June 1995, Volume 45, Issue 6

Original Article

Age and Intraocular Pressure: How are they Correlated?

lmran Ahmad Qureshi  ( Department of Physiology, Rawalpindi Medical College, Rawalpindi. )

Abstract

Background: The relationship between intraocular pressure and age is not fully understood, Intraocular pressure may increase or decrease with age.
Purpose: Study was planned to determine the effect of aging on intraocular pressure of an apparently healthy population of Karachi.
Subjects and Methods: Depending upon age, 8036 subjects were divided into seven groups. All were examined according to standard protocols. Measurements were taken by Goldmann applanation tonome­ter, after a complete rest for atleast 15 minutes and always first in the right eye.
Results: Mean intraocular pressure increases progressively with age until 60 yeais. When one age group is compared with its preceding, the increase is non-significant until 40 years but highly significant (P Conclusion: This study supports the conclusion that as age increases, intraocular pressure also increases, with an average of 0.28 mmHg per decade. Knowledge of the normal range of intraocular pressure in various age groups will help glaucoma screeners (JPMA 45:150,1995).

Introduction

With regard to the effect of age on intraocular pressure (lOP) fmdings are not consistent. Several univariate studies indicate that TOP increases with age among Eumpean and American populations1-7. Many studies have shown that with age, the entire population develops an increase in IOP1-3, such that the frequency of low readings drops and of the high readings increases significantly4, especially after the age of 40 years5,6. Martin5 reported that IOP increases by 1 mmHg, while Kass et al7 found 0.43 mmHg per decade after the age of 40 years. Risk for glaucoma, which is the second most important cause of permanent blindness in the Asia Pacific region, increases with the age8,9.
In contrast to these, in the Japanese population, TOP decreases with age, which is statistically significant after the age of 40 years10,11. Because of this contrast the present study was undertaken to determine the effect of aging on IOP in the apparently healthy population of Karachi.

Subjects and Methods

The sample consisted of 8036 healthy subjects (5188 men and 2848 women) which were collected from different hospitals, colleges, universities and factories. A medical history was taken from each subject, including questions concerning previous ocular diseases, presence of diabetes mellitus and the occurrence of glaucoma in the family. The blood pressure was taken in supine position after five minutes rest. The inclusion criteria met were absence of ocular complaints including refractive errors, absence-of ally history of eye surgery and diabetes, normal body temperature and blood pressure. Subjects were asked not to smoke or take tea and have a complete rest atleast 15 minutes before the measurement of IOP. 1 hey were asked to see the ophthalmolo­gist for further examination, if he/she had an IOP reading above 21 mmHg, or a difference of 5 mm Hg between the two eyes also if, they had a history of haloes or attacks of blurred vision. Out of 8455 subjects, 8036 fulfilled the criteria and were divided into seven age groups (Table). After instillation of O.25% fluorescein and 0.4%benox-mate hydrochloride (Fluress) eye drops, the IOP was meas­ured with the Goldmann applanation to no meter first in the right eye and then in the left. Three consecutive readings of each eye were taken and after each reading the to no meter was removed from contact and the measuring scale was returned to 10 mmHg. The average of the three readings for each eye and the mean of two averages is used as the person’s IOP for the present study. The measurements were taken at a fixed time from 9 to 11 A.M. to minimize the effect of diurnal variations. Significance of the difference between two groups is calcu­lated by applying the unpaired student’s “t” test and the differences are regarded as significant when the P value is less than 0.05.

Results

IOP increases progressively with age until 60 years. When the mean lOP of one age group was compared with its preceding age group, the increase is statistically non-signifi­cant until the age of 40 years and highly significant (P<0.001) in the age groups 41-50 and 51-60 years. There was non-sig­nificant decrease in the age group 61-70 years and increase in the age group above 70 years (Table).

Differences in mean IOP of one age group from its preceding age group were +0.31, +0.27, +0.54, +0.74, -0.23 and +0.06 minHg respectively. The very small difference between the last two groups is within the limits of chance fluctuation The average per decade increase in this study was found to be 0.28 mrnHg.

