This is an important publication by Carlos Gustavo De Moraes et al. which suggests an association between functional (visual field-VF) progression and changes in the curvature of the corneoscleral junction as measured by the 24-hour contact lens sensor (CLS) based on retrospective visual field data analysis. The authors suggest that a single CLS session can help in risk stratification of glaucoma patients. Although a number of CLS variables had an association with fast VF progression and the mean peak ratio while awake was the best variable and for every 10-U increase in this ratio, the mean rate of MD change was 0.02 dB/y faster on average. There are some important issues that need to be highlighted regarding this technology and its clinical utility as a diagnostic tool.
1. There is no doubt that a 24-hour monitoring of IOP is ideal and a dream for most glaucoma specialists. The CLS addresses this option remotely by measuring physical changes in ocular dimensions that may correlate well with IOP, although a few studies have shown a poor correlation. The CLS generates electric signals based on volumetric changes and these in turn depend on the biomechanical properties of the eye such as the scleral stiffness. Therefore we are actually measuring how ocular tissues respond to mechanical pressure based on their biomechanical properties and this is a very different and complex issue which requires further understanding before we incorporate it in risk stratification of glaucoma patients. The reader should thus be clear that the CLS is by no means a 24-hour IOP sensor.
2. The next important question is: does this study impact our current decision-making capability when treating glaucoma patients? The answer is a big NO. Although the study has reported a CLS-VF association, it does not have predictive capability and getting a high CLS value across any parameter does not indicate that the patient will be a future fast progressor. This will require a prospective visual field analysis for progression.
The next important question is: does this study impact our current decision-making capability when treating glaucoma patients?
3. Let us assume that the study was prospectively done and CLS variables were predictive of fast progression on a single day. We know that diurnal IOP curves vary from day to day and therefore an association between the two on a single day may not be there on the next day. Furthermore, our decisions on escalating medical therapy or performing surgery are now based on robust OCT structural parameters in early glaucoma and visual field parameters at an advanced stage. Would we be willing to modify treatment decisions based on CLS variables? (e.g., high CLS variable values in eyes with no structural/functional progression on follow-up).
4. On a more philosophical note, I prefer simplicity. To introduce a new technology to the armamentarium of glaucoma investigations will complicate matters for both the physician and the patient with 'RED' disease (false positive) scenarios, risk of un-necessary therapy and additional expenditure. In the current scenario, we have new and expensive technologies looking for indications to best fit in, when actually they may not be required at all.
5. Finally, I commend the authors on highlighting this new association and encourage future prospective studies on this topic looking at CLS variables in treatment naive eyes, incorporating corneal hysteresis and scleral rigidity parameters and prospective evaluation of both structural (OCT-RNFL, GCC) and functional (visual field - VFI) parameters for progression.