Intraocular Pressure, Ocular Hypertension, and Glaucoma : A Comparison of White and Blue Collar Workers

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1 Intraocular Pressure, Ocular Hypertension, and Glaucoma : A Comparison of White and Blue Collar Workers Imran Ahmad QURESH11 and Xiao Rong X12 'Department of Physiology Shanghai Medical University, Rawalpindi Medical College and 2Neurological Institute, Huashan Hospital, Abstract: Intraocular Pressure, Ocular Hypertension, and Glaucoma: A Comparison of White and Blue Collar Workers: Imran Ahmad QURESHI, et al Department of Physiology, Rawalpindi Medical College-The course of glaucoma is an insidious one and most cases remains asymptomatic until the visual field has been seriously diminished. Consequently, it is a disease suited to a preventive approach. The intraocular pressure (IOP) distribution and prevalence of ocular hypertension and glaucoma have never been described in industrial workers. After controlling all IOP affecting factors, we investigated levels of intraocular pressure and its association with certain health parameters along with the prevalence of ocular hypertension and glaucoma in healthy white and blue collar workers in Karachi, the largest city in the Islamic Republic of Pakistan. In both groups, the histogram shows a skew to the right, so that the distribution was not Gaussian. This study reports that on an average, per decade, white collars have 1.1 mmhg (p<0.001) higher IOP than blue collar subjects. The average per decade increases were 0.47 mmhg and 0.33 mmhg in white and blue collar workers respectively. The age effect was statistically insignificant until the age of 40 years in both groups, after which it became quite significant. Differences in mean IOP (left minus right) were found to be 0.15 mmhg (p<0.2), and 0.12 mmhg (p<0.05) in white and blue collar subjects, respectively. In normal subjects IOP was weakly but statistically significantly correlated with the heart rate and systolic blood pressure. Heart rate, systolic and diastolic blood pressures and age were found to be risk factors for ocular hypertension. In both normotensive and ocular hypertensive subjects, weight and height were not correlated significantly. Ocular hypertensive subjects (IOP>_21 mmhg) were 2.48 times more numerous in white collar than in blue collar subjects. Most of the ocular hypertensive and several glaucoma patients Received Oct 17, 1996; Accepted Dec 18, 1996 Correspondence to: I. A. Qureshi, Physiology Department, Rawalpindi Medical College, Rawalpindi, Pakistan were diagnosed during this survey. The results therefore strongly suggest that in routine health examination, tonometry should be included. (J Occup Health 1997; 39: ) Key words: Aging, Blood pressure, Blue and white collar subjects, Epidemiologic survey, Glaucoma, Intraocular pressure, Ocular hypertension, Tonometry From a functional standpoint, a normal intraocular pressure is one that does not result in glaucomatous optic nerve head damage. Leydhecker1 collected statistics on intraocular pressure (IOP) on 10,000 individuals with no ocular symptoms, and reported that average IOP in the total sampling was 15.5 ± 2.57 mmhg and that the distribution was regarded as normal. Leydhecker concluded that those who registered 20.5 mmhg (M + 2SD) and higher could be suspected of having glaucoma. The epidemiologic studies have made important contribution by determining that a large percentage of adults have intraocular pressure greater than 21 mmhg and no optic nerve damage 2' 3). Such individuals have been designated as ocular hypertensives, glaucoma suspects, or pre glaucoma cases. It has been reported that ocular hypertension is present in 5 to 10 per cent of adults3-5), Increased intraocular pressure is generally considered to be one of the risk factors for glaucoma. Glaucoma is a leading cause of preventable blindness and visual impairment 4, 5). The course of glaucoma is an insidious one and in most cases remains asymptomatic until the visual field has been seriously diminished. Consequently, it is a disease suited to a preventive approach. The IOP distribution and prevalence of ocular hypertension and glaucoma in industrial workers have never been described. After controlling all IOP affecting factors, we investigated levels of intraocular pressure and its association with certain health parameters along with the prevalence of

