Canadian Medical Association Journal 1995; 152: 1211-1222
[résumé]
Copies of this and other task force reports are available from the Health Services Directorate, Health Programs and Services Branch, Health Canada, Tunney's Pasture, Ottawa ON K1A 1B4.
© 1995 Canadian Medical Association
Options: Visual acuity screening with Snellen sight chart, funduscopy, retinal photography, tonometry and perimetry.
Outcomes: Delay or prevention of visual deterioration or blindness.
Evidence: A MEDLINE search for relevant articles published between January 1986 and December 1993 was undertaken, the bibliographies of the articles were scrutinized for additional articles, and experts were consulted. The highest available level of evidence was used in making recommendations.
Values: The evidence-based methods and values of the Canadian Task Force on the Periodic Health Examination were used. Preservation of vision was given the highest value in accordance with other guidelines regarding eyesight.
Benefits, harms and costs: Potential benefits are to maintain or improve visual acuity. Potential for harm to patients is minimal. Limited data are available on costs.
Recommendations: There is fair evidence to include in the periodic health examination visual acuity testing with a Snellen sight chart and funduscopy or retinal photography in elderly patients with diabetes of at least 5 years' duration (grade B recommendation). The place of funduscopy in the detection of age-related macular degeneration and glaucomatous changes is controversial. For patients at high risk for glaucoma (positive family history, black race, severe myopia or diabetes) it would be prudent to have a periodic assessment by an ophthalmologist.
Validation: Recommendations differ from those of the American Academy of Ophthalmology and the American Optometric Association. Recommendations for glaucoma screening are similar to those of the US Preventive Services Task Force. Present recommendations have been reviewed by experts in ophthalmology and optometry.
Sponsor: These guidelines were developed and endorsed by the task force, which is funded by Health Canada and the National Health Research and Development Program. The principal author (C.P.) was supported in part by the Educational Centre for Aging and Health, McMaster University, Hamilton, Ont. This article is intended to provide family physicians with recommendations on screening elderly patients (over 65 years of age) for visual impairment and its common clinical causes. The evidence-based methods and values of the Canadian Task Force on the Periodic Health Examination were used.[1]
MEDLINE was searched for articles published between January 1986 and December 1993 with the use of the following headings and key words: "glaucoma (MH)," "glaucoma, suspect (MeSH) screening or vision screening (MH)," "clinical trial (PT)," "glaucoma-drug therapy," "intraocular pressure-drug effect," "timolol-administration and dosage," "vision disorders," "aged," "diabetic retinopathy," "age-related macular degeneration," "cataract" and "retinal diseases." In addition, the bibliographies of relevant articles were scrutinized for additional articles, the recommendations of other groups were reviewed, and experts in ophthalmology and optometry were consulted to obtain the highest available level of evidence to make recommendations. The highest value selected was preservation of vision, in accordance with other guidelines regarding eyesight.
Visual impairment is defined as an acuity of less than 20/60 (6/18) in the better eye, with the best correction.[2] Legal blindness is defined as an acuity of less than 20/160 (6/48) in the United States and less than 20/200 (6/60) in Canada.[2] The World Health Organization (WHO) has standardized the definitions as follows: visual impairment, acuity of less than 20/60 (6/18), and legal blindness, acuity of less than 20/400 (6/120), with the best correction in both cases.[3] People with severe visual disability are eligible to be registered legally blind, which allows for dispensations related to income tax and other benefits. Registration in Canada requires examination by an ophthalmologist.
The question "When wearing glasses, can you see well enough to recognize a friend across the street?" had a sensitivity of 48% in detecting visual acuity of less than 20/40 (6/12).[9] Other questions have been found to have a sensitivity of only 20% to 30%.[10] Impaired visual acuity is readily detected with the use of a Snellen sight chart, which can be used in a family physician's office or, in a reduced size, as a portable tool.
A portable visual acuity box was used in the Visual Acuity Impairment Survey Pilot Study.[11] Nearly 1200 subjects were screened, and 123 (10.5%), mostly elderly people, were found to have poor acuity of some degree. Less than half of the subjects were then examined at an eye clinic. Compared with the clinic examination, the portable unit had a sensitivity of 94% and a specificity of 89%. Lowenstein and associates[12] found that when the sight chart was viewed through a pinhole (which minimizes refractive error) the sensitivity was 79% and the specificity 98%.
