Clinical Need: Condition and Target Population
There are two main types of glaucoma, primary open angle (POAG) and angle closure glaucoma, of which POAG is the more common type. POAG is diagnosed by assessing degenerative changes in the optic disc and loss of visual field (VF). Risk factors for glaucoma include an increase in intraocular pressure (IOP), a family history of glaucoma, older age and being of African descent. The prevalence of POAG ranges from 1.1% to 3.0% in Western populations and from 4.2% to 8.8% in populations of African descent.
Usually the IOP associated with POAG is elevated above the normal distribution (10-20 mmHg), but when IOP is not elevated it is often referred to as normal-tension glaucoma (NTG). In population based studies, approximately one-third to half of the patients with glaucomatous VF loss have normal IOP on initial examination.
People with elevated IOP (>21 mmHg), but with no evidence of optic disc or VF damage have ocular hypertension. It has been estimated that 3 to 6 million people in the United States including 4% to 7% of those older than 40 years have elevated IOP without detectable glaucomatous damage on standard clinical tests. An Italian study found the overall prevalence of ocular hypertension, POAG, and NTG in 4,297 people over 40 years of age to be 2.1%, 1.4% and 0.6% respectively.
Diurnal Curves for Intraocular Pressure Measurement
In normal individuals, IOP fluctuates 2 to 6 mmHg over a 24 hour period. IOP is influenced by body position with higher readings found in the supine relative to the upright position. As most individuals sleep in the supine position and are upright during the day, IOP is higher on average in people, both with and without glaucoma, in the nocturnal period. IOP is generally higher in the morning compared to the afternoon.
Multiple IOP measurements over the course of a day can be used to generate a diurnal curve and may have clinical importance in terms of diagnosis and management of patients with IOP related conditions since a solitary reading in the office may not reveal the peak IOP and fluctuation that a patient experiences. Furthermore, because of diurnal and nocturnal variation in IOP, 24-hour monitoring may reveal higher peaks and wider fluctuations than those found during office-hours and may better determine risk of glaucoma progression than single or office-hour diurnal curve measurements.
There is discrepancy in the literature regarding which parameter of IOP measurement (e.g., mean IOP or fluctuation/range of IOP) is most important as an independent risk factor for progression or development of glaucoma. The potential for increased rates or likelihood of worsening glaucoma among those with larger IOP swings within defined time periods has received increasing attention in the literature.
According to an expert consultant:
The role of a diurnal tension curves is to assess IOP in relationship to either a risk factor for the development or progression of glaucoma or achievement of a target pressure which may direct a therapeutic change.
Candidates for a diurnal curve are usually limited to glaucoma suspects (based on optic disc changes or less commonly visual field changes) to assess the risk for development of glaucoma or in patients with progressive glaucoma despite normal single office IOP measurements.
Clinically diurnal tension curves are used to determine the peak IOP and range.
Single IOP Measurements
Intraocular pressure fluctuation as a risk factor for progression of glaucoma has also been examined without the use of diurnal curves. In these cases, single IOP measurements were made every 3-6 months over several months/years. The standard deviation (SD) of the mean IOP was used as a surrogate for fluctuation since no diurnal tension curves were obtained.
To determine whether the use of a diurnal tension curve (multiple IOP measurements over a minimum 8 hour duration) is more effective than not using a diurnal tension curve (single IOP measurements) to assess IOP fluctuation as a risk factor for the development or progression of glaucoma.
To determine whether the use of a diurnal tension curve is beneficial for glaucoma suspects or patients with progressive glaucoma despite normal single office IOP measurements and leads to a more effective disease management strategy.
A literature search was performed on July 22, 2010 using OVID MEDLINE, MEDLINE In-Process and Other Non-Indexed Citations, EMBASE, the Cumulative Index to Nursing & Allied Health Literature (CINAHL), the Cochrane Library, and the International Agency for Health Technology Assessment (INAHTA) for studies published from January 1, 2006 until July 14, 2010. Abstracts were reviewed by a single reviewer and, for those studies meeting the eligibility criteria, full-text articles were obtained. Reference lists were also examined for any additional relevant studies not identified through the search. Articles with unknown eligibility were reviewed with a second clinical epidemiologist, then a group of epidemiologists until consensus was established. The quality of evidence was assessed as high, moderate, low or very low according to GRADE methodology.
Open angle glaucoma (established or OHT high risk) in an adult population
IOP measurement by Goldmann applanation tonometry (the gold standard)
Number and timing of IOP measurements explicitly reported (e.g., 5 measurements a day for 5 visits to generate a diurnal curve or 1 measurement a day [no diurnal curve] every 3 months for 2 years)
IOP parameters include fluctuation (range [peak minus trough] or standard deviation) and mean
Outcome measure = progression or development of glaucoma
Study reports results for ≥ 20 eyes
Most recent publication if there are multiple publications based on the same study
Angle closure glaucoma or pediatric glaucoma
IOP measured by a technique other than GAT (the gold standard)
Number and timing of IOP measurements not explicitly reported
Outcomes of Interest
Progression or development of glaucoma
There is very low quality evidence (retrospective studies, patients on different treatments) for the use of a diurnal tension curve or single measurements to assess short or long-term IOP fluctuation or mean as a risk factor for the development or progression of glaucoma.
There is very low quality evidence (expert opinion) whether the use of a diurnal tension curve is beneficial for glaucoma suspects or patients with progressive glaucoma, despite normal single office IOP measurements, and leads to a more effective disease management strategy.