Systemic, circadian factors challenge IOP control measures

Key Points

Durham, NC-Fluctuations in IOP may be influenced by several systemic and circadian factors that can make it challenging to achieve consistent control of pressure.

"Little is known and less might be true on this topic," said Sanjay Asrani, MD, associate professor of ophthalmology, Duke Eye Center, Duke University, Durham, NC.

Circadian IOP fluctuations, for example, occur in both normal and glaucomatous eyes. Much remains unknown, however, because no non-invasive method is available to measure IOP continuously in the patient's day-to-day environment, acccording to Dr. Asrani.

Risk factors

He cited a recent paper on open-angle glaucoma that found only two risk factors-increased IOP and increased diurnal IOP fluctuations, to be significant in the prevalence, incidence, and progression of glaucoma.¹ The study examined numerous other factors, including age, sex, family history, signs of damage, systemic disease, medications, and personal behaviors such as smoking and exercise.

Although the need for IOP control is clear, what remains unclear is which component of the pressure merits the most attention. It has long been known, for example, that the range of IOP fluctuations is larger in glaucomatous eyes than normal eyes.^2-3-4 The range includes ultra short-term fluctuations that occur in minutes, such as those associated with the Valsalva maneuver; short-term fluctuations that occur over hours or a few days; and long-term fluctuations that occur over months or years.

Dr. Asrani and his colleagues studied daytime short-term fluctuations using a home tonometer. The rate of visual field loss was found to be slower for those eyes with a smaller home IOP range.

"Large, short-term IOP fluctuations over a few days were found to be an independent risk factor for visual field progression," he said.

The Advanced Glaucoma Intervention Study (AGIS) and the Collaborative Initial Glaucoma Treatment Study (CIGTS) were re-analyzed recently regarding long-term variation of IOP. The Early Manifest Glaucoma Trial (EMGT) and the European Glaucoma Prevention Study (EGPS) were re-analyzed for variation of IOP and glaucoma progression and variation of IOP in glaucoma development, respectively.

"In the AGIS analysis, long-term IOP variation was found to be related to visual field progression despite taking into account the number of glaucoma interventions, while no relationship was found between mean IOP and visual field progression," Dr. Asrani said. "In the CIGT study as well, visual field loss over 5 years was found to be strongly associated with increased IOP variation."

In the EMGT, however, inter-visit IOP variation was not related to glaucoma progression, and in EGPS, inter-visit IOP variation was not found to be related to the risk of glaucoma developing in untreated subjects. This finding could be due to the fact that, at the very early stages of glaucoma, it may take a much longer time than 5 years to see an effect of IOP variation, he said.

For ophthalmologists who wish to detect the range of IOP fluctuation in patients, Dr Asrani suggested the following strategies: