Abstract
Objective(s)
Examine refraction, change in refraction, and risk factors for change in refraction in adults with type 1 and type 2 diabetes.
Methods
Population based study. Modified Early Treatment of Diabetic Retinopathy Study refractions and a standard history were obtained for all participants. Baseline and ten-year follow-up data were available.
Results
Age was significantly associated with refraction in persons with younger-onset diabetes (T1D) and those with older-onset diabetes (T2D); refractions were similar for both groups. Persons of similar age with T1D were likely to be more myopic than those with T2D (P<.01). Years of education were significantly associated with more myopic refraction (P<.0001). In those with T1D on average there was a −.35 diopter (D) change in refraction over 10 years. However, there was a systematic decrease in myopic shift with increasing age at baseline. Those with longer duration of diabetes and with proliferative retinopathy were more likely to have hyperopic shifts in refraction. In those with T2D there was, on average, a +.25D change in refraction over the 10 years but there was little consistency in the amount of change by age at baseline. There were no other significant effects on change in refraction in this group.
Conclusions
In persons of similar age, those with T1D are likely to be slightly more myopic than those with T2D. Overall, mean refractions and the important risk factors of age and education are similar to those reported in non-diabetic populations.
Keywords: Refraction, diabetes, myopia, education
Diabetes affects the eye with the most commonly reported chronic changes being cataract and diabetic retinopathy. Acute hyperglycemia is associated with myopic refraction but refraction becomes less myopic (or even hyperopic) with lowering in the levels of glycemia.1–3 The distribution of refraction in a study of free living persons with diabetes has not been well described. Some data are available from studies of eye diseases in general populations when persons with diabetes are included in the sampling frame. In the Tanjong Pagar study the mean refractive error was −.47 diopters (D) for those with diabetes and −.39D for those without diabetes, a difference that was not statistically significant.4 Similarly, in the Blue Mountains Eye Study, there was no significant difference in mean refractive error between those with and without diabetes.5 In the Beaver Dam Eye Study there was no difference in refractions between those with and without diabetes.6 There are, however, some studies that have reported more myopic refraction in those with diabetes.7 Nearly all of the persons with diabetes in these studies had type 2 diabetes. There is no community-wide data on refraction for persons with type 1 diabetes. We report on the distribution and change in refraction (spherical equivalent), as well as risk factor associations for refraction, in a large community-based study of persons with both types of diabetes who were first identified in 1978–1979.
Methods
Study Population
The Wisconsin Epidemiologic Study of Diabetic Retinopathy (WESDR), a population-based survey of diabetic patients residing and receiving their health care in 11 counties in southern Wisconsin, has been described in detail previously.8–13 From July 1, 1979 to June 30, 1980, 10,135 diabetic patients were identified. A sample of 2,990 persons selected for the baseline examination from 1980–1982 was composed of all patients with a diagnosis of diabetes before 30 years of age who took insulin (n=1210 persons, the "younger onset" group) and a probability sample of the 5431 patients who were diagnosed as having diabetes at 30 years of age with their diagnosis confirmed by a casual or a postprandial serum glucose level of at least 11.1 mmol/L or a fasting serum glucose level of at least 7.8 mmol/L on at least two occasions (n=1780 persons, the "older onset" group). Of the younger onset persons, 996 participated in the baseline examination (1980–1982),9,10 891 in the 4-year follow-up11 and 784 in the 10-year follow-up.13 Of the 1780 eligible older-onset persons, 1370 participated in the baseline examination,10 987 in the 4-year follow-up,12 and 550 in the 10-year follow-up.13 The reasons for nonparticipation and comparisons between participants and nonparticipants have been presented elsewhere. 9–13
At the time of the examinations of the cohort, a group of persons without diabetes (mostly spouses of the study participants) were examined with the same protocols. This group is referred to as the non-diabetic comparison group; 381 of these participated at baseline, 269 at the second examination and 211 at the third examination. Data from these persons are used for selected analyses but direct statistical comparisons between them and the study groups are not given.