In a study in Wales 202 elderly patients attending an outpatient clinic were questioned about their use of eyewear and their vision and then were tested with the use of a Snellen sight chart viewed through a pinhole.[13] Over one third of the patients were found to have impaired vision; 30 had refractive errors. Of the 42 patients with nonrefractive errors 27 had a treatable condition (most often cataracts or glaucoma) discovered by an ophthalmologist, and 15 had an untreatable, serious condition (usually ARMD). Only 9 of the 42 believed that their vision was inadequate.
Over 400 consecutive patients attending a primary care general medical clinic in Baltimore were asked to complete a brief questionnaire and undergo a standard vision test with a Snellen sight chart.[14] Nearly two thirds did not meet predefined criteria and were referred to an ophthalmology clinic. Of the 101 who showed up for the evaluation at the clinic, 96 were found to have serious eye disease, the most prevalent being cataracts, diabetic retinopathy, glaucoma and ARMD. Immediate medical therapy was required for 14% and surgical intervention for 18%. The vision test alone failed to identify most cases of diabetic retinopathy and glaucoma.
These case series illustrate the ability of simple questions and visual acuity testing to detect significant ophthalmic disease. Lack of complete follow-up in these studies precludes calculation of test characteristics for these manoeuvres.
Burden of illness
Although the prevalence of visual impairment from all causes is known, that of presbyopia alone is not available. Among 5300 people screened in the Baltimore Eye Survey the prevalence of visual impairment rose from 1.1% among white people aged 60 to 69 years to 14.6% among white people over 80; the corresponding figures among black people were 3.4% and 18.0%.[15] The respective rates for legal blindness (20/200 [6/60]) were 0.3% and 11.6% among the white people and 3.1% and 10.0% among the black people.
Effectiveness of intervention
Refractive errors due to presbyopia are readily corrected with eyeglasses or contact lenses. In the Baltimore Eye Survey visual acuity was measured with the person wearing his or her corrective lenses, if any. Following appropriate correction 54.0% of the subjects had improved vision by at least one line on the Snellen sight chart, and 7.5% had improved vision by three or more lines.
Burden of illness
The prevalence of cataracts is age dependent. That of cataracts sufficient to impair visual acuity to less than 20/30 (6/9) has been found to increase from 1% among people in their 40s to 100% among those in their 80s.[16-19] Cataracts account for 15% of cases of blindness in Canada[20] and 4.5% to 8.2% of new cases.[6] In the Baltimore Eye Survey blindness was caused by cataracts among 13% of elderly white subjects and among 39% of elderly black subjects.[5]
Detection manoeuvre
Symptoms include deterioration in visual acuity, increased glare in bright light and a "halo" seen around objects. In hyperopic patients "second sight," a temporary improvement, results from a myopic shift with the onset of cataract formation. Cataracts are readily detected by means of ophthalmoscopy. The test characteristics of examination in primary care are unknown.
Effectiveness of intervention
Medical treatment (pupil dilatation) may improve vision around a small central cataract. Definitive treatment requires surgical removal of the cataract. This procedure effectively restores vision, provided the retina functions well and refraction is adequate. Dense cataracts may obscure the presence of retinal disease (e.g., ARMD), which may affect the surgical outcome. The refractive error induced by aphakia can be corrected with the use of eyeglassses or contact lenses or with intraocular lens (IOL) implantation. IOL implantation is frequently performed during surgery to remove the cataract, and visual correction is far superior to that provided by eyeglasses, which produce substantial distortion. Increasingly, outpatient cataract surgery is being undertaken.
