- Email: [email protected]
Socioeconomic status and clinical features of patients undergoing photodynamic therapy or transpupillary thermotherapy for subfoveal choroidal neovascularization due to age-related macular degeneration
Socioeconomic status and clinical features of patients undergoing photodynamic therapy or transpupillary thermotherapy for subfoveal choroidal neovascularization due to age-related macular degeneration Hall Chew,* MD; David A.L. Maberley,† MD, FRCSC, MSc (Epid); Patrick Ma,† MD, FRCSC; Angela Chang,† BSc; Alan Maberley,† MD, FRCSC ABSTRACT • RÉSUMÉ Background: The purpose of this study was to compare baseline clinical and socioeconomic features of patients undergoing self-funded photodynamic therapy (PDT) or government-funded subthreshold transpupillary thermotherapy (TTT) with a diode laser for subfoveal choroidal neovascularization secondary to agerelated macular degeneration (AMD). Methods: Between July 2000 and August 2001, 115 patients with subfoveal choroidal neovascularization secondary to AMD were offered PDT as an initial intervention. If individuals believed that they could not afford or did not want PDT, then TTT was offered. In masked fashion, leakage pattern and lesion size were determined retrospectively from pretreatment angiograms. Baseline visual acuity was determined with autorefraction and subsequent Snellen testing. The mean income of each treatment group was estimated from the average sex-specific income for each subject’s postal code, based on the 1996 Canadian census data. The average education level for each subject’s postal code was also determined. Results: The patients who were not willing to pay for PDT had significantly worse macular disease before treatment (larger lesions and poorer visual acuity) and a significantly lower mean income than the patients who were willing to pay for PDT. Interpretation: The severity of exudative choroidal neovascularization appears to be associated with lower socioeconomic status. Contexte : Cette étude a pour objet de comparer les caractères cliniques et socioéconomiques de base des patients qui suivent une thérapie photodynamique (TPD) qu’ils doivent payer eux-mêmes ou la thermothérapie transpupillaire infraliminaire (TTT) avec laser diode, assumée par le gouvernement, pour une néovascularisation choroïdienne sousfovéale due à la dégénérescence maculaire liée à l’âge (DMLA). Méthodes : Entre juillet 2000 et août 2001, 115 patients ayant une néovascularisation choroïdienne sousfovéale due à une DMLA se sont vu offrir la TPD comme première intervention. S’ils n’avaient pas les moyens de défrayer les frais d’une TPD ou refusaient de le faire, on leur offrit alors une TTT. Suivant la méthode dite From *the Department of Ophthalmology, University of Toronto, Toronto, Ont., and †the Department of Ophthalmology, University of British Columbia, Vancouver, BC
BC V5Z 3N9; fax (604) 875-4699; [email protected]
Correspondence to: Dr. David A.L. Maberley, 2550 Willow St., Vancouver
Can J Ophthalmol 2005;40:384–8
384
Socioeconomic status and AMD—Chew et al
This article has been peer-reviewed.
Socioeconomic status and AMD—Chew et al
aveugle, le motif de diffusion et la taille de la lésion ont été établis rétrospectivement à partir des angiographies d’avant le traitement. L’acuité visuelle de base a été établie par autoréfraction et subséquemment le test de Snellen. Le revenu moyen de chacun des groupes de traitement a été estimé à partir du revenu moyen propre à chaque sexe en regard du code postal de chacun des sujets, fondé sur les données du recensement canadien de 1996. Le niveau d’instruction moyen a aussi été établi en regard du code postal de chaque sujet. Résultats : Les patients qui n’ont pas voulu assumer les frais de la TPD avaient une maladie maculaire plus grave avant le traitement (lésion plus grande et plus faible acuité visuelle) et un revenu significativement inférieur à ceux qui ont assumé le coût. Interprétation : La sévérité de la néovascularisation choroïdienne exsudative paraît associée avec une modeste situation socioéconomique.
