- Email: [email protected]
Diabetes and Senile Cataract
134
AMERICAN JOURNAL OF OPHTHALMOLOGY
about to search for previously published reports when I read Dr. Lubin's article. Perhaps this association is more common than has been supposed, and there may be a genetic association between the two anomalies. W I L L I A M BENSON,
Philadelphia,
M.D.
Pennsylvania
Diabetes and Senile Cataract Editor: In a brief review of cataract epidemiol ogy, 1 I pointed out that the available data suggested that diabetics were more likely to undergo cataract extraction than nondiabetics, but that the prevalence of se nile cataracts was reportedly similar in the two populations. The traditional ex planation of this apparent paradox is that the senile cataracts mature more quickly in diabetics. I offered an alternative pos sibility: that diabetics are more likely to consult ophthalmologists, thereby having their cataracts identified, or more likely to have visual loss from other causes wrongly ascribed to lens opacities. In an attempt to resolve this issue, F. Ederer, R. Hiller, and H. R. Taylor in their article, "Senile lens changes and diabetes in two population studies" (Am. J. Ophthalmol. 91:391, 1981), reanalyzed data from the Framingham Eye Study and the Health and Nutrition Examination Survey (HANES). Within the limitations of their data, their results suggested that diabetics do indeed have an increased risk of developing visually significant cat aracts. The authors assigned the subjects to one of three categories of lens abnormali ty: aphakia, "cataract," or "precataract." Cataracts were defined by the presence of senile opacities capable of partially (HANES) or fully (Framingham) explain ing the presence of a best corrected visual acuity of 6/9 (20/30) or worse.
JULY, 1981
Among subjects 50 to 64 years of age, aphakia and cataracts were associated with diabetes in both studies. The rela tionship between aphakia and diabetes was consistent with the results of the earlier studies but was subject to many of the same biases. The analysis of cataracts and diabetes avoided this problem but introduced potential biases of its own. Because the definition required reduced visual acuity, which may have had other causes, it was possible for a nondiabetic with an incidental opacity and a normal macula not to be classified as having a cataract even though a diabetic with an identical opacity and a mild macular or vitreoretinal abnormality would have been. It is reassuring that few cases of diabetic retinopathy were identified, al though the use of less experienced exami ners and the lack of fluorescein angiography precludes a definitive assessment of this claim. Were the examiners aware of the sub jects' visual acuities? If they were, there may have been observer bias, with im paired vision encouraging the examiner to look for and identify minimal opacities and to consider them significant. The data for the "precataract" group, composed of subjects with lenticular opacities who did not meet the visual acuity criteria for "cataracts," were po tentially the least biased. Precataract also had the lowest association with diabetes. In the Framingham study the relative risk of "precataracts" among diabetics was 1.35 times that of nondiabetics, a weak association at best. In the HANES study there was no association at all. As the Framingham data made clear, only a tiny minority of cataract patients are diabetics. Interest in the problem largely stems from suggestions that mod est, preclinical impairment of glucose metabolism may be responsible for a large proportion of senile cataracts. 2 In
VOL. 92, NO. 1
CORRESPONDENCE
135
examination. Neither study used fluores cein angiography. Among persons 50 to 64 years old, the observed relative risk of cataract in dia betics was 4.02 (P < .01) for the Framing ham study and 2.97 (P < .01) for the HANES study. (We found a less in creased risk for cataract at older ages.) If A L F R E D SOMMER, M.D. Sommer's hypothesis is accurate, these Baltimore, Maryland risks were overstated. Not knowing whether a bias existed at all, we cannot REFERENCES determine its magnitude. However, 1. Sommer, A.: Cataracts as an epidemiologic Summer's letter prompted us to estimate its maximum size for diagnosed diabetic problem. Am. J. Ophthalmol. 83:334, 1977. 