Abstract
Objectives. Little information exists regarding the causes of visual impairment and the most common eye problems in American Indians/Alaska Natives.
Methods. We randomly sampled American Indians/Alaska Natives older than 40 years from 3 tribes within the Northwest region.
Results. We found a higher prevalence of visual impairment and normal-tension glaucoma, as well as a lower prevalence of ocular hypertension, in American Indians/Alaska Natives compared with previous results in other racial/ethnic groups.
Conclusions. American Indians/Alaska Natives have a need for vision correction. Future interventions in American Indians/Alaska Natives should include providing spectacles for refractive error, detecting glaucoma, and preventing visual impairment from age-related maculopathy and cataracts.
Investigators need prevalence information to guide preventive health measures. Epidemiological studies have documented the prevalence and cause of visual impairment in non-Hispanic Whites, Hispanics, and Blacks in the United States.1–4 The Baltimore Eye Study indicated that undercorrected refractive error, cataracts, macular degeneration, and glaucoma were the most common causes of visual impairment and blindness in an urban population of Whites and Blacks.1,2 Proyecto VER (Project Vision, Evaluation, Research), a study examining the prevalence of diabetic retinopathy, cataracts, age-related macular degeneration, glaucoma, and other causes of visual loss in Mexican Americans, reported cataracts, macular degeneration, diabetic retinopathy, and glaucoma as the most common causes of visual impairment in Hispanics in southern Arizona.3 Macular degeneration was the most common cause of visual impairment in the Beaver Dam Study.4 The Los Angeles Latino Eye Study determined the risk factors for visual impairment in Latinos in urban Los Angeles County.5
Similar information regarding American Indian/Alaska Native (AIAN) populations does not exist. Most studies of AIAN populations have been chart reviews or convenience sample studies.6–8 These types of study designs do not reliably estimate the prevalence and causes of blindness because the selection criteria do not include randomization for all eligible participants of the population. Our purpose is to outline the common causes of visual impairment and the most common eye problems in a random sample of Northwest American Indians/Alaska Natives.
We randomly selected 3 tribes from the Northwest region of the United States (Oregon, Washington, and Idaho) for inclusion in the study. We assigned each tribe a computer-generated random number and invited the 3 tribes with the lowest numbers to participate. To be eligible, tribes needed to have at least 400 enrolled members aged 40 years or older. We used the tribal enrollment database to perform an age-stratified, random sample of these members. We excluded candidates who had died, were seriously ill, or had dementia (which prevents subjective testing such as visual acuity and visual field testing).
Each selected individual was invited to participate by phone and by mail. A tribal coordinator, a volunteer, or an ophthalmic technician interviewed and performed a baseline examination of all individuals. The interview determined AIAN heritage, ocular and medical history, family history, risk factors for eye disease with a modified Behavioral Risk Factor Surveillance Survey,9 and the effect of eye disease on quality of life with the National Eye Institute Visual Function Questionnaire (NEI-VFQ-25).10
The baseline examination included height; weight; blood pressure (taken after the participant had been sitting still for 5 minutes)11; automated refraction; keratometry; presenting and best-corrected near vision; Early Treatment Diabetic Retinopathy Study distance visual acuity on presentation and with best correction; intraocular pressure with Tono-Pen XL (Medtronic Solan, Jacksonville, Fla); random fingerstick blood glucose level and glycosylated hemoglobin; anterior chamber assessment by limbal chamber depth12,13; visual field testing with frequency-doubling technology (FDT) perimetry, program C-20-5; confocal scanning laser ophthalmoscopy; and nonmydriatic digital imaging of the lens, optic disc, and fundus.
The baseline examination contained several criteria for referral to a follow-up examination to allow the highest sensitivity (Table 1).12–15 An ophthalmologist performed this follow-up examination in all participants with abnormal findings and a subset of participants with normal findings to determine the accuracy of the baseline examination. The “normal” patients were selected with a random-number generator. The ophthalmologist used a data entry sheet separate from that used in the baseline examination to mask the results from the baseline examination and to reduce workup bias and review bias. The follow-up examination included biomicroscopy of the anterior segment, gonioscopy, Lens Opacity Classification System III grading of the lens,16 standard automated achromatic perimetry (24-2 Swedish interactive threshold algorithm standard, Humphrey Field Analyzer II, Carl Zeiss Meditech, Dublin, Calif), dilated fundus evaluation, and photographs of the optic disc and macula.