P
hotodynamic therapy (PDT) with verteporfin (VPDT) and transpupillary thermotherapy (TTT) are widely used for treating subfoveal choroidal neovascularization due to age-related macular degeneration (AMD). Randomized clinical trials — Treatment of Age-Related Macular Degeneration with Photodynamic Therapy1,2 (TAP) and Verteporfin in Photodynamic Therapy3 (VIP) — have demonstrated the therapeutic benefit of VPDT for both classic and occult choroidal neovascularization; however, TTT is still under evaluation for the management of occult choroidal neovascularization secondary to AMD. The initial purpose of our study was to compare PDT and TTT for all forms of subfoveal choroidal neovascularization secondary to AMD. While it was not ethical for us to randomly assign patients to one treatment or the other, given the proven benefit of PDT for exudative AMD, individuals who could not afford or did not wish to have PDT were secondarily offered TTT. This process allowed for the creation of 2 study groups that were based on ability or desire to pay for PDT. The study was possible for only 13 months, from July 2000 to August 2001, prior to the start of comprehensive coverage of VPDT at the University of British Columbia by the Medical Services Plan of British Columbia. Thereafter, it was not ethical for us to withhold PDT in the presence of good efficacy data and provincial funding. Thus, the purpose of our study became to compare baseline clinical and socioeconomic features of patients undergoing self-funded PDT or government-funded subthreshold TTT with a diode laser for subfoveal choroidal neovascularization secondary to AMD.
METHODS
For inclusion in this study, all subjects were required to have subfoveal choroidal neovascularization secondary to AMD. Individuals were excluded if (1) the underlying choroidal neovascular process was not secondary to AMD, (2) the lesion was juxta- or extrafoveal, (3) the lesion was larger than 3000 μm in basal diameter, (4) juxta- or subfoveal laser treatment had previously been administered, or (5) they were participants in other research projects. The choice of therapeutic intervention was not randomized but was based on whether the subject chose to pay for PDT. All 115 subjects were offered PDT as initial treatment. The presentation of treatment options was consistent, with a description by the attending retinal specialist of the known therapeutic benefits, risks and costs of each intervention. If the subject declined PDT (which had a cost of $1800 for drug purchase), he or she was offered TTT with a focal laser (entirely funded by the BC government). To determine whether those who chose TTT were truly financially disadvantaged compared with those who chose PDT, we generated an estimate of the mean income in each treatment group from the average sex-specific income for each subject’s postal code from the 1996 Canadian census data.4 For comparison purposes, we also determined the average education level for each participant’s postal code. In a masked fashion, 2 retinal specialists retrospectively regraded leakage pattern and lesion size from angiograms made within 7 days of initial treatment; their consensus was recorded. The basal diameter and overall lesion size (in disc areas) were evaluated with the use of standardized grids. Baseline visual acuity was determined in a masked fashion with a consistent
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Socioeconomic status and AMD—Chew et al
Table 1—Baseline characteristics of patients undergoing photodynamic therapy (PDT) or transpupillary thermotherapy (TTT) for subfoveal choroidal neovascularization secondary to age-related macular degeneration
Characteristic Demographic Mean age, yr Female
No. (and %) of patients, unless otherwise specified PDT TTT (n = 63) (n = 52)
p value
78 33 (52)
79 32 (62)
0.303 0.324
0.029* 0.011*
Clinical, pretreatment Lesion features Mean basal diameter, μm Size, mean no. of disc areas Composition Occult leakage Minimally classic Predominantly classic Mean visual acuity, logMAR score (and by Snellen testing)
3300 4.2
4100 6.4
25 (40) 17 (27) 21 (33) 0.84 (20/88)
32 (61) 6 (12) 14 (27) 1.26 (20/250)
Socioeconomic Mean income, $ % with postsecondary education†
23 695 49.1
21 547 49.3
0.032* < 0.0001*
0.05* 0.90
*Statistically significant differences, by chi-squared test for dichotomous and categorical variables and Student’s t-test for continuous variables. † Determined from average education level for each subject’s postal code.