Informed consent was obtained from each study subject at each examination. The procedures conformed to the tenets of the Declaration of Helsinki and Institutional Review Board approval was obtained for all phases of the examinations.
Examination procedures
The study procedures remained the same with few additions for each examination phase. All procedures were done according to codified protocols. Only pertinent parts are further described. A medical history was obtained which included information on age at onset of diabetes, medication usage, and education. Examinations included measurement of blood pressures by protocol, height, weight, refraction, dilated fundus examinations with examination of the lens for cataract or cataract surgery, fundus examination and seven standard field fundus photography of both eyes. Refractions for all participants at each examination were performed according to the Early Treatment of Diabetic Retinopathy Study (ETDRS) Protocol14 prior to pupil dilation. Blood was drawn for glycosylated hemoglobin which was measured by a microcolumn technique15 on a casual blood specimen.
Definitions
Cataract presence was defined by reference to photographic standards of nuclear and retroilluminated cataracts at the time of the examination.
Refraction was converted to spherical equivalents. The ETDRS retinopathy severity was categorized as follows: none (≤13), mild non-proliferative diabetic retinopathy (NPDR) (14–27), moderate/severe NPDR (38– 53) and PDR (60+).
Statistical Analysis
Data for the analyses in this paper are from the baseline examination and the ten-year follow-up. Data were excluded for aphakic or pseudophakic eyes and for those eyes where the best corrected visual acuity was 20/200 or poorer. Analyses are limited to those 20 years of age or older at the baseline examination (1370 in the older onset group, 724 in the younger onset group, and 269 in the non-diabetic comparison group). Means and standard deviations are presented for the right eyes as the data for the left eye are nearly identical. Model results are presented from generalized estimating equations (GEE) models that include both eyes using an independent correlation structure. Unless otherwise noted, all models include age, education, and nuclear cataract as these factors are important determinants of refraction in non-diabetic populations.
Results
Baseline
Younger Onset Group (T1D)
Those excluded from the analyses were significantly older, had more hyperopic refractive error, had higher blood pressures, longer duration of diabetes, were more likely to have nuclear cataract, and more severe retinopathy than those included (Table 1).
Table 1.
Baseline Characteristics for Those Included and Excluded from Analyses.
| T1D |
Included |
Excluded |
P-value | ||||
|---|---|---|---|---|---|---|---|
| Continuous Characteristics | |||||||
| N | Mean | SD | N | Mean | SD | ||
| Age (years) | 646 | 33.7 | 11.0 | 78 | 42.9 | 13.0 | <.001 |
| Education (years) | 646 | 13.4 | 2.5 | 78 | 12.2 | 2.9 | 0.32 |
| Refraction (D) - right eye | 646 | −1.5 | 2.2 | 33 | 5.5 | 6.7 | <.001 |
| Systolic blood pressure (mmHg) | 642 | 126.4 | 20.0 | 76 | 148.2 | 26.9 | <.001 |
| Diastolic blood pressure (mmHg) | 642 | 79.9 | 11.0 | 76 | 85.2 | 14.5 | <.001 |
| Duration (years) | 646 | 16.8 | 10.3 | 78 | 26.8 | 9.2 | <.001 |