Discussion

The effect of age on mean applanation pressure reported here is similar to that reported in Western population studies1-7,  while reverse is tme for Japanese population10,11. All these studies found that IOP increases with age and this effect was lost or atleast weakened at the oldest ages. In contradiction to these results, in the Japanese population the age dependent decrease of IOP has been consistently observed in both sexes but more markedly in men10,11. Because of this contrast, it is suspected that some other factors might be equally or more important than age in determining IOP.
The associations between IOP, age and blood pressure (BP) have previously been described 1,12-14 but inconsisten­cies are present. Klein et al1 reported that both age and BP are independently and significantly associated with TOP level, but others observed that systolic BP is positively correlated with the age, while IOP is significantly negatively correlated with systolic BP; any apparent association between IOP and age was fully accounted for through the correlation between systolic BP and age12. The age effect on IOP is merely mediatedby an increase in systolic BP and that age itself does not have an independent effect on lOP13.  IOP is positively and independently related to systolic BP and obesity index14.  A series of Japanese studies repeatedly confirmed that obesity index, systolic BP and age are three primary factors affecting IOP10,11. Multiple regression analysis of data in the Japanese, shows that TOP is physiologically maintained by a balance between the value decreasing effect of aping and value increasing effect of obesity and hypertension11. Based on this observation, the discrepancy can be explained, as among Pakistani, European and American populations, the ocular hypertensive effect of hypertension and obesity overwhelms the hypotensive effect of aging and TOP therefore, increases with age. However, in the Japanese population the hypoten­sive effect of aging has the dominant effect and lowering of IOP is the net result.
Alternatively, change in aqueous dynamics with age is a more likely explanation for this discrepancy. The tendency for IOP to decrease with age in Japanese may be due to decrease in the production of aqueous humour, because some studies have reported significant decrease in aqueous humourproduc­tion with the increase in age15. On the other hand the tendency for IOP to increase with age in the Pakistani population may be due to decreased ouLflow facility, as it has also been reported for the elderly16. IOP levels among blacks are higher than whites7. These findings suggest that a genetic factor may play a role in determining TOP level.
TOP decreases as the pregnancy advances because changes in circulating progesterone and relaxin levels in­crease the outflow facility by reducing corneoscleral rigid­ity17,18. Besides sex hormones, there is some evidence that vasopressin, thyroxin, insulin, glucocorticoids and mineralo­corticoids may also affect the physiological regulation of IOP19. The characteristics of ocular tissue and thus IOP, may change with changes in serum hormonal levels. Thus with advancing age, especially after the age of 40 years, the hormonal influence of IOP may adopt different paths in different races, determined by their genetic background. The suggested difference in hormonal influence on IOP could take the form of increased or decreased level, tissue sensitivity, or effectiveness of one or another hormone with age. The logical choices for target tissues in the eye are the ciliary epithelia, the sub-epithelial vascular plexus, the trabecular meshwork, outflow channels and the episcleral venous plexus. There is a possibility that hormones may alter IOP by affecting the rate of aqueous inflow or the facility of the outflow. At this time, collection of well documented clinical data of TOP change in endocrine conditions is desirable. It would appear that there is a hormonal component in the physiologic regulation of IOP. Whether this is one of the keys to understanding the differences in IOP with age, sex and racial groups and causes of glaucoma must be left to future investigators.
Among the many systemic factors, ages cannot be discussed in the same dimension as other variables. This is because all biological phenomena show age dependent changes. While there are individual variations, the phenome­non of aging becomes definitely apparent in those over 40 years, accompanied by increase in the incidence of various adult diseases, for example, diabetes niellitus. Diabetics have a higher mean IOP than non-diabetic persons20. Stoupel et al21 showed that environmental conditions also have a significant influence on IOP. Due to differences in inherent constitution. diet and environmental conditions, there may be some qualitative differences in important systemic and ocular characteristics in the Pakistani and Japanese populations, with particular reference to blood pressure. body mass index, height, haematocrit, senim glucose. glycohaemoglobin, cho­lesterol level, episcieral vein and corneal thicknesses. There is a possibility that with advancing age, changes in these factors may affect lOP differently in the two races. No comparable data is available between thesc two populations. These characteristics shouldbe considered infurther research on lOP, particularly when comparing lop in different populations. Among these, haemoglobin looks theoretically important, as resistance in the episcieral veins can be increased by rises in blood viscosity. TOP measurements in polycvthaemia and in severe anaemia can also help. What is needed is one or more population based studies in Pakistim and Japan in which TOP, hormonal levels and other important parameters are measured by the same investigators using uniform methods of measure­ment and subject selection.