2 ocular hypertension and glaucoma in the healthy white and blue collar workers of Karachi, the largest city in Islamic Republic of Pakistan. Materials and Methods All experimental procedures adhered to the Declaration of Helsinki of the World Medical Association. Each subject was informed of the nature of the study. The sample consisted of 1,693 white collar workers and 1,624 blue collar workers. The white collar workers were from various hospitals, colleges, and universities, whereas the blue collar workers were from steel mills and iron factories. A medical history was obtained from each subject, the questions including concerning previous ocular diseases, the presence of diabetes mellitus, and the occurrence of glaucoma in the family. The criteria met by the subjects were the absence of ocular complaints, absence of any history of eye surgery and diabetes, normal body temperature and blood pressure. It has been shown that, because refractive errors influence IOP values5), subjects with refractive errors were not included in the present study. Because it has been shown that IOP is positively related with systemic blood pressure and diabetes6.7), no hypertensive or diabetic subject was included in the study. If the subject has a history of haloes or attacks of blurred vision, his/her data were not included in this study. In recent years it has been noted that intraocular pressure is a dynamic function and is subject to many influences both acutely and over the long term. Many investigators have reported that IOP varies diurnally8. The measurements were taken at a fixed time between 9:00 and 11:00 to minimize the effect of diurnal variations. It has been reported that the drinking of water or coffee before measurement has a significant effect on IOP9). It has been shown that acute hyperglycemia decreases IOP10). Recently, it has been shown that IOP is decreased even. by simple exertion such as walking". For this reason, the intake of any fluid or food was also not allowed, and the subjects were asked not to smoke and have to a complete rest for at least 30 min before the measurement of IOP. Glaucoma patients were excluded on the basis of ophthalmoscopic findings as described by Coulehan et al. 12) Individuals with a normal optic disc but with IOP of 21 mmhg or more in at least one eye were identified as ocular hypertensive. The examination of the eye included the measurement of visual acuity with Snellen letters, tonometry and ophthalmoscopy. To avoid inter examiner and inter tonometer variances, all the IOP measurements were taken by the same ophthalmologist and with a single Goldmann applanation tonometer (Goldmann Topcon, Germany). The status of subjects was masked from the examiner. After installation of 0.25% fluorescein sodium and 0.4% benoxinate hydrochloride (Fluress) eye drops, the IOP was measured first in the right eye and then in the left. The measuring drum was turned until the inner borders of the fluorescein rings (adjusted for equal size) just touched each other at the midpoint of the ocular pulse and the overlap and separation of the mires with each pulse swing was equidistant from the midpoint on both sides. The measuring drum was not to be observed until this defined point was reached. Three consective readings of each eye were taken. After each reading the tonometer was removed from the contact and the measuring scale was returned to 10 mmhg. The practice of returning the tonometer to 10 mmhg after each reading would minimize observer bias. Statistical analyses: The mean of the three readings of IOP was computed separately for each eye. All data are expressed as the mean and standard deviation. The significance of difference between two age groups and between white and blue collar workers of the same age group was calculated by applying the two way analysis of variance (ANOVA). P value less than 0.05 was considered significant. Actual P values are also given. The influence of heart rate, blood pressure, weight, and height on the IOP were examined by multiple linear regression analysis with a Statistical Analysis System (SAS) 7613). Multivariate logistic risk function analysis was used to estimate the strength of potential risk factors for ocular hypertension. Results