E f f e c t s of C a f f e i n a t e d
C o f f e e on I n t r a o c u l a r
Pressure
Patricia H. Okimi, Susan Sportsman, Myrna R. Pickard, and Michael B. Fritsche
This study examined the effects of caffeinated coffee on the intraocular pressure of nonglaucomatous subjects. Subjects were randomly assigned to receive each of three treatments: caffeinated coffee, hot water, and no fluid. All subjects were given the three treatment conditions over 3 days. The study revealed that intraocular pressure after ingesting caffeinated coffee was significantly higher than after receiving the other two treatment conditions. It was further found that increased intraocular pressure was maintained at significant levels over a 3-hour period. No significant changes were found in the pulse rate, and findings on blood pressure were inconclusive. Copyright © 1991 by W.B. Saunders Company
LAUCOMA IS THE nation's leading cause of irreversible blindness, a condition due to optic nerve damage resulting from increased intraocular pressure (lOP) beyond an individual's tolerance level. Physiologically, the most common type of glaucoma is a disorder characterized by its singular lack of overt symptoms. Early diagnosis and prevention of complications through a skilled treatment regime and health teaching have been effective in preventing blindness. There are many types of glaucoma, and although the specific cause remains unknown, the major characteristic of the disease is the increase in lOP. Normally the aqueous humor is produced by the ciliary body, circulates behind the iris through the pupil into the anterior chamber, and drains through a network Of tissue. Any blockage in this system prevents the normal outflow of fluid and causes pressure to build within the eye. Blindness
G
From the School of Nursing, The University of Texas at Arlington, Arlington, TX; the Tarrant County Psychiatric Center, Fort Worth, TX; andAcademic Computing Sere'ices, Southern Methodist University, Dallas, TX. Patricia H. Okimi, PhD, RN: Associate Professor, School of Nursing. The University of Texas at Arlington, Arlington, TX; Susan Sportsman, PhD, RN: Director, Tarrant County Psychiatric Center, Fort Worth, I"X; Myrna R. Pickard, EdD, RN: Dean and Professor, School of Nursing. The University of Texas at Arlington, Arlington, TX; Michael B. Fritsche, MS: Analyst Programmer H, Academic Computing Services, Southern Methodist University, Dallas. TX. Address reprint requests to Patricia H. Okimi, PhD, RN, Associate Professor, School of Nursing, The University of Texas at Arlington. Box 19407, Arlington, TX 76019. Copyright © 1991 by W.B. Saunders Company 0897-189719110402-000855.00/0
72
occurs as a result of damage to the optic nerve when the IOP is increased and sustained l~eyond an individual's tolerance level. Many long-term and short-term factors have been identified as being influential in the increase or decrease of lOP. Long-term influences include heredity, age (lOP higher after age 40), sex (females after menopause onset), ethnic background (higher incidence among blacks), and refractive error (higher incidence among myopes). Shortterm influences include postural variations, lid and eye movements, hormonal influence, certain intraocular conditions, and certain foods and drugs (Shields, 1987). Among these foods and drugs, caffeine as an ingredient in coffee is of particular interest, as so many Americans consume this popular beverage. In the United States, regular coffee is the single most important source of caffeine (Graham, 1978; Rail, 1980). Eight out of ten Americans drink coffee, with an average daily consumption equaling 3V2 cups (Raebel & Black, 1984). Thus, the question arises of whether drinking caffeinated beverages increases the likelihood of damage to the optic nerve in glaucoma patients. Peczon and Grant (1964) did an extensive review of early studies of certain drugs and their effects on lOP. They also reported their original observations on the influence of the following drugs on lOP: pentobarbital, diphenylhydantoin, primidone, methylphenylethyl hydantoin, and dextro amphetamine. The results of their study were consistent with the findings they reviewed, suggesting little evidence of consistent relationship between certain sedatives, stimulants, tranquilizApplied Nursing Research, Vol. 4, No. 2 (May), 1991: pp. 72-76
CAFFEINATED COFFEE AND INTRAOCULAR PRESSURE
