Please note: In 2003, the CTF updated its Grades of Recommendations to include an "I Recommendation" for situations where insufficient evidence exists to allow a recommendation to be made. (Formerly, these situations were captured under a "C Recommendation".) This change is not retroactive, and all "C Recommendations" made prior to 2003 have not been reevaluated in light of the new "I" recommendation grade. For a discussion of these recommendation grades, please link to the 2003 article in the Canadian Medical Association Journal here.
Contents
OverviewBurden
of SufferingIn presbyopia the crystalline lens becomes thicker and less flexible, resulting in diminished accommodation, and commonly to refractive errors. This process is universal with aging, and leads to substantial visual impairment, although it does not usually result in blindness.
The presence of any opacity within the lens is defined as cataract. While cataracts may result from trauma, disease, ionizing radiation or medications (eg. corticosteroid and antineoplastic agents), in most cases they are idiopathic. The prevalence of cataracts sufficient to impair vision (less than 20/30) rises from 1.1% in the 5th decade to 100% in the 9th decade of life.
In Canada, blind registry data indicate that cataracts accounted for 15% of blindness in Canada.
ARMD is a leading cause of blindness in most Western countries, accounting for about 50% of new cases of blindness in Canada. It is a disease of multiple etiology, resulting in loss of central vision. The common atrophic or dry form accounts for 90% of ARMD but rarely results in vision loss greater than 20/80. Wet, exudative or disciform macular degeneration accounts for 10% of the total burden, although 90% of those with blindness (acuity less than 20/200) have this form. The prevalence of ARMD rises from less than 1% at age 55 to about 15% at age 80. If early macular changes (presence of any drusen) are included, the prevalence is 35% by age 64 and 50% by age 85. Risk factors include hyperopia, positive family history (odds ratio (OR) 2.9), smoking (OR 2.6), blue eyes (OR 1.7) and chemical exposure at work (OR 4.2). It is far more prevalent in white than in black people. It is not clear which individuals with drusen alone will develop exudative, or potentially serious changes, however, pigmentary changes, confluence of drusen and exudative changes in one eye, all increase the risk. Early symptoms include metamorphopsia or distortion of shapes, most easily recognized by viewing rectangular objects such as doors or windows.
Glaucoma is a clinical syndrome consisting of a triad of intraocular hypertension (usually greater than or equal to 20 mmHg, a characteristic peripheral visual field loss, and atrophy of the optic nerve head. The diagnosis of glaucoma requires two of these three factors in any combination. Elevation of intraocular pressure (IOP) in the absence of the other two factors is known as ocular hypertension or glaucoma suspect. Ninety percent of glaucoma is of the open angle type, and is initially asymptomatic. Prevalence estimates of glaucoma are complicated by variable diagnostic criteria in different studies. In a recent community study of over 4,000 individuals, carefully defined glaucoma was present in less than 1.5% below the age of 64 years, 2.2% (men), and 2.96% (women) between the ages of 65 and 74 years and 2.4% (men) and 6.9% (women) over the age of 75.<2> Less than 3% of people with IOP <21 mmHg will develop clinical glaucoma within 5 years. Of those with IOP >21 mmHg, 1.6% to 8.6% will develop glaucoma in 5 years. Risk factors for progression include: age, level of IOP, diabetes, myopia, black race, and vascular problems including systemic hypertension. In those with glaucoma, the visual field loss appears directly related to IOP. The fastest rate of visual loss occurs in the earlier stages of the disease.
Diabetic retinopathy (DR) occurs in both type I (ketosis-prone, insulin-dependent juvenile) and type II (non-ketosis prone, usually non-insulin requiring, adult onset) diabetes. It is recognized clinically as microaneurysms and "dot" or "blot" hemorrhages. Maculopathy is the most common cause of visual impairment in patients with diabetic retinopathy, and is more common in type II diabetics. Proliferative DR is more common in type I diabetes, and is due to new vessel formation within ischemic retinal areas. This type is particularly threatening to eyesight, which may be lost due to hemorrhage or retinal disruption. Inolder diabetics, DR is responsible for 33% of blindness. The prevalence of retinopathy in diabetics increases with the duration of disease and the age of the diabetic. At age 55-59 years the prevalence is about 10%, rising to 30% above age 80. By 20 years duration, virtually all type I and 60% of type II diabetes will have some degree of retinopathy. The estimated 5 year incidence of retinopathy in diabetics rises from 2.7% at age 55 to 5.4% at age 75.
