It’s no secret that the vitreous shifts based on its water:collagen ratio throughout life. When we’re young, the vitreous is firmly attached to the retina via adhesion molecules along the vitreoretinal interface. As we age, the vitreous releases from the retinal interface, inducing a posterior vitreous detachment (PVD).
On OCT testing, the area of visible vitreous is called the posterior cortical vitreous (PCV). As expected, the PCV can take on varying configurations.
Figure 1: The PCV is well attached to the macula with only a small perifoveal detachment noted (see red arrow).
Figure 2: The PCV remains attached to the foveal region (see white arrows), and can be seen to be bowing towards the optic nerve (see red arrows). This indicates that a complete PVD has not yet occurred.
Figure 3: The PCV is fully detached from the retina and optic nerve. This is a complete PVD that was subsequently confirmed by clinical examination.
But heads up! All of these concepts and evaluations are based on a single OCT raster scan. In reality, the vitreous is three-dimensional and using a single OCT scan doesn’t cut it when it comes to describing pathology.
Figure 4: This is a 3D rendering of the vitreous and its relationship to the retina in a case of vitreomacular traction.
In a recent study by Palacio et al, the authors used a neat trick to calculate the total area of adhesion. By marking the area of attachment on successive line scans and superimposing it onto a fundus image, the authors were able to calculate the total area of adhesion. They then plotted this number over time to demonstrate an age-related correlation with detachment.
At first glance, these results aren’t surprising, but the implications of this “trick” are really cool. Remember that the use of pharmacologic vitreolysis to treat vitreomacular traction has taken off in the past few years with the approval of injectable ocriplasmin. Ideal cases are typically defined as those having focal areas of traction (<=1500 ųm) (along with a slew of other clinical features). But with a release rate of less than 75%, there’s undoubtedly something we still don’t understand.
Now don’t get us wrong, 75% is pretty great… but 100% would be better. And as many of us have suspected for a while, the answer to the question of release rate may lie in the total extent of adhesion (rather than just the amount on a single scan). Based on Palacio et al’s method, we may be able to reclassify our definition of the extent of vitreomacular adhesion and upgrade our criteria for treatment.
Only time will tell if this work will lead to improvements in standards of care. But for now, it’s at least something to think about.
Always learning,
The EyeCarePD Team