procedure: all subjects underwent autorefraction and then Snellen acuity testing, manifest refinements being performed when substantial differences were observed between the results of the 2 techniques. For subjects in whom bilateral disease developed during the course of this study, we included data for only the first-affected eye. We used the chi-squared test to analyze dichotomous and categorical variables and the Student’s t-test to analyze continuous variables. A p value of less than 0.05 was considered statistically significant. The University of British Columbia Clinical Research Ethics Board granted ethical approval for the study. RESULTS
Of the 115 subjects (choroidal neovascularization was predominantly classic in 35 and minimally classic in 23; occult leakage was noted in 57), 63 chose PDT and 52 TTT. None refused treatment and none had incomplete data for baseline features. The mean age was equivalent in the 2 groups, as was the sex distri-
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bution (Table 1). Compared with the patients who received PDT, those who received TTT had significantly worse disease before treatment, larger lesions (in terms of both basal diameter and disc area) and poorer visual acuity. They were also significantly more likely to have an occult leakage pattern detected by fluorescein angiography. The average annual income was significantly lower for the subjects who received TTT than for those who received PDT ($21 547 vs. $23 695). There was no difference between the 2 groups in the proportion who had postsecondary education. INTERPRETATION
The most unusual feature of this study was the method used to assign subjects to their treatment group. The subjects received PDT or TTT according to their perceived ability or desire to pay for treatment. As a result, the treatment groups were not equivalent at baseline, those who declined PDT having more advanced disease. We found that those who declined PDT were actually economically disad-
Socioeconomic status and AMD—Chew et al
vantaged compared with those who accepted PDT, although the education levels of the 2 groups were statistically equivalent. The finding of an association between the severity of neovascular AMD and socioeconomic level is novel: we are not aware of any other studies that have linked economic disadvantage to the severity of neovascular macular degeneration at presentation. MEDLINE (1966–2003) and EMBASE (1980–2004) searches using the key words macular degeneration, economics, health economics, epidemiology and poverty did not produce any studies that directly linked the severity of neovascular AMD to socioeconomic status (SES). A link between lower levels of education and AMD was noted in the National Health and Nutrition Examination Survey,5 and the Beaver Dam Eye Study6 suggested that education level and service-related occupations were associated with early dry AMD. We suspect that there are 2 reasons for an association between lower SES and AMD. First, economic factors may delay an individual’s presentation to an eye care provider. Second, those with lower incomes may be at higher risk for AMD. People with lower incomes may have less visually demanding livelihoods or may have more difficulty accessing medical care once visual disability becomes apparent, or both. Although all our subjects had equivalent comprehensive government medical insurance, access to health care is not addressed simply by the presence of a universal medical system. Travel costs and proximity to care providers, for example, may be barriers to care for economically disadvantaged people. The link between eye disease and SES is becoming more clearly understood. There is early evidence that poorer vision-related quality of life is more prevalent in people with lower SES.7 Also, the economically disadvantaged have been noted to present with more advanced glaucoma, experience greater microvascular disease from diabetes and respond poorly to treatment for amblyopia.8–10 Although direct associations between exudative AMD and SES are lacking, certain risk factors for AMD relate to SES. For example, smoking, one of the most well established risk factors for AMD,11–13 has been strongly linked to lower SES in studies performed in the Netherlands, New Zealand, Minnesota, England and Ontario.14–18 Similarly, hypertension, obesity, elevated serum lipid levels, inadequate nutritional intake and cardiovascular disease have been independently linked to lower SES16,18–22 and to AMD.23–25
The criteria that give evidence for a causal relationship between an exposure and an outcome include strength of association, biologic credibility, consistency with other investigations, a dose–response relationship and temporal plausibility.26 Given the information we have presented, it is not possible to establish a causal link between SES and neovascular AMD. However, this association can now be considered a possibility, and our data may inform future evaluations in this area. Hall Chew was supported by a Novartis Student Research Grant.