Lens removal with IOL implantation improves vision in approximately 90% of patients;[21] 80% obtain a final visual acuity of 20/40 (6/12) or better. In 5% acuity worsens, and in another 5% it is unchanged.[22] In one study, before IOL implantation 75% of patients using eyeglasses complained about their quality of vision.[23] The degree of patient satisfaction with IOL implantation has been found to be similar to that with extended-wear contact lens.[24] After undergoing cataract surgery with IOL implantation nearly 300 elderly patients reported improvement in their vision, their ability to read newspapers, to drive and to perform daily activities, and their economic resources. The mean improvement in acuity was from 20/100 (6/30) to 20/40 (6/12). Objective improvement was evident in mental status, writing and fine-motor control.[25]
Complications of cataract surgery with IOL implantation include infection, which occurs in up to 3% of cases.[26] Macular edema occurs as a late complication in about 4%, retinal detachment in about 2% and lens dislocation in about 1%. Opacification of the posterior capsule, most commonly seen in posterior-chamber IOL implantation, occurs in up to 5% of cases and may be treated with laser capsulotomy.[27]
Ophthalmologists usually offer cataract surgery when an otherwise healthy patient senses a significant impairment in daily life caused by the vision loss. It is prudent to consult an ophthalmologist early in the cataract progression for a thorough examination of the retina. Retinal examination may be more difficult with mature or "ripened" cataracts.
There are two forms of ARMD. Atrophic ("dry") macular degeneration rarely results in a visual acuity worse than 20/80 (6/24). Exudative ("wet") or disciform macular degeneration is less frequent but potentially far more devastating. In this type a fragile subretinal neovascular membrane develops that can distort the macula, which results in metamorphopsia (distortion of vision) and may lead to severe and sudden visual loss from retinal detachment. Approximately 90% of people with ARMD have atrophic maculopathy; of those who are legally blind (visual acuity of less than 20/200 [6/60]) about 90% have exudative maculopathy.[28]
Burden of illness
The prevalence of ARMD is about 1% among people who are 55 years of age and increases to 15% among those who are 80.[16] The prevalence of macular changes (presence of any drusen) increases to 35% by age 64 and to 50% by age 85.[29] Risk factors include hyperopia, a family history of ARMD, smoking, blue eyes and chemical exposure at work.[28,30] ARMD is far more prevalent among white Americans than among black Americans.[5]
Natural history
Several factors identify people with drusen alone who are at greatest risk for exudative maculopathy or potentially serious macular changes. In one retrospective survey of 71 patients with bilateral macular drusen 15% had signs of neovascular change by 5 years and nearly 13% experienced severe visual loss.[31] Concurrent pigmentary changes and confluence of drusen increase the likelihood of neovascular change. Among people with one eye affected by exudative degeneration, the annual incidence of similar change in the other eye has been 12% to 15%.[32,33] Although drusen are the sine qua non of ARMD, not all people with drusen will experience visual loss.
Detection manoeuvre
Distorted near vision (in 29 cases) and blurred vision (in 22 cases) were the most frequent first symptoms among 103 people with ARMD who had recent vision loss from neovascular membranes.[34,35]
Funduscopy reveals drusen and fine pigment stippling in the macular area, which progresses to larger clumps of pigment. Although drusen are readily recognized by ophthalmologists and optometrists, sensitivity for their detection by primary care physicians is unknown. Most fundi in people over 20 years of age will show drusen histologically; however, only one third of those examined clinically in people over 52 were found to have drusen.28 The presence of many drusen, pigmentary changes or "softening" should be detectable by primary care physicians.
Retinal photography is a standardized way to record abnormalities of the fundus, but it is not available to primary care physicians. Fluorescein angiography evaluates the vascularity of the fundus and determines capillary leakage, but it is unsuitable for screening.
The Amsler chart is a grid 10 x 10 cm containing 20 5-mm squares to a side, with white lines on a black background. The patient is asked to view it daily to detect metamorphopsia, which indicates early retinal detachment, for which immediate treatment may be beneficial. Although the use of Amsler's chart has been described in case reports[33] compliance is often poor. Of 103 patients with recent onset of visual loss from neovascular maculopathy, 89 were given the chart, but only 49 used it regularly. All but 1 of the 49 had a demonstrable grid defect at the time of diagnosis; however, only 5 noticed the first visual symptom while observing the chart.[34] A modified Amsler's chart the size of a credit card has been found to detect metamorphopsia as well as the original model, but its use in practice has not been evaluated.[36] A suggested (but unproven) alternative is to ask patients at risk to observe carefully a rectangular object (e.g., a window or doorframe) daily to detect metamorphopsia.