ers, and anticonvulsants and IOP. In ordinary doses, these drugs had little orno influence on IOP in adult glaucomatous patients. In specific reference to caffeine, Peczon and Grant (1964) refer to the literature thoroughly examined and summarized by Leydhecker (1960). It appears that a single dose of 200 mg to 400 mg of caffeine (the average amount of caffeine found in one to two cups of coffee) can cause a transient rise of several millimeters Hg in IOP of both normal and glaucomatous patients. Repetitious administration of caffeine in the dosage involved in customary coffee drinking has not been demonstrated to maintain a significant sustained elevation of lOP. In the late 1960s and early 1970s, studies of caffeine and its effect on IOP were reported primarily in foreign literature (Gen6e, 1972; Graeber, 1968; Makabe, 1970; Ricklefs, 1968; Ricklefs & Pohls, 1969). Ricklefs (1968) found that two cups of caffeinated coffee, two cups of caffeine-free substitutes with the same taste, or two cups of tea did not raise the lOP of normal eyes or normalized glaucomatous eyes. In a further study, Ricklefs and Pohls (1969) investigated the effects of caffeine tablets and Coca-Cola (Coca Cola Company, Atlanta, GA) on the IOP of patients with regulated lOP. The IOP did not significantly increase after the administration of caffeine and Coca-Cola. Gen6e (1972) concluded that it was the increase of fluid rather than caffeine that caused an increase in lOP. Graeber (1968) found that eyes with regulated simple glaucoma reacted with an increase in lOP of more than 5 mm to 6 mm Hg in particular cases. He reported that previous therapy was significant; specifically, if the initial lOP is well within the normal range, the amount of caffeine in one to two cups of coffee did not appear to lead to a pathologic increase in IOP. In the presence of an elevated initial IOP, however, ingestion of caffeine may cause the tension rise into pathologic ranges. Graeber's study supported the earlier findings of Leydhecker (1960) that caffeine produces a transient increase in lOP. A later study by Makabe (I 970) also supported the relationship between caffeine intake and a transient increase in lOP. While the physiologic effects of caffeine on the cardiovascular and other body systems continue to be studied (McGowan, Devoe, Searle, & Altman, 1987; Passmore, Kondowe, & Johnston, 1987; Sarma, Leaf, & Bahl, 1989; Schneider, 1987; Tarnopolsky, Atkinson, MacDougall, Sale, & Sutton,
73
1989), only one recent study addresses the ocular system (Higginbotham, Kilimanjaro, Wilensky, Batenhorst, & Hermann, 1989). The investigators examined the effect of drinking regular coffee on lOP using a single-masked, randomized crossover design comparing coffee and herbal tea in 13 glaucomatous patients. They found a statistically significant difference in the change in lOP at 90 minutes when comparing coffee with herbal tea, but no significant difference at 30 and 60 minutes. HOWever, the investigators concluded that although there was a statistically significant difference in lOP at 90 minutes between coffee and tea drinkers, the change was not clinically significant. Thus, findings of the effects of caffeine on lOP are varied. The purpose of this study was to determine the effects of repeated ingestion of caffeinated coffee on the IOP immediately after ingestion and at regular intervals thereafter. This study was the first phase of a larger research project and was designed to provide data on subjects under 50 years of age with normal lOP. A further phase of the study is planned to investigate the effects of caffeinated coffee on subjects over 50 years of age with normal lOP, and a final phase will study the effects of caffeinated coffee on the lOP of subjects with glaucoma. METHOD
The study used a repeated measures, singlemasked, triple crossover research design. Treatment conditions were randomly assigned, and all subjects participated in all three treatment conditions. Instrument
A profile form was used to gather demographic data of subjects and pertinent information on health history and health practices. Blood pressure was taken using a stethoscope and a Tycos sphygmomanometer (Welch Allyn Company, Skaneateles Falls, NY). Pulse rates were monitored at the wrist using the second hand of a watch to measure time. A noncontact tonometer was used to measure lOP. According to Shields (1987), most stu~lies have indicated that noncontact tonometers, when compared against the Goldmann applanation tonometers, are reliable within the normal lOP range. Reliability is reduce'd in the higher pressure ranges and is limited by an abnormal cornea or
OKIMI ET AL
74
poor fixation. A significant advantage of the noncontact tonometer is the elimination of potential hazards associated with contact tonometers, including abrasion of the cornea, reactions to topical anesthetics, and spread of infection. Also, the instrument is advantageous in that it can be used reliably by paramedical personnel. For greater accuracy in the readings, it is recommended that a minimum of three readings within 3 mm Hg be taken and averaged as the IOP (Shields, 1987).
Subjects A total of 12 subjects comprised the sample for this study. All subjects were nursing students enrolled in a baccalaureate program who volunteered to participate in this project. A profile of the subjects showed that the majority were Caucasian (n = 9, 75%), married (n = 7, 58%), female (n = 9, 75%), and between the ages of 20 and 29 years (n = 9, 75%). Before involvement in tile study, participants were screened by a glaucoma specialist for elevation of IOP and any indications of glaucoma and/or other ocular disorders.
