioning of the elderly. Part I of this article will include cataract and glaucoma. Part II will look at age-related macular degeneration, diabetic retinopathy, and dry eye disease.^24,26,28-30

Cataract
Cataract has been called the leading cause of blindness in the world.³¹ The term “blindness” is commonly used rather loosely, referring to reduced vision of any cause. Ophthalmologists define blindness as total blindness (ie, no light perception). Uncomplicated cataracts do not cause this complete loss of vision.

Cataract surgery is the most frequent operation performed in our American Medicare population; recent statistics suggest about 2.8 million cataract operations are performed per year.^32,33 With the expected increase in life expectancy, the frequency of cataract surgery is expected to double as early as 2010. Despite the prevalence of cataract, common misconceptions still exist. As we know, a cataract is actually a clouding of the naturally clear lens within the eye, which sits behind the iris and the pupil. It is not, as is often believed, a film over the eye, a cancer that must be removed, a cause of irreversible blindness, or something that can spread from one eye to the other. Bilateral cataracts are very common, but marked asymmetry occurs often.

The symptoms of cataract are blurred vision, and variable glare and light sensitivity. As cataracts typically develop slowly and are characterized by “painless, progressive loss of vision,” patients may not be aware of the slow, insidious reduction of acuity or increasing light and glare intolerance until their visual problems are noted by others or become quite advanced. The cataract is much like an increasingly dark-colored, translucent filter in front of the eye blocking the clarity and intensity of light entering the eye and striking the retina.

Ophthalmologists divide cataracts into several types, depending upon the portion of the lens within the eye that contains the opacity or clouding.³⁴ Frequently, different types of cataract exist within the same eye. A nuclear cataract refers to a progressive clouding and opacification of the central portion of the lens called the nucleus. It is the most common type of age-related cataract, and often looks yellowish-brown, referred to by ophthalmologists as “brunescence.” In many patients, this progressive “sclerosis” of the nucleus imparts an increased refractive index, resulting in progressive myopia. In prior generations, this new myopia in older age was often referred to as “second sight” because it relieved patients of the need for reading glasses that they had previously been dependent upon. Of course, they then experienced a proportionate decrease in their distance vision!

Cortical cataracts refer to opacities in the surrounding cortical portion of the lens, often taking the form of spokes, dots, and patchy areas. When these opacities are peripheral in the lens and do not involve the central visual axis, they may have no visual significance whatsoever. They may, however, cause some glare at night with the pupil dilated and exposed to oncoming lights.

Posterior subcapsular cataracts also occur as an age-related phenomenon, although they are very characteristic of steroid-induced cataracts. They can be particularly troublesome when central, as they cause dramatic glare and light sensitivity, as well as disproportionately reduced vision in lighted conditions when the pupil is small and effectively occluded by the central opacity (Figure 4).

A mature or ripe cataract represents a completely opacified lens in which the pupil appears white and the eye sees nothing but the difference between light and dark.

The treatment of cataract is surgical. Pupillary dilation for certain types of cataracts may provide temporary and minimal improvement in vision, but is accompanied by increasing light sensitivity and is rarely tolerated. Obviously, attention to medications that can cause cataracts—most commonly corticosteroids—is worthwhile, and can prevent cataracts when alternative medications are appropriate. Smoking and excessive ultraviolet light exposure have been correlated with cataract development and should be avoided.

Modern cataract surgery represents one of the most successful and effective procedures available in medicine today. With foldable intraocular lenses, used to replace the cataractous lens, removal of the cataract and insertion of the new lens can be performed through a small incision, allowing rapid rehabilitation and restoration of near-normal vision. The procedure is commonly performed under local or topical anesthesia in an outpatient setting. It represents no significant risk to the overwhelming majority of patients, whatever their age, although a comprehensive medical evaluation and consideration of concomitant medications are always in order to minimize risks and maximize the chance of an optimal outcome.^35,36

In spite of the high success rate and outpatient setting, cataract surgery is not a trivial procedure. It is highly technical, with a steep learning curve, and as with any medical or surgical intervention, it carries no guarantee of success. With those caveats, the success rate in experienced hands is generally in the mid- to high-90% range.