2. van Heynigen, R. : What happens to the human retinopathy in persons aged 50 to 64 lens in cataract? Sei. Am. 233:70, 1975. years who participated in the Framing ham study by excluding from the analysis Reply all patients with diagnosed diabetic reti Editor: nopathy and cataract (but not aphakia). There was only one such patient, the Sommer suggests a new bias to account same one mentioned in our paper for the excess prevalence of cataract in (p. 391). With this patient excluded, the diabetics that we reported. This bias, relative risk changes from 4.02 to 3.53 stemming from the examiner's knowl (P < .01), a reduction of only 12%, indi edge of decreased visual acuity, would cating that the effect of the bias on diag have resulted in an overstatement of the nosed retinopathy was at most small. We prevalence of precataract and cataract. In have no way of testing for the effect on eyes with both diabetic retinopathy and undiagnosed retinopathy. lens opacities, this bias would have led to an overstatement of the prevalence of To say that bias was possible is not to cataract in diabetics. This would have say it actually occurred. There are factors been the case not only for diagnosed, but that suggest that if bias did occur, it was also for undiagnosed diabetic retinopa not of sufficient magnitude to nullify the thy, the latter being possible because less substantial excess cataract prevalence we experienced examiners were used and found among diabetics. Throughout the fluorescein angiography was not. Framingham study, intensive efforts were Sommer is essentially correct in his made to limit observer variation by stan statement of the facts and their possible dardizing procedures through a detailed consequences. The HANES examiners, protocol, training sessions for examiners, who were mostly ophthalmology resi and replication of examinations. 1 dents, either knew the visual acuity or In addition to the bias proposed by had access to the information. In the Sommer, the opposite bias may have ex Framingham study, the definitive cata isted: in the presence of diabetic retinop ract examiners, who were more experi athy and visual impairment, the examiner enced, knew that the visual acuity was might have misclassified a cataract as decreased because only persons with lens precataract, attributing the visual loss to opacities and decreased visual acuities the retinopathy alone. It is hard to say were referred for the definitive cataract which of these biases, if either existed,
the Framingham and HANES studies, the relative risk of "cataracts" among diabetics 50 to 64 years of age is high. But if the weaker association observed be tween "precataracts" and diabetes is the more reliable, it is unlikely that impaired glucose metabolism plays a major role in what is certainly a multifactorial disease.
AMERICAN JOURNAL OF OPHTHALMOLOGY
about to search for previously published reports when I read Dr. Lubin's article. Perhaps this association is more common than has been supposed, and there may be a genetic association between the two anomalies. W I L L I A M BENSON,
Philadelphia,
M.D.
Pennsylvania
Diabetes and Senile Cataract Editor: In a brief review of cataract epidemiol ogy, 1 I pointed out that the available data suggested that diabetics were more likely to undergo cataract extraction than nondiabetics, but that the prevalence of se nile cataracts was reportedly similar in the two populations. The traditional ex planation of this apparent paradox is that the senile cataracts mature more quickly in diabetics. I offered an alternative pos sibility: that diabetics are more likely to consult ophthalmologists, thereby having their cataracts identified, or more likely to have visual loss from other causes wrongly ascribed to lens opacities. In an attempt to resolve this issue, F. Ederer, R. Hiller, and H. R. Taylor in their article, "Senile lens changes and diabetes in two population studies" (Am. J. Ophthalmol. 91:391, 1981), reanalyzed data from the Framingham Eye Study and the Health and Nutrition Examination Survey (HANES). Within the limitations of their data, their results suggested that diabetics do indeed have an increased risk of developing visually significant cat aracts. The authors assigned the subjects to one of three categories of lens abnormali ty: aphakia, "cataract," or "precataract." Cataracts were defined by the presence of senile opacities capable of partially (HANES) or fully (Framingham) explain ing the presence of a best corrected visual acuity of 6/9 (20/30) or worse.