Effectiveness of intervention
There was no effective treatment for ARMD before the introduction of laser photocoagulation. Bursts of argon (blue-green) laser energy are used to obliterate the neovascular changes. In three randomized controlled trials photocoagulation was compared with no treatment among subjects over 50 years of age with drusen and subretinal neovascular complexes identified by means of fluorescein angiography.[37-40] In each study, photocoagulation improved preservation of visual acuity. Older patients and those with neovascular tissue distant from the fovea were the most likely to benefit.
The benefits of photocoagulation offer a rationale for early detection and observation of ARMD. Unfortunately, visual deterioration usually occurs and lesions progress beyond the point at which treatment is successful. For example, in one study the condition was treatable in 80% of patients who presented to an ophthalmologist within 2 weeks after symptoms developed; this rate dropped to 40% among those who presented after 1 month and to less than 10% among those who waited 4 months.[41] Disciform ARMD may be amenable to treatment in up to 50% of patients if it is identified early enough. Treatment is most beneficial for patients with a visual acuity of 20/60 (6/18) or better. In the event of retinal detachment, there is no benefit to photocoagulation.[38] Photocoagulation using krypton red laser energy has been found to be no more effective than that using argon green laser energy.[42,43]
Burden of illness
Prevalence studies are complicated by variable diagnostic criteria. Table 1 shows the prevalence of increased IOP in four populations and the proportion discovered to have glaucomatous visual field defects. Table 2 shows the prevalence of glaucoma in six populations. In the Beaver Dam Eye Study,[50] involving over 4000 people residing in a single community, the age-specific prevalence of glaucoma rose from less than 0.5% among people 50 years old to 2.5% among 75-year-old men and nearly 7% among 75-year-old women.
Natural history
An IOP of 21 mm Hg is the accepted upper limit of normal; however, glaucoma does not develop in many people with higher pressures and may develop in those with an IOP below 21 mm Hg. Among people over 60 years old, up to 3.7% of those with an IOP of 16 to 19 mm Hg will have glaucomatous visual field defects in 5 years;[51] of those with an IOP of 20 to 23 mm Hg, up to 9.3% will have such defects within 5 years. Thus, more cases of glaucoma will develop in people with an IOP of less than 21 mm Hg than in those with a pressure above 21 mm Hg. The sensitivity of the optic nerve to any given level of pressure determines progression to glaucoma. Risk factors for progression include age, IOP, diabetes, myopia, black race and vascular problems (e.g., hypertension). In people with frank glaucoma, there is some evidence that visual field loss is directly related to IOP and that eyes showing the fastest rate of loss are in an earlier stage of the disease.[52]
Detection manoeuvre
The earliest symptom of open-angle glaucoma is loss of peripheral vision, which frequently goes unnoticed. Acute deterioration of vision, with pain and redness of the orbit, is characteristic of acute angle-closure glaucoma, a condition that is much less common than open-angle glaucoma.
There are three methods of detecting chronic open-angle glaucoma: tonometry, inspection of the optic disc and perimetry.
Tonometry
Tonometry, or measurement of the IOP, is often carried out with the use of a Schiötz tonometer, which estimates pressure by indicating the ease with which the cornea is indented. Tonometry is relatively cheap and accessible to primary care physicians. Applanation tonometry requires a slit lamp, although a hand-held model (Perkins) is now available. Puff tonometry uses a jet of air to deform the cornea.
Readings do not accurately reflect the presence or absence of glaucoma, since normal pressure shows diurnal variations of as much as 5 mm Hg. Among people with glaucoma, variations may be as high as 8 to 10 mm Hg, and only 50% have elevated IOP in random measurement.[53] Biologic factors (position of the patient, presence of myopia, systemic drug use, variation between seasons) and position of the tonometer increase variability. In one study the sensitivity of the Schiötz tonometer was only 50%;[44] the positive predictive value for diagnosing glaucoma has been found to be only 2% to 5%.[44,53,54] Although Schiötz tonometry has been recommended in the past, poor sensitivity, low prevalence of glaucoma and the increasing ratio of elevated IOP to glaucoma with age are grounds to recommend against its sole use in screening.