REFERENCES 1. Treatment of Age-Related Macular Degeneration with Photodynamic Therapy (TAP) Study Group. Photodynamic therapy of subfoveal choroidal neovascularization in agerelated macular degeneration with verteporfin: one-year results of 2 randomized clinical trials — TAP report no. 1 [published erratum appears in Arch Ophthalmol 2000;118: 488]. Arch Ophthalmol 1999;117:1329–45. 2. Bressler NM; Treatment of Age-Related Macular Degeneration with Photodynamic Therapy (TAP) Study Group. Photodynamic therapy of subfoveal choroidal neovascularization in age-related macular degeneration with verteporfin: 2year results of 2 randomized clinical trials — TAP report 2. Arch Ophthalmol 2001;119:198–207. 3. Verteporfin in Photodynamic Therapy Study Group. Verteporfin therapy of subfoveal choroidal neovascularization in age-related macular degeneration: two-year results of a randomized clinical trial including lesions with occult with no classic choroidal neovascularization: Verteporfin in Photodynamic Therapy report 2. Am J Ophthalmol 2001;131: 541–60. 4. Statistics Canada. Census of population. In: 1996 census. Available: www12.statcan.ca/english/census01/info/census96. cfm (accessed 2005 Feb 17). 5. Goldberg J, Flowerdew G, Smith E, Brody JA, Tso MO. Factors associated with age-related macular degeneration. An analysis of data from the first National Health and Nutrition Examination Survey. Am J Epidemiol 1988;128:700–10. 6. Klein R, Klein BE, Jensen SC, Moss SE. The relation of socioeconomic factors to the incidence of early age-related maculopathy: the Beaver Dam Eye Study. Am J Ophthalmol 2001;132:128–31. 7. Frost A, Eachus J, Sparrow J, Peters TJ, Hopper C, DaveySmith G, et al. Vision-related quality of life impairment in an elderly UK population: associations with age, sex, social class and material deprivation. Eye 2001;15:739–44. 8. Fraser S, Bunce C, Wormald R, Brunner E. Deprivation and late presentation of glaucoma: case–control study. BMJ 2001;322:639–43. 9. Weng C, Coppini DV, Sonksen PH. Geographic and social factors are related to increased morbidity and mortality rates
CAN J OPHTHALMOL—VOL. 40, NO. 3, 2005
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Socioeconomic status and AMD—Chew et al
in diabetic patients. Diabet Med 2000;17:612–7. 10. Hudak DT, Magoon EH. Poverty predicts amblyopia treatment failure. J AAPOS 1997;1:214–5. 11. Klein R, Klein BE, Linton KL, DeMets DL. The Beaver Dam Eye Study: the relation of age-related maculopathy to smoking. Am J Epidemiol 1993;137:190–200. 12. Smith W, Mitchell P, Leeder SR. Smoking and age-related maculopathy. The Blue Mountains Eye Study. Arch Ophthalmol 1996;114:1518–23. 13. Smith W, Assink J, Klein R, Mitchel P, Klaver CC, Klein BE, et al. Risk factors for age-related macular degeneration: pooled findings from three continents. Ophthalmology 2001;108: 697–704. 14. Reijneveld SA. The impact of individual and area characteristics on urban socioeconomic differences in health and smoking. Int J Epidemiol 1998;27:33–40. 15. Whitlock G, MacMahon S, Vander Hoorn S, Davis P, Jackson R, Norton R. Socioeconomic distribution of smoking in a population of 10,529 New Zealanders. N Z Med J 1997; 110:327–30. 16. Iribarren C, Luepker RV, McGovern PG, Arnett DK, Blackburn H. Twelve-year trends in cardiovascular disease risk factors in the Minnesota Heart Survey. Are socioeconomic differences widening? Arch Intern Med 1997;157:873–81. 17. Connolly VM, Kesson CM. Socioeconomic status and clustering of cardiovascular disease risk factors in diabetic patients. Diabetes Care 1996;19:419–22. 18. Jagal SB, Goel V. Social inequity in risk of coronary artery disease in Ontario. Can J Cardiol 1994;10:439–43. 19. Cabrera C, Helgesson O, Wedel H, Bjorkelund C, Bengtsson C, Lissner L. Socioeconomic status and mortality in Swedish
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20.
21.
22.
23.
24.
25.