Procedure Blood pressure, pulse, and IOP were measured to .provide baseline data; subjects were then randomly assigned to ingest (a) four 8-oz cups of hot, black coffee, (b) four 8-oz cups of hot water, or (e) to ingest no fluid during the next hour. Hot water was used in this study to control for the possibility that any rise in lOP could be attributed to fluid intake rather than caffeine ingestion. Blood pressure, pulse, and IOP were measured hourly for 3 hours after the treatment conditions. The same procedure was followed on the following two mornings until all subjects had been assigned randomly to receive each of the three treatment conditions once: coffee, hot water, and no fluid. For the duration of the data collection period, coffee preparation was kept consistent as to brand, type, strength, amount, and equipment used. lOP was measured three times in each eye at each checking, and mean pressures were used for data analysis. The same individual measured all IOPs. During the 3-hour data collection period, subjects refrained from smoking, eating, and drinking anything other than the liquids administered for the study. Subjects studied, read, or quietly talked among themselves between measurements. All subjects refrained from ingesting caffeinated prod-
ucts (caffeinated soft drinks, tea, coffee, and chocolate), except for the coffee used in the study from midnight before the first day of data collection until the end of the entire data collection period 3 days later. All data were collected at the same time in the morning for the 3 days.
RESULTS The majority of subjects (n = 7, 58%) considered themselves to be in good to excellent health and had moderate stress in their lives (n = 8, 67%). While 50% (n = 6) of the subjects reported an exercise program of once or twice weekly, 42% (n = 5) reported no exercise on a regular basis. One subject reported exercising five to six times a week. Table 1 summarizes the subjects' patterns of daily caffeine consumption. The majority of the subjects consumed two or less caffeinated products in each of the categories of soft drinks, coffee/tea, chocolate drinks, and chocolate candy. Ten of the subjects stated they had never smoked on a regular basis. Two subjects had stopped smoking: one less than 5 years ago and the other between 5 and 10 years ago. Two subjects described themselves as drinking alcoholic beverages one to two times a week, while the other 10 stated they drank alcoholic beverages only on rare occasions. Ricklefs (1968) reports that alcoholic drinks lowered the pressure in 60% of all healthy or normalized glaucomatous eyes. None of the subjects had glaucoma in the family history, although one individual who was adopted could not be certain. Birth control pills and vitamins were the medications most frequently used on a regular basis. The mean lOP of the subjects after consumption of caffeinated coffee was significantly higher (p
C o f f e e on I n t r a o c u l a r
Pressure
Patricia H. Okimi, Susan Sportsman, Myrna R. Pickard, and Michael B. Fritsche
This study examined the effects of caffeinated coffee on the intraocular pressure of nonglaucomatous subjects. Subjects were randomly assigned to receive each of three treatments: caffeinated coffee, hot water, and no fluid. All subjects were given the three treatment conditions over 3 days. The study revealed that intraocular pressure after ingesting caffeinated coffee was significantly higher than after receiving the other two treatment conditions. It was further found that increased intraocular pressure was maintained at significant levels over a 3-hour period. No significant changes were found in the pulse rate, and findings on blood pressure were inconclusive. Copyright © 1991 by W.B. Saunders Company
LAUCOMA IS THE nation's leading cause of irreversible blindness, a condition due to optic nerve damage resulting from increased intraocular pressure (lOP) beyond an individual's tolerance level. Physiologically, the most common type of glaucoma is a disorder characterized by its singular lack of overt symptoms. Early diagnosis and prevention of complications through a skilled treatment regime and health teaching have been effective in preventing blindness. There are many types of glaucoma, and although the specific cause remains unknown, the major characteristic of the disease is the increase in lOP. Normally the aqueous humor is produced by the ciliary body, circulates behind the iris through the pupil into the anterior chamber, and drains through a network Of tissue. Any blockage in this system prevents the normal outflow of fluid and causes pressure to build within the eye. Blindness
G
From the School of Nursing, The University of Texas at Arlington, Arlington, TX; the Tarrant County Psychiatric Center, Fort Worth, TX; andAcademic Computing Sere'ices, Southern Methodist University, Dallas, TX. Patricia H. Okimi, PhD, RN: Associate Professor, School of Nursing. The University of Texas at Arlington, Arlington, TX; Susan Sportsman, PhD, RN: Director, Tarrant County Psychiatric Center, Fort Worth, I"X; Myrna R. Pickard, EdD, RN: Dean and Professor, School of Nursing. The University of Texas at Arlington, Arlington, TX; Michael B. Fritsche, MS: Analyst Programmer H, Academic Computing Services, Southern Methodist University, Dallas. TX. Address reprint requests to Patricia H. Okimi, PhD, RN, Associate Professor, School of Nursing, The University of Texas at Arlington. Box 19407, Arlington, TX 76019. Copyright © 1991 by W.B. Saunders Company 0897-189719110402-000855.00/0