The ophthalmologist used standard criteria to determine the prevalence of eye disorders. Table 2 summarizes the case definitions for the eye diseases.17–23 The ophthalmologist determined the primary cause of the decreased visual acuity. When multiple abnormalities were present, the ophthalmologist ranked the diseases most likely to cause decreased visual acuity. A separate ophthalmologist independently confirmed any abnormality found during the follow-up examination by reviewing the patient history, testing results, and photographs of the optic disc and macula.
An abnormal standard achromatic automated perimetry result was defined as a pattern standard deviation outside 95% of age-specific norms; a glaucoma hemifield test result outside 99.5% of age-specific norms (outside normal limits on Statpac2 [Carl Zeiss Meditech, Dublin, Calif); or a mean deviation outside the 95% limits without generalized reduction in sensitivity.
We compared the sample population demographic data with the demographic data contained within each tribe’s tribal enrollment database.
Our analysis required statistical weighting to accurately determine the prevalence of eye diseases, because not all persons with a normal baseline examination result were selected for the follow-up examination and not all persons with an abnormal baseline examination result completed a follow-up examination. The weighting was determined by dividing the total number of normal baseline examination results by the number of participants with normal baseline results who completed the follow-up examination (88/12 = 7.333) and by dividing the total number of abnormal baseline results by the number of participants with abnormal results who completed the follow-up examination (199/157 = 1.267). One participant had a home examination without a baseline examination; the result was not weighted.
We recruited a total of 288 participants: 98 participants from tribe A, 93 participants from tribe B, and 97 participants from tribe C. The overall enrollment was 32% of all possible selected participants. We were unable to contact 48% of possible participants. Reasons for noncontact included inactive telephone numbers and absence from home. Ten percent were unable to have an eye examination on the dates of testing. Another 10% scheduled an appointment but did not show up for the examination.
Table 3 lists the baseline characteristics of the participants.24 We found no age or gender differences between participants and those whom we were unable to contact (P>.05).
Thirty-four (19%) women and 24 (23%) men reported a medical history of diabetes. An additional 5 (2%) participants had previously undiagnosed diabetes with a random capillary blood glucose greater than 127 mg/dL and a hemoglobin A1c greater than 5.7%.14 Forty-six (26%) women and 37 (35%) men reported a medical history of high blood pressure. One hundred twenty (42.1%) participants without a medical history of high blood pressure had a systolic blood pressure greater than 135 mm Hg or a diastolic blood pressure greater than 85 mm Hg.11
Table 4 lists the prevalence of visual impairment, blindness, retinal diseases, cataract, glaucoma, and other eye problems. Under-corrected refractive error was the most common cause of poor visual acuity for both distance vision and near vision. From spectacle correction alone, 18% would gain an improvement from 20/40 or worse to 20/30 or better in their distance vision. Blindness (best-corrected visual acuity 20/200 or worse in the better eye) was found in 1 of 288 participants (0.3%). Visual impairment (best-corrected visual acuity 20/40 or worse in the better eye) was found in 9 of 288 participants (3.1%).
The cause of visual impairment was cataract in 4 persons, age-related maculopathy in 2 persons, glaucoma in 1 person, and multifocal choroiditis in 1 person. One participant with visual impairment refused the full eye examination.
Ocular hypertension was uncommon. Open-angle glaucoma was common, and all participants with glaucoma had “low-tension glaucoma,” defined as an intraocular pressure less than 22 mm Hg. No cases of primary angle-closure suspect, primary angle closure, primary angle-closure glaucoma, or pseudo-exfoliation were found. Other common conditions included age-related maculopathy (16.9%), cataract (12.2%), and diabetic retinopathy (6.0% overall). No participants had clinically significant macular edema from diabetic retinopathy.