The distributions of left eye intraocular pressure are shown in Fig. 1. Right eyes were similarly distributed (data not showed). In both groups, the histogram shows a skew to the right, so that the distribution was not Gaussian. In white and blue collar subjects, 72.7% and 83.8% individuals ranged form 11 to 16 mmhg, 19.4% and 8.5% ranged from 17 to 20 mmhg, 2.2% and 5.4% ranged from 7 to 10 mmhg, respectively. The effect of age is shown in Table 1. With age intraocular pressure increased in both eyes in both groups. The average per decade increases were 0.47 mmhg and 0.33 mmhg in white and blue collar subjects, respectively. This study showed that on an average per decade, white collars have 1.1 mmhg (p<0.001) higher IOP than blue collars' subjects. The age effect was statistically insignificant until the age of 40 years in both groups, after which it became quite significant. Similarly right and left

3 Table 1. Aging effect on intraocular pressure of white and blue collar subjects All values are expressed as the mean ±SD. Data for glaucoma patients are not included. Numbers in parentheses indicate the numbers of subjects. Asterisks (*) indicate that values are significantly lower than white collar subjects (* p<0.05 ; ** p<0.001). Daggers (t) indicate that values are significantly higher than in the previous age group (tp<0.05; ttp<0.001). Double daggers (') indicate that values are significantly higher than those for the right eyes in the same age group (* p<0.05). Table 2. Multiple Regression of IOP * on the Various health Parameters in normotensive subiects *Combined intraocular pressure (mmhg) in both eyes. Data for glaucoma and ocular hypertensive subjects are not included. t p<0.05. Fig. Percentage distribution of intraocular pressure. Diagrammatic representation of intraocular pressure distribution in left eyes in white and blue collar workers. The intraocular pressure in the right eye in both groups was similarly distributed. Each symbol corresponds to the identification shown in the upper round frame. The graph clearly shows that, in white collar subjects, the frequency cure is skewed more toward the right than in blue collar subjects. Data for glaucoma subiects are not included. eye difference remained statistically insignificant until the age of 40 years in both groups, after which it became statistically significant. Differences in mean IOP (left minus right) were found to be 0.15 mmhg (p<0.2), and 0.12 mmhg (p<0.05) in white and blue collar subjects, respectively. Because ocular hypertension (IOP>21 mmhg) was found in 5.7% and 2.3% of white and blue collar subjects, respectively, ocular hypertensive subjects were 2.48 times more numerous in white collars than in blue collar subjects. Out of 97 white collar ocular hypertensive subjects, only 21 were known ocular hypertensives, and the remaining were diagnosed by us. Out of 38 blue collar ocular hypertensive subjects, 29 were diagnosed for the first time in this survey. In white collar subjects, 11 of the 17, and in blue collar subjects, 9 of the 14 glaucoma patients were diagnosed before our examination and all of them were under treatment. The remaining subjects were diagnosed for the first time during this study and were referred to an ophthalmologist. No normal tension glaucoma subject was diagnosed during this study. In subjects with normal IOP, multiple correlation coefficients (R2) of IOP with heart rate, systolic and diastolic blood pressures, and weight are shown in Table 2. In these subjects heart rates and systolic blood pressure were only weakly correlated with IOP (p<0.05). In both normal and ocular hypertensive subjects of both groups height was negatively correlated with IOP (R= in all subjects of this study). In all subjects, weight and height were found to be insignificantly correlated with IOP. In all the ocular hypertensive subjects in this study, multivariate logistic risk function analysis showed that heart rate (r = 0.21), systolic blood pressure (r = 0.17), diastolic blood pressure (r=0.14), and age (r= 0.13) are risk factors for ocular hypertension. All these r values are statistically significant at the level of p<0.05, but when controlling for age, the r values for other factors were unaltered, indicating that their effect was not exerted through age to a significant degree.

