The Beaver Dam Eye Study is a population-based study of age-related eye diseases in persons ... of Ophthalmology, 600 Highland Avenue, Madison, WI 53792.
Investigative Ophthalmology & Visual Science, Vol. 33, No. 7, June 1992 Copyright © Association for Research in Vision and Ophthalmology
Intraocular Pressure in an American Community The Deover Dom Eye Study Barbara E. K. Klein, Ronald Klein, and Karhryn L. P. Linron The Beaver Dam Eye Study is a population-based study of age-related eye diseases in persons 43-86 yr of age. Applanation tonometry was done on all study subjects. Mean intraocular pressure (IOP) increased significantly with age. Mean IOP differed little between the sexes and was not significantly different after age adjustment (in right eyes of 2721 women, it was 15.5 mm Hg, and in right eyes of 2135 men, it was 15.3 mm Hg). There was an association of IOP with systolic and diastolic blood pressures, body mass index, hematocrit, serum glucose, glycohemoglobin, cholesterol level, pulse, nuclear sclerosis, season, and time of day of measurement. These data confirm that, in a general population, IOP is associated with important systemic and ocular characteristics. Those characteristics should be considered in further research on determinants of IOP. Invest Ophthalmol Vis Sci 33:2224-2228, 1992
Intraocular pressure (IOP) is an inherent physiologic characteristic of importance in maintaining structure and function of the eye. Correlates of this measurement include other important physiologic parameters that may need to be considered in investigating determinants of IOP. Because IOP is the ocular parameter that is associated most commonly with glaucoma,1"4 it may be important to evaluate these physiologic correlates of IOP; they may confound relationships between IOP and glaucoma. We briefly describe the distribution of IOP and investigate its correlates in the population participating in the Beaver Dam Eye Study.
persons in the target age range, 4926 were evaluated (83.14%). Relevant parts of the study evaluation included the date of birth and a history of ocular trauma, surgery, medications, glaucoma, and diabetes. Most of the participants were white (99.4%). Blood pressure was measured according to the Hypertension Detection and Follow-up Program protocol.6 Height and weight were measured with a Health-o-Meter scale (Continental Scale Corp., Bridgewater, IL). The IOP was measured with a Goldmann applanation tonometer. A drop of Fluress (Armour, Kankakee, IL) was instilled in each eye. The tonometer was set at 10. The measurement was taken as the examiner viewed the mires through the prism. When the end point was reached, the examiner moved the slit lamp away from the eye and recorded the reading. The procedure was repeated for the other eye. The time of measurement was recorded. Iris pigmentation was evaluated and compared with three standard color 35-mm slides. The protocol specifies categories of pigmentation from a lightly pigmented iris (blue) through a heavily pigmented one (brown).7 After assessing anterior chamber depth, the pupils were dilated with one drop each of tropicamide 1% and phenylephrine 2.5%. When the pupils were dilated, a clinical assessment of the presence and severity of cataract was made, and photographs were taken with the illuminating beam at 45° to the viewing system.7 These photographs subsequently were graded by comparison with standard photographs according to the protocol.7 A blood specimen was obtained, and glucose and glycosylated hemoglobin were measured. The subjects were classified as having no diabetes if there was a negative history of
Materials and Methods A private census of Beaver Dam was done, and the procedures have been published elsewhere.5 In brief, 6612 households were identified, of which 3715 had at least one occupant 43-84 yr of age. Thereafter, each individual in the target age range was contacted for a study appointment. Three subjects were examined whose age was 86 yr at the time of testing. Their data are included in this report. Of the total of 5925 From the Department of Ophthalmology, University of Wisconsin Madison, Madison, Wisconsin. Supported by National Institutes of Health (Bethesda, Maryland) grant 5U10 EY 10 6594 (RK and BEKK). Presented in part at the Annual Meeting of the Association for Research in Vision and Ophthalmology, Sarasota, Florida, April 28 to May 3, 1991. Submitted for publication: October 2, 1991; accepted December 21, 1991. Reprint requests: Barbara E. K. Klein, MD, MPH, Department of Ophthalmology, 600 Highland Avenue, Madison, WI 53792.