Inspection of the optic disc
An experienced ophthalmoscopist is able to recognize an increased optic cup-disc ratio in excess of 60%.[55] For ophthalmologists, the sensitivity and specificity of this sign can each exceed 90% for the diagnosis of glaucoma, although clinical disagreement occurs even with predefined criteria.[56,57] It is unlikely that this diagnostic accuracy could be equalled by family physicians. In a study involving 22 patients, 34 ophthalmologists, using funduscopy alone, detected glaucoma in only about half of the cases;[58] there was no evidence that greater experience would improve this rate.
Perimetry
Some 30% to 50% of the optic nerve fibres must be lost before a classic glaucomatous visual field defect consistently occurs. Perimetry has been used as a screening test for glaucoma. However, the equipment is costly and not generally available to primary care physicians. It has a high sensitivity for detecting loss of peripheral vision but has a low specificity for glaucoma. Automated visual field screening is feasible and may be practical in the future.[59] Humphrey automated perimetry, which takes about 30 minutes to perform, was found to have a sensitivity of 90% and a specificity of 91% when compared with the standard Goldmann perimetry device.[60]
Effectiveness of intervention
Visual loss in glaucoma is not generally reversible, although some improvement in the field of vision may occur in the first 6 months of topical treatment.[61] Treatment is aimed at reducing IOP with the use of topical agents (e.g., pilocarpine or alpha-adrenergic blockers [e.g., timolol and betaxolol]), systemic agents (e.g., acetazolamide) or surgery.
Although it is well accepted that reducing extremely high IOP (e.g., above 35 mm Hg) prevents visual loss, such levels rarely occur in the general population. The benefit of treating mild to moderate IOP is less clear. In seven randomized controlled trials of the benefit of lowering the IOP, the development of new visual field defects was measured by means of perimetry.[62-69] The recent studies used automated perimetry, which minimized observer bias. Although five of the studies showed a benefit,[62,64-68] two,[63,69] including the largest and most recent,[69] did not. The studies' methodologic differences make it difficult to draw definite conclusions. A recent meta-analysis of these studies concluded that the odds of progression to visual field deficits was reduced by 25%, but a wide 95% confidence interval (0.43 to 1.34) implied that the risk of worsening deficits could not be excluded.[70]
Systemic agents such as acetazolamide also reliably reduce IOP.[71] Side effects include hypokalemia and metabolic acidosis. Surgical treatment is effective in lowering IOP but is usually indicated only when medical treatment fails.[72] Argon laser trabeculoplasty has been introduced as an alternative treatment to topical medication in people with primary open-angle glaucoma. In a study involving 271 patients one eye was treated with laser therapy and the other with timolol eye drops.[73] After 2 years, the visual acuity and fields did not differ significantly, but fewer laser-treated eyes required two or more medications to control IOP.
Burden of illness
In older diabetec patients retinopathy accounts for 33% of cases of blindness.[74] In the Framingham Eye Study the 4-year incidence of blindness (visual acuity of less than 20/200 [6/60]) was about 3% among older subjects taking insulin or not.[75] By 20 years virtually all of the patients with type I diabetes and 60% of of those with type II diabetes are expected to have some degree of retinopathy. The 4-year incidence of macular edema among older people was about 8% among those using insulin and 3% among those not using insulin.[76] Risk factors for retinopathy include hypertension, poor control of diabetes, duration of diabetes, heavy alcohol consumption and cigarette smoking.
Detection manoeuvre
The WHO defines impaired carbohydrate tolerance as a blood sugar level of 7.8 mmol/L after fasting or 11.1 mmol/L 2 hours after eating.[3]
Background retinopathy and advanced proliferative retinopathy should be detectable by family physicians. In a study in which funduscopy was compared with retinal photography among patients known to have diabetes, signs of proliferative retinopathy were detected by all of the retinal subspecialists; however, 49% of these changes were missed by internists, diabetologists and senior medical residents.[77] In another study optometrists diagnosed the presence or absence of retinopathy in 77% of patients under ideal conditions.[78] In a study involving more than 2000 people with diabetes, there was exact agreement in categorizing retinopathy as absent, proliferative or nonproliferative between ophthalmologists, specially trained optometrists and ophthalmic technicians in 85.7% of cases (kappa 0.749).[79] The ability to detect serious retinopathy is highly dependent on technique and experience. Without pupillary dilatation the sensitivity of ophthalmoscopy was found to be between 38% and 50% when performed by diabetologists or experienced technicians.[80] With dilatation it was 70% and 82% when performed by diabetologists and retinal specialists respectively. When carried out by nurses the sensitivity was 0% and the specificity 100%.[80] The gold standard in these studies was a seven-field stereoscopic photograph of the fundus. There has been interest in nonmydriatic fundus photography with a single 45 degree view of the posterior pole of each eye. This technique compares favourably with ophthalmoscopy with dilatation and is considerably more accurate than ophthalmoscopy without dilatation by a trained observer.[80-83]
Retinal photography requires costly equipment. Because diabetic retinopathy is common, further evaluation is required to determine whether this technique is cost effective in screening people with diabetes.
