National Contact Lens Examiners (NCLE) Practice Exam

In cases of with-the-rule corneal astigmatism, the cornea is steeper in the vertical meridian compared to the horizontal meridian. When a gas permeable (GP) lens is fitted on such a cornea, the lens will typically align with the flatter meridian, which is horizontal in this case. As a result, the fluorescein pattern observed under a cobalt blue light will display a dark narrow band horizontally across the lens. This occurs because the central area of the GP lens will touch the cornea, creating an area of apical touch, with the periphery of the lens experiencing pooling of fluorescein due to the elevation from the flatter horizontal band. Therefore, when a GP lens is placed on a cornea with with-the-rule astigmatism, the fluorescein pattern will distinctly show a dark narrow band aligned with the horizontal plane, indicating where the lens is elevated away from the cornea. This pattern is crucial for practitioners to understand as it helps ensure proper lens fit and visual acuity outcomes for patients with corneal astigmatism.