Draft Recommendation Statement
Impaired Visual Acuity in Older Adults: Screening
This opportunity for public comment expired on August 17, 2015 at 8:00 PM EST
Note: This is a Draft Recommendation Statement. This draft is distributed solely for the purpose of receiving public input. It has not been disseminated otherwise by the USPSTF. The final Recommendation Statement will be developed after careful consideration of the feedback received and will include both the Research Plan and Evidence Review as a basis.
Recommendations made by the USPSTF are independent of the U.S. government. They should not be construed as an official position of the Agency for Healthcare Research and Quality or the U.S. Department of Health and Human Services.
Draft: Recommendation Summary
The USPSTF concludes that the current evidence is insufficient to assess the balance of benefits and harms of screening for impaired visual acuity in older adults.
See the Clinical Considerations for suggestions for practice regarding the I statement.
The USPSTF makes recommendations about the effectiveness of specific preventive care services for patients without related signs or symptoms.
It bases its recommendations on the evidence of both the benefits and harms of the service, and an assessment of the balance. The USPSTF does not consider the costs of providing a service in this assessment.
The USPSTF recognizes that clinical decisions involve more considerations than evidence alone. Clinicians should understand the evidence but individualize decisionmaking to the specific patient or situation. Similarly, the USPSTF notes that policy and coverage decisions involve considerations in addition to the evidence of clinical benefits and harms.
Impairment of visual acuity is a serious public health problem in older adults. In 2011, about 12% of Americans ages 65 to 74 years and 15% of those age 75 years or older reported having problems seeing, even with glasses or contact lenses.
There is convincing evidence that screening with a visual acuity test can identify persons with refractive errors. The USPSTF found convincing evidence that screening questions are not as accurate as visual acuity testing for assessing visual acuity. There is adequate evidence that visual acuity testing alone does not accurately identify early age-related macular degeneration (AMD) or cataracts.
Benefits of Detection and Early Treatment
There is inadequate overall evidence on the benefits of screening, early detection, and treatment to provide a coherent assessment of the overall benefits. Several studies evaluated the direct benefit of screening and reported no reductions in vision disorders or vision-related function in screened populations; however, these studies have limitations, including choice of comparator, high loss to followup, and low uptake of treatment. The USPSTF found adequate evidence that early treatment of refractive error, cataracts, and AMD improves or prevents loss of visual acuity.
Harms of Detection and Early Treatment
There is inadequate evidence on the harms of screening. There is adequate evidence that early treatment of refractive error, cataracts, and AMD may lead to harms that are small to none.
The USPSTF concludes that the evidence is insufficient to assess the balance of benefits and harms of screening for visual impairment in older adults. The evidence is lacking to provide a coherent assessment, and the balance of benefits and harms cannot be determined.
Draft: Clinical Considerations
Patient Population Under Consideration
This recommendation applies to asymptomatic adults age 65 years or older who do not present to their primary care clinician with vision problems.
Suggestions for Practice Regarding the I Statement
Potential Preventable Burden
In 2011, about 12% of Americans ages 65 to 74 years and 15% of those age 75 years or older reported having problems seeing, even with glasses or contact lenses.1 The prevalence of AMD is 6.5% in adults older than age 40 years and increases with age (2.8% in those ages 40 to 59 years and 13.4% in those age ≥60 years).2 About half of the cases of low vision are caused by cataracts. The prevalence of cataracts increases sharply with age; an estimated 50% of Americans age 80 years or older have cataracts. The prevalence of hyperopia requiring a correction of +3.0 diopters or more ranges from about 5.9% in U.S. adults ages 50 to 54 years, to 15.2% in adults ages 65 to 69 years, to 20.4% in adults age 80 years or older.1
Older age is an important risk factor for most types of visual impairment. Additional risk factors for cataracts are smoking, alcohol use, ultraviolet light exposure, diabetes, corticosteroid use, and black race. Risk factors for AMD include smoking, family history, and white race.1
The harms of screening in a primary care setting have not been adequately studied. Overall, the potential for harms from treatment are small to none. Harms of treatment of refractive error include a potential for increased falls with the use of multifocal lenses; infectious keratitis with the use of contact lenses, laser-assisted in situ keratomileusis (LASIK), and laser-assisted sub-epithelial keratectomy (LASEK); and corneal ectasia with LASIK. Harms of cataract surgery include posterior lens opacification and endophthalmitis. Treatment of AMD with antioxidant vitamins and mineral supplements is not associated with increased risk of most serious adverse events.
Although there appears to be benefit in longer-term outcomes, a systematic review found that treatment of AMD with laser photocoagulation was associated with greater risk of acute loss of ≥6 lines of visual acuity versus no treatment at 3 months (relative risk [RR], 1.41 [95% confidence interval (CI), 1.08 to 1.82]),3 and photodynamic therapy was associated with a nonstatistically significant increased risk of acute loss of ≥20 letters of visual acuity versus placebo at 7 days (three trials; RR, 3.75 [95% CI, 0.87 to 16]).4, 5 One of two trials found that treatment of wet AMD with intravitreal vascular endothelial growth factor (VEGF) inhibitor therapy was associated with greater likelihood of withdrawal versus sham therapy; there were no differences in serious or other adverse events, but estimates were imprecise.1, 4, 6, 7
About half of U.S. adults older than age 65 years reported having an eye examination within the last 12 months in a 2007 study.8
A visual acuity test (e.g., the Snellen eye chart) is the usual method for screening for visual acuity impairment in the primary care setting. Screening questions are not as accurate as visual acuity testing for identifying visual acuity impairment. Evidence is limited on the use of other vision tests, such as the pinhole test (a test to determine if a vision problem is due to a refractive error), the Amsler grid (a test of central vision to detect AMD), or fundoscopy (visual inspection of the interior of the eye), in primary care screening to detect visual impairment due to AMD or cataracts.
Several modalities of treatment are effective for improving visual acuity. Corrective lenses improve visual acuity in patients with refractive errors. Treatment of cataracts through surgical removal of the cataract is effective for improving visual acuity. Treatment of exudative (or wet) AMD includes laser photocoagulation, verteporfin, and intravitreal injections of VEGF inhibitors. Antioxidant vitamins and minerals are an effective treatment for dry AMD.
Other Approaches to Prevention
This recommendation statement does not include screening for glaucoma. The USPSTF’s recommendations on screening for glaucoma and falls prevention are available on its Web site (www.uspreventiveservicestaskforce.org).
Draft: Other Considerations
Research Needs and Gaps
More evidence is needed on accurate methods of screening in a primary care setting to identify disorders that do not manifest themselves through loss of visual acuity. More studies are needed that evaluate the link between vision screening in older adults and improved function, quality of life, and independence. Further studies are needed on the association between falls risk and corrective lenses, including possible associations with changes in lens prescriptions and the use of multifocal glasses.
Burden of Disease
Vision impairment is common in older adults. Older adults have a higher prevalence of primary ocular disease and systemic diseases associated with ocular disease than younger adults; in addition, older adults also have normal age-related changes in vision (i.e., presbyopia). In 2011, an estimated 12% of U.S. adults ages 65 to 74 years and 15% of those age 75 years or older reported vision loss.1
Refractive error, AMD, and cataracts are common causes of vision impairment in older adults. Severe refractive errors (requiring a correction of +3.0 diopters or more) affect an estimated 6% of U.S. adults ages 50 to 54 years, 15% of adults ages 65 to 69 years, and 20% of adults age 80 years or older.1 About 60% of refractive errors are deemed correctable to better than 20/40 visual acuity.9 In the United States, more than 15 million adults older than age 65 years have cataracts, and it is the most common cause of blindness in black adults older than age 40 years. AMD affects 1.5 million older adults in the United States and is the most common cause of blindness in white adults.2, 10
Scope of Review
In 2009, the USPSTF issued an I statement on screening for impaired visual acuity in older adults. In order to update its I statement, the USPSTF commissioned a systematic review to focus on evidence published since its last review. The USPSTF reviewed evidence on screening for visual acuity impairment associated with uncorrected refractive error, cataracts, and AMD in adults age 65 years or older in the primary care setting. The USPSTF also reviewed the evidence on the benefits and harms of screening, the accuracy of screening, and the benefits and harms of treatment of early vision impairment due to uncorrected refractive error, cataracts, and AMD.