| Glycosylated hemoglobin (%) | 608 | 10.7 | 2.0 | 76 | 10.9 | 2.3 | 0.51 |
| Categorical Characteristics | |||||||
|
Included |
Excluded |
||||||
| N | % | N | % | P-value | |||
| Gender | |||||||
| Female | 318 | 49.2 | 40 | 51.3 | 0.89 | ||
| Male | 328 | 50.8 | 38 | 48.7 | - | ||
| Education (years) | |||||||
| < 12 | 64 | 9.9 | 18 | 23.1 | 0.36 | ||
| 12 | 246 | 38.1 | 30 | 38.5 | - | ||
| 13–15 | 200 | 31.0 | 20 | 25.6 | - | ||
| 16+ | 136 | 21.1 | 10 | 12.8 | - | ||
| NSC | |||||||
| Absent | 484 | 75.7 | 15 | 30.0 | <.001 | ||
| Present | 155 | 24.3 | 35 | 70.0 | - | ||
| Hypertension | |||||||
| No | 491 | 76.5 | 31 | 40.3 | <.001 | ||
| Yes | 151 | 23.5 | 46 | 59.7 | - | ||
| Retinopathy severity, right eyes | |||||||
| None (≤13) | 138 | 21.4 | 3 | 3.9 | <.001 | ||
| Mild NPDR (14–27) | 287 | 44.4 | 7 | 9.2 | - | ||
| Moderate NDPR (38–53) | 91 | 14.1 | 2 | 2.6 | - | ||
| Proliferative (60+) | 130 | 20.1 | 64 | 84.2 | - | ||
| T2D |
Included |
Excluded |
P-value | ||||
|---|---|---|---|---|---|---|---|
| Continuous Characteristics | |||||||
| N | Mean | SD | N | Mean | SD | ||
| Age (years) | 1174 | 65.8 | 11.2 | 196 | 71.8 | 10.6 | <.001 |
| Education (years) | 1171 | 11.1 | 3.5 | 195 | 10.4 | 3.0 | 0.56 |
| Refraction (D)- right eye | 1174 | 0.7 | 2.1 | 123 | 7.7 | 5.7 | <.001 |
| Systolic blood pressure (mmHg) | 1170 | 147.0 | 23.9 | 196 | 149.9 | 24.4 | 0.76 |
| Diastolic blood pressure (mmHg) | 1165 | 79.8 | 11.6 | 196 | 75.4 | 13.7 | 0.05 |
| Duration (years) | 1174 | 11.1 | 7.9 | 196 | 16.0 | 8.8 | <.001 |
| Glycosylated hemoglobin (%) | 1086 | 9.6 | 2.0 | 184 | 9.5 | 2.0 | 0.49 |
| Categorical Characteristics | |||||||
|
Included |
Excluded |
||||||
| N | % | N | % | P-value | |||
| Gender | |||||||
| Female | 619 | 52.7 | 115 | 58.7 | 0.99 | ||
| Male | 555 | 47.3 | 81 | 41.3 | - | ||
| Education (years) | |||||||
| < 12 | 530 | 45.3 | 111 | 56.9 | 0.44 | ||
| 12 | 352 | 30.1 | 49 | 25.1 | - | ||
| 13–15 | 155 | 13.2 | 21 | 10.8 | - | ||
| 16+ | 134 | 11.4 | 14 | 7.2 | - | ||
| NSC | |||||||
| Absent | 201 | 17.3 | 2 | 2.2 | 0.03 | ||
| Present | 961 | 82.7 | 91 | 97.8 | - | ||
| Hypertension | |||||||
| No | 500 | 42.7 | 72 | 36.7 | 0.72 | ||
| Yes | 672 | 57.3 | 124 | 63.3 | - | ||
| Retinopathy severity, right eyes | |||||||
| None (≤13) | 630 | 53.8 | 53 | 30.5 | <.001 | ||
| Mild NPDR (14–27) | 388 | 33.2 | 63 | 36.2 | - | ||
| Moderate NDPR (38–53) | 103 | 8.8 | 15 | 8.6 | - | ||
| Proliferative (60+) | 49 | 4.2 | 43 | 24.7 | - | ||
Abbreviations: T1D, younger onset diabetes; T2D, older onset diabetes; D, diopters; NSC, nuclear sclerotic cataract; NPDR, nonproliferative diabetic retinopathy.
The mean spherical equivalent was −1.24 ± 2.02D. There was an increase in spherical equivalent with age (P<.001 per 5 year age category) from an average mean refraction of −1.68D in those 20–24 years of age to +0.11D in those 60 or more years of age (Figure 1). There was no significant difference in refraction by sex, glycosylated hemoglobin, or duration of diabetes (Table 2) in the adjusted models. More years of education were associated with a more myopic refraction as was more severe retinopathy. Cataract had no independent association with refraction. There was no significant effect of clinically significant macular edema on refraction.
