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Editors Selection IGR 15-2
Clinical Examination Methods: 24-hour IOP and Visual Field Changes
Comment by David Garway-Heath & International Glaucoma Panel on:
66229 Visual Field Change and 24-Hour IOP-Related Profile with a Contact Lens Sensor in Treated Glaucoma Patients, De Moraes CG; Jasien JV; Simon-Zoula S et al., Ophthalmology, 2016; 123: 744-753
Intraocular pressure (IOP) remains the only modifiable risk factor in glaucoma management, highlighting the importance of obtaining accurate IOP measurements in the diagnosis and management of glaucoma patients. A single office IOP may not reflect the true IOP load or range of IOP variation or fluctuations over time. Goldmann applanation tonometry (GAT) remains the reference standard for IOP measurement. However, 24-hour monitoring using GAT is not feasible in routine clinical practice. This has prompted clinicians to search for newer devices which may allow practicable and continuous IOP monitoring in order to supplement, or provide an alternative to, GAT measurements.
Several randomized controlled trials lend credence to the association between mean IOP or IOP fluctuations and visual field (VF) progression, which would support the notion of an association between 24 hour IOP profiling and VF progression in glaucoma patients. The contact lens sensor (CLS, Triggerfish, Sensimed, Sensimed AG, Lausanne, Switzerland) is a device, which allows easy and non-invasive 24-hour monitoring of corneal curvature that may relate to IOP. Its clinical applicability for glaucoma practice depends on the demonstration of a significant association between the CLS 24-hour IOP-related profiles and VF progression.
The manuscript by De Moreas et al. proposes an association between the 24-hour IOP-related profile based on CLS parameters and VF progression. The authors have identified CLS parameters that seem to be significantly associated with visual field progression, using robust statistical measures to smoothen 'noise' and fluctuations in mean deviations (MD), as well as bias due to collinearity among various CLS parameters. Although the paper provides some evidence that the CLS may provide clinically useful data, confirmation of the generalizability of the results is required. A larger number of parameters was entered into the statistical model and, indeed, the 24-hr CLS model did give a better fit than a GAT-related model. However, this may simply reflect the larger number of parameters in the CLS model compared to the GAT model. The uncertainty regarding which model is best compounded by the lack of information concerning GAT model. Statistical approaches which penalize the estimates of goodness of fit depending on the number of parameters in the model, such as the Akaike Information Criterion, would help interpretation of the data. Ultimately, the CLS model needs to be validated in an independent dataset to establish whether the data have simply been 'fitted' or whether there is underlying information in the model.
*Aparna Rao, Luis Pinto, Sergio Mahave, Jin Wook Jeoung, Gokulan Ratnarajan, Rachel Chong, Katarzyna Skonieczna, Antoine Rousseau, Karl Mercieca, Verena Prokosch-Willing David Garway-Heath is a co-applicant on a grant to develop a contact lens tonometer
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