72
occurs as a result of damage to the optic nerve when the IOP is increased and sustained l~eyond an individual's tolerance level. Many long-term and short-term factors have been identified as being influential in the increase or decrease of lOP. Long-term influences include heredity, age (lOP higher after age 40), sex (females after menopause onset), ethnic background (higher incidence among blacks), and refractive error (higher incidence among myopes). Shortterm influences include postural variations, lid and eye movements, hormonal influence, certain intraocular conditions, and certain foods and drugs (Shields, 1987). Among these foods and drugs, caffeine as an ingredient in coffee is of particular interest, as so many Americans consume this popular beverage. In the United States, regular coffee is the single most important source of caffeine (Graham, 1978; Rail, 1980). Eight out of ten Americans drink coffee, with an average daily consumption equaling 3V2 cups (Raebel & Black, 1984). Thus, the question arises of whether drinking caffeinated beverages increases the likelihood of damage to the optic nerve in glaucoma patients. Peczon and Grant (1964) did an extensive review of early studies of certain drugs and their effects on lOP. They also reported their original observations on the influence of the following drugs on lOP: pentobarbital, diphenylhydantoin, primidone, methylphenylethyl hydantoin, and dextro amphetamine. The results of their study were consistent with the findings they reviewed, suggesting little evidence of consistent relationship between certain sedatives, stimulants, tranquilizApplied Nursing Research, Vol. 4, No. 2 (May), 1991: pp. 72-76
CAFFEINATED COFFEE AND INTRAOCULAR PRESSURE
ers, and anticonvulsants and IOP. In ordinary doses, these drugs had little orno influence on IOP in adult glaucomatous patients. In specific reference to caffeine, Peczon and Grant (1964) refer to the literature thoroughly examined and summarized by Leydhecker (1960). It appears that a single dose of 200 mg to 400 mg of caffeine (the average amount of caffeine found in one to two cups of coffee) can cause a transient rise of several millimeters Hg in IOP of both normal and glaucomatous patients. Repetitious administration of caffeine in the dosage involved in customary coffee drinking has not been demonstrated to maintain a significant sustained elevation of lOP. In the late 1960s and early 1970s, studies of caffeine and its effect on IOP were reported primarily in foreign literature (Gen6e, 1972; Graeber, 1968; Makabe, 1970; Ricklefs, 1968; Ricklefs & Pohls, 1969). Ricklefs (1968) found that two cups of caffeinated coffee, two cups of caffeine-free substitutes with the same taste, or two cups of tea did not raise the lOP of normal eyes or normalized glaucomatous eyes. In a further study, Ricklefs and Pohls (1969) investigated the effects of caffeine tablets and Coca-Cola (Coca Cola Company, Atlanta, GA) on the IOP of patients with regulated lOP. The IOP did not significantly increase after the administration of caffeine and Coca-Cola. Gen6e (1972) concluded that it was the increase of fluid rather than caffeine that caused an increase in lOP. Graeber (1968) found that eyes with regulated simple glaucoma reacted with an increase in lOP of more than 5 mm to 6 mm Hg in particular cases. He reported that previous therapy was significant; specifically, if the initial lOP is well within the normal range, the amount of caffeine in one to two cups of coffee did not appear to lead to a pathologic increase in IOP. In the presence of an elevated initial IOP, however, ingestion of caffeine may cause the tension rise into pathologic ranges. Graeber's study supported the earlier findings of Leydhecker (1960) that caffeine produces a transient increase in lOP. A later study by Makabe (I 970) also supported the relationship between caffeine intake and a transient increase in lOP. While the physiologic effects of caffeine on the cardiovascular and other body systems continue to be studied (McGowan, Devoe, Searle, & Altman, 1987; Passmore, Kondowe, & Johnston, 1987; Sarma, Leaf, & Bahl, 1989; Schneider, 1987; Tarnopolsky, Atkinson, MacDougall, Sale, & Sutton,
73
1989), only one recent study addresses the ocular system (Higginbotham, Kilimanjaro, Wilensky, Batenhorst, & Hermann, 1989). The investigators examined the effect of drinking regular coffee on lOP using a single-masked, randomized crossover design comparing coffee and herbal tea in 13 glaucomatous patients. They found a statistically significant difference in the change in lOP at 90 minutes when comparing coffee with herbal tea, but no significant difference at 30 and 60 minutes. HOWever, the investigators concluded that although there was a statistically significant difference in lOP at 90 minutes between coffee and tea drinkers, the change was not clinically significant. Thus, findings of the effects of caffeine on lOP are varied. The purpose of this study was to determine the effects of repeated ingestion of caffeinated coffee on the IOP immediately after ingestion and at regular intervals thereafter. This study was the first phase of a larger research project and was designed to provide data on subjects under 50 years of age with normal lOP. A further phase of the study is planned to investigate the effects of caffeinated coffee on subjects over 50 years of age with normal lOP, and a final phase will study the effects of caffeinated coffee on the lOP of subjects with glaucoma. METHOD