Figure 1.
Baseline refraction by age and onset of diabetes.
Table 2.
Model Results for Baseline Refraction of Right Eyes by Onset of Diabetes Group.
| T1D |
N | Mean | S.E. | Adjusted Modela |
||
|---|---|---|---|---|---|---|
| β (95% CI) | P-value | TrendP-value (Per Category) | ||||
| Age (years) | <.001 | |||||
| 20–29 | 288 | −1.76 | 0.12 | referent | - | |
| 30–39 | 204 | −1.63 | 0.16 | 0.15 (−0.23, 0.52) | 0.44 | |
| 40–49 | 88 | −1.22 | 0.19 | 0.51 ( 0.07, 0.95) | 0.02 | |
| 50+ | 66 | −0.05 | 0.23 | 1.68 ( 1.19, 2.17) | <.001 | |
| Per 5 years | 0.19 ( 0.13, 0.26) | <.001 | ||||
| Gender | ||||||
| Male | 318 | −1.58 | 0.12 | referent | - | |
| Female | 328 | −1.35 | 0.12 | 0.22 (−0.08, 0.53) | 0.15 | |
| Education (years) | <.001 | |||||
| < 12 | 64 | −0.63 | 0.22 | referent | ||
| 12 | 246 | −1.24 | 0.13 | −0.41 (−0.86, 0.04) | 0.08 | |
| 13–15 | 200 | −1.58 | 0.15 | −0.54 (−1.03, −0.05) | 0.03 | |
| 16+ | 136 | −2.11 | 0.20 | −1.27 (−1.79, −0.75) | <.001 | |
| NSC | ||||||
| Absent | 484 | −1.60 | 0.10 | referent | - | |
| Present | 155 | −1.05 | 0.17 | −0.22 (−0.68, 0.23) | 0.34 | |
| Duration (years) | 0.03 | |||||
| 0 – 9 | 192 | −1.47 | 0.15 | referent | ||
| 10 – 19 | 242 | −1.83 | 0.14 | −0.48 (−0.86, −0.10) | 0.01 | |
| 20 + | 212 | −1.05 | 0.15 | −0.46 (−0.97, 0.05) | 0.08 | |
| Per 5 years | 0.09 (−0.20, 0.02) | 0.13 | ||||
| Glycosylated hemoglobin (%) | 0.34 | |||||
| < 9.5 | 151 | −1.71 | 0.18 | referent | - | |
| 9.5 – 10.4 | 142 | −1.41 | 0.19 | 0.03 (−0.44, 0.49) | 0.91 | |
| 10.5 + | 315 | −1.31 | 0.12 | 0.17 (−0.21, 0.56) | 0.38 | |
| Per 1% | 0.03 (−0.06, 0.11) | 0.54 | ||||
| Retinopathy severity, right eyes | 0.007 | |||||
| None (≤13) | 138 | −1.47 | 0.21 | referent | - | |
| Mild NPDR (14–27) | 287 | −1.34 | 0.12 | −0.14 (−0.56, 0.27) | 0.50 | |
| Moderate NDPR (38–53) | 91 | −1.65 | 0.21 | −0.70 (−1.21, −0.19) | 0.007 | |
| Proliferative (60+) | 130 | −1.60 | 0.19 | −0.50 (−0.98, −0.02) | 0.04 | |
| T2D |
N | Mean | S.E. | Adjusted Modela |
||
|---|---|---|---|---|---|---|
| β (95% CI) | P-value | TrendP-value (Per Category) | ||||
| Age | <.001 | |||||
| <50 | 96 | −0.67 | 0.19 | referent | - | |
| 50–59 | 254 | 0.23 | 0.13 | 0.84 ( 0.39, 1.28) | <.001 | |
| 60–69 | 394 | 0.71 | 0.10 | 1.27 ( 0.84, 1.69) | <.001 | |
| 70–69 | 312 | 1.27 | 0.11 | 1.80 ( 1.37, 2.22) | <.001 | |
| 80+ | 118 | 1.16 | 0.18 | 1.72 ( 1.23, 2.22) | <.001 | |
| Per 5 years | 0.23 ( 0.18, 0.27) | <.001 | ||||
| Gender | ||||||
