CAFFEINE AND IOP

Ophthalmologists may want to advise glaucoma patients to reduce their intake of caffeine. A recent study suggests that the greater the intake of caffeine, the more intraocular pressure increases, reported Damrong Wiwatwongwana MD at the 5th World Glaucoma Congress. Caffeine is known to produce a number of physiologic changes, including temporary increases in blood pressure and increased heart rate. It is a vasoconstrictor, and can affect muscle contractility. In the eye, animal studies show it can increase aqueous production, plus can reduce aqueous drainage by causing the fenestrae at the chamber angle to narrow, according to Dr Wiwatwongwana, Department of Ophthalmology at Chiang Mai University, Thailand.

The evidence in the scientific literature about the effects of caffeine on IOP is conflicting. Importantly, there were no studies investigating possible dose-effects of caffeine on IOP. To address this, Dr Damrong Wiwatwongwana and colleagues conducted a study comparing the effects of different levels of caffeine on the IOP of healthy, nonglaucomatous volunteers in a double-blinded, randomised, controlled trial. A total of 63 healthy young adults, half of who were female, were randomly assigned to one of three coffee-drinking groups, with 21 subjects in each. People with a baseline IOP of 21mmgHg or higher were excluded. Subjects were asked to avoid beverages that contained caffeine for three days before the study.

IOP was measured prior to coffee consumption, and again 30, 60 and 90 minutes after drinking coffee. Central corneal thickness (CCT) was also measured. Each subject was given 360ml of coffee, with the caffeine levels being 2.0mg of caffeine in the decaffeinated group; 170mg in the second group, and 340mg in the third.Baseline IOP was an average of 13.25 mmHg across the groups. Thirty minutes after caffeine consumption, there was no significant change in IOP in any of the groups. At 60 minutes, IOP had increased to an average of 14.6 mmHg in the 340mg group, 13.6 mmHg in the 170mg groups and 13.4 mmHg in the 170mg group. The change in the high dose caffeine group was statistically significant.

By 90 minutes after consuming caffeine, IOP in the 340mg group increased to an average of 15.19mmHg, a significant change Dr Wiwatwongwana said. Those in the 170mg caffeine and control groups had an average IOP of about 13.7 mmHg at 90 minutes. This level of an effect of higher levels of caffeine consumption over a short period of time could have clinical implications for both screening and monitoring of glaucoma patients, he said. Whether this effect is magnified in glaucoma patients needs further study.

Caffeine appears in a number of products including coffee, tea, cola beverages and chocolate. A regular cup of coffee of 236ml typically contains 135 to 150mg of caffeine. A single shot of espresso typically contains 106mg of caffeine. A 16 ounce or grande cup of brewed coffee usually contains the same as three espresso shots. “Patients who are heavy coffee drinkers should be advised to reduce their consumption,” he said.