4 Discussion In both white and blue collar subjects, the distribution of IOP evaluated by this study does not fit a normal bell shaped curve, but skews to the right. This finding is in agreement with other studies on general populations1416). In contrast to this, Leydhecker') reported that IOP had a normal distribution. The skew to the right may be caused by the mixture of the main population of healthy people and a partial population with ocular hypertension. It has been assumed that two different populations account for the skewed distribution. The "normal" population may have a true "normal" Gaussian distribution of IOP with a bell shaped curve. Superimposed on this normal curve is the population with glaucoma suspected or ocular hypertensive, which has high pressure and causes the long tail on the right hand side of the distribution curve. Since the upper end of the normal population and the lower end of the ocular hypertensive population overlap with regard to IOP, the curve is not biphasic, and hence separation of the ocular hypertensive individual from the "high" normal individual is not possible on grounds of pressure alone17). In the present study, ocular hypertension (IOP_21 mmhg) was found in 5.7% white and 2.3% blue collar worker. These subjects are the cause of a skew to the right of their respective distribution curves. The present study supports the suggestions that the upper limit of normal IOP obtained statistically is approximately 20 mmhg and those who registered 20.5 mmhg (M + 2SD) or higher could be regarded as ocular hypertensive. The main finding in the distribution curve is a higher skew to the right side in white collar than in blue collar subjects. The exact reason for this behavior in white collar subjects is not known. Because this type of study has not been done in the past, we can not compare our these results with others. In both groups in this study, IOP increased with age, but the increase remained insignificant until the age of 40, after which increases were significant until 60 (Table 1). The effect of age on the mean applanation pressure reported here is in all respects very similar to those reported by a number of Western population studies" 14, 17) All these studies found that IOP increases with age, especially after the age of 40. In the present study, the prevalence of ocular hypertension shows a tendency to increase with age, but it is worthwhile to point out that in contradiction to these results, in the Japanese population the age dependent decrease in IOP and tendency to ocular hypertension has been consistently observed8' 16, 1s) In all subjects, the average per decade increase was 0.41 mmhg, which is close to the 0.43 mmhg reported by Klein et a1.7) Differences in mean IOP (left minus right) were found to be 0.15 mmhg (p < 0. 2), and 0.12 mmhg (p<0.05) in white and blue collar subjects, respectively. These values are very near to the 0.10 mmhg and 0.12 mmhg reported by Bengtsson19) and Carel et al.20), in general populations, respectively. The data obtained in this study indicate that the mean IOP in the left eye was higher than that in the right after the age of 40 years. This finding is consistent with some studies 11, 20, 21) but in contrast to some other studies22 24). Asher and Spurgeon25) reported that there is a tendency for glaucoma to occur more readily in the left eye than in the right. In both groups, the left eye intraocular pressure was higher than the right, but in the majority of subjects, the intraocular pressure in the left eye was slightly higher, and probably without physiological implications, but in 0.52% and 0.71% of all blue and white collar subjects, intraocular pressure differences between two eyes exceed 3 mmhg, respectively, (higher in the left). In these subjects, therefore, the tendency for glaucoma to occur is higher in the left than in the right eye. The anatomical asymmetry of arterial and venous blood supply to the two eyes might be responsible for this IOP asymmetry since the right carotid artery originates in the innominate artery while the left takes its origin directly from the aortic arch. Arterial pressure could therefore be slightly higher in the left carotid and this could be transmitted to the left ophthalmic artery and thus contribute to a slightly higher IOP reading in the left eye. The right innominate vein is also shorter and straighter, the left one taking a longer and more winding course to reach the superior vena cava, so that a difference in blood pressure and resistance can be expected. In the present study, IOP increased with age in both eyes in both groups, but in Japanese, it decreases in both eyes5' 16, 18) Because of this contrast, it is suspected that some other factors might be equally or more important than age in determining IOP. Due to differences in inherent constitution, diet and environmental conditions, there may be some qualitative differences between the Pakistani and Japanese populations in important systemic and ocular characteristics, with particular reference to blood pressure, body mass index, height, haematocrit, serum glucose, glycohaemoglobin, cholesterol level, and episcleral vein thickness. It is possible that with advancing age, changes in these factors may effect IOP differently in the two races. Unfortunately, until now, no such data have been