| Male | 619 | 0.82 | 0.09 | referent | - | |
| Female | 555 | 0.53 | 0.08 | −0.27 (−0.49, −0.05) | 0.02 | |
| Education | <.001 | |||||
| < 12 | 530 | 0.95 | 0.09 | referent | - | |
| 12 | 352 | 0.64 | 0.10 | 0.12 (−0.12, 0.36) | 0.33 | |
| 13–15 | 155 | 0.62 | 0.17 | −0.09 (−0.42, 0.25) | 0.61 | |
| 16+ | 134 | −0.20 | 0.21 | −0.94 (−1.35, −0.54) | <.001 | |
| NSC | ||||||
| Absent | 201 | 0.12 | 0.14 | referent | - | |
| Present | 961 | 0.79 | 0.06 | 0.05 (−0.25, 0.36) | 0.72 | |
| Duration (years) | 0.20 | |||||
| 0 – 9 | 634 | 0.64 | 0.08 | referent | - | |
| 10 – 19 | 362 | 0.79 | 0.11 | 0.01 (−0.24, 0.25) | 0.95 | |
| 20 + | 178 | 0.65 | 0.14 | −0.25 (−0.55, 0.05) | 0.11 | |
| Per 5 years | −0.02 (−0.09, 0.05) | 0.54 | ||||
| Glycosylated hemoglobin (%) | ||||||
| < 9.5 | 527 | 0.69 | 0.10 | referent | - | 0.44 |
| 9.5 – 10.4 | 193 | 0.77 | 0.13 | 0.14 (−0.16, 0.43) | 0.36 | |
| 10.5 + | 366 | 0.72 | 0.10 | 0.09 (−0.16, 0.34) | 0.47 | |
| Per 1% | 0.02 (−0.04, 0.07) | 0.60 | ||||
| Retinopathy severity, right eyes | 0.35 | |||||
| None (≤13) | 630 | 0.59 | 0.09 | referent | - | |
| Mild NPDR (14–27) | 388 | 0.86 | 0.09 | 0.09 (−0.13, 0.30) | 0.42 | |
| Moderate NDPR (38–53) | 103 | 0.51 | 0.19 | −0.02 (−0.39, 0.35) | 0.92 | |
| Proliferative (60+) | 49 | 0.64 | 0.23 | 0.27 (−0.12, 0.66) | 0.17 | |
Abbreviations: T1D, younger onset diabetes; T2D, older onset diabetes; NSC, nuclear sclerotic cataract; NPDR, nonproliferative diabetic retinopathy.
Except for age, all p-values are from models that include age, gender, and education.
Older Onset Group (T2D)
Those excluded from the analyses were significantly older, had more hyperopic refraction, had longer duration of diabetes, were more likely to have nuclear cataract, and more severe retinopathy than those included (Table 1).
The mean spherical equivalent was 0.69 ± 2.05D. There was an increase in spherical equivalent with increasing age (P<.001 per 5 year age category) from an average mean refraction of −1.15D in those <45 years of age to +1.04D in those 85+ years of age (Figure 1). More education was associated with a more myopic refraction as was female sex (Table 2). There were no consistent associations of glycosylated hemoglobin, duration of diabetes, or severity of diabetic retinopathy with refraction (Table 2) in the adjusted models. Cataract had no independent association with refraction. There was no significant effect of clinically significant macular edema on refraction.