The study used a repeated measures, singlemasked, triple crossover research design. Treatment conditions were randomly assigned, and all subjects participated in all three treatment conditions. Instrument
A profile form was used to gather demographic data of subjects and pertinent information on health history and health practices. Blood pressure was taken using a stethoscope and a Tycos sphygmomanometer (Welch Allyn Company, Skaneateles Falls, NY). Pulse rates were monitored at the wrist using the second hand of a watch to measure time. A noncontact tonometer was used to measure lOP. According to Shields (1987), most stu~lies have indicated that noncontact tonometers, when compared against the Goldmann applanation tonometers, are reliable within the normal lOP range. Reliability is reduce'd in the higher pressure ranges and is limited by an abnormal cornea or
OKIMI ET AL
74
poor fixation. A significant advantage of the noncontact tonometer is the elimination of potential hazards associated with contact tonometers, including abrasion of the cornea, reactions to topical anesthetics, and spread of infection. Also, the instrument is advantageous in that it can be used reliably by paramedical personnel. For greater accuracy in the readings, it is recommended that a minimum of three readings within 3 mm Hg be taken and averaged as the IOP (Shields, 1987).
Subjects A total of 12 subjects comprised the sample for this study. All subjects were nursing students enrolled in a baccalaureate program who volunteered to participate in this project. A profile of the subjects showed that the majority were Caucasian (n = 9, 75%), married (n = 7, 58%), female (n = 9, 75%), and between the ages of 20 and 29 years (n = 9, 75%). Before involvement in tile study, participants were screened by a glaucoma specialist for elevation of IOP and any indications of glaucoma and/or other ocular disorders.
Procedure Blood pressure, pulse, and IOP were measured to .provide baseline data; subjects were then randomly assigned to ingest (a) four 8-oz cups of hot, black coffee, (b) four 8-oz cups of hot water, or (e) to ingest no fluid during the next hour. Hot water was used in this study to control for the possibility that any rise in lOP could be attributed to fluid intake rather than caffeine ingestion. Blood pressure, pulse, and IOP were measured hourly for 3 hours after the treatment conditions. The same procedure was followed on the following two mornings until all subjects had been assigned randomly to receive each of the three treatment conditions once: coffee, hot water, and no fluid. For the duration of the data collection period, coffee preparation was kept consistent as to brand, type, strength, amount, and equipment used. lOP was measured three times in each eye at each checking, and mean pressures were used for data analysis. The same individual measured all IOPs. During the 3-hour data collection period, subjects refrained from smoking, eating, and drinking anything other than the liquids administered for the study. Subjects studied, read, or quietly talked among themselves between measurements. All subjects refrained from ingesting caffeinated prod-
ucts (caffeinated soft drinks, tea, coffee, and chocolate), except for the coffee used in the study from midnight before the first day of data collection until the end of the entire data collection period 3 days later. All data were collected at the same time in the morning for the 3 days.
RESULTS The majority of subjects (n = 7, 58%) considered themselves to be in good to excellent health and had moderate stress in their lives (n = 8, 67%). While 50% (n = 6) of the subjects reported an exercise program of once or twice weekly, 42% (n = 5) reported no exercise on a regular basis. One subject reported exercising five to six times a week. Table 1 summarizes the subjects' patterns of daily caffeine consumption. The majority of the subjects consumed two or less caffeinated products in each of the categories of soft drinks, coffee/tea, chocolate drinks, and chocolate candy. Ten of the subjects stated they had never smoked on a regular basis. Two subjects had stopped smoking: one less than 5 years ago and the other between 5 and 10 years ago. Two subjects described themselves as drinking alcoholic beverages one to two times a week, while the other 10 stated they drank alcoholic beverages only on rare occasions. Ricklefs (1968) reports that alcoholic drinks lowered the pressure in 60% of all healthy or normalized glaucomatous eyes. None of the subjects had glaucoma in the family history, although one individual who was adopted could not be certain. Birth control pills and vitamins were the medications most frequently used on a regular basis. The mean lOP of the subjects after consumption of caffeinated coffee was significantly higher (p