26.
women: opposing trends for cardiovascular disease and cancer. Epidemiology 2001;12:532–6. Vogels EA, Lagro-Janssen AL, van Weel C. Sex differences in cardiovascular disease: Are women with low socioeconomic status at high risk? Br J Gen Pract 1999;49:963–6. Lynch JW, Kaplan GA, Cohen RD, Tuomilehto J, Salonen JT. Do cardiovascular risk factors explain the relation between socioeconomic status, risk of all-cause mortality, cardiovascular mortality, and acute myocardial infarction? Am J Epidemiol 1996;144:934–42. Ryan VC, Bower ME. Relationship of socioeconomic status and living arrangements to nutritional intake of the older person. J Am Diet Assoc 1989;89:1805–7. The Eye Disease Case–Control Study Group. Risk factors for neovascular age-related macular degeneration. Arch Ophthalmol 1992;110:1701–8. Klein R, Klein BE, Jensen SC. The relation of cardiovascular disease and its risk factors to the 5-year incidence of agerelated maculopathy: the Beaver Dam Eye Study. Ophthalmology 1997;104:1804–12. Age-Related Eye Disease Study Research Group. Risk factors associated with age-related macular degeneration. A case– control study in the Age-Related Eye Disease Study: AgeRelated Eye Disease Study report number 3. Ophthalmology 2000;107:2224–32. Hennekens CH, Buring JE. Epidemiology in medicine. Boston/Toronto: Little, Brown and Company; 1987. p. 39–43.
Key words: age factor, choroidal neovascularization, macular degeneration, photodynamic therapy, socioeconomic factors, transpupillary thermotherapy
BC V5Z 3N9; fax (604) 875-4699; [email protected]
Correspondence to: Dr. David A.L. Maberley, 2550 Willow St., Vancouver
Can J Ophthalmol 2005;40:384–8
384
Socioeconomic status and AMD—Chew et al
This article has been peer-reviewed.
Socioeconomic status and AMD—Chew et al
aveugle, le motif de diffusion et la taille de la lésion ont été établis rétrospectivement à partir des angiographies d’avant le traitement. L’acuité visuelle de base a été établie par autoréfraction et subséquemment le test de Snellen. Le revenu moyen de chacun des groupes de traitement a été estimé à partir du revenu moyen propre à chaque sexe en regard du code postal de chacun des sujets, fondé sur les données du recensement canadien de 1996. Le niveau d’instruction moyen a aussi été établi en regard du code postal de chaque sujet. Résultats : Les patients qui n’ont pas voulu assumer les frais de la TPD avaient une maladie maculaire plus grave avant le traitement (lésion plus grande et plus faible acuité visuelle) et un revenu significativement inférieur à ceux qui ont assumé le coût. Interprétation : La sévérité de la néovascularisation choroïdienne exsudative paraît associée avec une modeste situation socioéconomique.
P
hotodynamic therapy (PDT) with verteporfin (VPDT) and transpupillary thermotherapy (TTT) are widely used for treating subfoveal choroidal neovascularization due to age-related macular degeneration (AMD). Randomized clinical trials — Treatment of Age-Related Macular Degeneration with Photodynamic Therapy1,2 (TAP) and Verteporfin in Photodynamic Therapy3 (VIP) — have demonstrated the therapeutic benefit of VPDT for both classic and occult choroidal neovascularization; however, TTT is still under evaluation for the management of occult choroidal neovascularization secondary to AMD. The initial purpose of our study was to compare PDT and TTT for all forms of subfoveal choroidal neovascularization secondary to AMD. While it was not ethical for us to randomly assign patients to one treatment or the other, given the proven benefit of PDT for exudative AMD, individuals who could not afford or did not wish to have PDT were secondarily offered TTT. This process allowed for the creation of 2 study groups that were based on ability or desire to pay for PDT. The study was possible for only 13 months, from July 2000 to August 2001, prior to the start of comprehensive coverage of VPDT at the University of British Columbia by the Medical Services Plan of British Columbia. Thereafter, it was not ethical for us to withhold PDT in the presence of good efficacy data and provincial funding. Thus, the purpose of our study became to compare baseline clinical and socioeconomic features of patients undergoing self-funded PDT or government-funded subthreshold TTT with a diode laser for subfoveal choroidal neovascularization secondary to AMD.