Non-diabetic Comparison Group
The mean spherical equivalent was −0.15 ± 2.06D. There was an increase in spherical equivalent with increasing age (P<.001 per 5 year age category) from a mean refraction of −1.53D in those 20–24 years of age to +1.52D in those 75 years of age or older (Figure 1). After adjusting for age, more education was associated with a more myopic refraction (data not shown).
Refraction in those of similar age
We examined whether there was a difference in refraction between younger and older onset persons of similar age (40–59 years of age). We found that, after controlling for age and education, there was a significant difference in refraction between the groups (younger onset persons were significantly likely to be more myopic than older onset persons, P<.01).
Change in refraction
Younger Onset Group (T1D)
The mean change in spherical equivalent was −0.28 ± 1.08D. The youngest members of the group had, on average, a −.23D change over the 10-year interval (Table 3), but the amount of the myopic shift decreased with increasing age at baseline. After adjusting for age, women were more likely to have a myopic shift in refraction, while those with longer duration of diabetes and more severe retinopathy were likely to have hyperopic shifts in refraction (Table 3).
Table 3.
Model Results for 10-year Change in Refraction for Right Eye from 1980–82 to 1990–92 by Onset of Diabetes Group.
| T1D |
N | Mean | S.E. | Adjusted Modela |
||
|---|---|---|---|---|---|---|
| β (95% CI) | P-value | TrendP-value (Per Category) | ||||
| Age (years) | <.001 | |||||
| 20–29 | 217 | −0.23 | 0.06 | referent | - | |
| 30–39 | 144 | −0.05 | 0.07 | 0.18 ( 0.01, 0.35) | 0.04 | |
| 40–49 | 50 | 0.92 | 0.12 | 1.15 ( 0.89, 1.41) | <.001 | |
| 50+ | 17 | 0.68 | 0.25 | 0.91 ( 0.43, 1.40) | <.001 | |
| Per 5 years | 0.21 ( 0.16, 0.26) | <.001 | ||||
| Gender | ||||||
| Male | 224 | 0.12 | 0.06 | referent | - | |
| Female | 204 | −0.13 | 0.06 | −0.18 (−0.34, −0.02) | 0.03 | |
| Education (years) | 0.86 | |||||
| < 12 | 34 | 0.37 | 0.14 | referent | - | |
| 12 | 167 | −0.01 | 0.07 | −0.16 (−0.41, 0.09) | 0.20 | |
| 13–15 | 138 | −0.17 | 0.07 | −0.23 (−0.50, 0.04) | 0.09 | |
| 16+ | 89 | 0.14 | 0.11 | 0.08 (−0.37, 0.21) | 0.57 | |
| NSC | ||||||
| Absent | 348 | −0.15 | 0.04 | referent | - | |
| Present | 74 | 0.74 | 0.11 | 0.48 ( 0.24, 0.71) | <.001 | |
| Duration (years) | <.001 | |||||
| 0 – 9 | 152 | −0.37 | 0.06 | referent | ||
| 10 – 19 | 170 | −0.04 | 0.06 | 0.26 ( 0.09, 0.43) | 0.003 | |
| 20 + | 106 | 0.60 | 0.09 | 0.57 ( 0.29, 0.84) | <.001 | |
| Per 5 years | 0.14 ( 0.08, 0.20) | <.001 | ||||
| Glycosylated hemoglobin % | 0.15 | |||||
| < 9.5 | 101 | 0.00 | 0.08 | referent | - | |
| 9.5 – 10.4 | 103 | 0.15 | 0.09 | 0.00 (−0.21, 0.21) | 0.99 | |
| 10.5 + | 199 | −0.10 | 0.07 | −0.13 (−0.33, 0.07) | 0.19 | |