Acknowledgements

The author gratefully acknowledges Professor Dr. Ahniad Kamal Ansan, Professor Hui Li Chen and Dr. Murad Khan for their technical help and suggestions.

References

1. Klein, B. E., Klein, R. and Linton, K. L. Intraocular pressure in an american community: The beaver dam eye study. Invest. Ophthalmol Via. Sci., 1992;33:2224-2228.
2. Bcngtsson, B. Changing with age in Schiotz and Goldmann readings. Acts. Ophthalmol. (Copenh)., 1992;70:350-352.
3. Duckman, R. H. and Fitzgerald, D. E. Evaluation of intraocular pressure in pediatric population. Optom. Vis. Sci., 1992;69:705- 709.
4. Costagliola, C.. Trapanese, A. and Pagano, M. Intraocular pressure in healthy population: A survey of 751 subjects. Optom. Vis. Sci., 1990,67(3):204-206.
5. Martin, X. D. Normal intraocular pressure in man. Ophthalmologica, 1992;205:57-63.
6. Kahn, H. A. and Milton, R. C. Alternative definitions of open angle glaucoma. Effect on prevalence and associations in Framingham eye study. Arch. Ophthalmol., 1980;98:2172-2177.
7. Kass, M. A., Zimmerman, T. J., Alton, E. et al. Intraocular pressure and glaucoma in the Zuni indians. Arch. Ophthalmol., 1978;96:22 12-2213.
8. Reddy, R. S. Epidemiology ofglaucoma in Asia - Pacific. Yen. Ko. Hsueh Pao., 1992;8:21-2-1.
9. Klein,. B. E., Klein, R., Spoissel, W. E. et al. Prevalence of glaucoma. The beaver dam eye study. Ophthalmology, 1992;99: 1499-1504.
10. Shiose, Y. Intraocular pressure: New perspectives. Surv. Ophthalmol.. 1990;34:413-435.
11. Shiose, Y. and Kawase, Y. A new approach to stratified normal intraocular pressure in genera population. Am. J. Ophthalmol., 1986; 101:714-721.
12. Schulzer. M. and Drance. S. M. Intraocular pressure, systemic blood pressure and age, a correlational study. Br. J. Ophthalmol., 1987;71 :245-499.
13. Bengtsson. B. Some factors affecting the relationship between Schiotz and Goldmann readings in a population. Acta. Ophthalmol., 1973;51:798-810.
14. Bulpitt, C. J., Hodes, C. and Everitt, M. G. Intraocular pressure and systemic blood pressure in the elderly. Br. 3. Ophthalmol., 1975;59:717-720.
15. Brubaker, R. F., Nagataki, S., Townsend, D. J. et al. The effect ofageon aqueous humorformation in man. Ophthalmology, 1981 ;88:283-287.
16. Linner, E. Ocular hypertension. I. The clinical course during ten years without therapy. Aqueous humor dynamics. Acta. Ophthalmol., 1976;54:707-720.
17. Phillips C. I and Gore, S. M. Ocular hypotensive effect of late pregnancy with and without high blood pressure. Br. 3. Ophthalmol., 1985;69: 117-119.
18. Paterson, G. D. and Millar, S. J. H. Flormonaliniluence in simple glaucoma. Br.J. Ophthalmol., 1963;47:129-137.
19. Kass, M. A. and Sears, M. L. Hormonal regulation of intraocular pressure. Surv. Ophthalmol., 1977;22: 153-176.
20. Al-Sereiti, M. R., Turner, P. and Gale, E. A. Intraocular pressure and pupillary responses in patients with diabetes mellitus. Postgrad. Med. 3., 1991 ;67:250-251.
21. Stoupel, E., Goldenfeld, M. Shimshoni. M. et at Intraocular pressure in relation to four levels of daily geomagnetic and extreme yearly solar activity. Int. J. Biometerol., 1993;37:42- 45.

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