METHODS
For inclusion in this study, all subjects were required to have subfoveal choroidal neovascularization secondary to AMD. Individuals were excluded if (1) the underlying choroidal neovascular process was not secondary to AMD, (2) the lesion was juxta- or extrafoveal, (3) the lesion was larger than 3000 μm in basal diameter, (4) juxta- or subfoveal laser treatment had previously been administered, or (5) they were participants in other research projects. The choice of therapeutic intervention was not randomized but was based on whether the subject chose to pay for PDT. All 115 subjects were offered PDT as initial treatment. The presentation of treatment options was consistent, with a description by the attending retinal specialist of the known therapeutic benefits, risks and costs of each intervention. If the subject declined PDT (which had a cost of $1800 for drug purchase), he or she was offered TTT with a focal laser (entirely funded by the BC government). To determine whether those who chose TTT were truly financially disadvantaged compared with those who chose PDT, we generated an estimate of the mean income in each treatment group from the average sex-specific income for each subject’s postal code from the 1996 Canadian census data.4 For comparison purposes, we also determined the average education level for each participant’s postal code. In a masked fashion, 2 retinal specialists retrospectively regraded leakage pattern and lesion size from angiograms made within 7 days of initial treatment; their consensus was recorded. The basal diameter and overall lesion size (in disc areas) were evaluated with the use of standardized grids. Baseline visual acuity was determined in a masked fashion with a consistent
CAN J OPHTHALMOL—VOL. 40, NO. 3, 2005
385
Socioeconomic status and AMD—Chew et al
Table 1—Baseline characteristics of patients undergoing photodynamic therapy (PDT) or transpupillary thermotherapy (TTT) for subfoveal choroidal neovascularization secondary to age-related macular degeneration
Characteristic Demographic Mean age, yr Female
No. (and %) of patients, unless otherwise specified PDT TTT (n = 63) (n = 52)
p value
78 33 (52)
79 32 (62)
0.303 0.324
0.029* 0.011*
Clinical, pretreatment Lesion features Mean basal diameter, μm Size, mean no. of disc areas Composition Occult leakage Minimally classic Predominantly classic Mean visual acuity, logMAR score (and by Snellen testing)
3300 4.2
4100 6.4
25 (40) 17 (27) 21 (33) 0.84 (20/88)
32 (61) 6 (12) 14 (27) 1.26 (20/250)
Socioeconomic Mean income, $ % with postsecondary education†
23 695 49.1
21 547 49.3
0.032* < 0.0001*
0.05* 0.90
*Statistically significant differences, by chi-squared test for dichotomous and categorical variables and Student’s t-test for continuous variables. † Determined from average education level for each subject’s postal code.
procedure: all subjects underwent autorefraction and then Snellen acuity testing, manifest refinements being performed when substantial differences were observed between the results of the 2 techniques. For subjects in whom bilateral disease developed during the course of this study, we included data for only the first-affected eye. We used the chi-squared test to analyze dichotomous and categorical variables and the Student’s t-test to analyze continuous variables. A p value of less than 0.05 was considered statistically significant. The University of British Columbia Clinical Research Ethics Board granted ethical approval for the study. RESULTS
Of the 115 subjects (choroidal neovascularization was predominantly classic in 35 and minimally classic in 23; occult leakage was noted in 57), 63 chose PDT and 52 TTT. None refused treatment and none had incomplete data for baseline features. The mean age was equivalent in the 2 groups, as was the sex distri-
386
CAN J OPHTHALMOL—VOL. 40, NO. 3, 2005
bution (Table 1). Compared with the patients who received PDT, those who received TTT had significantly worse disease before treatment, larger lesions (in terms of both basal diameter and disc area) and poorer visual acuity. They were also significantly more likely to have an occult leakage pattern detected by fluorescein angiography. The average annual income was significantly lower for the subjects who received TTT than for those who received PDT ($21 547 vs. $23 695). There was no difference between the 2 groups in the proportion who had postsecondary education. INTERPRETATION