Eighteen (6%) right eyes and 20 (7%) left eyes had best-corrected visual acuity of 20/40 or worse. One person with visual acuity worse than 20/40 in both eyes refused a full eye examination, and 2 other persons with visual acuity worse than 20/40 in the left eye refused a full eye examination. The ophthalmologist determined that cataract (n = 7), age-related maculopathy (n = 3), other retinal diseases (n = 6), and glaucoma (n = 1) were the primary causes of poor vision in the right eye. Other retinal diseases included branch retinal vein occlusion, central retinal vein occlusion, macular scar, multifocal choroiditis, cystoid macular degeneration, and chronic retinal detachment, each occurring in 1 right eye. The ophthalmologist determined that the primary causes of poor visual acuity in the left eye were cataract (n = 6), diabetic retinopathy (n = 3), amblyopia (n = 2), age-related maculopathy (n = 1), other retinal diseases (n = 3), and unknown (n = 2). Other retinal diseases included multifocal choroiditis (n = 1) and macular scar secondary to trauma (n = 2). Retinal diseases were the primary cause of poor vision (best-corrected visual acuity of 20/40 or worse) in the right eye for 9 of 17 (53%) participants and in the left eye for 6 of 17 (35%) participants.
Determining prevalence information is an important first step toward meeting the Healthy Vision 2010 objective of decreasing the impact of blindness from diabetes and glaucoma, especially in minority groups such as American Indians/Alaska Natives. Eye and vision problems are the second leading cause of impairment in AIAN populations.25 However, little information exists about the causes of visual impairment and the most common eye problems in AIAN populations.
In Northwest AIAN populations, cataract and age-related maculopathy were the most common causes of visual impairment, with a prevalence similar to that found among the White participants in the Baltimore Eye Study2 and the mostly Hispanic participants in Proyecto VER.3 The prevalence of visual impairment among American Indians/Alaska Natives in our study (3.1%) was similar to that among Latinos in the Los Angeles Latino Eye Study (3.0%)5 but higher than that among the mostly White participants in the Beaver Dam Eye Study (0.8%).26 We realize that comparisons with these other prevalence studies present problems. Our study had a small sample size, which resulted in large confidence intervals for our estimates and prevented us from making age–strata comparisons. We recruited only 32% of those people that we randomly selected. Our methods of recruitment may have missed potential participants of lower socioeconomic status because such persons are less likely to have a permanent address or phone number. To decrease this potential bias, future studies should include door-to-door recruitment of eligible participants. Door-to-door recruitment will also allow better ascertainment of ineligible candidates who have moved away or who have otherwise become unavailable. We were unable to measure socioeconomic status in persons who did not participate; however, our results suggest consistency in age and gender of these individuals with the overall AIAN population.
One of our intriguing findings was that all patients with glaucoma had intraocular pressure less than 22 mm Hg, otherwise known as low-tension glaucoma.27 Previous studies have shown that low-tension glaucoma may account for up to 69% of all glaucoma in patients with glaucoma.27 In our results, the proportion was even higher (100%). Only 1 study, a recent investigation with Japanese participants, had a similar proportion of low-tension glaucoma (92%).28 We also found a low prevalence of ocular hypertension (0.004%), which is present in approximately 5% of individuals older than 40 years in the US population.29 The Los Angeles Latino Eye Study found ocular hypertension in 3.6% of Latinos.30 The high prevalence of low-tension glaucoma and the low prevalence of ocular hypertension found in our study indicate a need for further analysis in AIAN populations of ocular factors (corneal thickness, intraocular pressure, optic disc characteristics) and risk factors for glaucoma (systemic hypertension, diabetes).
The results of our study show similarities with and differences from the results of other vision studies in AIAN populations, which have mostly consisted of chart reviews or convenience samples at a local village. In particular, angle-closure glaucoma was not found in our study but has been found to be a common cause of blindness in Alaskan Eskimos by previous studies.7,8 Diabetic retinopathy was a common eye condition in our study but not a common cause of visual impairment, a finding that contrasts with studies in Navajos and Pima Indians.6,31,32 We found no cases of psuedoexfoliation, a risk factor for open-angle glaucoma, a finding contrary to results among Navajo Indians, among whom 38% of persons 60 years and older had psuedoexfoliation.33 However, our results are similar to those of other studies of AIAN populations that showed cataracts to be a common cause of visual impairment.32 To our knowledge, age-related maculopathy has not been shown to be a common cause of visual impairment in AIAN populations. Overall, these findings suggest heterogeneity in AIAN populations that is probably related to variations in genetics, environment, diet, and other factors.