JULY, 1981
Among subjects 50 to 64 years of age, aphakia and cataracts were associated with diabetes in both studies. The rela tionship between aphakia and diabetes was consistent with the results of the earlier studies but was subject to many of the same biases. The analysis of cataracts and diabetes avoided this problem but introduced potential biases of its own. Because the definition required reduced visual acuity, which may have had other causes, it was possible for a nondiabetic with an incidental opacity and a normal macula not to be classified as having a cataract even though a diabetic with an identical opacity and a mild macular or vitreoretinal abnormality would have been. It is reassuring that few cases of diabetic retinopathy were identified, al though the use of less experienced exami ners and the lack of fluorescein angiography precludes a definitive assessment of this claim. Were the examiners aware of the sub jects' visual acuities? If they were, there may have been observer bias, with im paired vision encouraging the examiner to look for and identify minimal opacities and to consider them significant. The data for the "precataract" group, composed of subjects with lenticular opacities who did not meet the visual acuity criteria for "cataracts," were po tentially the least biased. Precataract also had the lowest association with diabetes. In the Framingham study the relative risk of "precataracts" among diabetics was 1.35 times that of nondiabetics, a weak association at best. In the HANES study there was no association at all. As the Framingham data made clear, only a tiny minority of cataract patients are diabetics. Interest in the problem largely stems from suggestions that mod est, preclinical impairment of glucose metabolism may be responsible for a large proportion of senile cataracts. 2 In
VOL. 92, NO. 1
CORRESPONDENCE
135
examination. Neither study used fluores cein angiography. Among persons 50 to 64 years old, the observed relative risk of cataract in dia betics was 4.02 (P < .01) for the Framing ham study and 2.97 (P < .01) for the HANES study. (We found a less in creased risk for cataract at older ages.) If A L F R E D SOMMER, M.D. Sommer's hypothesis is accurate, these Baltimore, Maryland risks were overstated. Not knowing whether a bias existed at all, we cannot REFERENCES determine its magnitude. However, 1. Sommer, A.: Cataracts as an epidemiologic Summer's letter prompted us to estimate its maximum size for diagnosed diabetic problem. Am. J. Ophthalmol. 83:334, 1977. 2. van Heynigen, R. : What happens to the human retinopathy in persons aged 50 to 64 lens in cataract? Sei. Am. 233:70, 1975. years who participated in the Framing ham study by excluding from the analysis Reply all patients with diagnosed diabetic reti Editor: nopathy and cataract (but not aphakia). There was only one such patient, the Sommer suggests a new bias to account same one mentioned in our paper for the excess prevalence of cataract in (p. 391). With this patient excluded, the diabetics that we reported. This bias, relative risk changes from 4.02 to 3.53 stemming from the examiner's knowl (P < .01), a reduction of only 12%, indi edge of decreased visual acuity, would cating that the effect of the bias on diag have resulted in an overstatement of the nosed retinopathy was at most small. We prevalence of precataract and cataract. In have no way of testing for the effect on eyes with both diabetic retinopathy and undiagnosed retinopathy. lens opacities, this bias would have led to an overstatement of the prevalence of To say that bias was possible is not to cataract in diabetics. This would have say it actually occurred. There are factors been the case not only for diagnosed, but that suggest that if bias did occur, it was also for undiagnosed diabetic retinopa not of sufficient magnitude to nullify the thy, the latter being possible because less substantial excess cataract prevalence we experienced examiners were used and found among diabetics. Throughout the fluorescein angiography was not. Framingham study, intensive efforts were Sommer is essentially correct in his made to limit observer variation by stan statement of the facts and their possible dardizing procedures through a detailed consequences. The HANES examiners, protocol, training sessions for examiners, who were mostly ophthalmology resi and replication of examinations. 1 dents, either knew the visual acuity or In addition to the bias proposed by had access to the information. In the Sommer, the opposite bias may have ex Framingham study, the definitive cata isted: in the presence of diabetic retinop ract examiners, who were more experi athy and visual impairment, the examiner enced, knew that the visual acuity was might have misclassified a cataract as decreased because only persons with lens precataract, attributing the visual loss to opacities and decreased visual acuities the retinopathy alone. It is hard to say were referred for the definitive cataract which of these biases, if either existed,
the Framingham and HANES studies, the relative risk of "cataracts" among diabetics 50 to 64 years of age is high. But if the weaker association observed be tween "precataracts" and diabetes is the more reliable, it is unlikely that impaired glucose metabolism plays a major role in what is certainly a multifactorial disease.