The most unusual feature of this study was the method used to assign subjects to their treatment group. The subjects received PDT or TTT according to their perceived ability or desire to pay for treatment. As a result, the treatment groups were not equivalent at baseline, those who declined PDT having more advanced disease. We found that those who declined PDT were actually economically disad-
Socioeconomic status and AMD—Chew et al
vantaged compared with those who accepted PDT, although the education levels of the 2 groups were statistically equivalent. The finding of an association between the severity of neovascular AMD and socioeconomic level is novel: we are not aware of any other studies that have linked economic disadvantage to the severity of neovascular macular degeneration at presentation. MEDLINE (1966–2003) and EMBASE (1980–2004) searches using the key words macular degeneration, economics, health economics, epidemiology and poverty did not produce any studies that directly linked the severity of neovascular AMD to socioeconomic status (SES). A link between lower levels of education and AMD was noted in the National Health and Nutrition Examination Survey,5 and the Beaver Dam Eye Study6 suggested that education level and service-related occupations were associated with early dry AMD. We suspect that there are 2 reasons for an association between lower SES and AMD. First, economic factors may delay an individual’s presentation to an eye care provider. Second, those with lower incomes may be at higher risk for AMD. People with lower incomes may have less visually demanding livelihoods or may have more difficulty accessing medical care once visual disability becomes apparent, or both. Although all our subjects had equivalent comprehensive government medical insurance, access to health care is not addressed simply by the presence of a universal medical system. Travel costs and proximity to care providers, for example, may be barriers to care for economically disadvantaged people. The link between eye disease and SES is becoming more clearly understood. There is early evidence that poorer vision-related quality of life is more prevalent in people with lower SES.7 Also, the economically disadvantaged have been noted to present with more advanced glaucoma, experience greater microvascular disease from diabetes and respond poorly to treatment for amblyopia.8–10 Although direct associations between exudative AMD and SES are lacking, certain risk factors for AMD relate to SES. For example, smoking, one of the most well established risk factors for AMD,11–13 has been strongly linked to lower SES in studies performed in the Netherlands, New Zealand, Minnesota, England and Ontario.14–18 Similarly, hypertension, obesity, elevated serum lipid levels, inadequate nutritional intake and cardiovascular disease have been independently linked to lower SES16,18–22 and to AMD.23–25
The criteria that give evidence for a causal relationship between an exposure and an outcome include strength of association, biologic credibility, consistency with other investigations, a dose–response relationship and temporal plausibility.26 Given the information we have presented, it is not possible to establish a causal link between SES and neovascular AMD. However, this association can now be considered a possibility, and our data may inform future evaluations in this area. Hall Chew was supported by a Novartis Student Research Grant.
REFERENCES 1. Treatment of Age-Related Macular Degeneration with Photodynamic Therapy (TAP) Study Group. Photodynamic therapy of subfoveal choroidal neovascularization in agerelated macular degeneration with verteporfin: one-year results of 2 randomized clinical trials — TAP report no. 1 [published erratum appears in Arch Ophthalmol 2000;118: 488]. Arch Ophthalmol 1999;117:1329–45. 2. Bressler NM; Treatment of Age-Related Macular Degeneration with Photodynamic Therapy (TAP) Study Group. Photodynamic therapy of subfoveal choroidal neovascularization in age-related macular degeneration with verteporfin: 2year results of 2 randomized clinical trials — TAP report 2. Arch Ophthalmol 2001;119:198–207. 3. Verteporfin in Photodynamic Therapy Study Group. Verteporfin therapy of subfoveal choroidal neovascularization in age-related macular degeneration: two-year results of a randomized clinical trial including lesions with occult with no classic choroidal neovascularization: Verteporfin in Photodynamic Therapy report 2. Am J Ophthalmol 2001;131: 541–60. 