ManeuverThe ability to detect serious DR (proliferative retinopathy or macular edema) is dependent upon technique and experience but there was good agreement between ophthalmologists, specially trained optometrists and ophthalmic technicians (Kappa 0.75 for none, proliferative and non-proliferative DR) in a large Wisconsin case series.<10> The sensitivity of ophthalmoscopy without pupillary dilatation is 38-50% when carried out by diabetologists or experienced technicians,<11> but 0% when carried out by nurses. In these studies the gold standard was a seven field stereoscopic fundus photograph. An alternative to fundoscopy for screening diabetics to detect retinopathy is fundus photography with a single 45 degree field of the posterior pole of each eye without mydriasis.
Perimetry will detect visual field loss, a highly sensitive but non-specific finding in glaucoma. Automated visual field screening is feasible and may be practical in the future. The Humphrey automated perimeter device has a sensitivity of 90% and specificity of 91% when compared with Goldman Perimetry. It takes about 30 minutes to perform.<15>
Effectiveness
of Prevention and TreatmentFor cataract, while medications to dilate the pupil may be helpful in improving vision where a small central opacity is present, the only definitive treatment is surgical removal. This procedure is highly effective in restoring vision providing the retina functions well and that adequate refraction is undertaken. When a cataract is extremely dense, it may not be possible to detect retinal disease such as macular degeneration, which may impair a successful surgical result. This supports the case for early detection of cataract. Lens removal, particularly when combined with intraocular lens implantation, results in improved vision in approximately 90% of cases.<16> In 5% of cases post-surgical visual acuity is worse, and is unimproved in another 5%. Serious complications occur in 1% or less.
Before Argon laser photocoagulation, there was no effective treatment for ARMD. Three controlled trials of this technique have demonstrated that photocoagulation of neovascular complexes preserves vision when compared with no treatment.<17-20> Older patients and those with neovascular tissue distant from the fovea were more likely to benefit. The results of these studies offer a rationale for early detection and observation of ARMD. Unfortunately, in most cases the visual deterioration continues and lesions progress beyond the point for successful treatment.
In glaucoma visual loss is not generally reversible. Measures aimed at early detection include tonometry (measuring intraocular pressure), fundoscopy to examine the optic nerve head and manual or automated perimetry to detect early peripheral field loss. Treatment is aimed at reducing intraocular pressure by topical agents (beta-adrenergic blocking drugs or pilocarpine). Some improvement in visual fields has been documented in the first six months of treatment.<21> While it is well accepted that reducing extremely high levels of IOP (>35 mmHg) prevents visual loss, such levels occur very infrequently in the general population. The benefit of treating mild to moderate intraocular hypertension is less clear. A number of randomized controlled trials of IOP reduction in intraocular hypertensives have been carried out using the development of new visual field defects as the outcome measure. Although the results of these studies are not consistently positive,<22-25> and methodological flaws are present in most studies, it has become generally accepted treatment.
In type I diabetics there is evidence that close glycemic control delays the progress of DR.<26> It remains to be seen whether retinopathy in type II diabetics can be similarly retarded. Photocoagulation by Xenon Arc or Argon laser is effective treatment for various types of DR. Several randomized studies have confirmed that photocoagulation maintains vision and reduces the risk of visualloss.<27-29> The best results occur in those whose initial vision is better than 20/30.
Recommendations
of OthersThe American College of Physicians, American Diabetes Association and the American Academy of Ophthalmology recommend regular screening of diabetics with stereoscopic fundus photography when available, or annual dilated ophthalmoscopic examination.<32>
Conclusions
and RecommendationsEarly identification of individuals with ARMD offers the opportunity to intervene with photocoagulation when neovascular change threatens vision. However, the ability of the primary care physician to detect such changes by fundoscopy remains uncertain, and there is insufficient evidence to guide the inclusion or exclusion of fundoscopy for this purpose (C Recommendation). It remains, however, a prudent recommendation. For early diagnosis of glaucoma, there is at present insufficient evidence to include or exclude tonometry, fundoscopy or automated perimetry in the periodic health examination (C Recommendation). For those individuals with a positive family history and for those who are black, highly myopic or diabetic, there is a greater risk of developing glaucoma. In such individuals a prudent recommendation would be to include periodic assessment by an ophthalmologist with access to automated perimetry.
Unanswered
Questions (Research Agenda)EvidenceThis review was initiated in March 1990 and recommendations were finalized by the Task Force in January 1994.
Acknowledgements
Link to Structured Abstract of this review
Link to Summary Table of this review
Link to Selected References list of this review
Link to 1995 update: Screening for visual problems among elderly patients
Reprinted in modified format by the Canadian
Task Force on Preventive Health Care
with permission.
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Original Copyright
© 1994 Minister of Supply and Services Canada.
Last modified March 27, 1998.