| Per 1% | −0.02 (−0.06, 0.02) | 0.30 | ||||
| Retinopathy severity, right eyes | <.001 | |||||
| None (≤13) | 104 | −0.32 | 0.08 | referent | - | |
| Mild NPDR (14–27) | 215 | 0.04 | 0.06 | 0.20 ( 0.02, 0.37) | 0.03 | |
| Moderate NDPR (38–53) | 52 | 0.08 | 0.12 | 0.26 ( 0.05, 0.47) | 0.02 | |
| Proliferative (60+) | 57 | 0.40 | 0.12 | 0.52 ( 0.24, 0.80) | <.001 | |
| T2D |
N | Mean | S.E. | Adjusted Modela |
||
|---|---|---|---|---|---|---|
| β (95% CI) | P-value | TrendP-value (Per Category) | ||||
| Age | <.001 | |||||
| <50 | 63 | 0.58 | 0.09 | referent | - | |
| 50–59 | 121 | 0.74 | 0.07 | 0.17 (−0.05, 0.38) | 0.14 | |
| 60–69 | 123 | 0.35 | 0.08 | −0.23 (−0.47, 0.01 | 0.06 | |
| 70–69 | 43 | 0.00 | 0.17 | −0.58 (−0.95, −0.20) | 0.002 | |
| 80+ | 3 | 0.33 | 0.21 | −0.25 (−0.62, 0.13) | 0.20 | |
| Per 5 years | −0.08 (−0.13, −0.03) | <.001 | ||||
| Gender | ||||||
| Male | 198 | 0.55 | 0.06 | referent | - | |
| Female | 155 | 0.40 | 0.07 | −0.18 (−0.37, 0.01) | 0.07 | |
| Education | 0.25 | |||||
| < 12 | 111 | 0.45 | 0.10 | referent | - | |
| 12 | 150 | 0.56 | 0.06 | −0.01 (−0.24, 0.22) | 0.95 | |
| 13–15 | 47 | 0.50 | 0.14 | 0.03 (−0.32, 0.38) | 0.85 | |
| 16+ | 45 | 0.29 | 0.10 | −0.22 (−0.49, 0.05) | 0.11 | |
| NSC | ||||||
| Absent | 110 | 0.52 | 0.07 | referent | ||
| Present | 237 | 0.47 | 0.06 | 0.09 (−0.11, 0.29) | 0.37 | |
| Duration (years) | 0.77 | |||||
| 0 – 9 | 225 | 0.49 | 0.06 | referent | ||
| 10 – 19 | 105 | 0.49 | 0.10 | 0.03 (−0.19, 0.24) | 0.81 | |
| 20 + | 23 | 0.43 | 0.18 | 0.04 (−0.31, 0.39) | 0.84 | |
| Per 5 years | 0.04 (−0.03, 0.11) | 0.30 | ||||
| Glycosylated hemoglobin % | 0.03 | |||||
| < 9.5 | 184 | 0.38 | 0.07 | referent | ||
| 9.5 – 10.4 | 52 | 0.41 | 0.12 | 0.00 (−0.27, 0.26) | 0.98 | |
| 10.5 + | 93 | 0.69 | 0.09 | 0.26 (0.04, 0.48) | 0.02 | |
| Per 1% | 0.04 (−0.00, 0.08) | 0.07 | ||||
| Retinopathy severity, right eyes | 0.47 | |||||
| None (≤13) | 229 | 0.48 | 0.06 | referent | ||
| Mild NPDR (14–27) | 91 | 0.45 | 0.10 | 0.10 (−0.09, 0.29) | 0.30 | |
| Moderate NDPR (38–53) | 23 | 0.68 | 0.18 | 0.13 (−0.17, 0.43) | 0.40 | |
| Proliferative (60+) | 10 | 0.39 | 0.29 | −0.04 (−0.63, 0.55) | 0.90 | |
Abbreviations: NSC, nuclear sclerotic cataract; T1D, younger onset diabetes; T2D, older onset diabetes; NPDR, nonproliferative diabetic retinopathy.
Except for age, all p-values are from models that include age, gender, and education.
Older Onset Group (T2D)
The mean change in spherical equivalent was 0.48 ± 0.89D. The youngest members of the group had, on average, a +.58D change in refraction over the 10-year interval (Table 3), but the largest change happened in the next oldest age group with smaller positive changes occurring for each age group thereafter. After adjusting for age, there were no significant effects of the other variables on change in refraction (Table 3).