2224
INTRAOCULAR PRESSURES IN DEAVER DAM / Klein er ol
No. 7
2225
We investigated the relationship between nuclear sclerosis and IOP (Table 2). There was a significant trend of increasing IOP with increasing severity of nuclear sclerosis. In those eyes that were either aphakic or had intraocular lens implants, the mean IOP was between the mean for those eyes in thefirsttwo categories of severity of nuclear sclerosis (Table 2). A history of other eye surgery or trauma was not associated with increased mean IOP. The participants were categorized as to definite, possible, or no history of diabetes. There was a significant difference between the IOP means among these groups (Table 2). There also was a seasonal effect on IOP; measurements during the summer months (July, August, and September) were significantly lower (15.2 mm Hg) than those during the winter months (January, March, and April; 15.7 mm Hg). There was no significant effect of iris color, refractive error, cigarette smoking, or alcohol consumption on IOP. A history of cardiovascular disease was not related to IOP. Table 3 describes the multiple linear-regression analysis for the variables significantly associated with IOP. Data for persons who reported receiving medicine for glaucoma or who had had surgery for glaucoma were excluded from this analysis. Systolic blood pressure, time of day of examination, body mass index, glaucoma history, refractive error, cholesterol level, hematocrit, female sex, month of examination, pulse rate, severity of nuclear sclerosis, diastolic blood pressure, and glycosylated hemoglobin were all selected in the stepwise analysis. Age did not enter as a significant factor when considered with the other variables.
diabetes, blood glucose was less than 200 mg/dl, and glycosylated hemoglobin was within two standard deviations of the mean for the particular age-sex subgroup. Informed consent was obtained for each subject. We used the Statistical Analysis System (SAS, Cary, NC) to analyze the data.8 Because the distribution of IOP does not differ from normality, parametric tests were chosen where applicable. Univariate associations with IOP were detected by Student's t-test, and analysis of variance techniques were used for categoric factors, with Pearson correlation coefficients for continuous factors. Confidence intervals for the correlation coefficients were calculated using the method developed by Fisher.9 Results There was little difference between the mean IOP of right and left eyes (0.14 ± 2.11 m m Hg) or their association s with other variables. Therefore, data for right eyes only are presented. The distribution of IOP in the right eye by sex and age is given in Table 1. There was a small but significant change in mean IOP with increasing age (P < 0.05). We found IOP greater than 21 mm Hg to be more frequent in older age groups (P < 0.01, by test for trends). Women had higher mean IOP than did men, but the difference was not great and was only borderline significant (P = 0.06) when adjusted for age (by multiple-linear regression). During the interview, the participants were asked whether they had glaucoma or were receiving medication for this disease. The mean IOP was significantly higher (20.1 mm Hg) in those with a positive compared with a negative history (15.3 mm Hg).
Table 1. Percent distribution of intraocular pressure in right eyes by age and sex IOP (mm Hg) Age (years)
Sex
N
0-12
13-15
16-18
19-21
22-24
25+
Mean
SD
43-49
F M F M F M F M F M F M F M F M F M
448 385 340 327 347 287 348 325 391 299 340 233 276 168 231 111 2721 2135
21.9 22.9 21.8 24.2 23.6 16.4 17.8 15.1 12.5 20.1 15.3 15.9 16.3 19.6 18.2 22.5 18.5 19.6
35.5 37.4 33.2 39.1 29.4 40.8 28.5 32.9 29.4 32.4 32.7 36.1 31.2 30.4 36.8 31.5 32.0 35.4
32.6 31.2 32.4 24.2 34.9 27.2 38.2 36.0 39.4 30.8 32.9 31.8 31.5 32.7 29.4 33.3 34.2 30.5
6.9 6.2
2.7 1.3 2.7 2.1 4.3 2.4 3.2 4.0 4.9 4.7 3.5 5.6 6.2 6.0 3.5 2.7 3.8 3.4
0.5 1.0 0.3 0.9 0.3
15.0 14.7 15.1 14.9 15.1 15.4 15.6 15.8 16.0 15.4 15.9 15.6 15.9 15.8 15.5 14.9 15.5 15.3
2.9 3.1 3.0 3.3 3.2 3.4 3.1 3.3 3.4 3.4 3.3 3.3 3.6 4.2 3.6 3.9 3.3 3.4
50-54 55-59 60-64 65-69 70-74 75-79 80-86 TOTAL
Twenty-seven "unreliable" and 43 "not obtainable" excluded from the analyses.
9.7 9.5 7.5
12.2 11.8 10.5 12.3 11.4 14.7 10.3 13.4 9.5 9.5 9.0 10.6 9.7
1.1
0.6 1.5 1.5 0.7 0.9 0.4 1.5 1.8 2.6 0.9 0.9 1.0
2226
Vol. 33
INVESTIGATIVE OPHTHALMOLOGY & VISUAL SCIENCE / June 1992
Table 2. Mean intraocular pressure in right eyes by subject characteristics Variable Nuclear sclerosis