We found a great need for eyeglasses in the study population. Eighteen percent of participants had distance vision worse than 20/40, and approximately 30% had near vision worse than Jaeger 4 (20/40 for near vision) owing to undercorrected refractive error. The need for eyeglasses for distance vision (18%) was more common than that found by the Baltimore Eye Study (Blacks, 6.5%; Whites, 7.8%).1 This finding could be related to underuse of eye care providers or the known high prevalence of astigmatism in AIAN populations.34–37 Poor vision from refractive error restricts otherwise healthy individuals from succeeding in educational endeavors and employment opportunities, propagating low educational attainment and poverty; it limits social interaction that requires good distance vision and artisan work that requires good near vision, work such as beadwork and jewelry making. Future interventions addressing vision should include the provision of spectacles for refractive error.
We found a high prevalence of diagnosed and undiagnosed diabetes among our study population. Similarly, high blood pressure (defined as systolic blood pressure >135 mm Hg or diastolic pressure > 85 mm Hg) was common. Our finding of a high prevalence of undiagnosed hypertension should be viewed with caution, because a high proportion of cases may have been “white coat” hypertension, caused by anxiety experienced while answering a questionnaire and undergoing multiple tests. Follow-up and further analysis of participants with undiagnosed hypertension is warranted.
Our pilot study showed a higher prevalence of visual impairment and low-tension glaucoma among American Indians/Alaska Natives compared with among other racial and ethnic groups. American Indians/Alaska Natives have an unmet need for vision correction. Interventions for vision among American Indians/Alaska Natives may include provision of spectacles for refractive error, detection of glaucoma, and prevention of visual impairment from cataracts and age-related maculopathy. Future studies will require larger sample sizes to increase the accuracy of prevalence estimates in AIAN populations.
Note. NPDR = nonproliferative diabetic retinopathy; IRMA = intraretinal microvascular angiopathy; PDR = proliferative diabetic retinopathy; CSME = clinically significant diabetic macular edema; ARM = age-related maculopathy; GON = glaucomatous optic neuropathy; IOP = intraocular pressure; OHTN = ocular hypertension; PACS = primary angle-closure suspect; PAC = primary angle closure; PACG = primary angle-closure glaucoma; LOCSIII = Lens Opacity Classification System III. Note. HS = high school; GED = general equivalency diploma; AIAN = American Indian/Alaska Native. aAccording to 2001 federal poverty level.24
History of glaucoma, diabetes, or eye abnormalities Capillary blood glucose glucometer reading > 127 mg/dL random and capillary hemoglobin A1c > 5.7%14 Visual acuity 20/40 or worse with best correction Intraocular pressure > 21 mm Hg Limbal chamber depth ≤ 25% of the corneal optical section12,13 Abnormal, unreliable, or indeterminate frequency-doubling technology perimeter result Difficulty with confocal scanning laser ophthalmoscopy imaging or contour line placement Borderline or abnormal report from confocal scanning laser ophthalmoscopy according to Moorfields criteria15 Signs of optic nerve disease, diabetic retinopathy, macular degeneration, or other eye disease with nonmydriatic digital imaging Eye Abnormality Definition NPDR Mild to moderate Small microaneurysms, minimal venous changes, and IRMA17 Severe Contains 1 of the 3 characteristics of the 4:2:1 rule: (1) approximately 20 dot-blot hemorrhages in all 4 midperipheral quadrants, (2) venous beading in 2 quadrants, or (3) severe IRMA in 1 quadrant17 Very severe Contains 2 of the 3 characteristics of the 4:2:1 rule17 PDR High risk Neovascularization of one third of the area of the optic disc or vitreous hemorrhage associated with neovascularization of any part of the eye of one half disc diameter in area18 Low risk Neovascularization without high-risk characteristics18 CSME Retinal edema within 500 microns of the fovea, exudates associated with retina edema within 500 microns of the fovea, or retinal edema 