Accuracy of Screening Tests
Asking screening questions to elicit self-perceived problems with vision has been studied as a screening modality. However, compared with a standard eye chart, they are not accurate for identifying persons with vision impairment.1, 4
In the United States, a standardized visual acuity test is the usual method for identifying the presence of vision impairment. Visual acuity tests assess the patient’s ability to recognize letters of different sizes arranged in rows from a prespecified distance (typically 20 feet). Standardized visual acuity tests are good at identifying refractive errors.
Compared with a detailed ophthalmological examination, no visual acuity screening test has both high sensitivity and specificity for the diagnosis of any underlying visual condition (e.g., AMD or cataracts). Few studies have focused on the accuracy of the Amsler grid, clinical examination, pinhole test, or fundus examination in the primary care setting. One study on the Amsler grid reported poor accuracy for detecting any visual condition compared with ophthalmological examination, and one study reported that geriatricians correctly identified most patients with cataracts and AMD through a clinical examination.1, 4
Two recent studies evaluated the accuracy of the Computer Vision Screen and its flip-chart version compared with a “gold standard” eye examination that included detailed history and symptoms and a comprehensive eye examination. These studies reported moderate sensitivity (0.75 to 0.80) and specificity (0.68 to 0.77).11 A third recent study evaluated the accuracy of the Minimum Data Set Version 2.0 Vision Patterns section compared with a standard visual acuity test. The study reported poor accuracy, depending on the cutoff score; sensitivity ranged from 0.11 to 0.52 and specificity ranged from 0.25 to 0.96.12 These studies have methodological limitations, including uncertainty as to whether the reference standard was interpreted independently from the screening test and the lack of a predefined threshold to determine a positive result.
Effectiveness of Early Detection and/or Treatment
There is limited direct evidence on the effectiveness of screening for visual impairment in the primary care setting. Three fair-quality cluster randomized, controlled trials (RCTs) found no difference with respect to vision and other clinical or functional outcomes between vision screening (as part of a multicomponent screening) with visual acuity testing or questions compared with usual care, no vision screening, or delayed screening.13-15 The application of this evidence to screening in a primary care setting has limitations. Issues with the study methods include failure to report allocation concealment, lack of intention-to-treat analysis, and unclear blinding. Other limitations to the applicability of this evidence to the primary care setting include the fact that the recommended interventions are provided by eye care specialists and that many patients do not get the recommended glasses.
Consistent evidence shows that most older adults with refractive errors could achieve visual acuity better than 20/40 with refractive correction. Evidence from a few trials indicates that immediate correction of refractive error with eyeglasses in older adults is associated with improved short-term vision-related quality of life or function compared with delayed treatment. A systematic review of 179 RCTs and observational studies found that refractive surgery was highly effective at improving refractive error; 92% to 94% of persons with myopia and 86% to 96% of persons with hyperopia achieved visual acuity of 20/40 or better. However, most of these studies were done in younger adults, limiting its generalizability to older adults.16
Cataract surgery is consistently associated with improved visual acuity in observational studies. About 90% of patients have postoperative visual acuity better than 20/40.1, 4, 17 The effects of cataract surgery on vision-related quality of life and function are mixed. One trial reported a decreased risk of falls after immediate versus delayed cataract surgery (RR, 0.66 [95% CI, 0.45 to 0.96]).18 Another trial reported no effect on falls or fracture risk.19 Some studies showed improvements in measures of function and quality of life associated with cataract surgery, while others reported no effect on these measures. Evidence from observational studies on effects on motor vehicle accidents and death is sparse and inconclusive. No randomized trials were identified that evaluated clinical outcomes associated with cataract surgery versus no surgery.
