Due to some extreme irregular corneal shapes, alignment of the lens is difficult and sometimes impossible therefore, bubbles may constantly occur with the fenestrated lenses. Non fenestrated lenses allow the fitter an easier and simpler fit. As a result, more practitioners opt for non fenestrated lenses.

When using fenestrated trial lenses, if you have difficulties
determining the best possible sag depth value due to the
presence of bubbles, reinsert the diagnostic lens with the
fenestration tucked under the upper lid. This prevents air from entering temporarily, giving you enough time to diagnose the proper sagittal depth value.

Note: Small bubbles that move around, providing they do not cross the pupil are acceptable. Bubbles that remain and are fairly stationary are not.

Some lenses without fenestration may need to be removed for cleaning during the patient’s wearing schedule, as metabolic debris could migrate to the centre of the lens. Keep in mind the unique tear pump (hinge) will keep this to a minimum.