4. Statistics Canada. Census of population. In: 1996 census. Available: www12.statcan.ca/english/census01/info/census96. cfm (accessed 2005 Feb 17). 5. Goldberg J, Flowerdew G, Smith E, Brody JA, Tso MO. Factors associated with age-related macular degeneration. An analysis of data from the first National Health and Nutrition Examination Survey. Am J Epidemiol 1988;128:700–10. 6. Klein R, Klein BE, Jensen SC, Moss SE. The relation of socioeconomic factors to the incidence of early age-related maculopathy: the Beaver Dam Eye Study. Am J Ophthalmol 2001;132:128–31. 7. Frost A, Eachus J, Sparrow J, Peters TJ, Hopper C, DaveySmith G, et al. Vision-related quality of life impairment in an elderly UK population: associations with age, sex, social class and material deprivation. Eye 2001;15:739–44. 8. Fraser S, Bunce C, Wormald R, Brunner E. Deprivation and late presentation of glaucoma: case–control study. BMJ 2001;322:639–43. 9. Weng C, Coppini DV, Sonksen PH. Geographic and social factors are related to increased morbidity and mortality rates
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Socioeconomic status and AMD—Chew et al
in diabetic patients. Diabet Med 2000;17:612–7. 10. Hudak DT, Magoon EH. Poverty predicts amblyopia treatment failure. J AAPOS 1997;1:214–5. 11. Klein R, Klein BE, Linton KL, DeMets DL. The Beaver Dam Eye Study: the relation of age-related maculopathy to smoking. Am J Epidemiol 1993;137:190–200. 12. Smith W, Mitchell P, Leeder SR. Smoking and age-related maculopathy. The Blue Mountains Eye Study. Arch Ophthalmol 1996;114:1518–23. 13. Smith W, Assink J, Klein R, Mitchel P, Klaver CC, Klein BE, et al. Risk factors for age-related macular degeneration: pooled findings from three continents. Ophthalmology 2001;108: 697–704. 14. Reijneveld SA. The impact of individual and area characteristics on urban socioeconomic differences in health and smoking. Int J Epidemiol 1998;27:33–40. 15. Whitlock G, MacMahon S, Vander Hoorn S, Davis P, Jackson R, Norton R. Socioeconomic distribution of smoking in a population of 10,529 New Zealanders. N Z Med J 1997; 110:327–30. 16. Iribarren C, Luepker RV, McGovern PG, Arnett DK, Blackburn H. Twelve-year trends in cardiovascular disease risk factors in the Minnesota Heart Survey. Are socioeconomic differences widening? Arch Intern Med 1997;157:873–81. 17. Connolly VM, Kesson CM. Socioeconomic status and clustering of cardiovascular disease risk factors in diabetic patients. Diabetes Care 1996;19:419–22. 18. Jagal SB, Goel V. Social inequity in risk of coronary artery disease in Ontario. Can J Cardiol 1994;10:439–43. 19. Cabrera C, Helgesson O, Wedel H, Bjorkelund C, Bengtsson C, Lissner L. Socioeconomic status and mortality in Swedish
388
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20.
21.
22.
23.
24.
25.
26.
women: opposing trends for cardiovascular disease and cancer. Epidemiology 2001;12:532–6. Vogels EA, Lagro-Janssen AL, van Weel C. Sex differences in cardiovascular disease: Are women with low socioeconomic status at high risk? Br J Gen Pract 1999;49:963–6. Lynch JW, Kaplan GA, Cohen RD, Tuomilehto J, Salonen JT. Do cardiovascular risk factors explain the relation between socioeconomic status, risk of all-cause mortality, cardiovascular mortality, and acute myocardial infarction? Am J Epidemiol 1996;144:934–42. Ryan VC, Bower ME. Relationship of socioeconomic status and living arrangements to nutritional intake of the older person. J Am Diet Assoc 1989;89:1805–7. The Eye Disease Case–Control Study Group. Risk factors for neovascular age-related macular degeneration. Arch Ophthalmol 1992;110:1701–8. Klein R, Klein BE, Jensen SC. The relation of cardiovascular disease and its risk factors to the 5-year incidence of agerelated maculopathy: the Beaver Dam Eye Study. Ophthalmology 1997;104:1804–12. Age-Related Eye Disease Study Research Group. Risk factors associated with age-related macular degeneration. A case– control study in the Age-Related Eye Disease Study: AgeRelated Eye Disease Study report number 3. Ophthalmology 2000;107:2224–32. Hennekens CH, Buring JE. Epidemiology in medicine. Boston/Toronto: Little, Brown and Company; 1987. p. 39–43.
Key words: age factor, choroidal neovascularization, macular degeneration, photodynamic therapy, socioeconomic factors, transpupillary thermotherapy