A systematic review reported that antioxidants were effective for slowing the progression of dry AMD; its conclusions were primarily based on one large good-quality trial (Age-Related Eye Disease Study).20 It found that an antioxidant multivitamin (composed of vitamins C and E and β-carotene with zinc) was associated with reduced likelihood of progression to advanced AMD (adjusted odds ratio [OR], 0.68); however, the differences in the likelihood of losing measurable visual acuity did not reach statistical significance. A recent 10-year followup study of the Age-Related Eye Disease Study reported similar results; an antioxidant multivitamin with zinc was associated with reduced likelihood of progression of AMD (OR, 0.66 [95% CI, 0.53 to 0.83]). The likelihood of losing measurable visual acuity did reach statistical significance in this followup study (OR, 0.71 [95% CI, 0.57 to 0.88]).21
For wet AMD, laser photocoagulation seems to be superior to no treatment for slowing the progression of vision loss (≥6 lines of visual acuity) after 2 years (RR, 0.67 [95% CI, 0.53 to 0.83]), although these studies have important limitations.3 Two good-quality systematic reviews of photodynamic therapy found verteporfin, a photoreactive agent, to be superior to placebo for preventing loss of visual acuity associated with wet AMD; quality of life outcomes were not reported.5, 22 Injection of VEGF inhibitors (e.g., pegaptanib and ranibizumab) to suppress growth of abnormal blood vessels associated with wet AMD was effective for reducing risk of visual acuity loss (<15 letters of visual acuity) (RR, 1.46 [95% CI, 1.22 to 1.75]).4, 23 Evidence on vision-related functional outcomes is limited; one trial reported small improvements in vision-related functional scores in the treatment group and one trial reported a higher likelihood of driving in the treatment group.1
Potential Harms of Screening and/or Treatment
No studies are available on the harms of screening in a primary care setting. Several studies evaluated the harms of treatment of refractive error, cataracts, and AMD. Most of these studies are older and were reviewed for the 2009 USPSTF recommendation. Data on harms of treatment of refractive error in older adults are limited. A small observational study reported an association between multifocal lens use and increased risk of falls in older adults.24 Serious harms, including vision loss, are rare as a result of contact lens use or refractive surgery. Corneal ectasia, a known harm of refractive surgery, occurs at a median rate of 0.2%.1, 4 Cataract surgery can lead to posterior capsule opacification of the implanted lens, requiring further procedures; reported rates of this complication vary widely from 0.7% to 48%.18, 25 More recent studies report an incidence of 28% at 5 years.26 Endophthalmitis, bullous keratopathy, dislocation of intraocular lens, macular edema, and retinal detachment are other complications associated with cataract surgery.
Pooled data on harms of treatment of AMD from trials of antioxidant vitamins and minerals reported no association with withdrawal due to gastrointestinal symptoms.1, 4 The largest trial reported an increased risk of hospitalization due to genitourinary causes with zinc and an increased risk of yellowing skin with antioxidants; it found no association with death or lung cancer.1, 4 Two recent trials on the treatment of early AMD reported no association between supplement use and any adverse event, serious adverse events, serious ocular events, or withdrawal due to adverse events.1
Treatment of wet AMD with laser photocoagulation is associated with increased risk of acute visual acuity loss at 3 months after the procedure, but, as described earlier, is also associated with reduced risk of visual acuity loss at 2 years.1, 4 Photodynamic therapy with verteporfin carries an initial risk of acute visual acuity loss and greater risk of back pain related to the infusion.5 Other reported harms of photodynamic therapy include visual disturbance, injection site reactions, and photosensitivity. Potential harms associated with intravitreal injections of VEGF inhibitors include endophthalmitis, uveitis, increased intraocular pressure, traumatic lens injury, and retinal detachment.1, 4 In three recent trials, these outcomes were infrequent, and differences between the intervention and sham therapy groups were not statistically significant; however, estimates were imprecise, with wide confidence intervals given the rarity of these outcomes.1, 6, 7, 27
Estimate of Magnitude of Net Benefit
The limited direct evidence from three fair-quality cluster RCTs show no difference in vision and other clinical or functional outcomes between vision screening and usual care, no vision screening, or delayed screening.
Although visual acuity testing is adequate for identifying refractive error, it is inadequate for identifying early AMD or early cataracts in a primary care setting. Effective treatments are available for uncorrected refractive error, cataracts, and AMD. The overall harms seem to be small; however, many of the treatments carry a small risk of serious complications, including acute visual loss. Although treatments that entail little harm can correct impaired visual acuity, limited evidence is available on the effect of screening and treatment on quality of life and overall and vision-related function, especially in older adults with screen-detected visual problems.
The limitations of the direct evidence and the inadequacy of the evidence on key pieces of indirect evidence prevent the USPSTF from developing a coherent assessment of the overall net benefit; therefore, the balance of benefits and harms cannot be determined.
Draft: Update of Previous USPSTF Recommendation
This recommendation is an update of the 2009 recommendation on screening for impaired visual acuity in older adults, which also concluded that the evidence is insufficient to assess the balance of benefits and harms of screening for visual acuity for the improvement of outcomes in older adults.
