Flexure could be defined as the bending of a contact lens in an effort to conform to the corneal shape. This is a concern gas permeable lens fitters come across when monitoring their patients. The reason it becomes problematic is because an initially, perfectly fit lens, now presents with new fitting characteristics and new power requirements.
So why do we see flexure or the reshaping on these lenses? Put simply, the amount of flexure is dependent on various factors including lens thickness and flexibility. Did you know that thin lenses can flex a third of the corneal astigmatism?
Flexure is noted on follow up and is reported by the patient as CONSTANT blurred vision. Your diagnosis is confirmed by obtaining keratometry measurements over the lens. If the anterior surface of the lens was originally spherical or another noted parameter, alterations in shape will be detected here.
There are certain lens characteristics that will increase the likelihood of flexure. These factors include a high amount of astigmatism, steep base curves, thin lenses or large optic zones. Once diagnosed alterations to lens designs are your only option.
The key to addressing flexure is understanding the underlying mechanism.
Is the lens thin? Solution: Get a more rigid material (i.e. increase center thickness, lower dk, etc.).
Are we correctly aligned to the cornea? Solution: Adjust the fit (i.e. consider toric curves, use a flatter base curve, decrease optic zone, etc.).
Troubleshooting is a part of the job description for a specialty contact lens fitter. Flexure is just one of those issues we might find ourselves contending with. Understanding the potential impact of this finding will save you both time and money. Learn it well, and this will be yet another factor that puts you ahead of the rest.
[Feb 02, 2013]