5 available to compare these two populations. These characteristics should be taken into account in further research, in the determination of IOP and when comparing IOP in different populations. Among these haemoglobin looks theoretically important, as resistance in the episcleral veins can be increased by rises in blood viscosity. In this regard IOP measurements in polycythaemia and in severe anaemia can also help. Like Carel et a1.26) the results of present study also revealed that in each age group the individuals with higher IOP values are more likely to be those with a higher heart rate and systolic blood pressure. Whatever the mechanism involved in the correlation of ocular hypertensive with heart rate, systolic and diastolic blood pressures, and age, it should be stressed that their contributions are statistically significant but quantitatively small. Other factors must therefore be responsible for ocular hypertension. Compared to other studies, R values obtained in the present study are very small. The most important risk factors for glaucoma and ocular hypertension are systemic hypertension 4, 27) and diabetes4' 28). It is very important to note that in this study, all major IOP affecting factors were controlled, and all subjects were apparently healthy and without hypertension or diabetes (diabetics were excluded from the last medical checkup record of our subjects). These therefore weakly correlated risk factors are within certain limitations. The main findings of present study can be summarized as : (i) As an average per decade, white collars have 1.1 ±0.04 mmhg (p<0.001) higher IOP than blue collars subjects. (ii) A significantly lower incidence of ocular hypertension in blue collar subjects than in white collar subjects. (iii) Similarly, the prevalence of glaucoma was also slightly low in the blue collar subjects. We do not yet know the exact reasons of these differences between the two groups. What one can expect is a difference in physical fitness between the two groups. It is generally believed that blue collar workers are physically more fit than white collar workers. We have recently shown that physical fitness through regular exercise can reduce the resting intraocular pressure29' 30) In the subjects of the present study we did not measure physical fitness, and are therefore not sure whether or not physical fitness was the cause of these differences. One alternate possibility may be the difference in plasma lipids. It had been shown that an increase in physical fitness through regular exercise can decrease plasma lipids, and that is why exercise has been recommended to decease the risk of cardiac ischemic disease 31). The lower lipid levels may be associated with lower IOP, and hence with a lower incidence of ocular hypertension. At the present time, along with several other factors, we are investigating the relationship among IOP, physical fitness and plasma lipids in blue and white collar workers. It has been recommended that ocular hypertensive subjects should remain under the observation of an ophthalmologist'' 32). Before their present examination, most of the ocular hypertensive subjects of present study were not aware of their higher intraocular pressure. This study strongly suggests that in routine health examination, tonometry should be included. Acknowledgments: This study was supported by "smile" -Spreading Medical Information for better Life through Electronic media. The authors gratefully acknowledge Prof. Dr. Ahmad Kamal Ansari, Prof. Dr. Mohammad Nawaz, Miss Kauser Tasneem, Dr. Noor-ul-Huda Ansari and Dr. Nusrat Pasha for their technical help and suggestions. References 1) Leydhecker W. The intraocular pressure and clinical aspects. Ann Ophthalmol 1976; 8: ) Bengtsson B. The prevalence of glaucoma. Br J Ophthalmol 1981; 65: ) Leske MC. The epidemiology of open-angle glaucoma : a review. Am J Epidemiol 1983; 118: ) Morgan RW, Drance SM. Choronic open-angle glaucoma and ocular hypertensive : An epidemiological study. Br J Ophthalmol 1975; 59: ) Shiose Y. Intraocular pressure : new perspectives. Surv Ophthalmol 1990; 34: ) Williams BI, Peart WS, Letley E. Abnormal intraocular pressure control in systemic hypertension and diabetes mellitus. Br J Ophthalmol 1980; 64: ) Klein BE, Kein R, Linton KL. Intraocular pressure in an American community : The Beaver Dam Eye Study. Invest Ophthalmol Vis Sci 1992; 33: ) Wilensky JT, Gieser DK, Dietsche ML, Mori MT, Zeimer R. Individual variability in the diurnal intraocular pressure curve. Ophthalmol 1993; 100: ) Buckingham T, Young R. The rise and fall of intraocular pressure : the influence of physiological factors. Ophthalmic Physiological Optics 1986; 6 : ) Poinoosawmy D, Winder AF. Ocular effect of acute hyperglycaemia. Br J Ophthalmol 1984; 68: ) Qureshi IA. The effects of mild, moderate, and severe exercise on intraocular pressure in glaucoma patients. Jpn J Physiol 1995; 45: ) Coulehan JL, Helzlsouer KJ, Rogers KD, Brown SI.

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