Draft: Recommendations of Others
The American Optometric Association recommends that asymptomatic adults age 61 years and older receive an eye examination every year.28 The American Academy of Ophthalmology recommends a comprehensive eye examination that includes visual acuity testing and dilation every 1 to 2 years for all adults age 65 years or older without risk factors or more frequently if risk factors are present.29 This recommendation is based on descriptive studies, case reports, and expert consensus. The American Academy of Family Physicians’ recommendation is currently under review.30 The American Congress of Obstetricians and Gynecologists recommends that vision assessments be part of well-woman visits for all women age 65 years or older.31
1. Chou R, Dana T, Bougatsos C, Grusing S, Blazina I. Screening for Impaired Visual Acuity in Older Adults: A Systematic Review to Update the 2009 U.S. Preventive Services Task Force Recommendation. Evidence Synthesis No. 127. AHRQ Publication No. 14-05209-EF-1. Rockville, MD: Agency for Healthcare Research and Quality; 2015.
2. Congdon N, Vingerling JR, Klein BE, West S, Friedman DS, Kempen J, et al; Eye Diseases Prevalence Research Group. Prevalence of cataract and pseudophakia/aphakia among adults in the United States. Arch Ophthalmol. 2004;122(4):487-94.
3. Virgili G, Bini A. Laser photocoagulation for neovascular age-related macular degeneration. Cochrane Database Syst Rev. 2007;(3):CD004763.
4. Chou R, Dana T, Bougatsos C. Screening for Visual Impairment in Older Adults: Systematic Review to Update the 1996 U.S. Preventive Services Task Force Recommendation. Evidence Synthesis No. 71. AHRQ Publication No. 09-05135-EF-1. Rockville, MD: Agency for Healthcare Research and Quality; 2009.
5. Wormald R, Evans J, Smeeth L, Henshaw K. Photodynamic therapy for neovascular age-related macular degeneration. Cochrane Database Syst Rev. 2007;(3):CD002030.
6. Rosenfeld PJ, Brown DM, Heier JS, Boyer DS, Kaiser PK, Chung CY, Kim RY; MARINA Study Group. Ranibizumab for neovascular age-related macular degeneration. N Engl J Med. 2006;355(14):1419-31.
7. Gragoudas ES, Adamis AP, Cunningham ET Jr, Feinsod M, Guyer DR; VEGF Inhibition Study in Ocular Neovascularization Clinical Trial Group. Pegaptanib for neovascular age-related macular degeneration. N Engl J Med. 2004;351(27):2805-16.
8. Zhang X, Saaddine JB, Lee PP, Grabowski DC, Kanjilal S, Duenas MR, Narayan KM. Eye care in the United States: do we deliver to high-risk people who can benefit most from it? Arch Opthalmol. 2007;125(3):411-8.
9. Vitale S, Cotch MF, Sperduto RD. Prevalence of visual impairment in the United States. JAMA. 2006;295(18):2158-63.
10. Centers for Disease Control and Prevention. Improving the Nation's Vision Health: A Coordinated Public Health Approach. Atlanta: Centers for Disease Control and Prevention; 2009. Accessed at http://www.cdc.gov/visionhealth/publications/vhi_report.htm on 9 July 2015.
11. Jessa Z, Evans BJ, Thomson DW. The development & evaluation of two vision screening tools for correctable visual loss in older people. Ophthalmic Physiol Opt. 2012;32(4):332-48.
12. Swanson MW, McGwin G Jr, Elliott AF, Owsley C. The nursing home minimum data set for vision and its association with visual acuity and contrast sensitivity. J Am Geriatr Soc. 2009;57(3):486-91.
13. Eekhof J, De Bock G, Schaapveld K, Springer M. Effects of screening for disorders among the elderly: an intervention study in general practice. Fam Pract. 2000;17(4):329-33.
14. Smeeth L, Fletcher AE, Hanciles S, Evans J, Wormald R. Screening older people for impaired vision in primary care: cluster randomised trial. BMJ. 2003;327(7422):1027.
15. Moore AA, Siu A, Partridge JM, Hays RD, Adams J. A randomized trial of office-based screening for common problems in older persons. Am J Med. 1997;102(4):371-8.
16. Murray A, Jones L, Milne A, Fraser CM, Lourenço T, Burr J. A Systematic Review of the Safety and Efficacy of Elective Photorefractive Surgery for the Correction of Refractive Error. London: National Institute for Health and Clinical Excellence; 2005.