Glaucoma
While there are many types of glaucoma (eg, narrow angle and acute glaucoma, secondary glaucoma, pigmentary glaucoma, congenital glaucoma), this discussion will be limited to the topic of chronic open angle glaucoma, which is by far the most common type and one that increases with dramatic frequency with age. There are about 2.5 million or more Americans diagnosed with glaucoma at the present time; about 2% of all Americans over age 40 years are suspected to have glaucoma, and about 1% are diagnosed.^37,38

Glaucoma is a very insidious disease, having been characterized as a “thief of sight in the night.” Loss of central visual acuity occurs very late in the disease. The peripheral visual field is slowly nibbled away and reduced, such that patients are rarely aware of the almost subliminal loss of peripheral vision, irregular blind spots, and reduced contrast sensitivity until extensive damage to the optic nerve and overall visual field has occurred.³⁹ By this time, the damage is almost always irreversible.

While statistically increased intraocular pressure is a most significant risk factor for glaucoma, it is not a simple, straightforward cause of glaucoma. We know that a very large percentage of the glaucoma population records untreated pressures, occasionally or consistently, well within range of the age-adjusted statistical “normal” level. We categorize these patients as “normal tension” glaucoma, and, depending on the study, this group may comprise anywhere from 30-50% of the population with glaucoma. For this reason, glaucoma screening clinics, in which only the pressures were measured, have been largely abandoned as a result of too many false-negatives, as well as frequent false-positives. The sine qua non for diagnosis of glaucoma is evidence of optic nerve damage with visual field defects characteristic of glaucomatous optic neuropathy.⁴⁰

Most visual field testing is now performed with an automated, computerized device that determines the retinal threshold for light stimulation at numerous points within the field. These examinations can be repeated and compared, subjected to statistical testing for reliability and significance, and thus, represent valuable indicators for diagnosis and adequacy of treatment.

While constantly improving, visual field tests still represent a tedious experience for the patient and a subjective determination highly dependent on patient attentiveness, ability, and reliability. New and exciting devices—that quantitatively and precisely characterize the volume of the optic nerve cup and/or the thickness of the retinal nerve fiber layer at and around the optic nerve head, the vulnerable tissue in glaucoma—are finding increasing acceptance, although subjective visual field testing remains the definitive “gold standard” for diagnosis and follow up.⁴¹

The best screening test remains careful ophthalmoscopy and evaluation of the optic nerve head by a skilled practitioner. As mentioned, the intraocular pressure may well be within the normal range in a glaucoma patient. Characteristic changes in the optic nerve—such as hemorrhages along the disk margin, notches along the nerve fiber accumulation constituting the rim of the optic nerve cup, and extensive and/or asymmetric cupping of the nerves—are among the signs of early and/or advanced glaucoma. Risk factors include increasing age, African ancestry, significant near-sightedness, and a positive family history for glaucoma.^42,43

Treatment for glaucoma in most developed countries is medical, using topical eye drops. It is particularly noteworthy for primary care physicians and internists to recognize that these topical treatments may have significant systemic effects, especially the topical beta-blockers. While rare, instances of bradycardia, heart block, and severe exacerbation of asthma and bronchospastic pulmonary disease have been reported to be associated with the use of topical beta-blockers. Fortunately, newer classes of effective topical therapies are now available, allowing less dependence on beta-blockers and other poorly tolerated drops. Lasers and invasive surgery are also utilized to treat this disease, which can progress to complete blindness without adequate control.⁴⁴

Lastly, as with any chronic disease requiring regular medication, the elderly need particular attention paid to compliance, due to memory or other problems. Simple charts and checklists prove very helpful as reminders to take regularly scheduled medications. With appropriate control, the overwhelming majority of patients with glaucoma will retain useful eyesight for life.