Non-diabetic comparison group
There were no significant effects of age or other variables we considered on change in refraction (Table 3).
Change in those of similar age
Because change was affected by age in most analyses, we examined change in refraction for those of similar ages (40–59 years of age at baseline). We found that after adjusting for age and education there was a borderline significant difference in the change in refraction between the groups (persons with T2D had smaller changes than those with T1D, P=.08).
Discussion
We have found that risk factors for refraction and risk factors for change in refraction in adults with diabetes are similarly distributed in those with T1D and T2D after adjusting for age and education. Additionally, the mean change in refraction in our population with T2D is similar to that found in diabetic persons over a 10-year interval in another Wisconsin study.16 Most importantly, we have found that refraction and its correlates in adults with diabetes regardless of type are very similar to those reported for adults without diabetes.4–6
In particular, our data indicate the importance of current age and education in refraction. With regard to change in refraction during adult years, age appears to be a consistent factor. The primary purpose of the current investigation was not to compare refractions in those with diabetes to those without this condition but to compare refractions among those with T1D and T2D. The same risk factors for refraction were found in these groups. However, we found that in persons of the same age, those with T1D were likely to have more myopic refractions. It is possible that relatively elevated glucose levels earlier in life in those with T1D affected refraction and that there is a residual effect. Since those analyses were adjusted for education, the difference is unlikely to reflect greater education in the younger onset group.
We had anticipated that glycemia would be an important determinant of refraction; it has been reported that refractions tend be more myopic in those persons with diabetes who have relatively acute elevations in their blood glucose levels, inferred from the rapid hyperopic shift in refraction that has been reported for markedly hyperglycemic persons who are rapidly brought under control.2 We did not find that the level of glycemia as reflected in baseline glycosylated hemoglobin had a significant effect on refraction in either diabetic group. We could not assess the potential effects of glycemia as reflected in fasting blood glucose as we did not measure this analyte.
Others have reported that those with high myopia are less likely to have more severe retinopathy than those with emmetropia, hyperopia or small to moderate myopic refractions.17,18 Our cross-sectional data do not support a relationship between severity of retinopathy and refractive error in those with T1D or T2D. However, we have very few high myopes in our study and those with severe retinopathy were often excluded for refraction analyses because of poor visual acuity.
There are some limitations to this study which may have influenced our results. Those excluded from the baseline analyses were significantly older, had more hyperopic refraction, had longer duration of diabetes, were more likely to have nuclear cataract, and more severe retinopathy in both groups than those included. Thus, these exclusions might be expected to bias our baseline estimates of refraction toward myopia. Age adjustment in subsequent likely analyses reduces some of these effects.
In summary, we have examined correlates of refraction and change in refraction in a large population based study of persons with T1D and T2D. The most important correlates for both groups are age and education, which are similar to those for the general population.
Acknowledgments
This research is supported by National Institutes of Health grant EY03083 and EY016379 (Ronald Klein, MD, MPH, Barbara E.K. Klein, MD, MPH) and, in part, by the Research to Prevent Blindness (R. Klein and BEK Klein, Senior Scientific Investigator Awards), New York, NY. The National Eye Institute provided funding for entire study including collection and analyses and of data; RPB provided further additional support for data analyses. The content is solely the responsibility of the authors and does not necessarily reflect the official views of the National Eye Institute or the National Institutes of Health.
Footnotes
Financial Disclosure
There are no financial disclosures to report.
The authors have had full access to all the data in the study and take responsibility for the integrity of the data and the accuracy of the data analysis.
Author contributions
Conception and design (BEKK, KEL), acquisition of data (BEKK, RK), analysis and interpretation of data (BEKK, KEL), drafting of the manuscript (BEKK), critical revision of the manuscript for important intellectual content (KEL, RK), statistical expertise (KEL), obtaining funding (BEKK, RK), administrative/technical/material support (BEKK).
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