17. Powe NR, Schein OD, Gieser SC, Tielsch JM, Luthra R, Javitt J, Steinberg EP; Cataract Patient Outcome Research Team. Synthesis of the literature on visual acuity and complications following cataract extraction with intraocular lens implantation. Arch Ophthalmol. 1994;112(2):239-52.
18. Harwood RH, Foss AJ, Osborn F, Gregson RM, Zaman A, Masud T. Falls and health status in elderly women following first eye cataract surgery: a randomised controlled trial. Br J Ophthalmol. 2005;89(1):53-9.
19. Foss AJ, Harwood RH, Osborn F, Gregson RM, Zaman A, Masud T. Falls and health status in elderly women following second eye cataract surgery: a randomised controlled trial. Age Ageing. 2006;35(1):66-71.
20. Evans JR. Antioxidant vitamin and mineral supplements for slowing the progression of age-related macular degeneration. Cochrane Database Syst Rev. 2006;(2):CD000254.
21. Chew EY, Sperduto RD, Milton RC, et al. Risk of advanced age-related macular degeneration after cataract surgery in the Age-Related Eye Disease Study: AREDS report 25. Ophthalmology. 2009;116(2):297-303
22. Meads C, Salas C, Roberts T, Moore D, Fry-Smith A, Hyde C. Clinical effectiveness and cost-utility of photodynamic therapy for wet age-related macular degeneration: a systematic review and economic evaluation. Health Technol Assess. 2003;7(9):v-vi, 1-98.
23. Vedula SS, Krzystolik MG. Antiangiogenic therapy with anti-vascular endothelial growth factor modalities for neovascular age-related macular degeneration. Cochrane Database Syst Rev. 2008;(2):CD005139.
24. Lord SR, Dayhew J, Howland A. Multifocal glasses impair edge-contrast sensitivity and depth perception and increase the risk of falls in older people. J Am Geriatr Soc. 2002;50(11):1760-6.
25. Powe NR, Tielsch JM, Schein OD, Luthra R, Steinberg EP; Cataract Patient Outcome Research Team. Rigor of research methods in studies of the effectiveness and safety of cataract extraction with intraocular lens implantation. Arch Ophthalmol. 1994;112(2):228-38.
26. Schaumberg DA, Dana MR, Christen WG, Glynn RJ. A systematic overview of the incidence of posterior capsule opacification. Ophthalmology. 1998;105(7):1213-21.
27. Regillo CD, Brown DM, Abraham P, Yue H, Ianchulev T, Schneider S, Shams N. Randomized, double-masked, sham-controlled trial of ranibizumab for neovascular age-related macular degeneration: PIER Study year 1. Am J Ophthalmol. 2008;145(2):239-48.
28. American Optometric Association. Adult Vision: 19 to 40 Years of Age. St. Louis, MO: American Optometric Association; 2014. Accessed at http://www.aoa.org/patients-and-public/good-vision-throughout-life/adult-vision-19-to-40-years-of-age?sso=y on 9 July 2015.
29. American Academy of Ophthalmology Preferred Practice Patterns Committee. Preferred Practice Pattern® Guidelines: Comprehensive Adult Medical Eye Evaluation. San Francisco, CA: American Academy of Ophthalmology; 2010. Accessed at http://www.aao.org/preferred-practice-pattern/comprehensive-adult-medical-eye-evaluation--octobe on 9 July 2105.
30. American Academy of Family Physicians. Clinical Preventive Service Recommendation: Visual Difficulties, Adults. Leawood, KS: American Academy of Family Physicians; 2015. Accessed at http://www.aafp.org/patient-care/clinical-recommendations/all/visual.html on 16 July 2015.
31. American Congress of Obstetricians and Gynecologists. Ages 65 Years and Older: Health Topics. Washington, DC: American Congress of Obstetricians and Gynecologists; 2015. Accessed at http://www.acog.org/About-ACOG/ACOG-Departments/Annual-Womens-Health-Care/Well-Woman-Recommendations/Evaluation-and-Counseling-Ages-65-Years-and-Older on 9 July 2015.
Internet Citation: Draft Recommendation Statement: Impaired Visual Acuity in Older Adults: Screening. U.S. Preventive Services Task Force. July 2015.