Effectiveness of intervention
Although tighter metabolic control delays most diabetic complications, one study comparing regular treatment with intensified diabetic control (continuous subcutaneous insulin therapy) revealed that retinopathy appeared to accelerate initially in the latter group.[84] After 2 years the degree of retinopathy was indistinguishable between the two groups, with a trend toward lesser overall deterioration in the continuous insulin group.
Xenon arc and argon laser photocoagulation maintain vision and reduce the risk of visual loss associated with various types of diabetic retinopathy. In cases of proliferative retinopathy two major studies have confirmed the benefit of photocoagulation.[85-87] Xenon arc and argon laser photocoagulation have also been found to reduce the risk of visual loss in people with diabetic macular edema.[88,89] The best results occurred in people whose initial vision was good (20/20 [6/6] to 20/30 [6/9]). Medical treatment with sorbinil or acetylsalicylic acid has proven ineffective.[90-92]
Proliferative retinopathy affects patients with either type of diabetes, and its incidence depends on the duration of the diabetes. Treatment with photocoagulation is effective in preserving sight. Screening patients with type I diabetes beginning 5 years after the onset of the diabetes has been calculated to produce an average expected benefit of 2.7 person-years of sight saved per person screened, with a net saving of medical and social security costs of about $3300 (US) per person screened.[93,94] For patients with type II diabetes not taking insulin, it was estimated that each year of sight saved would cost $1500 (US).[95] Screening of patients with insulin-dependent diabetes, type I or type II, is cost saving. Screening with fundus photography was slightly more effective than that with ophthalmoscopy.[95]
It is uncertain how many elderly Canadians receive regular eye care, or from whom. Family physicians traditionally provide primary eye care. Many elderly people, particularly in urban centres, receive regular eye care from ophthalmologists. Optometrists are distributed throughout urban and rural Canada.
Underreporting of visual impairment is common in the elderly population. Testing for visual acuity has been widely recommended. Although many abnormalities will be discovered, there is scant evidence that correction of poor visual acuity will improve function or quality of life or reduce hazards of daily life.
Visual impairment due to presbyopia and other refractive errors is common in elderly people, and its prevalence increases with age. Visual loss is often underreported. Detection is straightforward, and useful improvements in vision frequently result from refraction and corrective eyewear.
Notwithstanding the lack of evidence of benefit, there is no reason to believe that screening or case finding for visual impairment would be harmful. Given the high prevalence rates and effective treatment, there is fair evidence to include visual acuity testing with a Snellen sight chart in the periodic health examination of elderly patients (grade B recommendation). The optimal frequency of testing is uncertain.
Tests of visual acuity will not detect early signs of exudative ARMD or of macular edema from diabetic retinopathy. Both conditions are detectable by means of funduscopy and are likely treatable with photocoagulation; patients with better visual acuity are most likely to benefit. The accuracy of primary care physicians in diagnosing these conditions is unknown. A British survey showed that referrals to ophthalmologists from ophthalmic opticians (optometrists) were more appropriate and showed more highly developed funduscopic skills than referrals from family physicians.[98] Whether the initial assessment should be done by a primary care physician or by an optometrist is uncertain, as is the optimal frequency of re-examination. Until the characteristics of retinal examination by primary care physicians have been better defined, there is insufficient evidence to include funduscopy in or exclude it from the periodic health examination (grade C recommendation). Since diabetic retinopathy and ARMD may have dire consequences and there is good evidence of effective treatment, the prudent physician may wish to include funduscopy in the periodic health examination. If ARMD is detected, patients should be referred to an ophthalmologist.