1500 microns in diameter within 1500 microns of the fovea19 Diabetic retinopathy Presence of NPDR, PDR, or CSME ARM Early Soft drusen > 125 microns, or drusen with pigmentary changes without late ARM, not caused by any other disorder Late Macular fluid, geographic atrophy, or neovascular maculopathy within the macula, not caused by any other disorder20 GON Category 1 Cup-to-disc ratio ≥ 0.8 or glaucomatous optic disc features (rim thinning, nerve fiber defect, excavation) and definite glaucomatous visual field loss Category 2 Cup-to-disc ratio ≥ 0.8 or glaucomatous features and inability to complete visual field testing satisfactorily Category 3 Visual field testing not possible and optic disc unable to be viewed, with either IOP > 22 mm Hg or evidence of glaucoma surgery21 OHTN IOP > 22 mm Hg without GON22 PACS Posterior trabecular meshwork cannot be seen in 3 or more quadrants by gonioscopy21 PAC PACS with peripheral anterior synechiae, OHTN, or signs of acute angle closure without glaucomatous optic neuropathy21 PACG PAC with GON21 Cataract Pseudophakia, aphakia, or vision ≤ 20/40 associated with lens opacities (LOCSIII score ≥ 2.0 for cortex, posterior subcapsular, or nuclear or hypermature cataract) without any other causes of vision loss23 Poor visual acuity caused by undercorrected refractive error Distance vision After manifest refraction, improvement of distance visual acuity at presentation from 20/40 or worse to 20/30 or better Near vision After manifest refraction, improvement of near visual acuity at presentation from Jaeger 4 or worse to Jaeger 3 or better Need for spectacles Undercorrected refractive error or current use of spectacles Visual impairment Best-corrected visual acuity 20/40 or worse in the better-seeing eye17 Blindness at presentation with best correction Best-corrected distance visual acuity 20/200 or worse in the better-seeing eye1 No. (%) Gender Male 106 (36.8) Female 182 (63.2) Age, y 40–49 116 (40.3) 50–59 83 (28.8) 60–69 49 (17.0) ≥ 70 40 (13.9) Marital status Married 132 (45.8) Other 150 (52.1) Unknown 6 (2.1) Education < HS/GED 45 (15.6) HS/GED 79 (27.4) > HS/GED 159 (55.2) Unknown 5 (1.7) Employed Yes 162 (56.3) No 121 (42.0) Unknown 5 (1.7) Income, % povertya < 100 49 (17.0) 101–150 52 (18.1) 151–200 35 (12.2) > 200 127 (44.1) Unknown 25 (8.7) Percentage AIAN ≤ 25% 37 (12.8) > 25%–50% 49 (17.0) > 50% to < 100% 79 (27.4) 100% 104 (36.1) Unknown 19 (6.5) Eye Problema Overall, % (95% CI) Right Eye, % (95% CI) Left Eye, % (95% CI) Undercorrected refractive error Distance vision 18.1 (13.6, 22.6) 13.2 (9.2, 17.2) 11.5 (7.7, 15.3) Near vision 30.6 (25.2, 36.0) 21.5 (16.7, 26.3) 23.6 (18.6, 28.6) Blindness 0.3 (0.0, 1.0) . . . . . . Visual impairment 3.1 (1.0, 5.0) . . . . . . Age-related maculopathy Early 16.9 (12.5, 21.3) 16.8 (12.4, 21.2) 17.2 (13.1, 22.1) Late 1.4 (0, 2.8) 1.3 (0, 2.6) 0.4 (0, 1.1) Cataract 12.2 (8.3, 16.1) 10.4 (6.8, 14.0) 10.0 (6.5, 13.5) Glaucoma 6.2 (2.6, 7.8) 3.6 (1.4, 5.8) 6.1 (3.3, 8.9) Ocular hypertension 0.004 (0, 1.1) 0.004 (0, 1.1) . . . Diabetic retinopathy Nonproliferative diabetic retinopathy 4.2 (1.8, 6.6) 4.0 (1.7, 6.3) 4.0 (1.7, 6.3) Proliferative diabetic retinopathy 1.8 (0.2, 3.4) 1.8 (0.2, 3.4) 1.8 (0.2, 3.4)
This study was supported by the American Glaucoma Society, Alcon, Allergan, and the National Eye Institute (grant NEI 1 K23 EY0155501-01 to S.L.M.), the Lions Sight and Hearing Foundation (grant to C.A.J.), the Center for Healthy Communities (grant to T.M.B. and S.L.M), the Peel Medical Research Trust (grant to B. E.), and the TFC Frost Charitable Trust (grant to B. E.).
This study was presented in part at the 14th Annual Meeting of the American Glaucoma Society, Sarasota, Fla, March 4–7, 2004.
We thank Shaban Demirel, Peter Francis, Cindy Blachly, Judy Thompson, Kathryn Sherman, Douglas Romero, and Karin Novitsky for assistance with data collection.
Human Participant Protection The institutional review boards of the Portland Area Indian Health Service and Legacy Health System approved this pilot study. The leadership committees of the participating tribes signed tribal resolutions allowing us to perform the study. All identifying information was kept confidential. The participants signed a consent form.
