A gas permeable lens that fits on a flatter K results in what type of lacrimal lens?

When a gas permeable lens is fitted on a flatter K (the flattest curvature of the cornea), the resulting lacrimal lens that forms beneath the lens tends to introduce more minus power. This occurs because the gas permeable lens creates a tear film beneath it that has a different curvature compared to the cornea.

In this situation, the flatter K indicates that the cornea has a less steep curvature. When a lens is placed on a flatter corneal surface, the tear film essentially creates a 'virtual lens' that is slightly steeper. The prescriptive power of this tear layer, along with the lens curvature, results in an increased converging effect on light, effectively causing a net increase in minus power.

Understanding this concept is key in fitting gas permeable lenses effectively since it directly impacts the refractive power and vision correction that the patient will experience. In clinical practice, this highlights the importance of carefully measuring and considering corneal curvature to ensure proper lens fit and vision correction.