During a hybrid lens workshop with third-year optometry school students in February, the students all had the opportunity to wear a hybrid lens designed for normal eyes as well as to assess a hybrid lens fit on one of their classmates. Their previous experience with evaluating corneal GP lenses taught them that bubbles under the lens meant that the lens was fit too steep. But, this is not always the case with bubbles under a hybrid contact lens.
Bubbles Under the GP Center
Hybrid lenses are typically fit steeper than the flat keratometric readings, so it’s no surprise that small bubbles, otherwise known a dimple veiling, can get trapped between the GP center and the corneal surface (Figure 1). Patients typically have increased lens awareness when this occurs. Simply removing the lens and reapplying it with a drop of artificial tears in the lens bowl can solve the problem.
If your keratometric readings are accurate, you should not see larger bubbles under the GP center. However, this was observed in one student who had undergone refractive surgery; her pre-surgical K readings were incorrectly used for her lenses. The GP center of this hybrid lens was fit steep in the traditional sense.
Bubbles at the Edge of the GP
In neophyte hybrid lens wearers applying new lenses right out of the vial, fluctuating bubbles along the perimeter of the GP (right before the hybrid junction) with each blink are common even in well-centered lenses (Figure 2). These bubbles often work themselves out by the end of the first week of lens wear or can be alleviated by instilling a drop of artificial tears prior to the next lens application.
A larger bubble under the edge of the GP (Figure 3) often results from lens decentration and warrants a lens change. Either steepening the base curve or steepening the skirt curve can help to center the lens and eliminate these large bubbles.
Bubbles Under the Skirt
Bubbles can become trapped beneath the skirt, especially when a lens seals off on the surface of the eye and becomes immobile (Figure 4). Flattening the skirt curve can rectify this.
On the contrary, bubbles that occur closer to the edge of the skirt and that are variable in size with each blink are often associated with lens edge fluting (Figure 5). In this case, steepening the skirt curve can help to stabilize the lens on eye and eliminate any non-alignment of the edge of the soft skirt. CLS