Cataracts are common and cause progressive visual loss, which can be effectively treated by means of cataract removal and corrective lenses. Early detection and referral to an ophthalmologist may facilitate assessment of retinal disease before the fundus is obliterated by advancing cataract; however, most patients will complain of visual loss, and primary care physicians can readily identify cataract and arrange for referral when visual problems occur. Thus, there is no convincing rationale for early detection.
Annual screening for diabetic retinopathy is recommended for all patients with type I diabetes who have had the disease for at least 5 years. For patients with type II diabetes the same recommendation can be made; however, if seven-field stereoscopic photographs of the fundus show no signs of retinopathy at the time of diagnosis, screening may be delayed for 4 years.[96] Examination is preferably carried out by an ophthalmologist, but if this is not possible, funduscopy with dilatation or fundus photography are alternatives.
Although open-angle glaucoma is a relatively common cause of visual loss among older people, there are problems with the screening manoeuvres. Automated perimetry, a new technique, shows promise but has not been widely evaluated in community surveys. Treatment of isolated IOP probably prevents visual field loss and provides the rationale for screening with tonometry. Because of the poor sensitivity and low positive predictive value of Schiötz tonometry, this technique is not recommended for screening.[99] Other methods of measuring IOP (e.g., Perkins tonometry or puff tonometry) are now available, and a high research priority is to determine the performance of these methods in community screening. The calculated average cost per year of vision saved is lower for ophthalmoscopy than for tonometry with increasing age.[100] Screening with automated perimetry is the most cost-effective approach among people over 65 years old.[70] Detection of visual field loss may be the preferred method of screening for glaucoma in future.[59] Older people who have a family history of glaucoma, are black, have severe myopia or have diabetes are at greatest risk of glaucoma. A prudent recommendation is to include periodic assessment by an ophthalmologist who has access to automated perimetry; the optimal interval is uncertain.
The task force is funded by the Health Services and Promotion Branch, Health Canada, and by the National Health Research Development Program (grants 6605-2702-57X and 6603-1375-57X). Dr. Christopher Patterson was supported in part by the Educational Centre for Aging and Health, McMaster University, Hamilton, Ont.
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Options : Test d'acuité visuelle à l'aide de l'échelle de Snellen, examen du fond de l'oeil, photographie de la rétine, tonométrie et périmétrie.
Résultats : Retard ou prévention de la détérioration de la vue ou de la cécité.
Preuves : On a cherché, dans MEDLINE, des articles sur la question publiés entre janvier 1986 et décembre 1993, examiné les bibliographies des articles pour y trouver d'autres articles, et consulté des experts. On a fondé les recommandations sur le niveau de preuve le plus élevé disponible.
Valeurs : On a utilisé les méthodes fondées sur la preuve et les valeurs du Groupe d'étude canadien sur l'examen médical périodique. On a accordé la valeur la plus importante à la préservation de la vision conformément à d'autres lignes directrices sur la vue.
Avantages, préjudices et coûts : Les avantages possibles consistent à maintenir ou améliorer l'acuité visuelle. Les risques de préjudices pour les patients sont minimes. Les données disponibles sur les coûts sont limitées.
Recommandations : Des preuves raisonnables incitent à inclure dans l'examen médical périodique des tests d'acuité visuelle effectués à l'aide de l'échelle de Snellen et d'un examen du fond de l'oeil ou d'une photographie de la rétine chez les patients âgés atteints de diabète depuis au moins 5 ans (recommandation de catégorie B). Le rôle de l'examen du fond de l'oeil dans la détection d'une dégénérescence de la macule et de changements glaucomateux liés à l'âge suscite la controverse. Il serait prudent, pour les patients à risque élevé de glaucome (antécédents familiaux positifs, race noire, myopie grave ou de diabète), de subir un examen périodique effectué par un ophtalmologue.
Validation : Les recommandations diffèrent de celles de l'American Academy of Ophthalmology et de l'American Optometric Association. Les recommandations relatives au dépistage du glaucome sont semblables à celles du Preventive Services Task Force des États-Unis. Les recommandations en vigueur ont été examinées par des experts des domaines de l'ophtalmologie et de l'optométrie.
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