Methodological quality of the review: Low confidence
Author: Health Quality Ontario
Geographical coverage: Not reported
Sub-sector: Progression of glaucoma
Equity focus: None specified
Review type: Effectiveness review
Quantitative synthesis method: Narrative synthesis
Qualitative synthesis method: Not applicable
Background: In normal individuals, intra-ocular pressure (IOP) fluctuates between 2 to 6 mm Hg 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. This may have clinical importance in terms of the diagnosis and management of patients with IOP-related conditions since a solitary reading during office hours 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 the 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 the 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.
Main findings: No studies were identified that met the inclusion criteria and directly compared diurnal or 24-hour IOP curves to single measurements. Therefore, no evidence was found to determine which measurement method is more effective for assessing the risk of development or progression of glaucoma.
Seven non-comparative studies examining IOP parameters as a risk factor for glaucoma progression met the inclusion criteria. Five studies were retrospective sub-set analyses from randomised controlled trials (RCTs) that were designed to compare drugs and/or surgical techniques for the treatment of ocular hypertension or established glaucoma. The other two studies were observational in design.
The methodology used for these studies, using diurnal or 24-hour or serial single IOP measurements, was multivariate regression or multivariate Cox hazards models in order to clarify the relationship between the measured IOP parameters and risk of glaucoma, i.e. which of the IOP parameters (range, mean IOP, peak IOP or SD of the mean IOP) is/are an independent risk factor(s) for VF progression.
Overall studies showed mixed results in terms of risk associated with IOP levels and fluctuations using an eight-hour diurnal curve for IOP measurement, using >eight-hour diurnal curve or single IOP measurements. Additionally, the overall quality of these studies was very low. Therefore, review authors conclude that there is very low-quality evidence for the use of a diurnal tensions curve or single measurements to assess short- or long-term IOP fluctuation or mean as a risk factors for the development or progression of glaucoma.
Methodology: Inclusion criteria consisted of studies reporting: open glaucoma in an adult population; IOP measurement by Goldmann applanation tonometry; number and timing of IOP measurement; IOP parameters include fluctuation and mean; and study reports results for ≥ 20 eyes. Outcomes of interest included progression or development of glaucoma. If there were multiple publications based on the same study, the most recent study was included. Studies were excluded if: studies reported on angle closure glaucoma or paediatric glaucoma, were case reports, IOP was measured by a technique other than GAT, and the numbers and timings of IOP measurements were not explicitly reported.
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 2005 to 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 an unknown eligibility were reviewed with a second clinical epidemiologist, and then a group of epidemiologists, until consensus was established.
Authors assessed the quality of the evidence as high, moderate, low or very low according to the GRADE Working Group criteria.
Applicability/external validity: Authors note that due to the very low quality of evidence available, it is not possible to make recommendations for the use of a diurnal tensions curve or single measurements to assess short or long-term IOP fluctuation or mean as a risk factors for the development or progression of glaucoma.
Geographic focus: Studies from Sweden, Germany, US and Korea were included.
Summary of quality assessment: Low confidence was attributed in the conclusions about the effects of this study as important limitations were identified. This review may be prone to publication bias as authors did not report searching grey literature and contacting authors or experts for further potentially relevant studies for inclusion in the review.
Additionally, it is not clear if language bias was not avoided as authors did not report including studies in languages other than English. Review authors did not avoid selection bias as abstracts were reviewed by a single author. It is not clear if characteristics of included studies were reliably reported as methods to extract data as well as critical appraisal methods were not reported in the review.
Although authors did not draw strong conclusions based on the evidence found and clearly reported limitations of included studies, authors did not report limitations on the methods used to conduct the review.